Dark Matter Found? $2 Billion Orbital Experiment Detects Hints

astroengine writes "A $2 billion particle detector attached to the International Space Station has detected the potential signature of dark matter annihilation in the Cosmos, scientists have announced today. The Alpha Magnetic Spectrometer (AMS) was attached to the space station in May 2011 by space shuttle Endeavour — the second-to last shuttle mission to the orbital outpost. Since then, the AMS has been detecting electrons and positrons (the electron's anti-particle) originating from deep space and assessing their energies. By doing a tally of electrons and positrons, physicists hope the AMS will help to answer one of the most enduring mysteries in science: Does dark matter exist? And today, it looks like the answer is a cautious, yet exciting, affirmative."

Comments

Dark matter

[Intrepid imaginaut]

So if I have this right and someone please correct me if I don't, dark matter is transparent, we can see right through it, it's intangible and doesn't appear to interact with normal matter except through gravitational effects. Could such a thing be used to make some sort of dark matter highway to provide a gravity well between stars for ships to travel down without expending much energy?

Re:Dark matter

[Anonymous Coward]

No.

Re:Dark matter

[Anonymous Coward]

If it's intangible, how would you move/organize it to said highway?

Re:Dark matter

[Anonymous Coward]

Gravity tractors. http://en.wikipedia.org/wiki/Gravity_tractor

Re:Dark matter

[Intrepid imaginaut]

Shovel it off the back of a flatbed, obviously.

It has to have a process of creation, by the time we get to the stage of seriously contemplating interstellar voyages perhaps we will know how to make it, in the same way we can generate x-rays and similar.

Re:Dark matter

[Intrepid imaginaut]

http://en.wikipedia.org/wiki/Gravity_assist

I'd rather move all that matter and equipment once to lay a trail than do it every time, even antimatter produces brutally poor returns over those kinds of distances.

Re:Dark matter

[idji]

probably not, because you would have to expend energy to move the stuff around in to the position and density to do your bidding, perhaps a bit like moving a moon in front of your spaceship to be pulled along by its gravity, or perhaps like putting a big fan on a yacht to blow wind into the sails.

Re:Dark matter

[Intrepid imaginaut]

You'd have to expend energy anyway, rocket propulsion technologies of various sorts are pretty much laying down the highway in front of the car as they go, and ripping it up after themselves. While a highway construction crew might be a lot slower and more energy intensive than a car, they only do the job once and make it easier for all the cars that come after them.

What I'm wondering is, would the nature of dark matter lend advantages over any other material in terms of highway construction.

Re:Dark matter

[The Raven]

Sure thing, as soon as we can make a road that is downhill both ways. Since that is impossible, your idea is impossible. That is completely ignoring all other practical concerns such as 'if gravity can be felt light years away, it would alter the orbit of the sun' and 'if we could create something with measurable gravitational effects spanning light years between stars, then the amount of energy we expend accelerating and decelerating a spaceship is pretty puny (dozens of orders of magnitude puny) in comparison.'

Re:Dark matter

[TheRealMindChild]

You are describing Aether in which Einstein proved does not exist

Re:Dark matter

[Intrepid imaginaut]

Once again, http://en.wikipedia.org/wiki/Gravity_assist

You don't want a giant lump of gravity at either end, you want a trail of breadcrumbs between A and B. As for energy expended, while you're talking about an incorrect understanding of what I'm saying, a highway construction crew uses many times more energy and time than a car, but it makes the car's journey a lot more energy efficient, and there are dozens of orders of magnitude more cars on highways than there ever were construction crews.

Re:Dark matter

[steelfood]

Gravity is very, very weak. Your highway would have to be incredibly dense. And the amount of energy you're going to expend making that is probably better off spent ripping wormholes in the fabric of space and time.

Re:Dark matter

[Intrepid imaginaut]

Your highway would have to be incredibly dense.

Or very very long, which handily enough describes the distances between the stars quite nicely.

Re:Dark matter

[Baloroth]

That is absolutely not how gravity assists work. Gravity assist work because the planet you are "assisting off" is moving: you can rob a little bit of that kinetic energy to give yourself a boost. But a "gravity highway"? No, you can't do that.

Re:Dark matter

[Intrepid imaginaut]

The stars themselves are moving, if you wanted to build a connecting chain it would have to similarly move. The question I'm asking is would dark matter offer advantages in this regard... maybe a highway isn't the best description, a river perhaps?

