Hubble Telescope Maps Dark Matter in 3D

dido writes "The BBC reports that the Hubble Space Telescope has been used to make a map of the dark matter distribution of the universe, providing the best evidence of the role dark matter plays in the structure and evolution of the universe. From the article: 'According to one researcher, the findings provide "beautiful confirmation" of standard theories to explain how structures in the Universe evolved over billions of years.'"

Comments

And yet...

[clifgriffin]

Pluto is still not a planet.

*bitter*

you can't stop the spin machine

[macadamia_harold]

According to one researcher, the findings provide "beautiful confirmation" of standard theories to explain how structures in the Universe evolved over billions of years.'

... thereby proving god exists.

Re:you can't stop the spin machine

[loganrapp]

I like how the Jesuits operate, really. "God does not fit into the laws of physics - stop trying." Just makes things simple. Science people believe what they do, religious people believe what they do, and some people can believe both without contradiction.

Re:you can't stop the spin machine

[4D6963]

Oh God, why do you Slashdotters always have to start talking about religion or politics whenever we get an article about science?

Re:you can't stop the spin machine

[Icarus_SFX]

You must be new here...

Re:you can't stop the spin machine

[4D6963]

You must be new here...

...

If I was new here I couldn't yet have noticed the recurrence of comments about religion and politics when come the science related articles. I complain about it because I've noticed it for quite a while and am getting tired of it.

And while you're much older than me here I'm the one with the excellent karma lol.

This is pretty cool.

[lordvalrole]

I wonder what a 3d model of dark matter around a black hole would look like? Does it share the same properties as regular matter near a black hole?

Re:This is pretty cool.

[Tx]

I wonder what a 3d model of dark matter around a black hole would look like?

Maybe I've just been around here for too long, but the parent post reads like goatse.cx meets GNAA.

Re:This is pretty cool.

[Coucho]

GNAA Shhhh.. if you don't say it, it's not real!

Re:This is pretty cool.

[andersa]

Black holes are too small to have any influence on the distribution of dark matter. It is a common misconception that black holes are these huge gravity monsters that suck up everything that get closer than a parsec to them.

In reality you have to get within a few thousand kilometers of the event horizon for you to notice anything peculiar. Further away and the gravity well looks and behaves almost identical to an ordinary star.

Black holes doesn't play any role in the distribution of cosmological dark matter, which is what this experiment focusses on.

Does Dark Matter exist?

[Anonymous Coward]

I'm woefully ignorant on this, but is there any evidence towards the existence of dark matter, or is it something that would be necessary in order for certain theories on the composition of the universe to work?

Re:Does Dark Matter exist?

[clifgriffin]

Think of it this way. On slashdot you have a lot of posts. Some of them are good. But they can't all be good all the time. So it follows that there has to be bad posts. Lot's of them.

That's dark matter.

I think that should be a modifier. -1, Dark Matter

Don't be mad that you didn't think of it...

Re:Does Dark Matter exist?

[HarveyTheWonderBug]

Yes, there is, but we do not have a clue yet of what it is made of.
Astronomers have ways to measure the mass of objects, like galaxies, and cluster of galaxies, using a theory of the gravitation. For galaxies, the classical newtonian theory is enough: they just measure how fast the stars and the gas orbit around the galaxy, and derive directly their mass from kepler laws. For clusters of galaxies, or large structure, they use the bending of light by mass from general relativity. These measure are getting reasonably accurate. When they compare these masses to the mass they actually can see (stars, gas, etc..), they find that they can only account for 1/6 of the total mass they measure, well above all the uncertainties of the measurments. Therefore, there must be some matter (that is, something with a mass), that we cannot see (that does not interact via electromagnetism). This is the dark matter.
For more info, there is a [wikipedia] entry.

Re:Does Dark Matter exist?

[Anonymous Coward]

First off, I am an astrophysicist, but my field isn't particularly related to dark matter, I do instrumentation mostly, although I do try to follow brane theory research on the side.

There's a lot of disagreement about whether "darkmatter" exists or rather why we see the things we think we see - what causes the effects? There's a lot of other potential theories which seem (give or take) similarly plausible, MOND for instance or something coming out of M or brane theory. The fact is that we just don't know, and a lot of this sort of mediahumping is driven by folk anxious for 5 minutes of fame who jump to conclusions. If this were religion rather than science, each side (the different sorts of darkmatter believers) would be calling the other "fanatics" and extremists, but most scientists aren't as good at mediaspin as religionists... yet.

Budgets and penis-size competitions are what drive a lot of astrophysics today.

Re:Does Dark Matter exist?

[Anonymous Coward]

There's a lot of disagreement about whether "darkmatter" exists or rather why we see the things we think we see - what causes the effects? Actually, dark matter has become pretty mainstream. The disagreement now is mostly over what it is, not whether it exists.

There's a lot of other potential theories which seem (give or take) similarly plausible, MOND for instance or something coming out of M or brane theory. That's also not true. The stringy stuff has been relatively poorly tested, and MOND runs into trouble in several areas over the last few years, most recently and notoriously with the Bullet Cluster. MOND still isn't totally dead, but it's looking more and more like even if MOND is true, you're still going to need at least some dark matter to explain things (just not as much as with no MOND).

Re:Does Dark Matter exist?

[calice]

This is what I don't get about dark matter, and this is just how I see it, and no one has ever given me a decent explanation. Why is it that scientists think that dark matter exists simply because the observed galaxies don't conform to Newton's Laws? Wouldn't a simpler solution be to take a step back and consider that, maybe, Newton's Laws are flawed? I am not trying to disprove dark matter, I certainly am no cosmologist, but it just seems odd that so much attention is given to dark matter, and very little is given to competing theories, such as MOND (Modified Newtonian Dynamics), that to me, at least, make more sense.

My basic point is, from a layman's perspective, dark matter just sounds like something physicists pulled out of thin air to explain something they don't understand. Your observations don't make sense? Well, throw in some dark matter and we're good!

Can someone explain to me why dark matter is the prevalent theory? Or perhaps why something like MOND is always ignored? As I said, I don't know what is right, but it just seems like a hack-job to me.

Re:Does Dark Matter exist?

[Plutonite]

I think that should be a modifier. -1, Dark Matter

Are you kidding? It's called Over-rated, and mysterious drunken moderators use it all the time.

Re:Does Dark Matter exist?

[Ambitwistor]

Why is it that scientists think that dark matter exists simply because the observed galaxies don't conform to Newton's Laws? Wouldn't a simpler solution be to take a step back and consider that, maybe, Newton's Laws are flawed? You want a solution that is simple enough to explain the facts, but no simpler. Modifying the laws of gravity runs into difficulty explaining everything that dark matter can, although you can get it to explain some things (such as galactic rotation curves).

Can someone explain to me why dark matter is the prevalent theory? In short, because it works and none of the alternatives people have proposed over the decades work as well. I can get into details if you want, but you should probably just start at Wikipedia.

Or perhaps why something like MOND is always ignored? MOND isn't ignored. Go to the astro-ph arXiv or the Smithsonian/NASA ADS Abstracts and search for MOND papers. You'll find them, along with criticisms of MOND. Here is a nice but somewhat outdated set of slides on how well MOND fares against the evidence, and a more recent blog post by the same author discussing newer evidence that tightens the screws on MOND even further.

As I said, I don't know what is right, but it just seems like a hack-job to me. I don't know why all the hate for dark matter. Screwing around with the laws of gravity isn't any more elegant, and there are plenty of plausible candidate particles for dark matter lying around in various extensions to the Standard Model.

Re:Does Dark Matter exist?

[HarveyTheWonderBug]

It's not completely true that MOND does not get any attention, there are very regularly publications in refereed journals about it, to prove it, disprove it, or try to make it better. Here is the problem as I see it:

1. The current accepted theory of gravitation, general relativity, works extremely well: it's predictive power has so far never be successfully challenged. Many have tried, noone has succeeded.
2. MOND had some success in explaining various observational puzzles, but has also some problems with others, as the wikipedia entry you link indicates.
3. MOND is an ad-hoc theory, just like dark matter is an ad-hoc solution
4. It is very hard to change your theoretical framework, much easier to add some stuff to the universe.

This explains to me why, right now, the current accepted paradigm is dark matter. While it is not satisfying, it is enough to explain both the rotation curves of disk galaxies, and the formation and evolution of the large scale structure of the Universe. I don't think many astronomers are satisfied with this current situation, and some are trying to resolve the issue, either explaining dark matter or getting rid of it. The others find with dark matter a framework where they can go on in exploring other scientific questions, like the evolution of galaxies, where you need to explain how their (normal) matter was assembled together, but also how this matter (gas) is made into stars, etc...

Re:Does Dark Matter exist?

[WilliamSChips]

Personally I think the simplest solution is that dark matter is made up of neutrinos. Although I don't know whether that would be possible or not.

Re:Does Dark Matter exist?

[Ambitwistor]

No. Neutrinos aren't massive enough to be (most of the) dark matter. See here for a brief but more detailed discussion.

Re:Does Dark Matter exist?

[Anonymous Coward]

Holy shit... you're smart for a car.

Re:Does Dark Matter exist?

[pln2bz]

The real story of how we ended up with dark matter is not widely understood or accepted.

Some time ago, a man named Hannes Alfven, who is today considered the father of plasma physics, founded the field of magnetohydrodynamics, which astrophysicists have been using to model plasma in the universe for several decades now. This field treats plasma as a fluid and assumes that currents cannot flow through the plasma because it treats plasma as an ideal conductor with no resistance. This is actually not *anything* like the way that plasma operates in the real world, and since plasma represents 99%+ of all observable matter within the universe, this massively incorrect assumption yields absurd results in astrophysics today. Plasma is in fact electrically conductive and its electrical properties interact with its mechanical motions, and vice-versa. If you've ever seen a novelty plasma globe, then you intuitively know that plasma is not like a fluid. You can tell by looking closely at a plasma globe that the plasma creates filaments and these filaments pair up and twist around one another. These twisting currents are called Birkeland Currents. As the current flow increases through them, they pinch together with increasing force and this pinching action can actually condense matter into a ball. This is a big deal because there is no good reason to believe that molecules will gravitationally collapse from a diffuse collection of matter in space; in fact, gases obviously expand in a vacuum. Contrary to the more popular beliefs propagated in astrophysics and the media today, the z-pinch effect is likely actually how planets and stars form. Astrophysicists don't understand this because of their earlier assumptions regarding plasma being a fluid with no currents. But we can see strong evidence of Birkeland Currents and Z-Pinches happening through our telescopes.

The thing is, astrophysicists will see what they want to see through the telescope. All observations today are interpreted through mainstream concepts like stellar evolution and Big Bang theory. When an anomaly pops up, it can be a very simple matter to propose a "patch" for the theory to keep it going. Astrophysicists will invoke collisions, black holes, gravitational lensing or malformed electrical theory in order to explain away anomalies. But you will notice that anomalies are discovered nearly every week these days (especially with stellar evolution), and this is a problem because things like collisions should not actually be happening as often as they are being invoked to dismiss the anomalies.

When Hannes Alfven received his nobel prize for plasma physics in the 70's, he recused himself from the field that he created (MHD) and warned astrophysicists to abandon it, and that the path they were taking would eventually dead-end. But they completely ignored him and continue to do so. So, now we have mysterious forces tugging on matter throughout the universe that we can't see. This is what we call dark matter. Dark energy is supposed to be matter that can gravitationally repel. Electrical forces can accomplish both of these feats without any mysterious matter. All you have to do is drop the earlier incorrect assumptions about plasma and accept that extremely diffuse plasma flows can and do exist. You will notice over time that the dark matter studies will reveal some details that correspond with the properties of electricity over plasma. For this particular article, it was noticed that the structure of the dark matter was in places filamentary. Filamentary structures are far easier to generate with electricity than with gravity. It was also mentioned that dark matter can exist in the absence of physical matter. This is to be expected with plasma because plasma can consist of just electrons and ions, or it can also be coexisting with or collecting dust.

Some brave scientists and electrical engineers called Electric Universe Theorists are working on understanding the universe in terms of real plasma physics -- which makes p

Re:Does Dark Matter exist?

[tangenterine]

There are physicists who express similar dissatisfaction with this theory. Perhaps you'd be interested in Philip Mannheim's opinion at the University of Connecticut. I won't try to paraphrase his work, since I'm only a physicist-in-training, but he teaches an astrophysics class in which he addresses this problem. My take: If the theory doesn't work witht the data, it's because the theory is wrong--you don't go invent something just to satisfy the theory. Likewise, "laws" are theories we really like while the non/existence of something is absolute (well, generally). There are various takes on the evidence for dark matter, but altogether my understanding is that it's virtually undetectable (no E&M interaction)--so it can't be disproven, only "not yet verified". see for more info

Re:Does Dark Matter exist?

[iamstretchypanda]

Taken directly from CERN

"What is "Dark matter" made of?

Measurements in astronomy imply that up to 90% or more of the Universe is not visible (i.e. does not emit electromagnetic radiation) . Scientists call this undetectable "stuff" dark matter.

Its presence is felt through the gravitational effects on the matter we can see. Stars in galaxies, for example, appear to be moving much faster than they would if they were influenced only by the visible matter in the galaxy.

The nature of dark matter and its role in the evolution of the universe are still unknown.
Probably it is made of several components, among which are neutrinos, dust, cold gas, and special particles predicted by the grand unification theories but not yet seen, the so called "superparticles".

Physicists hope to identify some of the elementary constituents of dark matter at the LHC."

As we can all see, the experts aren't even sure of the elementary principals yet.

Anyone want to expand on "superparticles." Seems as if they are referring to neutrinos.

Re:Does Dark Matter exist?

[NotZed]

# The current accepted theory of gravitation, general relativity, works extremely well: it's predictive power has so far never be successfully challenged. Many have tried, noone has succeeded.

You mean, apart from the fact that you need to create 90+ percent more matter in the universe than what is visible to prevent galaxies from flying apart?

i.e. without dark matter (and dark energy), gravity doesn't predict much.

Re:Does Dark Matter exist?

[pudro]

Dark matter is a crutch of a theory with so many problems they had to invent an imaginary substance to explain them.

The term "dark matter" originally referred to normal matter that we couldn't see because it wasn't lit up. Once this idea was proven inadequate, dark matter became something new and its definition was shaped solely by what the theorists needed it to be. Later on, they found even more problems with their theories and had to invent dark energy, which was once again defined solely by what the theorists needed it to be. But even with these inventions, they are routinely surprised by what they find in the universe. The only explanations they can come up with range from "it's a mystery" to claiming that previously accepted "universal" laws work differently out there in the universe.

Since you seem to be open minded, let me introduce you to a different (though never claiming to be definite) explanation. A growing number of people are starting to realize that these surprises are no longer surprising once you start to imagine that electric currents can flow throughout space (contrary to popular opinion). It is the Electric/Plasma Universe theory.I have only known about it for a relatively short time, but the bulk of what I have read is from this site:
http://www.thunderbolts.info/home.htm

I have spent a lot of time just going through the Picture of the Day archive section and reading the explanations below the pictures (which is actually the point of that section - not showing pretty pictures or something like that). (Be warned - some entries are repeated several times.) Many anomalies can be explained simply as electric discharges (or the results thereof). And all of their theories are directly relatable and scalable to physical tests carried out in labs on Earth.

I'll point out a couple of my favorite examples so far: Io and the "Greatest Surprise" and V838 Mon (which also happens to be one of my favorite pictures as well).

It never did sit right with me how things like the Cat's Eye Nebula were supposed to have formed through explosions and gravitational forces. Now I know why: it's electric!


P.S.
I keep having the thought of how funny (and sad) it would be if the conventional model just keeps making up more rules and invisible entities until those evolve into the Electric/Plasma model.

Re:Does Dark Matter exist?

[Plutonite]

That wasn't funny! Well it was, but..my karma you insensitive clod!

Re:Does Dark Matter exist?

[Anonymous Coward]

Yes, there is, but we do not have a clue yet of what it is made of.
Well, most of science has yet to agree what it is, but Randy Mills has a pretty solid theory backed by observations.

Mainstream says the 10% of the universe that is observable is 90% hyrogen, 9% helium, and 1% everything else. Mills says that the 90% unobservable universe is a lower-state hydrogen atom that he calls a "hydrino". The Mills theory explains the answers to some very old scientific questions, such as 'what happens to a photon upon absorption' and explains why the Sun's corona is so hot (>1,000,000 K) in spite of the fact that Sun's surface is so cool (6,000 K), and correctly predicted the accelerating expansion of the universe before it was observed (there was no big bang, just a sinusoidal expansion/contration where we are currently on the accelerating region of the curve).

The foundation of Mills theory is that an electron is spherical shell, not a point. From this posit pretty much everything can be explained with 4 dimensions, Newtwon, Maxwell, and relativity - with no need for string theory, spooky interaction, uncertainty, or quantum mechanics.

Re:Does Dark Matter exist?

[Anonymous Coward]

You mean a wrong theory backed by no observations? Mills has been bilking weathly investors for years with nothing to show. He doesn't have a coherent, consistent theory of quantum mechanics with hydrino states. He doesn't have a consistent relativistic cosmology. He doesn't, really, have anything.

Incidentally, there are already answers to questions of "what happens to photons upon adsorption" and "why ths Sun's corona is so hot".

Re:Does Dark Matter exist?

[Ambitwistor]

Dark matter is a crutch of a theory with so many problems they had to invent an imaginary substance to explain them. The history of science is filled with examples of new particles that were predicted — and discovered — on the basis of experimental discrepancies. You're going to have to do better than that.

The term "dark matter" originally referred to normal matter that we couldn't see because it wasn't lit up. Once this idea was proven inadequate, dark matter became something new and its definition was shaped solely by what the theorists needed it to be. You say that like it's a bad thing. Theories that don't work are replaced by theories that do.

But even with these inventions, they are routinely surprised by what they find in the universe. So? Nobody has claimed that we know everything about the universe. Dark matter and dark energy are features of our universe, but they don't explain everything about it.

Re:Does Dark Matter exist?

[Ambitwistor]

My take: If the theory doesn't work witht the data, it's because the theory is wrong--you don't go invent something just to satisfy the theory. You don't "invent something to satisfy the [wrong] theory". You invent a new theory. Dark matter is one such theory.

(Incidentally, sometimes the data is wrong, or the interpretation of the data.)

There are various takes on the evidence for dark matter, but altogether my understanding is that it's virtually undetectable (no E&M interaction)--so it can't be disproven It interacts gravitationally, and can be disproven that way. In fact, a number of specific dark matter proposals have already been disproven that way. (e.g., we know that the dark matter is not mostly made up of compact astrophysical bodies, and we know that it's not made up of light particles.) Future observations could potentially rule out the remaining dark matter proposals, but so far they have not.

Re:Does Dark Matter exist?

[Ambitwistor]

i.e. without dark matter (and dark energy), gravity doesn't predict much. That is an absurd statement. See, for instance, this review article for a truly extensive list of successful predictions of general relativity.

Re:Does Dark Matter exist?

[Umbrel]

Thanks, pretty interesting but I dislike the way you call them astrophysicists in general, since you're pointing out that there are some that are pursuing electrouniverse theory, I just don't like such an unaccurate generalization. BTW I think you mixed two subjects, I can't see why the Big Bang theory and the Electric Universe theory are muttually exclusives, since the BB is about the origin and the EU is about the evolution, I mean, EU needs mass and energy for a start and BB just says than mass and energy suddenly popped in (nothing proved but both theories don't deny each other)

Re:Does Dark Matter exist?

[pln2bz]

Actually, it's a big problem to deduce that there was a Big Bang with the z-pinch effect because z-pinch basically recycles matter. Although the astrophysical community still denies his observations, Halton Arp has published results that indicate that some spiral galaxies are ejecting quasars from their centers. He's basically demonstrated images that show high redshift quasars in *front* of opaque, low redshift spiral galaxies and you can easily notice for some specific situations that these quasars tend to align themselves along axes that center at the spiral galaxy. These quasars then apparently trade their ejection velocity for mass as their redshift decreases (for the full story, get Halton Arp's book "Seeing Red"), and they appear to become spiral galaxies themselves. It's a little bit unusual, but the statistics demonstrating the link between quasars and spiral galaxies have since been confirmed by others (keep in mind that Halton Arp made this observation in the 60's and has been ignored since then). Not only does this cast doubt upon using redshift to deduce distance, but when matter is being recycled like that, it becomes impossible to just "rewind" the universe back to a singular point in time or space. The arguments against his observations tend to be unconvincing. I think we're supposed to believe that some sort of gravitational lensing is occurring, but this assumes that the spiral galaxy can be treated like a point source of light (an ideal mathematical entity projected onto reality) and it's not always the case that the quasars appear on symmetric sides of the galaxy. To be honest, any time that somebody tells you to believe their theory over your own eyes, you should be very wary, regardless of the explanation. There has never been an adequate disproof of Halton Arp's findings and yet astrophysicists will tell you with conviction that he must be wrong.

There are many other similar problems with the Big Bang. For a comprehensive review, you might want to check out "The Cult of the Big Bang" by William C Mitchell or "The Big Bang Never Happened" by Lerner. EU Theory is basically a *static* universe theory. It assumes that the universe is infinite in both time and space. There are other potential explanations for redshift that are not being funded as much as the doppler shift explanation (tired light is an example). There have also been numerous anomalies observed with redshifts. Our own Sun varies slightly in redshift over time enough to rule out doppler shift as an explanation and we've observed objects in the sky whose spectral lines are so unusual that redshift is meaningless. There is a tendency to push aside anomalies like this until a later time when somebody can propose an explanation, but in fact, there are enough problems with the traditional paradigms by now that it's long overdue for us to start considering alternative cosmologies. You don't get *any* of this information through the mainstream press because there is no investigative journalism within the space reporting industry. The reporters are incapable of evaluating the statements being made by astrophysicists, which actually oftentimes leads to some rather amusing space articles.

Many of the claimed successes of the BB Theory are in fact oversold as proofs. But because these proofs tend to be extremely mathematical in nature, it can be very difficult for most people to honestly evaluate them. But you can generally find an anti-proof for each of the proofs that are being sold for the BB. You just need to know where to look and be willing to believe that a bunch of people can possibly be wrong. More than anything else, that's probably the biggest hangup for people -- admitting that so many people can be so wrong. Our culture tends to assert more certainty within geology, archaeology and astronomy than is really possible because we oftentimes have no way to validate the results of those fields (conclusions are best guesses) and we cannot perform input-output experiments within those fields. Like astronomy

Re:Does Dark Matter exist?

[jstott]

The real story of how we ended up with dark matter is not widely understood or accepted.

I'm have flashbacks of sci.physics and Petr Beckman...

-JS

Re:Does Dark Matter exist?

[Clayhill Dub]

Woefully ignorant as well. With gravitational lensing upon gravitational lensing, how do we know what the universe really looks like in the first place. Sorry for a dumb question.

Re:Does Dark Matter exist?

[Ambitwistor]

There isn't a lot of gravitational lensing — it's only significant when light passes near dense collections of matter. The net effect is that some images of distant stars or galaxies are sometimes displaced a bit from where they "should" be. Usually the light doesn't get lensed multiple times on its way to us, simply because it's rare for several lensing objects to exist on a line between us and the source. Most objects we see are not lensed at all, and those that are, aren't usually lensed much.

Anyway, to be kind of facetious, the universe with lensing is what the universe "really looks like".

Re:Does Dark Matter exist?

[pudro]

I like how you conveniently ignored half of my post. Like all of the parts that countered your reply.

I didn't just rant against the conventional theory without justification. The problem isn't just that the theory is complicated, but that there is a much less complicated theory that explains everything better. (And a man by the name of William of Ockham has something to say about that.)

Just so I'm clear and not picking apart your post as best suits me (as you did mine):

The history of science is filled with examples of new particles that were predicted -- and discovered -- on the basis of experimental discrepancies. You're going to have to do better than that.

How about the fact the Electric/Plasma theory predicts cosmological occurrences better than the traditional one, and without all of the "experimental discrepancies" that plague the traditional theory. Never mind the fact that the current theory isn't even testable through controllable experiments in a lab or even on a computer (excluding self-fulfilling experiments), contrast to Electric/Plasma theories which are entirely testable.

You say that like it's a bad thing. Theories that don't work are replaced by theories that do.

Thanks for making my point for me. The traditional theory doesn't work (even after extensive tweaking), so it should be replaced by one that does work (Electrical/Plasma). (And when I say "replaced", I mean it deserves the majority of the focus of scientific research and funding until it is proven to be at least as flawed as the current theory. I don't mean we should be subjected to indoctrination of it with a Nazi-like fervor as is the case with the current theory.)

So? Nobody has claimed that we know everything about the universe. Dark matter and dark energy are features of our universe, but they don't explain everything about it.

They don't explain everything because they are flawed devices invented to patch the holes in a sinking ship. Not to say the Electric/Plasma theory explains everything, but it explains a hell of a lot more than the currently accepted theory. And it does so without trying to isolate us from the rest of the universe (no electricity in between celestial bodies), and also without shitting on Galileo and putting us (as a solar system or galaxy this time) back at the center of the universe (as the current model seems to with its extension 13-odd billion light-years spherically around us and the Fingers of God pointing at us from every direction).

Re:Does Dark Matter exist?

[Ambitwistor]

I didn't just rant against the conventional theory without justification. The problem isn't just that the theory is complicated, but that there is a much less complicated theory that explains everything better. Except that there isn't. That's the point. There is no EU/plasma theory of the vast majority of observations that lead to dark matter. Galactic rotation curves are the only phenomena that they even attempt to explain, that is only at a qualitative level, and most importantly, there is no explanation for why we don't observe the fields that they claim exist and are responsible for the observed rotation curves.

How about the fact the Electric/Plasma theory predicts cosmological occurrences better than the traditional one Except that it actually doesn't. It doesn't account for the CMBR anisotropies, it doesn't reproduce the supernova redshift/luminosity relations, it doesn't yield correct nucleosynthesis, it doesn't correctly explain cosmological redshifts, and so on.

Never mind the fact that the current theory isn't even testable through controllable experiments in a lab or even on a computer (excluding self-fulfilling experiments), It is testable both through astrophysical observations and computer simulation, and some models are testable in particle experiments. (Well, all of them are in principle, but only some of them are within reach of current technology.)

The traditional theory doesn't work (even after extensive tweaking) Sure, if by "doesn't work" you mean "passes dozens of experimental tests including galactic rotation curves, the motions of satellite dwarf galaxies, gravitational lensing, measurements of galactic gas temperatures, anisotropies in the CMBR, the rate and structure of large-scale cosmological structure formation, and so on".

so it should be replaced by one that does work (Electrical/Plasma) Sure, if by "working" you mean "making few predictions, most of which are wrong".

And it does so without trying to isolate us from the rest of the universe (no electricity in between celestial bodies), There are plasma currents and such within galaxies, but they do not account for galactic rotation curves.

and also without shitting on Galileo and putting us (as a solar system or galaxy this time) back at the center of the universe (as the current model seems to with its extension 13-odd billion light-years spherically around us and the Fingers of God pointing at us from every direction). The current model does not put us in the center of the universe. In fact, Big Bang cosmology does exactly the opposite.

Incidentally, the "Fingers of God" do not point to us from "every direction", but from two directions, and furthermore, the universe is highly isotropic on scales much larger than those structures.

Re:Does Dark Matter exist?

[Ambitwistor]

Oops, by "Fingers of God" I thought you were referring to a particular filamentary structure that I've heard referred to by that name. You may, however, have been referring to this phenomenon, which also does not imply that we are at the center of the universe (as noted in that article); an observer anywhere in an isotropic universe will observe radial elongation in redshift space towards themselves.

Re:Does Dark Matter exist?

[pudro]

I'll be the first to admit that I don't know everything about these theories, but you don't seem to understand either of them fully ( especially the Electric/Plasma theory).

Electric/Plasma theory may not be complete (though it's far more complete than you claim), but that is better than being wrong. If they wanted to fill in the gaps, they could just invent some imaginary property of plasma to stick in the equation like some self-fulfilling prophecy. (Look everyone! Our equations work because we randomly inserted a device to compensate for the previously unexplained inaccuracies! And it was so much easier than real science!)

Re:Does Dark Matter exist?