Re:Dark matter

[lgw]

Morbo says "Gravity Assist does not work that way!" Gravity assist uses a planet moving in the direction you want to go - you speed up by slowing down the planet. Energy is conserved.

You still have to expend the same energy to get to the same destination, if you have to put a moving planet there in the first place! Plus a bunch of overhead.

You gain little by being able to move through the planet - gravity assist works fine with normal planets.

Dark matter doesn't clump the way normal matter does (clumping requires friction, which is a very non-dark process): there's no obvious way to grab or move a bunch of it around. Think diffuse cloud of non-interacting particles.

Re:Dark matter

[Intrepid imaginaut]

By all means point me in the direction of a better description of dark matter then.

Re:Dark matter

[Intrepid imaginaut]

Dark matter doesn't clump the way normal matter does (clumping requires friction, which is a very non-dark process): there's no obvious way to grab or move a bunch of it around. Think diffuse cloud of non-interacting particles.

Surely it can be created though, even if it can't be moved it should be something we can make, eventually. I'm obviously not settled on any of the details, just casting a net and seeing what flops up on deck. Stations generating a stream of the stuff off to the side? More practical than trying to catch antimatter pellets at near relativistic speeds, even if the energy needed to get refuelling lumps to that velocity didn't make the effort pointless.

Re:Dark matter

[tnk1]

I will say this: right now a great deal of the problem with rocket engines is that you have a reaction mass and throw it out the back to make the ship move in the direction you want. That means you generally have a low energy to weight ratio which makes accelerating/decelerating the ship much more difficult because you do have to carry around your road with you.

If you can find some way to manipulate the situation so that you don't have to carry that reaction mass around to get the needed velocity changes, it becomes easier to deal with. In essence, even if you need to spend a gigantic amount of energy to put say, planets in the right place, if you can do that in such a way that you can use a more efficient process to place them, you may make real gains on "normal" engines over the lifetime of the "highway". That's one reason why you might want some sort of propulsion system that instead uses energy to warp spacetime, as opposed to a rocket: you'll still need a crapton of energy, but it can probably be attained by something with a much higher energy density, like antimatter.

Note I am NOT suggesting that dark matter has anything to do with the above ideas. Like neutrinos, dark matter is so weakly interacting that you probably can't manipulate it usefully. In fact, some theories indicate that dark matter IS neutrinos, or neutrinos are a significant component of what is collectively considered "dark matter".

Re:Dark matter

[wonkey_monkey]

Could such a thing be used to make some sort of dark matter highway to provide a gravity well between stars for ships to travel down without expending much energy?

No more than it could be used to create a unicorn that poops cookie dough.

Re:Dark matter

[Intrepid imaginaut]

Thanks, that's very useful. I'll make sure there's a wikipedia entry for every comment I make henceforth and not throw out blue sky ideas for discussion among the interested.

Re:Dark matter

[wonkey_monkey]

Surely it can be created though

If it can, it would be at the expense of incredible amounts of energy, and the mass of the equipment and fuel required to generate the energy would probably outweigh the generated dark matter by billions of times. No free lunches in this universe.

Re:Dark matter

[wonkey_monkey]

a river perhaps?

Implying that you've imparted momentum to the dark matter - momentum you may as well just impart directly to your spaceship.

Re:Dark matter

[Intrepid imaginaut]

If it can, it would be at the expense of incredible amounts of energy, and the mass of the equipment and fuel required to generate the energy would probably outweigh the generated dark matter by billions of times. No free lunches in this universe.

How do you know it would require incredible amounts of energy to generate dark matter? We aren't even sure what it is.

Re:Dark matter

[Anonymous Coward]

Yet you are in full fantasy mode about sci-fi garbage. You seem to know what it is.

Re:Dark matter

[Intrepid imaginaut]

Maybe you missed this bit: "The question I'm asking is would dark matter offer advantages in this regard". If it can be generated or laid down in a way that is more efficient than blasting reaction mass out the back end of a spaceship, which wouldn't be difficult, it's worth consideration. Keep in mind I'm not making assertions here.