[Umbrel]

I'm certainly short of astrophysical knowledge, as to have an idea about BB vs z-pinch (is z-pinch the effect of threads like grouping of mass), specially since every webpage about astronomy that I've checked (not many) give standar info. AFAIK the "evidence" for BB is some constant expansion of the universe (which of course I don't know if it's really happening) I guess that has been deduced from the red shift and that's why you're mentioning the abnormalities of it. However given what you just said there sould be several galaxies aligned by axis and I haven't heard of that (not that I should or would :) ), also I think that thread-like galaxies should be more usual than spiral galaxies (I think, feel free to ignore) since electromanetic force is far stronger than gravitational. Fun though: since time & mass are related there is no time 0 (neither negative) because when "rewinding" towards BB (if it happened) the closer to it, the longer the time (something like the limit for 1/x when x tend to 0), so even with the BB the universe is still of infinite age. i still don't know why they sey that the BB was XX... years ago

Re:Does Dark Matter exist?

[pln2bz]

My personal thoughts are that people who have been trained in Big Bang Theory are "contaminated" insofar as they are oftentimes unable to conceive of electricity in space. But our observations are increasingly telling us otherwise. For instance, there was a big supernova some time ago called 1987A. When we finally had instruments that could image the remnants of that supernova, this is what we found:

http://www.thunderbolts.info/tpod/2006/arch06/0601 24solar3.htm

Our conventional theory regarding supernovae do not describe that *thing* at all. The problem is that the structure is bipolar symmetric when in fact traditional theory was expecting a shock wave emitted symmetrically in all directions. And those beads ... How do those beads have *anything* to do with nuclear fusion? They appear to float out in the middle of nowhere! I highly recommend reading through the story of that link. It's a good example of the problems popping up for conventional astrophysics today. The plasma universe theories continue to be observationally driven, whereas the traditional paradigms are more or less being dragged along by the observations.

Although it is important to understand the basics of astrophysical theories, it is far easier to understand Electric Universe theory. Astrophysics owes a lot of its complexity to the fact that it treats phenomenon as if they are disjointed, isolated bodies. Gravity is too weak to account for many of these observations, so instead of energy transfer, astrophysicists must work with energy accumulated. This isolation forces them to postulate a separate exotic mechanism for just about every phenomenon they observe in space. But space is connected by plasma and that plasma in fact conducts electricity. And many of those exotic phenomenon, like magnetic reconnections for the Sun, can be replicated with just characteristics of plasma in space. So, if you learn about plasma and electricity+magnetism, you basically understand the universe. It's a really simple concept that's just taking a *really* long time to permeate through science and culture right now. In fact, we're approaching 60 years now since Immanuel Velikovsky first proposed it. Hannes Alfven, Ralph Juergens and a handful of other plasma/electricity geniuses have come and gone with little fanfare. When Albert Einstein died, Immanuel Velikovsky's book "Worlds in Collision" was ominously left open on his desk. It's emblematic in a way because we still haven't closed that book.

The www.thunderbolts.info site has a "resources" link that will point you to a collection of books that generally support EU Theory. If you were going to start out with any particular book, I recommend "The Electric Sky". I've found the web useful for checking out the arguments on the astrophysics side. Tim Thompson, for instance, has a webpage that offers the arguments *against* the concept of an Electric Sun. I've read both arguments by now and I'm personally more convinced by Wallace Thornhill's Electric Sun model than Tim Thompson's solar fusion arguments. Tim Thompson is a very intelligent man, but it is clear to me that he's proposing that astrophysicists have more confidence in their models than they actually do. He oftentimes cites the *existence* of peer-reviewed papers as reason to not consider alternative theories. And you will find on his webpage plenty of materials related to magnetic reconnections, which is, as mentioned, completely bunk. Oftentimes, when we evaluate whether or not to believe people on very complicated issues, we consider an issue that they talk about that we already understand. Similarly, when I see somebody even talking about magnetic reconnections, it's a clue to the education that they've had.

However given what you just said there sould be several galaxies aligned by axis and I haven't heard of that (not that I should or would :) ), also I think tha

Re:Does Dark Matter exist?

[Anonymous Coward]

While cosmological redshift does exist, it doesn't turn a finite universe into an infinite one. The Big Bang happened about 14 billion years ago according to an observer "at rest" with respect to the cosmic background radiation. (The Earth is such an observer for practical purposes.)

There are not actually "anomalies" with cosmological redshift. There are some objects that we can't get a good spectrum off of, as the previous poster said, and the Sun is irrelevant to cosmological redshift. Tired light is a non-viable idea.

Re:Does Dark Matter exist?

[pln2bz]

Cosmic Microwave Background is actually a contentious issue when you get down to the science of it. Many people like to believe that it is a proof of the Big Bang, but it only is insofar as you ignore all of the other potential explanations for it. We zero in on one particular explanation because astrophysicists are so certain that their Big Bang model is true. But in fact, they have made many incorrect assumptions about plasma in order to arrive at their traditional paradigms in the first place. Plasma is *not* an ideal conductor; it in fact has resistance and can conduct electricity even over diffuse flows. Any plasma laboratory experimenter will tell you so, and since space basically *is* plasma, we'd be wise to listen. Astrophysicists choose to disregard laboratory plasma experiments, proclaiming that they do not scale in time *or* space when in fact some plasma researchers have been able to accurately simulate spiral galaxies with electricity over plasma (Peratt) without any imaginary matter. To dismiss laboratory experiments based upon non-idealized plasma science that we already understand quite well and substitute them with invisible matter that we don't know anything about and that was derived from models of the universe based upon idealized plasma science is not only counterproductive. It's nonsensical. Dark matter is nothing more than the error that results from the creation of a bad physical model for plasma.

There are not actually "anomalies" with cosmological redshift.

I suppose that you're going to tell me to not believe any of the work that Halton Arp has done? That the images of high redshift quasars in front of opaque, low redshift spiral galaxies are just due to some sort of accidental imaging? I'm interested in hearing why I should disbelieve my eyes and believe your theory instead? I can clearly see quasars in front of NGC 7319 at the bottom of this page:

http://www.electric-cosmos.org/arp.htm

What is your explanation for these observations?

There are some objects that we can't get a good spectrum off of, as the previous poster said, and the Sun is irrelevant to cosmological redshift. Tired light is a non-viable idea.

I'm curious about this link you sent to me (http://www.astro.ucla.edu/~wright/tiredlit.htm) because it appears to draw conclusions on the basis of assumptions about supernovas:

The tired light model does not predict the observed time dilation of high redshift supernova light curves. This time dilation is a consequence of the standard interpretation of the redshift: a supernova that takes 20 days to decay will appear to take 40 days to decay when observed at redshift z=1.

How is that people *know* that redshift is expanding the time it takes for supernova light curves to decay? This appears to *assume* that supernovae are a standard that we can measure things by. That would be interesting because we've seen supernova remnants like 1987A that we didn't understand at all. Many supernovae -- including 1987A and Keppler's Supernova remnant -- exhibit a bipolar configuration that does not follow from the earlier assumptions about supernovae being expanding spherical shells of gas blowing away from a central point. Why would these explosions frequently only come out the sides like an hourglass?

Traditional astrophysics has dug a very deep hole in terms of assumptions in order to maintain a sense of "progress". But in fact, those earlier assumptions were never really validated. If anything, we've been seeing observations that discount those earlier assumptions, and rather than making predictions about future observations, astrophysicists these days spend nearly all of their time trying to postulate ways to fit the observations to those earlier assumptions.

Enlighten me

[Original Replica]

To those /.ers that know more of physics than I do, is Dark Matter supposed to be some actual particle, or is it a kind of natural gravitational topography? Everything I read ( quick google search/old copy of "Elegant Universe") about it seems to be rather vague and mysterious.

Re:Enlighten me

[LiquidCoooled]

I've always been sceptical of dark matter as something mysterious.
It's fucking obvious that if there is no light illuminating an object it will be dark.
In this solar system there is loads of dark matter, unless of course people and most objects naturally glow.

Re:Enlighten me

[Anonymous Coward]

To those /.ers that know more of physics than I do, is Dark Matter supposed to be some actual particle, or is it a kind of natural gravitational topography?

Yes.

Re:Enlighten me

[bloobloo]

Anything with a temperature above absolute zero glows. You've just got to be about the temperature of a star to emit most of your light at visible (to human) wavelengths.

Re:Enlighten me

[syousef]

Kosh, is that you?

Re:Enlighten me

[ceoyoyo]

Nobody knows.

Some portion of it could be ordinary matter that's simply non-luminous, but I think there are observations that limit that to a small proportion.

The rest seems to be something that interacts only gravitationally... it might be a particle we haven't discovered yet. That's not as far fetched as it sounds -- neutrinos are just such a particle. They have mass so they interact gravitationally but they interact with ordinary matter extremely weakly in all other ways. Massive neutrinos were also candidates to explain some of the dark matter for a while, but I believe once their actual mass was measured it was too little to explain more than a bit of the dark matter.

Re:Enlighten me

[Anonymous Coward]

What is 'fucking obvious' is that you've never read up on dark matter. As the other poster already said, all 'normal' matter made up of proton, neutrons, and electrons, 'glows' in a way if it is above absolute zero. Dark matter is supposed to be made of other stuff. I think thousands of physicists who do physics for a living thought accounted for 'stuff light isn't shining on' before some idiot on /.

They might not be right on it existing, or being what they thought, but they've at least bothered to learn the basics of the theory.

Re:Enlighten me

[a.d.trick]

I'm not an expert on physics but AFAIK I don't think anyone knows much at all about dark matter. It seems to me like it's just a poor excuse for why the observed facts don't fit our lovely theories.

Damned facts, always getting in the way.

Re:Enlighten me

[Anonymous Coward]

The general belief is that it is an actual particle. There are other competing theories such as MOdified Newtonian Dynamics which have slight corrections to our current laws of gravity, but more and more evidence is ruling out the simplest of these models and it's pretty clear that at least some of the dark matter is actually particles. Another thing people thought dark matter could be was normal matter which doesn't produce light, things like planets and failed stars. However, extensive astronomical searches for these objects (called MACHO's) using both the fact that they should occassionally block our view of stars and their potential to cause gravitational lensing have turned up nothing. This basically leaves some sort of new particle as the dark matter canidate. The current theory is that this particle only interacts via the weak nuclear and gravitational forces. It Is is called a WIMP (weakly interacting massive particle). There are a bunch of different models of what this particle is. Basically nearly every theory of physics beyond our current Standard Model has some sort of particle that it's proponents hold up as a dark matter canidate.

There are a wide variety of dark matter searches being conducted which directly search for the particle. The general idea is to see their interaction through the recoil of an atom when one strikes the atom's nucleus. This is very difficult. The most common current technique is searching for the "sound" a dark matter particle interacting with cryogenically cooled germanium crystals produces.

Re:Enlighten me

[Dachannien]

Some string theorists believe dark matter may be gravitons, emitted by matter on adjacent branes, that intersect our own universe's brane, resulting in a gravitational distortion that becomes huge at cosmological scales. A similar concept is used to explain why the gravity exhibited by real matter in our own universe has a strength many orders of magnitude smaller than the other forces - most of the gravitons leave our universe's brane, while the mediating particles of other forces (gluons, photons, etc.) are constrained to move within the brane.

See also http://en.wikipedia.org/wiki/Brane_cosmology .

Re:Enlighten me

[ceoyoyo]

Yeah, I find that one of the more interesting theories since it would give us our only way of detecting what's on adjacent branes. Whatever it turns out to be, dark matter and dark energy seem to be some of the most interesting anomalies going today. Maybe one day I'll get my faster than light yacht.

Re:Enlighten me

[marcosdumay]

Only if it interacts with light. Neutrinos, for example, don't glow (and don't absorb light either).

Re:Enlighten me

[LiquidCoooled]

Bad choice of wording from me, but something has to glow pretty damn brightly to be seen at the distances we are discussing.

If everything was visible the night sky would be bright instead of dark.
The illumination must be bright enough that we can see it at distance - its like us trying to see the lights onboard the ISS.

Re:Enlighten me

[kiyoshilionz]

Really, the evidence for "dark matter" has been made through its effects - it bends light, and makes galaxies spin at a different rate than what we're currently observing. Scientists have inferred its existance from its effects. Not a really bad practice, but as the other posts around here indicate, we've got a long way to figuring out what the hell is really going on.

Re:Enlighten me

[cold fjord]

The rest seems to be something that interacts only gravitationally... it might be a particle we haven't discovered yet.

It is possible that most of the dark matter needed by current theories to explain the universe we see doesn't really exist, and that our understanding of gravity is wrong. The TeVeS theory, developed from MOND, may be able to explain the universe without requiring that most of it be made of dark matter and dark energy. See Gravity's dark side. Also mentioned in a previous Slashdot story. To really know, TeVeS will need a lot more work done with it. That will be a challenge since the dark matter theories get the vast majority of attention, time, and funding.

Re:Enlighten me

[Kagura]

Don't people glow in the infrared? Remember that infrared is also light, just not visible light.

Re:Enlighten me

[glwtta]

Some string theorists believe dark matter may be gravitons, emitted by matter on adjacent branes

Yeah, but string theorists make theoretical physicists look like scientists :)

Re:Enlighten me

[radtea]

Some portion of it could be ordinary matter that's simply non-luminous, but I think there are observations that limit that to a small proportion.

Big Bang nucleosynthesis limits the amount of baryonic (that is, "normal") matter to a relatively small fraction of the total observed mass of the universe. The basic idea is that we know how big the universe was when protons and neutrons (collectively known as nucleons) were being formed--at some point the cosmic fireball cooled off to the point where quarks were no longer free, so they condensed into nucleons. We also know that the lifetime of a free neutron is about 15 minutes, so there was only about an hour for nuclei more complex than hydrogen to form.

So, if the universe was VERY dense in the hour or so after nucleon formation then every single proton would have run into a neutron or two and there would be almost no plain old hydrogen in the universe--everything would be helium and deuterium. On the other hand, if the the universe were extremely diffuse during that single hour there would be hardly any helium--only the few percent made by stellar fusion and supernova in the past ten billion years. As it is, we are pretty sure based on observations and theory that about 20% of the helium in the universe was formed in the Big Bang. That, plus some more problematic numbers from deuterium and lithium and helium-3, give us a very good estimate of the total baryonic mass in the universe.

The visible mass is quite a bit smaller than the total baryonic mass, and there is some reason to believe that the flat rotation curves of spiral galaxies are due to baryonic dark matter, although it would have to be in the form of small clumps of matter like comets or dead stars or something to not do any significant scattering of light.

Dark matter on larger scales is completely unrelated to galactic dark matter--the use of the single term "dark matter" for these totally unrelated problems is unfortunate and confusing, as I point out every time this topic comes up on /.

The observation reported here, like the colliding galactic clusters observation reported a month or so ago, is amongst our first clear view of extra-galactic dark matter, which is too copious to be explained as normal baryonic matter.

The problem that cold dark matter theorists have to deal with is that the extra-galactic dark matter can't just interact gravitationally, because gravity is too weak a force to produce structures in the short time the universe has been around. To clump in the manner observed, extra-galactic dark matter has to have some mechanism for losing energy. Otherwise two pieces of dark matter (or a piece of dark matter and a peice of ordinary matter) would just pass through each other. The dark matter would never be slowed down by anything, and so would never form clumps on any scale.

So it is probable that extra-galactic dark matter is pretty exotic, or that something was sufficiently different in the early universe to make gravity sufficiently dissipative to form the observed clumps. Either way, the flood of observations using these new microlensing techniques is going to start killing off theories in droves--at least those theories that make actual predictions.

Re:Enlighten me

[ceoyoyo]

It is possible, but observations seem to be making it less and less likely. It doesn't explain these Hubble observations very well, and it doesn't explain the colliding galaxies observation.

Even without those, as you said, modifying gravity might explain most of the observations. That still leaves some others, that we'd need something else to explain. Even the modified gravity researchers are saying ou still need some dark matter to make everything work.

So, Occam's razor -- which is the simplest explanation: dark matter, or dark matter plus modified gravity?

Not to say that gravity research wouldn't pay dividends, but the reason dark matter is getting the most attention is because it's the most likely.

Re:Enlighten me

[ceoyoyo]

Good explanation. Thank you.

Re:Enlighten me

[forand]

Sorry this is not true. It is true on the subset of KNOWN matter that we deal with on a day to day basis. However you can get rather strange states of matter or collections of unique particles that do not, like a room full of neutrinos isn't going to radiate anything other than neutrinos.

Re:Enlighten me

[TapeCutter]

Close, dark matter is the "hack" we use to make our theories fit our obervations. If we had not observed "something" we would not need to invent the name "dark matter" to label it.

I fail to see how it is a "poor excuse" for anything, it's mearly a description of something we don't fully undersatnd but can indirectly observe and therfore label. Maybe our elegant theories will need to change to account for future observation but right now our notion of what we label as "dark matter" explains the observed anomolies better than any other concept, including the proposed modifications to gravitational theory.

For a historical perspective you just need to go back a hundered years to a time when scientists were having a similar debate about the existance and structure of atoms. Sure the model of atoms looking like "a pudding with razor blades stuck in it" fell by the wayside when it failed to explain all the observations. That is how science progresses, it's an evolution of ideas and analogies, not a static statement of "the truth".

Re:Enlighten me

[Carmelbuck]

...there is some reason to believe that the flat rotation curves of spiral galaxies are due to baryonic dark matter, although it would have to be in the form of small clumps of matter like comets or dead stars or something to not do any significant scattering of light.

Microlensing surveys have already placed upper limits of well under half the dark matter in a typical galactic halo being baryonic.

Dark matter on larger scales is completely unrelated to galactic dark matter--the use of the single term "dark matter" for these totally unrelated problems is unfortunate and confusing, as I point out every time this topic comes up on /.

On what, exactly, are you basing this statement? It's certainly not the majority scientific view.

To clump in the manner observed, extra-galactic dark matter has to have some mechanism for losing energy.

Do you have a citation for this? To the best of my knowledge, none of the (generally quite successful) structure formation simulations include any interaction for dark matter besides gravity.

I'm not criticising (yet), but you're making what appear to be claims based on evidence, and I'm wondering what that evidence is.

Re:Enlighten me

[TMB]

Just one minor quibble:

The problem that cold dark matter theorists have to deal with is that the extra-galactic dark matter can't just interact gravitationally, because gravity is too weak a force to produce structures in the short time the universe has been around. To clump in the manner observed, extra-galactic dark matter has to have some mechanism for losing energy. Otherwise two pieces of dark matter (or a piece of dark matter and a peice of ordinary matter) would just pass through each other. The dark matter would never be slowed down by anything, and so would never form clumps on any scale.

Actually, gravity on its own is easily enough to produce the structure we see. The dark matter doesn't dissipate any energy to form clumps, it simply falls toward the overdense regions, which become even more overdense because of all the infalling dark matter, ad infinitum. Each individual dark matter particle may pass right through all the other dark matter particles and go out the other side, but as long as it's moving at less than the escape speed then it turns around and comes back, bouncing around inside the clump forever.

In fact, one of the main problems now is that cold dark matter produces too many small clumps compared to the observations.

[TMB]

Re:Enlighten me

[noigmn]

I'm not in theoretical physics so don't know much on the topic, but there seems to be a lot of beating around in the dark so I'll ask.

Is there any chance that there's two classes of graviton? Like the electromagnetic force has attract opposite, repel like. Could the gravitational force which has some similarities to the electromagnetic force have attract like, repel opposite. Hence to a point perhaps keeping this opposite stuff away from really close contact with our stuff and maybe causing expansion and a few other effects.

And while I'm at it, is it possible stuff escapes black holes because passing matter causes small changes in the gravitational field hence shifting the event horizon and causing the photons that are orbiting near the event horizon to escape orbit.

Re:Enlighten me

[Khyber]

Brrrrrraaaaannnneeesssss *shambles around aimlessly*

Re:Enlighten me

[elrous0]

"Dark Matter" always struck me as a kind of dodge. We discover that the universe doesn't have enough mass to account for the current pet theories in physics, and so rather than question the theories themselves, we invent a mysterious new "dark matter" that we can't actually see (but which MUST be there because the theories can't POSSIBLY just be wrong).

It strikes me as a wishful-thinking fiction more than a testable, observable phenomenon.

-Eric

Re:Enlighten me

[Ambitwistor]

"Dark Matter" always struck me as a kind of dodge. We discover that the universe doesn't have enough mass to account for the current pet theories in physics, and so rather than question the theories themselves, we invent a mysterious new "dark matter" that we can't actually see (but which MUST be there because the theories can't POSSIBLY just be wrong). This doesn't have anything to do with "pet theories", it has to do with the very basic fact that bodies in space aren't behaving gravitationally in the way we think they should. There are really only two possibilities: there are sources of gravity other than what we can see, or the laws of gravity are different from what we think. Both possibilities have been considered, and the first is the one that has stood up best to observational tests.

You have a simplistic characterization of the situation which has nothing to do with the reality. The astrophysics community didn't say around and insist, "Duh, we must be right about everything — except the sources of matter — and therefore dark matter has to exist." Dark matter was resisted for decades. Heavily. It's just that it has continued to work, and pass new tests, and the alternatives haven't.

It strikes me as a wishful-thinking fiction more than a testable, observable phenomenon. Despite the numerous independent observational tests it has passed, and alternative theories have failed. Curious.

Re:Enlighten me

[Ambitwistor]

Is there any chance that there's two classes of graviton? Like the electromagnetic force has attract opposite, repel like. Could the gravitational force which has some similarities to the electromagnetic force have attract like, repel opposite. That would require a vector theory of gravity. General relativity is a tensor theory. There are combined tensor-vector theories that have features of both, as you suggest. But there is no observational evidence in their favor right now.

And while I'm at it, is it possible stuff escapes black holes because passing matter causes small changes in the gravitational field hence shifting the event horizon and causing the photons that are orbiting near the event horizon to escape orbit. No. An event horizon, by definition, is a region from which nothing can ever escape. The horizon of a black hole can distort, and something near a black hole can be perturbed away from it, but anything that escapes a black hole was never within the event horizon to begin with — by definition.

Re:Enlighten me

[Anonymous Coward]

So in other words, its a lot like evolution. No one has observed a species evolve but we're pretty sure it happens. Funny how the most important things can't be proven or disproved isn't it.

Re:Enlighten me

[Ambitwistor]

We have observed new species evolving. And evolution certainly can be disproved; it makes plenty of concrete predictions.

Re:Enlighten me

[Omnifarious]

This is actually made a much less tenable theory by the latest gravitational lensing result involving colliding galaxies. Presumably matter on an adjacent brane would interact with itself other than gravitationally, but it's clear from the lensing that the dark matter didn't interact with itself other than gravitationally.

Perhaps the laws of physics are different on the other brane, but it still seems odd that the two bunches of matter would pass right through eachother.

Well, there could be two adjacent branes I suppose. But that's just starting to get silly.

Re:Enlighten me

[TapeCutter]

"Funny how the most important things can't be proven or disproved isn't it."

Funny how that statement proves you are an AC wanker, but I suppose that's not important.

Re:Enlighten me

[IHateEverybody]

This is actually made a much less tenable theory by the latest gravitational lensing result involving colliding galaxies. Presumably matter on an adjacent brane would interact with itself other than gravitationally, but it's clear from the lensing that the dark matter didn't interact with itself other than gravitationally.

Perhaps the laws of physics are different on the other brane, but it still seems odd that the two bunches of matter would pass right through each other.

Well, there could be two adjacent branes I suppose. But that's just starting to get silly.

Actually, some string theories require that this "silliness" occur. Branes interact gravitationally and one theory suggests that the universe came into existence when our brane collided with another. The branes would have to be adjacent if they are close enough to collide.

Re:Enlighten me

[Omnifarious]

Actually, some string theories require that this "silliness" occur. Branes interact gravitationally and one theory suggests that the universe came into existence when our brane collided with another. The branes would have to be adjacent if they are close enough to collide.

Yes, I know. But in order to have two large clumps of dark matter pass right through eachother, the dark matter (which is supposedly matter on an adjacent brane) has to either not interact with itself or the two clumps of dark matter that used to be part of the two separate galaxies have to each be on a different adjacent brane so they can't interact with eachother.

In the galaxies colliding gravitational lensing thing, it was very clear that a large portion of the mass of each of the two colliding galaxies just sailed straight on by without interacting significantly with either itself or the other matter other than gravitationally.

Re:Enlighten me

[noigmn]

No. An event horizon, by definition, is a region from which nothing can ever escape. Not sure on this, wouldn't it probably depend at what angle it crosses and the sequence of events. ie. if a photon enters the event horizon at a shallow angle so it has not dropped below the event horizon by very much, then the event horizon is perturbed by a large mass passing close to the black hole, would the photon escape again? And if not, why not?

Re:Enlighten me

[Ambitwistor]

ie. if a photon enters the event horizon at a shallow angle so it has not dropped below the event horizon by very much, then the event horizon is perturbed by a large mass passing close to the black hole, would the photon escape again? And if not, why not? No, it would not escape, because as I said, an event horizon is defined to be a region from which nothing ever escapes. To precisely locate it, you have to know everything about what will happen in the vicinity of the black hole, including everything that will perturb it at any time in the future — only then can you tell which objects will or will not eventually be able to escape.

In many respects, that makes an "event horizon" a very difficult concept to work with, and it means that you can't actually locate an event horizon exactly. There is nothing physically special that happens at an event horizon; it's defined by what may happen infinitely far in the future. For that reason, there are concepts such as "apparent horizons" that are physically possible to locate.

Re:Enlighten me

[noigmn]

Cool, that makes sense. Thanks for the replies.

Mod parent up a few.

dark matter does not exist

[ars]

"beautiful confirmation" of standard theories?????

What standard theories? Dark matter does not exist, as least not as far as anyone (except astronomers with good imaginations) knows. There is a very nice (and complete!) standard model of physics, and dark matter holds no place.

I should qualify, I'm talking about theroes of non-baryonic dark matter and even worse dark energy.

Regular matter, that is simply dark - i.e. cold, and not emiting light, does not bother me. But making up particles no one has ever seen just because you don't understand what you are seing is fitting facts to the data.

Scientists often discuss new theories, etc, and in that context dark matter has it's place, but to claim it exists - as this story does - without being able to actually measure anything is quite silly and premature. If you don't understand something, say so, don't invent plausable explanations that have nothing supporting them except your lack of knowledge.

Re:dark matter does not exist

[ars]

I shouldn't have used the phrase "is fitting facts to the data", please ignore it, I misstyped. Pretend the sentence just ended in a ?

Re:dark matter does not exist

[ceoyoyo]

Isn't that exactly what they did? They measured mass distributions through gravitational lensing and noted the places where there was more apparent mass then there should be. You can theorize that gravity works strangely at large scales, and inconsistently too, since they found clumps, but the simplest explanation that matches the observations is that there is something with mass that we can't see. It might be normal matter, but the fact that there's an enormous amount of it and it somehow avoids rubbing together and getting hot like all the other matter we know of is problematic. When galaxies collide it also seems to just keep on going while the normal matter slows down when it hits something going the other direction. Given those two observations (dark and appears not to interact other than gravitationally), a subatomic particle isn't so bad an explanation. It's not so far fetched either -- we know of other particles that have those properties. They're called neutrinos.

Re:dark matter does not exist

[HarveyTheWonderBug]

"beautiful confirmation" of standard theories?????

Yes indeed. The standard paradigm for the evolution of the Universe is the widely accepted lambda-CDM model, or Cold Dark Matter with a cosmological constant (or dark energy). The recent results of WMAP, of the high-z supernovae, all point toward a set of cosmological parameters where the energy density of the universe is made of:

• 70% of dark energy
• 30% of matter
  • out which, stars, gas, neutrino are making at most 5%
  • so we are left with 25% of dark matter

So yes, dark matter is widely accepted. It's not satisfying because we have no clue about what it is (it clearly does not interact electromagnetically), but we can feel its gravitational pull. Coming up with a good theory on its nature is one of the hardest challenges in modern astrophysics.

Re:dark matter does not exist

[Too Much Noise]

But making up particles no one has ever seen just because you don't understand what you are seing is fitting facts to the data.

You do realize that science is 'just' fitting theoretical models to data, do you? And that, while a model survives by being able to fit more types of data, it usually starts by fitting one or a handful?

Scientists often discuss new theories, etc, and in that context dark matter has it's place, but to claim it exists - as this story does - without being able to actually measure anything is quite silly and premature.

You are in error here. There are observations seeing dark matter (see here for example) - it's just that they don't provide information on what it is. And ultra-low cross-section particles are not as fantastic as you seem to make them - just because we don't know they exist we shouldn't rule them out. Or in. File it as usually under 'maybe' until further testing.

Re:dark matter does not exist

[Ambitwistor]

What standard theories? The standard theories of large-scale structure formation in the early universe, which is mediated by non-baryonic dark matter.