Re:Dark matter

[Intrepid imaginaut]

The parent post is a prime example of the kind of dunce that is more of a threat to scientific advancement than any creationist. If it doesn't already exist or is unlikely to happen in his lifetime, it's wild fantasy which no right thinking folk should countenance. He'd have run Jules Verne out of town on a rail to appease his insecurities. Imagination is a primary ingredient in the development of our species.

Re:Dark matter

[Anonymous Coward]

So if I have this right and someone please correct me if I don't, dark matter is transparent, we can see right through it, it's intangible and doesn't appear to interact with normal matter except through gravitational effects. Could such a thing be used to make some sort of dark matter highway to provide a gravity well between stars for ships to travel down without expending much energy?

No, you're talking out your ass. Not only would your metaphorical highway be asinine if built the way you've described, but the property you've assumed would be helpful (not interacting electromagneticly) would be the single biggest hurdle to building the less asinine version out of dark matter instead of regular matter.

You could use a gravity tractor to propel a spaceship, but that doesn't actually gain you anything over just using whatever will propel your gravity tractor to propel the space ship directly.

You could place an artificial object or objects in orbits that are favorable for gravity assists, but conservation of momentum means that doing so would require you to put all the momentum gained by ships over the lifetime of the "highway" into the object up front for later use (plus it'll only be usable when the orbits align correctly). So again just attache that engine to your spaceship instead.

In both of those cases you want some massive object you can move with an engine of some sort. Since engines are made from baryonic matter they will not be capable of propelling a dark matter cloud. So even ignoring that they both end in "just attach the engine to your space ship it'll work better that way" you still can't use dark matter for any meaningful advantage.

Re:Dark matter

[lgw]

How do you know it would require incredible amounts of energy to generate dark matter? We aren't even sure what it is.

We are sure that it is dark. We are sure that it is matter. We are sure that matter and energy are collectively conserved. If it has mass, it requires E = mc^2 energy to create it.

Re:Dark matter

[Intrepid imaginaut]

Yes but in the absence of a perfect 1:1 propulsion system using reaction mass, or anything even close to it, the question is could this possibly offer advantages. Of course the stars have relative velocities as well so any putative link between them would also have to be in motion.

Re:Dark matter

[lgw]

What I'm wondering is, would the nature of dark matter lend advantages over any other material in terms of highway construction.

From what we know: no, quite the reverse. Dark matter does not seem to form "structures" of any size. For normal matter, gravity + friction + entropy gives us clumping: atoms into molecules into dust into planets. That doesn't seem to happen with dark matter.

Re:Dark matter

[lgw]

You're throwing out fantastical ideas about stuff that is far outside of what might even be possible. That's not science, nor even science fiction (what might be possible one day): that's just fantasy. Not very interesting.

Re:Dark matter

[Intrepid imaginaut]

Eh, yes it does. http://en.wikipedia.org/wiki/Dark_matter#Structure_formation There's even a nice picture of the dark matter structures.

Re:Dark matter

[Intrepid imaginaut]

How would you know, you've already made two entirely false assertions, the first is the structure one, the second, well I'll quote another poster below: "No, dark matter contains more baggage than just embodying the discrepancy in galaxy rotation shear. For one thing, the title dark matter presumes that it is, in fact, matter. This is a different hypothesis than various modifications of gravitational force theories (which are not tenable now).". And this is aside from your misuderstanding about the relative velocities of stars, which I'll chalk up to me just not explaining the idea fully.

Re:Dark matter

[RMingin]

Because we're assuming that creating dark matter isn't significantly different from creating non-dark matter?

Hint: Matter is not easily created.

Re:Dark matter

[Anonymous Coward]

let the private sector do it once and charge a toll over a bizillion yearsm is that how its supposed to work?

Re:Dark matter

[lgw]

Sigh. That's on the scale of galaxies and clusters, where gravity wins. Dark matter on the scale of stars is uncertain. That's not on the scale of a rocket, or a planet, which requires something other than gravity to keep bits stuck together - on that scale the evidence is there's no such force for Dark Matter. Below the scale of molecules, again, no evidence either way.

Re:Dark matter

[Intrepid imaginaut]

It's fairly uncertain that dark matter even is matter.

Re:Dark matter

[lgw]

Look, if you just want to ignore science, fine, believe whatever, but don't expect adult conversation. So far all you've said is "what if dark matter, instead of being what we think it is, were magic in this very convenient way?". Beyond that, did you have some coherent point to make?