Dark matter does not exist, as least not as far as anyone (except astronomers with good imaginations) knows. Wow, that's a compelling counterargument. However, it neglects the decades worth of observational evidence in favor of dark matter in the form of galactic rotation curves, the motions of satellite dwarf galaxies, gravitational lensing, measurements of galactic gas temperatures (which depend on the local gravitational neighborhood), anisotropies in the CMBR, the rate and structure of large-scale cosmological structure formation, etc.

There is a very nice (and complete!) standard model of physics, and dark matter holds no place. Actually, one of the leading dark matter candidates is the axion, which was introduced into the Standard Model to resolve the strong-CP problem. However, the astronomical evidence indicates that the Standard Model of particle physics is most likely not complete, and that at least one new weakly-interacting massive particle is needed.

Regular matter, that is simply dark - i.e. cold, and not emiting light, does not bother me. But making up particles no one has ever seen just because you don't understand what you are seing is fitting facts to the data. There is nothing wrong with "making up particles no one has ever seen" in order to explain discrepancies in either theory or observation. It's rather the point of science, to frame new hypotheses. Historically, see the prediction of the positron, on the basis of theoretical consistency between quantum mechanics and relativity, or the prediction of the neutrino, on the basis of apparent non-conservation of energy.

Scientists often discuss new theories, etc, and in that context dark matter has it's place, but to claim it exists - as this story does - without being able to actually measure anything is quite silly and premature. If you don't understand something, say so, don't invent plausable explanations that have nothing supporting them except your lack of knowledge. Dark matter is a plausible explanation precisely because it is supported so well by numerous disparate observations. There are other ways one can attempt to explain various discrepant observations (e.g., by modifying the laws of gravity), but dark matter is far and away the most successful, as it passes all known independent tests. There's no reason why an ad-hoc patch designed to explain galactic rotation curves should also end up explaining, say, cosmological expansion, or large-scale structure. And it's silly to claim that we cannot measure anything: we can measure the gravitational effects of dark matter.

Sure, everyone would love it if we could detect dark matter particles directly — and if they interact non-gravitationally, we hopefully will someday. But what's silly is to claim that we have little reason to believe that dark matter particles exist.

Re:dark matter does not exist

[Carmelbuck]

Every time an article regarding dark matter is posted on Slashdot, there are nonsense "fudge factor!!1!" postings like the above. And every time, like-thinking idiots mod them up as "Insightful" or "Interesting". And every time, I suspect, people like me get the urge to go through and respond to every single one, but have to limit ourselves.

So let's start at the beginning, shall we? Galaxy rotation curves indicate that there is more mass in galaxies than would be inferred from the luminous matter. How do we know that it's not clouds of cold gas? Because that's ruled out by 21cm observations and by studying the absorption spectra of extragalactic objects. How do know that it's not clouds of hot gas? Becasue that's ruled out by UV and X-ray observations. How do we know that it's not brown dwarfs and black holes? Because that's ruled out by microlensing surveys.

Now, studies of galaxy dispersion velocities in clusters indicates that there's more mass in galaxy clusters than than would be inferred from the galaxies themselves, plus the intracluster medium which is observed in the X-ray. This is verified to high accuracy (i.e., the estimates of the total cluster mass are in close agreement) by hydrostatic X-ray mass measurements and by weak lensing observations. How do we know that it's not clouds of cold gas? Because that couldn't coexist with the hot gas, and because the dark matter spatial distributions are clearly different from the gas distributions. How do we know that it's not clouds of hot gas? See "intracluster medium" above. How do we know that it's not brown dwarfs and black holes? Because there's no mechanism for moving large numbers of objects out of the galaxies into the ICM (there are some intracluster stars, yes, but relatively very few--and the number of those gives us hints as to the number of non-luminous objects similarly ejected). How do we know that it's not neutrinos? Because neutrinos are experimentally shown to be too light and too fast, and cosmological constraints show that too few would have been produced in the Big Bang.

Now, studies of cosmological structure formation indicate that the size and number of galaxy clusters in the universe are not consistent with what would be expected given an all-baryonic universe. How do we know that...er...well, that's that. Cold collisionless dark matter is required to make the simulations work.

How do we know that modified gravity isn't the answer? See multiple independent lines of evidence above. There are no theories of modified gravity that come even close to explaining all of the above. The MOND people cheerfully acknowledge this, even if their advocates on Slashdot don't.

Look, the history of physics is replete with things whose existence was inferred long before they could be directly observed--neutrinos, quarks, atoms themselves, and much, much more. It's simply asinine to suggest that "we haven't directly measured it" means "it doesn't exist". Heck, we only really "see" subatomic particles because of the photons given off when they interact with one thing or another--"seeing" dark matter via measurements of its gravitational effects is hardly less direct.

And we'll just ignore the nonsensical "fitting facts to the data". The bottom line is, there are multiple, independent lines of evidence that dark matter exists, and that it is non-baryonic. Uninformed posters on Slashdot can pat themselves on the back for their intelligence as much as they want, but they're only fooling themselves.

Re:dark matter does not exist

[fermion]

On one level, I consider dark matter to have the same credibility as the æther. An interesting concept, but largely created as hack to the model. The æther is shown not to exist and we have a more robust theory for the propagation of light. I suspect that the same will be true dark matter, and it will lead to a more robust theory of gravity.

That said, as the universe is explored in more detail, we increasingly see that the standard model is robust but has some issues, in the same way that more detailed analysis of the solar system validated Newtonian mechanics with caveats. Many things behave as they should. The Hubble recently detected dark matter behaving as predicted. Certain unexplained acceleration in the cosmos has renwed interest in the Einstein cosmological constant, which if it exists, renews the presence of the æther, albeit in a different form.

The evolutionary shifts in our understanding of the universe cannot be predicted. Dismissing a concept simply because it is a mathematical hack is a mistake. In reality we use mathematics because it is a precise language that will often lead us to an unobserved reality. Recall that quantum mechanics is based on Plank proposing the ludicrous mathematical hack that energy cannot be any arbitrary value. Recall that special relativity is based on Einstein's assertion that equations should be symmetric. And, for the record, we must also admit that there is no evidence for a particle of magnetic or gravitation force.

In any case, the search for the implausible particle that only interacts with the universe through gravity, and is unaffected by all other forces, will continue. What is for sure is the no matter what happens, the future likely holds a much stranger picture anything we might imagine today.

Re:dark matter does not exist

[HarveyTheWonderBug]

mod parent up !

Re:dark matter does not exist

[Ambitwistor]

Seconded.

Re:dark matter does not exist

[Ambitwistor]

On one level, I consider dark matter to have the same credibility as the æther. An interesting concept, but largely created as hack to the model. Aether theories didn't make any predictions that correctly explained any new observations. Dark matter does.

Certain unexplained acceleration in the cosmos has renwed interest in the Einstein cosmological constant, which if it exists, renews the presence of the æther, albeit in a different form. The cosmological constant is a modification of the laws of gravitation, not anything like what was historically referred to as the aether.

Dismissing a concept simply because it is a mathematical hack is a mistake. In reality we use mathematics because it is a precise language that will often lead us to an unobserved reality. This point is well taken. However,

Recall that special relativity is based on Einstein's assertion that equations should be symmetric. That wasn't Einstein's motivation for introducing special relativity. (On the other hand, the complete form of Maxwell's equations of electromagnetism were based on Maxwell's assertion that the equations should be symmetric.)

And, for the record, we must also admit that there is no evidence for a particle of magnetic or gravitation force. The electromagnetic force is mediated by the photon, for which there is abundance evidence. Gravitons, as you say, currently have no experimental evidence in their favor.

Re:dark matter does not exist

[sholden]

It's pretty clear the phrase that was meant to be typed was "making shit up".

Because galaxies don't rotate the way our current theory of gravity says they should, because gravitational lensing isn't working the way our current theory of gravity says it should, because of a bynch of other thing I guess, the accepted solution it to declare that 95% of the universe is made of stuff we can't directly detect, can't do experiments on, doesn't exist locally, and is completely different from the universe we do observe and interact with.

But it makes the numbers work, so it's all good.

Re:dark matter does not exist

[NeoSkink]

Indeed! Carmelbuck covered the reasons Dark Matter is part of the standard cosmological model very well. His comment really should be the highest moded, not the above uninformed "Dark Matter is just made up!" rants.

Re:dark matter does not exist

[Ambitwistor]

Because galaxies don't rotate the way our current theory of gravity says they should, because gravitational lensing isn't working the way our current theory of gravity says it should, because of a bynch of other thing I guess, You act as if having a bunch of observational evidence for dark matter is unimportant.

the accepted solution it to declare that 95% of the universe is made of stuff we can't directly detect, Would dark matter be more palatable to you if it only made up 5% of the universe? Why does it suddenly become more implausible if it makes up most of the universe. It's because it makes up most of the universe that we can even tell it's there.

can't do experiments on, That remains to be seen; we may be able to create such particles in accelerators, and we may also be able to detect them in the Sun, in cosmic ray experiments, etc.

That being said, even if we can't do experiments on dark matter, why does that suddenly make dark matter implausible, in the face of all the other astrophysical phenomena it explains? Is there some law of the universe that says that all matter must be easily producible and manipulable by humans?

doesn't exist locally, That's false. It surely does exist locally.

That being said, even if it didn't exist locally, why does that suddenly make dark matter implausible, in the face of all the other astrophysical phenomena it explains? Is there some law of the universe that says that everything interesting or important in the universe has to exist nearby?

and is completely different from the universe we do observe and interact with It's not that different. Ordinary neutrinos have most of the properties needed to be dark matter; they're just not massive enough.

That being said, ... well, you get the idea.

Re:dark matter does not exist

[yusing]

70% of the universe is made of some theoretical "substance" that hasn't shown up in several decades of particle physics observations??

I smell a Thomas Kuhn moment in the making. Or at least, a phlogiston moment.

Explaining the universe is hard. But saying stuff like "it's real", even implying that it is ... when there's not even a working theory about it yet ... is dangerous to the craft. When people get religious about stuff like string theory, it endangers science.

Re:dark matter does not exist

[Ambitwistor]

70% of the universe is made of some theoretical "substance" that hasn't shown up in several decades of particle physics observations?? Why should it, if it's weakly interacting and massive? (Which are precisely the properties it needs to explain the astrophysical observations, by the way.)

I smell a Thomas Kuhn moment in the making. Or at least, a phlogiston moment. The difference is that dark matter keeps on passing new and independent observational tests.

Re:dark matter does not exist

[Ambitwistor]

Oops, you were referring to dark energy, not dark matter. Dark energy may not be a "substance" at all; the best current explanation of dark energy (the cosmological constant) is a modification of the laws of gravity, not a new kind of particle.

Re:dark matter does not exist

[yusing]

Dismissing a concept simply because it is a mathematical hack is a mistake.

But talking about hypotheses as if they were solidly established theoretical constructs, dovetailing with the framework of well-established physics, does, IMHO, a disservice to science. For one thing, it tends to make it hard to see alternatives by freezing an attitude and blinkering the imagination needed to see alternatives. For another, it tends to make some laymen skeptical about *any* claims of science.

IIW, a hypothesis repeated with too much zealousy becomes an icon.

Re:dark matter does not exist

[Ambitwistor]

But talking about hypotheses as if they were solidly established theoretical constructs, dovetailing with the framework of well-established physics, does, IMHO, a disservice to science. Dark matter is a solidly established theoretical construct. It hasn't risen to the level of "proven" (insofar as anything can be "proven" in science), but there is a hell of a lot of evidence in its favor.

For one thing, it tends to make it hard to see alternatives by freezing an attitude and blinkering the imagination needed to see alternatives. There are alternatives to dark matter. They're not faring too well compared to dark matter when it comes to explanatory power, but they exist. I know you'd like to play amateur psychologist to the astrophysics community, but alternatives are considered. It's just becoming harder and harder to come up with alternatives that work, since observations have excluded so many of them. That's the reason why dark matter has become the mainstream explanation. Not because of "blinkered imagination", but because it works and the alternatives just don't. Alternatives that have at least some success do get attention, in proportion to the number of tests they pass.

For another, it tends to make some laymen skeptical about *any* claims of science. Possibly because said layman are unaware of the decades of extensive testing the theory has undergone and all of the alternatives that have failed to measure up.

Re:dark matter does not exist

[HarveyTheWonderBug]

I was refering to the energy density of the universe. You are mixing dark energy and dark matter.

Since the famous E = mc2 we can compare the energy content of the universe (like photons) and matter (like the atoms you are made of). So yes, to explain all the current observations, we need a lot of dark energy (or call it a cosmoligical constant if you'd like). There are theories to explain it, like a scalar field, etc...

But that's not the subject of the paper and press releases. They are about dark matter. That is something with a mass, so you can actually observe it's gravitational effect on the normal luminous matter. And there are some clues as to its nature, but no definitive answers yet...

Re:dark matter does not exist

[radtea]

Scientists often discuss new theories, etc, and in that context dark matter has it's place, but to claim it exists - as this story does - without being able to actually measure anything is quite silly and premature.

The whole point of these observations is that they are an entirely new probe of extra-galactic dark matter, and they are consistent with dynamical estimates of extra-galactic dark matter distributions.

Ergo, they consistute compelling evidence that extra-galactic dark matter is not just a mistake fix for an error in our understanding of the dynamics of the universe on a large scale, but rather a real, observable component of the universe that has multiple unrelated effects.

The new lensing and colliding-cluster measurements are precisely "measuring something" that compels anyone who does not have a faith-based epistemology to believe that extra-galactic, non-baryonic dark matter exists, in the ordinary and always somewhat uncertain meaning of the term "exists".

Previously, dark matter was plausible but unconvincing. Now it would be surprising as hell if anything else turned out to be the correct explanation for the dynamical anaomalies that gave rise to the hypothesis in the first place.

Re:dark matter does not exist

[YttriumOxide]

Picture for a moment, two universes "side by side" in a dimension we can not physically see, but effectively "overlaid" in all dimensions we can measure/see. No interactions take place between these two universes other than gravity (for reasons that are exaplainable, but beyond the scope of this post).

The influence of the gravitational pull from the one universe would certainly have the exact same features/constructs as what is described here (clumped in parts, not in others etc)

Because these two universes interact gravitationally, it would make sense that matter and "dark matter" would tend to be found in the same places as well, which is exactly what has been observed. The occasional area where they're not found together (dark matter without matter) is also not so hard to comprehend (as would be matter without dark matter if we found that as well).

For those of you who think I'm talking nonsense - this is a dramatic oversimplification of what brane theory (related to string theory/M theory) would have to say on the subject. For those of who you think it's not science because it's not provable, you're probably right... but it's an avenue that I think requires some scientific thought put in to it so that one day it may well become "true" science.