Re:Dark matter

[Intrepid imaginaut]

Look, if you just want to ignore science, fine, believe whatever

That's rich coming from the guy that said dark matter didn't form structures. Again, spare your keyboard the wear and tear.

Re:Dark matter

[lgw]

Ahh, I see adult conversation wasn't your goal in the first place. Fair enough.

Re:Dark matter

[Intrepid imaginaut]

Two false assertions displaying complete ignorance of the topic, a couple of dollops of personal abuse, and a sprinkling of complete misunderstanding. Buh bye now.

Re:Dark matter

[Anonymous Coward]

You've already made it abundantly clear that you've no idea what you're talking about

As have you

Re:Dark matter

[dreamchaser]

Your idea is just not feasible, for a lot of reasons people have tried to point out to you and that I won't bother repeating since you seem to keep ignoring them. It is a quaint and novel idea that might have a place in soft science fiction but for all those reasons already pointed out it just isn't workable based on our current understanding of physics, and isn't likely to be workable even in the far future.

Re:Dark matter

[Anonymous Coward]

Well then why not suggest flying unicorns fed by maple syrup? Why is my idea any worse than yours?

Re:Dark matter

[ButchDeLoria]

Because flying unicorns make people mad. Just ask Hasbro.

Re:Dark matter

[TwentyCharsIsNotEnou]

You're assuming that you start from nothing, or from pure energy. Creating dark matter could just mean converting ordinary matter in some way.

Converting hydrogen and oxygen into 1 tonne of water doesn't require E = 1000*c^2 (rocket engineers might tell you it actually gives you energy out), but you get 1000kg of water at the end.

Re:Dark matter

[TheDarkMaster]

I think it is something simpler: The "dark matter" would simply ordinary matter, but not detectable by us because it do not emit enough radiation and/or is not dense enough to block radiation.

Re:Dark matter

[TheDarkMaster]

Welcome to the actual Slashdot. Full of people who do not bother to think "could work?"

Re:Dark matter

[sFurbo]

We know it is not baryonic, matter as we have a pretty good idea about the concentration of baryons at the big bang from the distribution of nuclei from the big bang nucleosynthesis. Furthermore, the study of the variations in the cosmic microwave background tells use that around five-sixths of the total matter is in a form which does not interact significantly with ordinary matter or photons. Both facts are mentioned in the WP article on dark matter.

Re:Dark matter

[Anonymous Coward]

Your comment was so ignorant and content-free, that there's nothing to do BUT mock you for it. You use English words in the correct frequency and order, but the resulting question had zero meaning.

You might just as well have asked, "Say, since warp drive is so frequently described in Star Trek, is it possible that scientists could create a real warp drive?"

The GP's response invoking unicorns was my first reaction, so instead, I'll mock you with;
"No more than the tiny blue fairies that make up baryonic matter could be coaxed into pulling your spaceship between the stars, like a tiny mule team."

You retard.

Re:Dark matter

[Anonymous Coward]

No, lots of us wasted enough time on Insipid Ignorantnaut's comment to realize he was just spouting nonsense words.

Re:Dark matter

[Anonymous Coward]

Wow, just wow.

Why don't you get back to your "Ghost in the Shell" fanfic? Those pages aren't going to mimeograph themselves, you know.

Re:Dark matter

[TheDarkMaster]

I'm aware of that. I just point out that perhaps the explanation is somewhat simpler than a form of "exotic" matter, given that our means of long-range detection may not be good enough. Just another option.

Re:Dark matter

[TheDarkMaster]

You have no imagination (as millions of people these days). Nor education, given that when disagrees with the the ideas of someone, it is necessary to do so in a civilized manner rather than plain and stupid offense. Especially when you have no way of knowing if the idea in question is valid or not.

Re:Dark matter

[Anonymous Coward]

I don't think you are aware of that, as it directly contradicts what you've said in the previous post and in this post here, short of you using "ordinary matter" to mean something it doesn't. There is good evidence that dark matter is not ordinary matter. On top of that, astronomers are aware that detection methods can't detect everything, especially since the same evidence that says dark matter is non-baryonic also shows that there is a lot of ordinary matter missing from observations too. But that missing ordinary matter is not called dark matter, as it doesn't address any of the issues that dark matter seems to solve.

Re:Dark matter

[Anonymous Coward]

Also full of people who won't try to think, "couldn't work."