Re:dark matter does not exist

[complete loony]

I'd also add; Even if (and that's a pretty big if) the theory of dark matter is wrong and there's a better answer, if it's the closest model we have to reality it's still worth using. Newton was slightly wrong about gravity, and we still use his model in situations where relativity has negligible impact.

Re:dark matter does not exist

[anandsr]

"How do we know that modified gravity isn't the answer? See multiple independent lines of evidence above. There are no theories of modified gravity that come even close to explaining all of the above."

True. Nothing can really provide better answers than saying god does everything. Fact is that Dark Matter and Dark Energy are not falsifiable theories. They can only be proven true, by finding the so called dark matter, but cannot be proven false by any means.

The best Dark Matter theories require 2 parameters per galaxy to fit a galaxy and this does not include the M/L ratio. While MOND fits almost all galaxies and the remaining within limits, with a single universal parameter, in addition to the M/L ratio. Also compared to the Dark Matter fits MOND fits even the wiggles in the curves very well.

There is no dispute on the success of MOND to fit Galaxies. The fact that it is not widely accepted is because it is ad-hoc, and it is not an effective theory. But now with TeVeS it is now an effective theory. Now, it can also fit gravitational lensing and WMAP data.

It is good that you agree that MOND people accept their failings. I only wish that the scientific establishment did the same with their own theories and accepted the short comings of Dark Matter and Dark Energy.

It is a well established fact that Einsteins GR is not the ultimate theory. Einstein himself never believed that. It is a fact that it doesn't work well with Quantum theories. All the other 3 forces are defined by a type of Conformal field thoery, except for Gravity. It seems obvious to me that ultimately Gravity will also be defined by a type of Conformal Field theory. Which will not look like the Newtonian gravity of today, except at solar system scales. It will also resolve all the numerous problems of Cosmology, flatness problem Dark Matter Dark Energy etc. Unfortunately there is only one person working on a Conformal field of gravity.

I think MOND and TeVeS will be a better approximation at the Galactic level in the mean time. I am sure it will not work very well at Cluster level and larger structures.

Re:dark matter does not exist

[Ambitwistor]

Fact is that Dark Matter and Dark Energy are not falsifiable theories. Of course they are. You can't explain any arbitrary set of independent phenomena using dark matter. (And I would like to hear your reason why "dark matter" is not falsifiable, but "modified gravity" is.)

There is no dispute on the success of MOND to fit Galaxies. The fact that it is not widely accepted is because it is ad-hoc, and it is not an effective theory But mostly because it fails other observational tests that dark matter passes. MOND does great on galaxies, as you say, but that's no good if it's wrong!

But now with TeVeS it is now an effective theory. Now, it can also fit gravitational lensing and WMAP data. The existence of TeVeS doesn't make MOND suddenly able to explain results, such as the Bullet Cluster, that MOND currently gets wrong.

It is good that you agree that MOND people accept their failings. I only wish that the scientific establishment did the same with their own theories and accepted the short comings of Dark Matter and Dark Energy. Sigh. I doubt you know anything about what the "scientific establishment" thinks about dark matter.

All the other 3 forces are defined by a type of Conformal field thoery, except for Gravity. That's wrong. The Standard Model is not a conformal field theory. It can't be in any theory with massive particles.

It seems obvious to me that ultimately Gravity will also be defined by a type of Conformal Field theory. [...] It will also resolve all the numerous problems of Cosmology, flatness problem Dark Matter Dark Energy etc. That's a lot of faith in a theory that has shown no ability to actually solve any of those problems, let alone all of them.

Re:dark matter does not exist

[fm6]

They can only be proven true, by finding the so called dark matter, but cannot be proven false by any means.

You're saying that there are no crucial experiments relating to dark matter and never can be. That's a big claim, and one you're going to have to justify.

"There's something out there"

[Anonymous Coward]

Why is it easier for Slashdotters to believe in dark matter than it is to accept another's believe in a God? Dark matter is an unproven theory.. all scientists really know is that there is something out there that may or may not be exherting somekind of magical force that may or may not explain away some unbalanced numbers (42).

Re:"There's something out there"

[thryllkill]

Maybe because Dark matter doesn't damn you to hell for wanting to have sex? Or because it is not based on campfire tales of desert nomads from thousands of years ago, but rather mathematical equations, observations, you know, scientific stuff.

Re:"There's something out there"

[wrf3]

Why is it easier for Slashdotters to believe in dark matter than it is to accept another's believe in a God?

Dark matter doesn't make a claim on one's life. The other replier who said, "dark matter doesn't damn you to hell for wanting to have sex", while wrong, illustrates this point. "If God doesn't want what I want then screw Him/Her/It/Them".

Re:"There's something out there"

[Anonymous Coward]

Treating theories as fact and a foundation for further research hardly seems "scientific." Another that comes to mind is the _theory_ of evolution... why is this taught in the public schools as if it were any more proven than some theory of a supreme being?

Re:"There's something out there"

[chazwurth]

Next time you get an infection, please do us all a favor and take the ID challenge: http://www.doonesbury.com/strip/dailydose/index.ht ml?uc_full_date=20060702

Re:"There's something out there"

[Anonymous Coward]

hmm... "evolved"? I'd say more like "adapted." When the cold bug natually mutates enough to no longer be a cold bug let me know.

Re:"There's something out there"

[Maekrix]

Well, while I don't have the time to explain the complex equations, dark matter is simply the substance that makes up the Flying Spaghetti Monster's two delicious meat balls. Praise His Noodliness. And don't worry, Pastafarians have flimsy moral standards. FSM doesn't care if you have sex- evidence? Heaven has a Beer Volcano and Stripper Factories..

Re:"There's something out there"

[chazwurth]

Have you read Darwin? You do understand that according to the theory, speciation occurs over vast periods of time, and in the short term, this occurs through adaptation, right? If you get that much, you must understand that your gripe boils down to this: we can't have adequate evidence that something occurs without watching the process from beginning to end, and thus observation of adaptation plus the fossil record plus common genes shared between distinct species isn't good evidence.

If that's your position, please let me know the next time God shows up at your house; I have some complaints I'd like to make.

Hmmm...

[kitsunewarlock]

The map streches back to half the life-span of this universe. That means that if a single unit of a radioactive atom exists in the universe with just the right value...
Uh-oh! It just reached half-life! Nasa better hurry up and find this long lasting nuclear element before its lost forever. We wasted the first half of this universe's existance, lets not waste the second.
Oh wait...this statement would only be true if the universe was ending at exactly this moment and the hubble did this scan half-a-universe's-life-span ago.

RTFA

[Swimport]

"We understand statistically what those galaxies are supposed to look like,"
 
So this map is based on what they assume the universe should look like. Then they use how its different to find where the dark matter might be. Doesnt sound 100% certain by any means, but its a nice picture.

Re:RTFA

[HarveyTheWonderBug]

Actually astronomers do :). Most galaxies are "disk galaxies", i.e. lenticulars and spirals. Face-on (viewed from above), they look like a disk. So they should look like ellipsoids when viewed on the sky, due to their inclination. But this basic shape gets distorted when viewed through a lens (in this case, the lens is a massive object in front). The distortions are very small, so what astronomers do is that they measure the shape of as many galaxies as possible in a given region, and look for a statistical departure from the expected one.
There is no assumption on the Universe is supposed to look like in this map. The only assumption is that the General Relativity of gravitation is correct. So far, it has not been disproved.

Re:RTFA

[TMB]

It's not so much that they assume what the universe should look like, as that they assume a particular property of the universe - that it's isotropic on large scales. Therefore, on average we view galaxies from a random angle and so the orientation of their images on the sky is random. You then look for statistical deviations in the orientations of the images due to lensing of the light by matter along the line of sight.

Isotropy is an assumption, but we have never detected a significant deviation from isotropy on large scales except for that due to effects that we expect - like the gravitational lensing that's used in this study.

[TMB]

Density Issues affecting the shape?

[popo]

Are all the "solid" areas of the 3d shape a roughly similar density of dark matter?

Seems to me there would be a wide range of density distributions. If so there must have been a human decision to decide
which level of density constitutes matter vs. empty space in this 3d depiction. I wonder how the 3d shape would change
if we arbitrarily moved this balance point of requisite density up or down the scale.

A Cool-Blue Model

[css-hack]

I don't know how much weight this "dark matter" theory holds (pun intended). But I was immediately interested when I saw their translucent blue 3d render of the stuff.

I wonder how many other people that works for...

Politically incorrect

[AlphaLop]

You should call it "Light Challenged" matter in this age of political correctness. Be more sensitive to other matter people!

Re:Blue Humor

[Anonymous Coward]

finger smelly?

HubbleSite.org press release

[grimJester]

Here.

I've tried to find something about whether this tells us something new about the properties of dark matter, but so far no luck. Anyone have a link to something more informative?

More links to PR

[HarveyTheWonderBug]

Here are the press release links: Nature, Hubble Space Telescope, European Space Agency and Subaru Telescope. The COSMOS project web page can be found there.

MOD PARENT UP

[Anonymous Coward]

mods on crack today. am i the only one that gets the joke?

Fermi paradox

[Anonymous Coward]

It's life, dammit. That's where everybody is.

Standard Model Complete... With Caveats

[BlackGriffen]

It misses one of the four fundamental forces of nature. You know, an unimportant little thing we call "gravity." Naturally, if there's a particle that only interacts gravitationally, it would also have to be missing from the standard model.

There's also the unresolved matter of actually observing a little particle that is in the Standard Model called the Higgs boson.

Trust me, the standard model is really really good, but it's far from complete.

More Theories

[Anonymous Coward]

'According to one researcher, the findings provide "beautiful confirmation" of standard theories to explain how structures in the Universe evolved over billions of years.'

More 'theories' with supposed scientific evidence propagated my the liberal media. Evolution, dark matter, next thing you know they'll have a 'theory' as to why we don't float off into space. Thank God that the force of his holy bowel movements keep us bound to this 3,000 year old center of the entire universe called Earth.

wtf is "dido"?

[r_jensen11]

and why is it a related link? Is there something special about dido@@@imperium...ph?

What's It Like, Other Than Dark?

[Doc Ruby]

Dark matter is becoming as household a term as "black hole". But what makes it dark? It's matter that doesn't interact with electromagnetism, so we can't see it - though its gravitation makes it detectable by other means. But what kind of matter doesn't interact with electromagnetics? Have we ever physically obtained any? Synthesized any? And supposedly something like 70% of the dark "matter" is energy. How does non-dark energy interact with electromagnetism, where the dark "stuff" does not?

Re:What's It Like, Other Than Dark?

[Ambitwistor]

But what kind of matter doesn't interact with electromagnetics? Any elementary particle that is electrically neutral.

Have we ever physically obtained any? Synthesized any? If by "any" you mean "electromagnetically non-interacting", then there are neutrinos. If you mean "the kind of dark matter that is needed to account for astronomical observations", then no, we haven't.

 

And supposedly something like 70% of the dark "matter" is energy. How does non-dark energy interact with electromagnetism, where the dark "stuff" does not? What is "non-dark energy"? Photons? I don't understand the question.

Re:What's It Like, Other Than Dark?

[Doc Ruby]

AFAIK, the Standard Model doesn't call for 70% of the mass of the universe to reside in neutrinos, or even 10%. Does the standard model describe the majority of mass as non-electromagnetic?

Photons aren't energy, they're matter with an energy equivalence proportional to their frequency. Maybe the descriptions of "dark energy" are inaccurate - they're describing dark matter at high energy. Perhaps neutrinos, or some other non-interacting particle in motion. But dark energy is described as different from familiar energy: negative pressure, something like "antigravity".

It just seems strange that we've never directly experienced dark matter/energy on or near Earth, when it's the large majority. Not that we should have it on our unique planet (in Feynman's terms - because we're on it, it's unique) - but can't we synthesize it, to study it? Especially if it's got nearly magical properties of undetectability and/or antigravity.

Re:What's It Like, Other Than Dark?

[Ambitwistor]

AFAIK, the Standard Model doesn't call for 70% of the mass of the universe to reside in neutrinos, or even 10%. No, it doesn't.

Does the standard model describe the majority of mass as non-electromagnetic? We have not discovered any dark matter candidates, if that's what you're asking. The Standard Model can be argued to contain the axion, although that's more of a solution to a fine tuning problem than a logical requirement of the model. The axion is a dark matter candidate. There are also extensions to the Standard Model (such as supersymmetry) which contain other dark matter candidates.

Photons aren't energy, they're matter with an energy equivalence proportional to their frequency. Photons are massless bosons and as such are generally not considered "matter".

Maybe the descriptions of "dark energy" are inaccurate - they're describing dark matter at high energy. Dark energy has nothing to do with dark matter. Dark energy could be modified gravity (the cosmological constant) or a new kind of particle (probably scalar, and therefore not "matter" as we know it).

It just seems strange that we've never directly experienced dark matter/energy on or near Earth, when it's the large majority. It's not strange, if it's both massive and weakly interacting (which are precisely the properties needed to make it work as dark matter). Massive means that we may not be able to produce it in particle accelerators, and weakly interacting means it's very hard to detect. It's actually possible that dark matter interacts only by gravity, which essentially means that we can never directly detect it. We hope that's not the case.

Not that we should have it on our unique planet (in Feynman's terms - because we're on it, it's unique) - but can't we synthesize it, to study it? Especially if it's got nearly magical properties of undetectability and/or antigravity. There is no reason why every particle in the universe has to be easy for humans to detect and produce, and there are certainly plenty of particles hypothesized to solve one problem or another which are neither. It's possible that some particles can be detected only, or most readily, by their gravitational influence on astrophysical scales. There is certainly evidence in favor of that scenario.

Aliens

[jrmiller84]

This dark material bends light in much the same way as light is bent when travelling through a lens.

Anyone else read this as... This dark material bends light in much the same way as light is bent when travelling through aliens.

But I thought...

[Conspiracy_Of_Doves]

I thought that we weren't 100% certain that dark matter even exists

Hubble spys on Litter Tray

[RavensDark]

Why are we using the hubble to spy on Nibbler using the litter box.

Dark matter == epicycles?

[alienmole]

I don't know why all the hate for dark matter.

Some skepticism is certainly in order. Since we currently have no way of independently confirming the existence of dark matter, we also have no way of distinguishing between two possible cases: one case is that dark matter corresponds to some real, physical material; the other is that the theory of gravity we're using is flawed. The fact that a better theory of gravity hasn't been produced doesn't mean that the current one is correct.

There are pretty strong parallels between dark matter and the infamous epicycles. The case for epicycles was about as strong as that for dark matter: epicycles were a construction required to make the theory work, but there was no way to independently verify their existence, and they turned out to be essentially fictitious (assuming one doesn't take the position that they could be turned into a valid way of describing the solar system's orbital motion taking the Earth as center.)

The real problem is that there are no checks and balances here: by adjusting the mass distribution of dark matter, we can get whatever result we want, and there's nothing to either prove or disprove the proposed distribution. It's the ultimate hack, since it can be adjusted to suit every individual galaxy we observe.

Screwing around with the laws of gravity isn't any more elegant,

In the absence of independent evidence of dark matter, it would be more elegant if laws of gravity were discovered which explained the observations well without dark matter.

and there are plenty of plausible candidate particles for dark matter lying around in various extensions to the Standard Model.

That's a pretty weak position. It certainly doesn't do anything to counter the accusation that objects are being invented just to make the theory work.

Re:Dark matter == epicycles?

[Ambitwistor]

Since we currently have no way of independently confirming the existence of dark matter, we also have no way of distinguishing between two possible cases: one case is that dark matter corresponds to some real, physical material; the other is that the theory of gravity we're using is flawed. No one has actually succeeded in producing a modified gravity theory that can mimic the effects of dark matter. It is not true a priori that this can be done; there are a lot of constraints on both the possibilities for dark matter and the possibilities for a gravitational theory, and they don't necessarily intersect.

There are pretty strong parallels between dark matter and the infamous epicycles. Dark matter is not like epicycles. Epicycles are essentially a Fourier expansion of any orbital motion, and as such, they are totally non-predictive and unfalsifiable. Dark matter theories do make predictions, and it is not possible to explain away all gravitational anomalies we see using dark matter. It's capable of being falsified, and a number of specific proposals for dark matter have been falsified.

The real problem is that there are no checks and balances here: by adjusting the mass distribution of dark matter, we can get whatever result we want, and there's nothing to either prove or disprove the proposed distribution. This is false. If you take any one phenomenon, such as galactic rotation curves, you can explain it by postulating a particular distribution and type of dark matter. But there's no reason why that same distribution and type should also account for other, independent phenomena — which it does. We can't get "whatever result we want" by fudging the dark matter distribution. If we fudge it one way, it can disagree with other observations. The fact that it doesn't is the reason why dark matter has become a mainstream theory.

In the absence of independent evidence of dark matter, it would be more elegant if laws of gravity were discovered which explained the observations well without dark matter. I say they're equally elegant, regardless of whether we detect dark matter. Either way, we have to alter the laws of physics (to alter gravity or to include new particles). Saying that one is better than the other is just prejudice. The true measure is which idea works better.

That's a pretty weak position. It certainly doesn't do anything to counter the accusation that objects are being invented just to make the theory work. That's also wrong. Particles like axions, neutralinos, etc. were hypothesized for reasons completely independent of the justifications for dark matter. However, they easily could be dark matter. Once again, there's no reason a priori why a new type of particle introduced to solve the strong-CP problem in QCD or the hierarchy problem or grand unification in the Standard Model should also happen to solve astrophysical anomalies, but they can, if they exist (depending on their masses, which we can't predict yet).

I think you need to learn a lot more about dark matter theories and the evidence for them before you so casually dismiss them.

Re:Dark matter == epicycles?

[alienmole]

This is false. If you take any one phenomenon, such as galactic rotation curves, you can explain it by postulating a particular distribution and type of dark matter. But there's no reason why that same distribution and type should also account for other, independent phenomena -- which it does. We can't get "whatever result we want" by fudging the dark matter distribution. If we fudge it one way, it can disagree with other observations. The fact that it doesn't is the reason why dark matter has become a mainstream theory.

Yes, but is there any corroboration of dark matter that doesn't involve gravitational theories? Obviously, observing dark matter via radiation emissions would be quite convincing, for example. However, I'm not aware of any such corroboration, and as such, the fact that there are constraints on the dark matter distribution is hardly surprising. But it's still not constrained in the way it would be if there were some other way of observing it, independent of gravitational inference. IOW, my point stands.

I say they're equally elegant, regardless of whether we detect dark matter. Either way, we have to alter the laws of physics (to alter gravity or to include new particles). Saying that one is better than the other is just prejudice. The true measure is which idea works better.

I agree. Elegance is not really the criterion I'm interested in -- what works best, corresponds to observable features, and has the best predictive power is what we want. What I'm saying is that we're currently comparing dark matter to a possible theory of gravity we don't have. Obviously dark matter currently wins that contest, just as competing versions of epicycles were once the winning theory of solar system orbits. But that in itself says very little about the possibilities for better theories of gravity.

Particles like axions, neutralinos, etc. were hypothesized for reasons completely independent of the justifications for dark matter. However, they easily could be dark matter. Once again, there's no reason a priori why a new type of particle introduced to solve the strong-CP problem in QCD or the hierarchy problem or grand unification in the Standard Model should also happen to solve astrophysical anomalies, but they can, if they exist (depending on their masses, which we can't predict yet).

Yes, but the reason that this is a weak position is that you're relying for the completion of the theory on a range of possible postulated entities. That's a catch-all response which basically amounts to "we don't know". It makes the theory less complete than it would otherwise be. The fact that you have a menu of possible choices doesn't make the theory stronger, all it does is hold out the possibility that the theory may be improved in future.

I think you need to learn a lot more about dark matter theories and the evidence for them before you so casually dismiss them.

I'm not dismissing them, and certainly not casually. There's a large middle ground between acceptance on faith and rejection. The former shouldn't have too much place in science. I'm pointing out that there's a lot of uncertainty here, and a lack of independent corroboration, and that responsible scientists shouldn't blind themselves to possible alternatives by according too much weight to intrinsically weak theories. I'm not saying that dark matter theories shouldn't be pursued -- that's the only way they'll be strengthened -- but given the current state of the field, it seems more reasonable to me to treat dark matter as a proxy for better theories that haven't yet been developed, than as a well-established phenomenon.

Re:Dark matter == epicycles?

[Ambitwistor]

Yes, but is there any corroboration of dark matter that doesn't involve gravitational theories? No. It's possible there never will be, if we're unlucky and have dark matter that only interacts gravitationally (e.g., massive sterile neutrinos). Hopefully there will.

But it's still not constrained in the way it would be if there were some other way of observing it, independent of gravitational inference. IOW, my point stands. IOW, your point doesn't stand. Certainly we would be able to infer more about dark matter if we could get some non-gravitational evidence. But the gravitational constraints alone mean that we can't get "whatever result we want" with dark matter, contrary to your claim.

What I'm saying is that we're currently comparing dark matter to a possible theory of gravity we don't have. Obviously dark matter currently wins that contest, just as competing versions of epicycles were once the winning theory of solar system orbits. Once again, epicycles were never a theory of anything, because they were entirely non-predictive. This is not the case with dark matter. Furthermore, the reason why we don't have a competing theory of gravity is because modified gravity is not very good at reproducing the successes of dark matter. It's possible that someone will come up with such a theory, but right now it looks like the dynamics will have to be so complex and contrived that it makes dark matter look appealing by comparison. This is on the basis of the many gravitational theories that have been tried.

Yes, but the reason that this is a weak position is that you're relying for the completion of the theory on a range of possible postulated entities. That's a catch-all response which basically amounts to "we don't know". You will recall that your original claim was that dark matter was invented "just to make the theory work", by which you mean gravitational dynamics in astrophysical phenomena. My point is that dark matter is not "just" there to make theory work; there are other, non-astrophysical reasons to believe that dark matter particles may well exist.

Incidentally, this characterization as a fudge to maintain "existing theory" is rather silly. Dark matter is a new theory, just like modified gravity theories are. Both of them replace our previous notion of astrophysics.

I'm pointing out that there's a lot of uncertainty here, and a lack of independent corroboration, and that responsible scientists shouldn't blind themselves to possible alternatives by according too much weight to intrinsically weak theories Dark matter is not an intrinsically weak theory. By now it has passed dozens of independent observational tests. And nobody is blinding themselves to possible alternatives. That's another silly characterization of what's going on. Dark matter was resisted for decades, and even today there are still alternatives like modified gravity being worked on. It's just that there is less and less room for them, as new evidence has disagreed with alternatives and continued to agree with dark matter.

Re:Dark matter == epicycles?

[alienmole]

Certainly we would be able to infer more about dark matter if we could get some non-gravitational evidence. But the gravitational constraints alone mean that we can't get "whatever result we want" with dark matter, contrary to your claim.

"Whatever result we want" is true as far as it needs to be, in this situation. The situation is that we can observe a certain amount of mass via various means, but it doesn't behave according to the theory of gravity that we think ought to apply. So one question is whether we can introduce invisible matter into the system in such a way that the theory of gravity in question will work. The fact that the answer seems to turn out "yes" does not in any way demonstrate that the invisible matter actually exists. This is why the theory as it currently stands is intrinsically weak.

Dark matter may not be entirely non-predictive, but it's the next best thing. If a dark matter prediction fails, there's a high probability that it'll be possible to adjust the dark matter distribution to make it succeed.

It's possible that someone will come up with such a theory, but right now it looks like the dynamics will have to be so complex and contrived that it makes dark matter look appealing by comparison. This is on the basis of the many gravitational theories that have been tried.

If the history of science teaches us anything, it's that it's very difficult to judge such things prior to the right discovery being made.

My point is that dark matter is not "just" there to make theory work; there are other, non-astrophysical reasons to believe that dark matter particles may well exist.

But there's no independent theory which dictates the quantity and distribution of those particles in a way that supports dark matter, without first assuming dark matter's requirements. If there were, you wouldn't need to point to a whole pantheon of possible particles, and the theory of dark matter would be stronger.

Incidentally, this characterization as a fudge to maintain "existing theory" is rather silly. Dark matter is a new theory, just like modified gravity theories are. Both of them replace our previous notion of astrophysics.

Dark matter theories assume that existing theories of gravity can be suitably applied unchanged at galactic and super-galactic scales. In that sense, dark matter may very well be a fudge to allow existing gravitational theories to be used to describe the phenomena in question.

Dark matter was resisted for decades, and even today there are still alternatives like modified gravity being worked on. It's just that there is less and less room for them, as new evidence has disagreed with alternatives and continued to agree with dark matter.

As we run up against the limits of our observational capabilities in areas like astrophysics, cosmology, and particle physics, it's going to become increasingly important to be sophisticated about recognizing the limits of our knowledge and the consequences of that. Otherwise, we'll simply be doing exactly what religious folk sometimes accuse us of: indulging in faith. We need to be able to recognize and acknowledge weaknesses in theories even when we don't have good alternatives. Having no alternatives for a theory in no way increases that theory's strength.

Re:Dark matter == epicycles?

[Ambitwistor]

So one question is whether we can introduce invisible matter into the system in such a way that the theory of gravity in question will work. The fact that the answer seems to turn out "yes" does not in any way demonstrate that the invisible matter actually exists.

It doesn't prove it, but it is strong evidence in its favor, because of the number of independent phenomena that dark matter are able to explain. You continue to dismiss this point as if it is unimportant. There is no reason why introducing dark matter should be consistent with all of those observations.

If a dark matter prediction fails, there's a high probability that it'll be possible to adjust the dark matter distribution to make it succeed.

Dark matter is not as adjustable as you think it is. Humans don't determine how dark matter distributes; it has to distribute in a way that is consistent with the laws of gravity. What we can mostly adjust in theory is how much of it was produced in the Big Bang, and some statistical aspects of how it was distributed at that time. The large-scale structure of galaxies didn't have to be consistent with what the CMBR tells us about dark matter's distribution when it was produced, but it is. The distribution of dark matter within individual galaxies didn't have to be consistent with the distribution necessary to seed the large-scale structure, but it is.

But actually, you're right, but not for the reasons you think. Dark matter is now consistent with a large amount of observational evidence, so there is a high probability it will remain consistent with new evidence simply because some dark matter candidate is likely to be correct. That was once not the case: there are plenty of ways that galaxies could have rotated, or the CMBR spectrum could have fluctuated, that could not have been explained by dark matter. It turns out, however, that they rotated, fluctuated, etc. in ways that are compatible with dark matter.

If the history of science teaches us anything, it's that it's very difficult to judge such things prior to the right discovery being made.

It can be, but on the other hand, historically it's rarely the case that under intensive study, evidence continues to mount for an explanation that ultimately turns out to be largely incorrect. You act as if the evidence counts for nothing.

But there's no independent theory which dictates the quantity and distribution of those particles in a way that supports dark matter, without first assuming dark matter's requirements.

That's wrong. There are a number of such theories which make no assumptions about dark matter's requirements. We don't know which of them may be correct. (We know many that are incorrect.)

If there were, you wouldn't need to point to a whole pantheon of possible particles, and the theory of dark matter would be stronger.

The "pantheon of possible particles" strengthens the case for dark matter, not weakens it. What it tells us is that dark matter candidates are naturally found in most of the most plausible extensions of the Standard Model (as well as one which is found in the Standard Model itself). That is not because they were introduced in order to have any of the requirements for dark matter. The Standard Model axion was introduced to solve the strong-CP problem. The neutralino was introduced along with supersymmetry to help solve the hierarchy and grand unification problems. Kaluza-Klein scalars were introduced with extra dimensions for purposes of unification. Nobody invented any of these to solve any astrophysical problems, yet most of the outstanding problems in particle physics end up implying particles that behave like dark matter. We would thus be led to introduce dark matter even if we hadn't made any astrophysical observations — yet another independent line of argument which leads to dark matter.

Dark matter theorie

Re:Dark matter == epicycles?

[alienmole]

You repeatedly raise the issue of my dismissing evidence as though it counts for nothing. What I'm actually attempting to say is that given a lack of independent confirmation via some other means than gravitional inference, dark matter is on less firm ground than many theories in other areas of physics and astrophysics. This is the grounds for (healthy) skepticism about dark matter that I originally suggested. The way I read your position, you seem to be denying that dark matter has any such weaknesses.

The "pantheon of possible particles" strengthens the case for dark matter, not weakens it. What it tells us is that dark matter candidates are naturally found in most of the most plausible extensions of the Standard Model (as well as one which is found in the Standard Model itself).