Re:Dark matter

[TheDarkMaster]

Read again, carefully. What is the basic problem? The basic problem is: According to the calculations and according to observations, should have more matter than we observe around us. We looked and did not find this "missing matter", but realize the effect of her presence. What can be then? It may be a new type of matter (the "dark matter") or our means of detection are not good enough to detect this missing matter. Now it was clear what I am suggesting?

Re:Dark matter

[Anonymous Coward]

There is a difference between asking a "What if?" and assuming some premise is true, and seeing where that goes, and asking, "Could this happen?" where essentially the premise is real life as we know it. A vast majority of the time, science fiction falls into the former category, even if there is some variation in how close the assumed premise is to what could happen. And at some point of asking, "Could this happen... if we suppose this other thing," quickly becomes the former category, because what you are assuming/supposing has no connection to current theories. While it is good to foster the imagination and practice figuring out what would happen even in sometimes absurd set ups, it is only healthy if you can keep clear what is supposed fantasy and what is not. Otherwise, you are regressing back to natural philosophy, to the idea that the workings of the universe can be deduced with no regard toward observation and evidence.

As far as your original question, dark matter behaves gravitationally like other matter, and none of the other properties would make its usefulness as gravitational structure on interstellar scales any different than normal matter on the timescales of human civilization. So there would be nothing special about dark matter, and without assuming it gets easier to manipulate, find or make, you might as well make such structures out of normal matter. In either case, it would be significantly inefficient, as the amount of energy needed to set up just the kinetic energy of such structures, only a fraction of which would be accessible by gravitational assists, would be much more than a direct approach.

Re:Dark matter

[ceoyoyo]

Which Einstein showed didn't work the way some models of it assumed. And which quantum field theory brought back in spades.

Re:Dark matter

[ceoyoyo]

You're insisting on misunderstanding the guy replying to you. There is evidence from multiple sources that dark matter cannot be ordinary (i.e. baryonic) matter.

Re:Dark matter

[lgw]

The little that's known about dark matter is that it doesn't interact with normal matter (and only weakly at best with itself). That's a disadvantage, not an advantage, in any engineering scenario I can see. The hydrogen and oxygen interaction is exactly the sort of thing that dark matter doesn't do (as far as the minimal evidence known about it).

Maybe I'm not just imaginative enough around the engineering qualities of diffuse clouds, but there just doesn't seem to be any fodder for good science fiction in dark matter.

Re:Dark matter

[TheDarkMaster]

Well... I've seen the evidences, but they do not seem good enough to me to be able to say that the cause of the problem "can only be" the existence of a new type of matter, you understand (And if you know of a good enough evidence, please cite it to me)? Dark matter seems to me to be a good explanation for the phenomenon, but they are discarding other possibilities too fast, and ignoring possible measurement errors (such not finding the "missing" matter by not having how to detect it).

Re:Dark matter

[painandgreed]

I think it is something simpler: The "dark matter" would simply ordinary matter, but not detectable by us because it do not emit enough radiation and/or is not dense enough to block radiation.

Has been thought of. Has been tested. Empirical data shows that there is not enough non-radiative normal matter for it to be anything near dark matter. Via gravitational lensing and other large scale cosmological experiments, non-radiative matter has already been taken into account when studying other galaxies, and normal matter still comes up as only one sixth of the matter in the universe. All that was being done way back when they were trying to account for the rotational speeds of gravity. Since then, other data has shown up such as cosmic background radiation which allowed us to extrapolate back to what the early conditions of the universe were like, and they also gave evidence of dark matter in similar amounts as needed to account for galactic rotation speeds. The thing is that the arguement for dark matter is no longer one example that could be explained away with a different simple explaination. It is the result of several different paths that all point to the same conclusion. Any other method that would account for all of them would be a much more complicated cause which we have no idea what it would be. Take MOND for example. If the rotational speeds of galaxies were to be solved by changes to the equations of gravity, they are so complicated that nobody has yet been able to come up with a hypothetical equation that fits all the data we already have on how gravity is working. Even if they did, you'd still have about six more "that's interesting" observations in physics to deal with.

Re:Dark matter

[TheDarkMaster]

Finally a useful reply, thanks.

Re:Dark matter

[ceoyoyo]

There can never be "can only be" in science. But the evidence against dark matter being normal matter is pretty overwhelming. That hypothesis wasn't discarded lightly. If you go back about ten years there was a big debate about competing dark matter hypotheses, the MACHOs versus the WIMPs. MACHO is Massive Astrophysical Compact Halo Object, WIMP is Weakly Interacting Massive Particle. MACHOs are what you're describing - normal matter that's just too dark to see. WIMPs are something else.

The MACHO hypothesis has been largely discarded because it doesn't agree with what we think we know about nucleosynthesis in the big bang, with various observations of the cosmic microwave background, with some star occlusion and other baryonic dark matter searches, and with observations such as the mass distribution in the Bullet Cluster. The WIMP hypothesis is consistent with all of those. So for MACHOs to be the true explanation we'd have to be wrong about a lot of basic astrophysical stuff, and likely some basic quantum mechanics as well, the MACHOs would have to be rather suspiciously distributed and things like the Bullet Cluster might not have a good explanation (depending on just what kind of MACHO you hypothesize).

People make out WIMP dark matter to be some kind of unprecedented made up thing. It isn't. Neutrinos are WIMPs. Neutrinos would actually make an excellent dark matter candidate except that they have the same problems as MACHOs - various other observations tell us that there aren't enough neutrinos, and their mass isn't high enough, to explain the observed amount of dark matter.

Your posts strongly imply that the only objection to the MACHO hypothesis is just direct observation failing to find them. It's not. As the other poster said, there are a lot of fundamental things arguing strongly against MACHOs, not just astronomers not seeing them through their telescopes.

Re:Dark matter

[Anonymous Coward]

String theory brings the aether back. It just works differently than how people thought the aether back in the day.

BTW, it was the Michelson Morley experiment back in 1887 that showed it didn't exist as thought of back then.

http://en.wikipedia.org/wiki/Michelson%E2%80%93Morley_experiment

Re:Dark matter

[TheDarkMaster]

Ahhhhh... Yes. Thanks, I was just looking for a clearer explanation of the reason for believing in dark matter. And no, I'm not saying that "not being able to see" is the only objection, only that they should consider the possibility. In my work, is my job to consider all imaginable (and even some unimaginable) possibilities.

Re:Dark matter

[Anonymous Coward]

ignoring possible measurement errors (such not finding the "missing" matter by not having how to detect it).

This is covered, quite extensively, in literature. Astronomers are actually quite aware they cannot see everything and even have evidence pointing to how little they may actually be seeing. This is heavily incorporated into modern work on dark matter. Suggesting that astronomers ignore that possibility as a whole is on par with trying to claim astronomers don't think about equipment calibration. Such subjects might not show up in pop-sci work as much, although at one time they did as I distinctly remember several shows and books discussing the results that places upper bounds on MACHO dark matter theories (back before "dark matter" converged as a term to mean non-baryonic lost matter).

, but they are discarding other possibilities too fast,

There are still whole research groups dedicated to look at various alternatives proposed. Besides those still trying to pin down the location of ordinary matter they know is missing, there are groups continuing to try to find alternative gravity models that can explain the things dark matter is used to explain. Although, the last few such seminars I sat through, even some of the people on the alternative gravity models are getting pessimistic about the ability of such models to explain observations, and are starting to wonder about possibilities were effects can be explained by both an alternative gravity theory and dark matter together.

Re:Dark matter

[TheDarkMaster]

Why posting as AC? Your reply is a good one. It means so I'm just looking for the "why dark matter" in the wrong places.

Re:Dark matter

[ceoyoyo]

The strange thing about scientific communities is that they do consider all sorts of possibilities. Theoretical physicists in particular consider lots of things that they know are impossible just to see how theories work. Despite what you might read on Slashdot, baryonic dark matter, modifications to how gravity works on large scales and other dark matter hypothesis were certainly considered, over the last twenty years. That the WIMP dark matter hypothesis is the current leader isn't because it sounds like a neat idea, it's because it has a LOT of advantages over all the other contenders.

Re:Dark matter

[Anonymous Coward]

Why posting as AC?

Over the years I feel like I've lost the ability to tell which discussions and arguments online will turn into a quagmire. And I don't want to risk my name being associated with stupid internet arguments, regardless if I was correct or not. Many of my colleagues have given up on answering questions on the internet (even via more moderated places) and kind of give a weird look to others that haven't come to the same conclusions about people on the internet.