But it doesn't tell us how or why the distribution of those dark matter candidates should correspond to the inferred distribution. At best, it's a speculative suggestion as to how gaps in our knowledge may (if we're lucky) be filled in future. What would strengthen the case for dark matter is a model in which the gravitationally inferred quantities of dark matter match amounts arrived at by other means, for example.

Yes, it's possible that someone will come up with an alternative that works, but after many people have tried for many years, it's increasingly less likely.

Do you have any evidence to support this supposition? Back before theories of decoherence were developed (or propagated), you could have said something similar about certain interpretations of QM, and you would have been wrong.

Re:Dark matter == epicycles?

[Ambitwistor]

What I'm actually attempting to say is that given a lack of independent confirmation via some other means than gravitional inference, dark matter is on less firm ground than many theories in other areas of physics and astrophysics. I will agree that it's on "less firm ground than many theories in other areas of physics and astrophysics", but I disagree that the evidence for dark matter is weak. It is, by now, quite strong, even if it is indirect.

What would strengthen the case for dark matter is a model in which the gravitationally inferred quantities of dark matter match amounts arrived at by other means, for example. Yes, it would strengthen the case for dark matter even more, but the mere existence of a wide variety of plausible dark matter candidates within frontier particle physics has already strengthened the case for dark matter beyond just astrophysical evidence.

Do you have any evidence to support this supposition? You can't prove it, but it's basically how science works: a theory becomes mainstream when people try to come up with alternatives and fail; eventually, as the body of evidence in favor of the mainstream theory increases, viable alternatives come along less and less frequently.

Back before theories of decoherence were developed (or propagated), you could have said something similar about certain interpretations of QM, and you would have been wrong. That's nonsense. All of the interpretations of QM are physically equivalent to each other, by design; that's why they're interpretations, not theories. (There are a few truly different theories, such as Penrose's objective state reduction, which may be experimentally distinguished from standard QM.) Some interpretations are favored over others in their ease by which they can explain phenomena, but they all make the same predictions. You need a better example than that.

"You Are Here"

[Gaian-Orlanthii]

---> . Always nice to know where you are, right?

Proof of dark matter = proof of God?

[macraig]

Physicists and cosmologists searching for a "unifying theory" of the universe are, in my assessment, searching for the exact same thing as people who believe in God. For religious people, their god is their unifying theory. Dark matter, and dark energy, are their latest fictional creations to justify their obsessive need to find certainty.

This Hubble "map" is a CONSTRUCTION. It's not actual evidence; it proves nothing. I just love how the "anomalies" are discussed so dismissively, as if they aren't the crack in the dike threatening to bring the whole house of cards down.

I'm really sick of religious fanatics masquerading as "scientists".

Re:Proof of dark matter = proof of God?

[Ambitwistor]

Physicists and cosmologists searching for a "unifying theory" of the universe are, in my assessment, searching for the exact same thing as people who believe in God. For religious people, their god is their unifying theory. Dark matter, and dark energy, are their latest fictional creations to justify their obsessive need to find certainty. Dark matter and dark energy have little to do with unification. And unified theories don't have anything to do with "finding certainty", either. A unified field theory would be no more nor less certain than a non-unified theory. Dark matter and dark energy don't have anything to do with "finding certainty" either; they are no different from any other scientific endeavor: to provide explanations for unexplained natural phenomena. Nothing in science is certain.

This Hubble "map" is a CONSTRUCTION. It's not actual evidence; it proves nothing. It is a visualization of the observational data that has been measured, and it is evidence for dark matter insofar as it is a confirmation of the predictions of that theory.

I just love how the "anomalies" are discussed so dismissively, as if they aren't the crack in the dike threatening to bring the whole house of cards down. You have a naive view of science. People like to paint a revolutionary picture of science, but in reality, 99% of the time, anomalies don't actually revolutionize anything; they are resolved as mundane instrumental errors, systematic model approximation errors, etc. Yes, it's possible that dark matter can be torn down, but there is now enough evidence in its favor that there has to be a correspondingly large amount of evidence against it. That was not always the case, but it is today.

DM does not exist in galaxies.

[anandsr]

Galactic dark matter has a problem called MOND. If we don't agree with MOND on the galactic scale then we need to obtain MOND from our theories of formation of dark matter, because MOND agrees very well with the observed galactic data, even predicting the very low dark matter and the very high dark matter ratios obtained for the different galaxies, which this report calls problematic.
See http://www.astro.umd.edu/~ssm/mond/ for further information on MOND.

Re:DM does not exist in galaxies.

[Ambitwistor]

MOND does do very well for galaxies. In some respects, it does better than dark matter (although dark matter is not wrong for galaxies). However, MOND runs into serious problems explaining other phenomena, and in light of that, it is more plausible that dark matter is in galaxies after all. See this post for more discussion.

excellent....

[binarybum]

now I can hang my map of dark matter up right next to my picture of albino polar bears walking the tundra in a blizzard.

maybe it's nothing ...

[Anonymous Coward]

just a thought, but maybe dark matter is nothing.
not particle in anyway or wave or whatnot ...

remember that there "dark matter" is on a HUGE scale.
difficult to imagine. but maybe the effect of
"dark matter" isn't really somthing you can touch or such.

maybe it is just a virtual field.
by this i mean, u have to imagine all the interactions of real
particle and whatnot since the big bang.
now i state that EVERYTHING that has ever happend matters (since
the beginning(tm).
some interactions, say a fusion only fuse for ... 1 sec or whatnot,
and then decay again. if i remeber correctly say to get carbon,
you need a rare 3 hydrogen fusion process .. etc.

maybe this "effect" of creating a heavier element that then decays again
seemingly is a net-to-zero-again process, please remeber that i stated before
that EVERYHTING that happens matters.
so the two possibilities are:

1) two elements just sit beisde eachother and do nothing
2) two elements fuse to form a unstable heavier element that then decays again
(to the two elements we had before).

both are the same, but not really. the dynamic process of 2),
i think, MUST yield something else. not a force or particle or anything,
just THAT fact must have some kind of influence.

i dunno if i can explain it any better. maybe dark matter is like in
a account book, the "waste" the univers needs to write down, for things
that it has been doing uselessly (see above 2) ).

dunno. the whole thing is still evolving.
virtual photons and stuff.

why is this myth about dark matter still out there

[Kashgarinn]

Why do people think that dark matter still exists? Has everyone forgotten we're looking at light which is millions, even billions of years old? The fact that we're inventing "dark matter" to explain inaccuracies in light which has moved billions of AU through billions of years.. it's just bloody stupid. the phenomena which dark matter tries to explain only really says that something has happened to the light while traveling through space, probably some kind of expansion or change in the time/space continuum, which is more interesting from a historical perspective regarding the universe, and in my view not indicative of "dark matter". Dark matter must be one of the dumbest popular 'belief' in astrophysics, and is only hindering people from trying to find the real reason for why the light has changed its' course this way in the universes history. Sometimes I think people forget we're looking at reflections of objects millions of years old, and millions of lightyears away.. not the objects themselves. K.

My Theorey

[ahayes_m]

There is no dark matter, the laws of physics are just wrong.

Re:My Theorey

[Ambitwistor]

Your theory has been proposed, but nobody has been able to come up with new laws of physics that can explain the observations without dark matter, and it's not for lack of trying.

Is Milgrom's MOND theory still in the running?

[ashley_moran]

I saw Milgrom on telly a while back, talking about this: http://en.wikipedia.org/wiki/Modified_Newtonian_dy namics

The search for dark matter seems a bit like the search for the ether. Not that MOND is necessarily correct because it's the simplest solution, but that often seems to be the case. What's the current opinion on dark matter vs MOND?

Re:Is Milgrom's MOND theory still in the running?

[Ambitwistor]

See this post for links about the status of MOND vs. dark matter. In short: not looking good for pure MOND, although MOND + dark matter might be possible — but that kind of defeats the purpose of MOND.

More of the story...

[dynky]

Here's HubbleSite's full release on the topic -- more comprehensive than the BBC article imo: http://hubblesite.org/newscenter/archive/releases/ 2007/01/

Do photons self-gravitate?

[Anonymous Coward]

They are affected by gravity, so the quantum theory of gravity would say that they must be able to exchange gravitons and hence self-gravitate.

My maths isn't up to the task and I haven't heard anyone else working this idea, though it may be an old problem and sorted before I looked.

Re:Do photons self-gravitate?

[Ambitwistor]

They are affected by gravity, so the quantum theory of gravity would say that they must be able to exchange gravitons and hence self-gravitate. Yes, photons do self-gravitate, for the reason you gave. This is true even in classical general relativity; you don't need to bring quantum mechanics into it.

Re:why is this myth about dark matter still out th

[Ambitwistor]

Has everyone forgotten we're looking at light which is millions, even billions of years old? No.

The fact that we're inventing "dark matter" to explain inaccuracies in light which has moved billions of AU through billions of years.. it's just bloody stupid. "Inaccuracies in light"? It gets redshifted, some of it gets scattered or adsorbed, but that doesn't prevent us from measuring the gravitational dynamics of distant galaxies.

he phenomena which dark matter tries to explain only really says that something has happened to the light while traveling through space, probably some kind of expansion or change in the time/space continuum The expansion of space redshifts light, but that doesn't have much to do with dark matter, and is irrelevant for nearby galaxies.

I think you are extremely confused about what dark matter is and what evidence supports it.

Re: myth about dark matter still out there ..

[rs232]

Galaxys clump more than they should or even form never mind keep their distinctive shape given the current theory of gravitation. Rather than update Newton they invent dark matter. There is also the case of that probe that is leaving the solar system faster that it should. Does dark matter account for that too. Why don't they just bring back the aether.

"Modified Newtonian Dynamics (MOND) is a theory that explains the galaxy rotation problem without assuming the existence of dark matter"

"'Ether' returns in a bid to oust dark matter"

Re: myth about dark matter still out there ..

[Ambitwistor]

Galaxys clump more than they should or even form never mind keep their distinctive shape given the current theory of gravitation. Rather than update Newton they invent dark matter. They tried updating Newton, in the form of the MOND theory you mention. It worked for galactic rotation curves, true, but failed at a lot of other things like clusters and cosmology. That's why dark matter is still the leading candidate. Even MOND advocates are now admitting that at least some dark matter seems necessary. Modified gravity theories are still looked at, but they haven't lived up to the promise.

There is also the case of that probe that is leaving the solar system faster that it should. The Pioneer anomaly.

Does dark matter account for that too. No. Why should it?

too small of a solid angle

[Anonymous Coward]

looks interesting, although I'm skeptical of their 3d image having any significant meaning. The best they'd be able to do is take 2d projections through a relatively small solid angle. I'd assume the solid angle they are working with is on the order of a single degree. You generally need 180 degrees to reconstruct a 3d image from 2d projections assuming no known symmetries. In either case, it's an iteration on what's already been done so it should at least provide a means for understanding what the next step ought to be or can at least separate which theories, in second order, are acceptable and which are not. It's always nice to remove non physical theories. Although, even this can be dangerous since it too would assume a certain degree of symmetry.

These findings probe dark matter existence.

[jotaeleemeese]

These clever chaps have done just that.

They actually mapped it.

On 3D!

If it was a hack, it would be one of the cleverest, more accurate hacks in the history of science.

Holly cow...

[jotaeleemeese]

They just mapped the damn thing.

On 3D.

How do you explain that?

um

[Anonymous Coward]

If you're making shit up as you go along, why can't you measure your made-up matter based on your made-up observations and get a made-up 3D model?

Re:um

[pln2bz]

LOL! Well put.

The real heart of the problem is that we're believing *everything* that we're being told by a group of people without critically thinking about it. People have *total* faith in organizations and people like NASA, Stephen Hawking, Albert Einstein, Carl Sagan, etc. We are a brand name loyalty culture. In other words, we've been trained by the PR industry since the 20's to believe in the brand rather than questioning the message. Back in the 20's, people only bought the stuff they needed. Buying something that you didn't need didn't seem necessary. So, the PR industry was born here in the United States to convince the public to buy things that they didn't need. This created brand names and this brand name loyalty has seeped into every aspect of our culture. When you think of IBM, you think of guys in suits and mainframe computers. When you think of Nike, you think of shoes, that swoosh symbol and maybe even sweatshops. When you think of black holes, you probably think of Stephen Hawking, his books and maybe some shows you've seen about them on Nova or Discovery Channel. When you think of the Sun, most people imagine a nuclear reaction. And most importantly, when you hear the term "astrophysics", you imagine things that you cannot possibly understand -- and most people don't even try. Your brain switches from critically thinking to listening and memorizing. We've been brainwashed in a sense to not think about what we're being told about space because we've been told that it's just far too complicated to understand. And sure enough, if you try to talk to astrophysicists or intelligent amateur astronomers about it, they will oftentimes try to scare you out of your preposterous notions of electricity in space -- as if you are some sort of threat to them -- by invoking all sorts of exotic physics. You'll oftentimes notice that they don't care if you actually *understand* what they're saying; they would prefer that you don't because then you'll get out of their way so that they can go back to their work. This process has led to conformity within astrophysics, but the problem is that conformity is the enemy of science. The last thing we want to be doing is voting on science. Science is best when scientists are left to believe what they want and pursue those beliefs as they see fit. Some form of peer review is necessary to weed out the pseudoscience, but pseudoscience can accidentally creep into the peer review process itself when the scientists stop *listening* to the other intelligent people around them. And this is where things stand now.

They laughed at Velikovsky even though he made accurate predictions about Jupiter and Venus that were completely unexpected. Carl Sagan frequently claimed in his arguments against Velikovsky that ancient astronomical-literate cultures who recorded the arrival of Venus were not smart enough to accurately understand the movements of planets. They ignored Alfven even though he earned a Nobel Prize and most astrophysicists are to this day so unaware of his recusal from magnetohydrodynamics that they sometimes refer to magnetic reconnections as "Alfvenic reconnection". And they similarly scoffed at Wallace Thornhill's accurate predictions for the Deep Impact mission to comet Tempel 1 even though they have yet to offer any real alternative explanation that can include all of the observations made. When an amateur astronomer coincidentally took a picture of the Space Shuttle Columbia's plasma tail lit up by upper atmosphere lightning at the exact moment that the Shuttle malfunctioned, NASA refused to believe it, arguing that upper atmospheric lightning should not exist and they never heard the lightning on their instruments anyways. Time after time, they've decided that they knew better than the people around them when in fact they might have been wise to listen. Their field is, after all, interdisciplinary.

And so, here we are: pouring millions of dollars into fairy tale imaginary objects that capture the imagination of the public and ma