Re:Dark matter

[TheDarkMaster]

I got it. Well, thanks again, I will search for better (primary if possible) sources about the dark matter subject

Re:Dark matter

[Anonymous Coward]

It is a name for something that behaves like matter in a multitude of ways... pretty much in every way that would be used in a modern definition of matter. Unless we change how we define matter, dark matter is most certainly a type of matter or otherwise doesn't exist due to some other explanation being more correct.

Re:Dark matter

[V!NCENT]

Physics are written in Math. Math is written in logic. Logic is form.

If we are to believe the theory (and there is no point in not doing that after 20.000 years of radation before the big bang started happening) that the Higgs Boson is made out of form(ing a shitload of dimensions), then dark matter is simply another dimensional fold. Once these folds clash, they unfold eachother, leaving nothing but nothing, realy.

And then there is the gravity thing, which is, of course, Einstein's stuff; it's the Newton physics of the holographic universe interpretation. In other words: only valid when it comes to interpretation.

There is no gravity, if we are to believe information theory (and one would be a genius to disprove). In fact, we don't even have evidence of gravity, so information theory comes closest to this. But anyway: the universe is like the WipEout HD Fury Playstation 3 disc: the actual raster (so called space time bla bla bla) is 2D. So a very large polygon+texture+shader model could eat up a lot of space on the disk surface and therefore come close to a small model. It doesn't mean that on the 3D TV, the model actually appears close to the large polygon model, displayed 'holographicaly', but the actual space between the storage surface of the game disc is small, faking some 'warped BluRay SpaceTime'.

So there is no gravity thing going on. Gravitational effects are... no wait: the effect is gravity, and is not going on at the dark matter information level. And since you don't want ships made out of matter to smash into anti-matter, because that's not what Huston wants to hear, you could still put a highway there, by simply increasing mass between point A and B, which means less storage between point A and B, which means less shit going on between A and B, which means less 'time' going on between A and B, which means 'OMG TUNNEL!!!!!1111 one one eleven" aka no distance whatsoever.

So there I crushed the magic behind the universe. Where is my price?

But what is it?

[Hatta]

Of course dark matter exists. There's a discrepancy in our observations, and dark matter is defined as whatever is responsible for that discrepancy. The real question is, what is dark matter? How do we explain its existence?

Re:But what is it?

[brantondaveperson]

Unless the responsibility for the discrepancy falls upon incorrect theories / understanding of the observations. In which case dark matter turns out to be an iffy equation. Yes, it still technically exists, but the $2 billion dollar particle detector isn't going to find it.

Re:But what is it?

[Nadaka]

And that is part of what this device attempts to answer.

The readings are consistent with the WIMP theory of dark matter.

Re:But what is it?

[wisnoskij]

I disagree. Dark Matter is defined as one possible specific solution to this discrepancy.
Specifically:
It has to be matter.
It has to be made up of particles.
It has to be invisible.
It has to make up most of the matter of our universe.

If it did not at least meet all of these criteria, Dark Matter would not exist.

Re:But what is it?

[Anonymous Coward]

Unless the responsibility for the discrepancy falls upon incorrect theories / understanding of the observations. In which case dark matter turns out to be an iffy equation. Yes, it still technically exists, but the $2 billion dollar particle detector isn't going to find it.

We can say, with a very high degree of uncertainty, that the discrepancies are not due to bad theories.

If our only line of reasoning for Dark Matter was Newtonian physics (for example, if the only evidence for Dark Matter was from rotation curves of galaxies), your thought would be entirely reasonable. Maybe Newtonian mechanics were just wrong on the scale of galaxies. This is one reason why Modified Newtonian Dynamics theories (MoND) were somewhat popular a while ago.

But the problem is that multiple, *completely independent*, physical theories all show that not only does Dark Matter exist, but all the theories predict consistent amounts of Dark Matter. For example, you can use Einstein's Theory of General Relativity to find out how much Dark Matter there is based on how much light is curved by gravitational effects. Or you can use various areas of Thermodynamics to look at temperatures in galaxy clusters.

These theories are based on completely different principles and laws. Yet they all predict the same thing.

So if you want to claim that we being confused by bad theories, you would have to be able to explain why multiple, completely independent theories are not only all wrong, but all wrong in a way such that they return the same wrong answer. That seems extremely implausible, so Dark Matter is, by far, the best explanation.

Re:But what is it?

[lgw]

Of course dark matter exists. There's a discrepancy in our observations, and dark matter is defined as whatever is responsible for that discrepancy

To clarify: the "dark matter" hypothesis of the discrepancy in our observations of galaxy (and cluster) rotation rates has already been confirmed by observations of the cosmic microwave background radiation. There were many hypotheses for that discrepancy, but dark matter predicted the correct ratio of baryonic/non-baryonic matter in the early universe - to multiple significant digits (rare in cosmology).

So while most properties of dark matter have yet to be understood, some are well defined. As far as "how do we explain its existence?", that same question applies equally to "normal" matter.

Re:But what is it?

[idontgno]

Like luminiferous aether existed until it didn't.

That said, these particle detections seem analogous to if Morley and Michelson had detected discrepancies in the speed of light attributable to earth's motion through the universe (and therefore relative to the aether). They didn't and the aether theory began to be disproved

In this case, the theoretical construct (dark matter) is beginning be supported by experimental observations, rather than disproved. So dark matter continues to be a useful concept, even if we're not sure what its tangible form of existence is.

Re:But what is it?

[Hentes]

Theories trying to explain gravitational anomalies can be classified in two categories, dark matter theories and modified gravity law theories. Furthermore, the measurements of this experiment can be explained by WIMPs, which is a specific dark matter theory.

Re:But what is it?

[MozeeToby]

There are other possible ways to explain the effects than dark matter. The evidence has slowly been building that dark matter is the best explanation, but at one point modifications to our understanding of gravity was also considered. This data adds another piece of evidence that there is mass floating out there that we don't understand, as opposed to there being a term missing from our equations. More interesting, since we've been pretty sure dark matter is the answer for a while now, if they know the energies of these electrons and positrons, we can start to narrow down exactly what kinds of particles actually make up dark matter

Re:But what is it?

[steelfood]

Dark matter only accounts for around 30% of the universe's mass. It's gravitational effects are visible, so we're pretty sure it exists in some form or another. It could be a new subatomic particle. It could even be existing bayronic matter that's masked by some advanced alien technology. But it has been observed to exist.

Dark energy, which makes up the rest of the mass in the universe, is where the alternate ideas based on our incomplete understanding of subatomic physics is possible.

Re:But what is it?

[Anonymous Coward]

And the aether has now been reborn as the quantum vacuum which is now hypothesized as the reason for the speed of light.

Re:But what is it?

[mbkennel]

The luminiferous aether didn't have any observational or experimental evidence, and the theory was known to be problematic at the time.

Re:But what is it?

[PolygamousRanchKid]

I think this is best explained with a computer analogy, using the concepts of real and virtual:

If it's there, and you can see it, it's real.

If it's not there, but you can see it, it's virtual.

If it's there, but you can't see it, it's Dark Matter.

If it's not there, and you can't see it, it's gone.

Re:But what is it?

[Khashishi]

No, dark matter contains more baggage than just embodying the discrepancy in galaxy rotation shear. For one thing, the title dark matter presumes that it is, in fact, matter. This is a different hypothesis than various modifications of gravitational force theories (which are not tenable now).

Re:But what is it?

[Livius]

Like luminiferous aether existed until it didn't.

And then it did again. Space-time has curvature and energy - that sure isn't the classical meaning 'empty' space. The aether just wasn't material in the sense it was originally conceived.

Similarly, dark matter is *something* which is explaining a wide variety of observed phenomena with several limits on what it could possibly be. The name is just a matter of labelling.

Re:But what is it?

[Anonymous Coward]

If we considered gravity not as a property of matter, but as a phenomena associated with the packet of energy that a mass represents... If that were the case, then in theory - regions of space with high enough energy density (but no matter) would also produce gravitational effects.

Maybe somebody should work from that angle and see if dark matter still holds up.

Re:But what is it?

[excelsior_gr]

with a very high degree of uncertainty

Gotcha!

*ducks*

Re:But what is it?

[lgw]

If we considered gravity not as a property of matter, but as a phenomena associated with the packet of energy that a mass represents... If that were the case, then in theory - regions of space with high enough energy density (but no matter) would also produce gravitational effects.

Maybe somebody should work from that angle and see if dark matter still holds up.

The cosmic microwave background radiation studies debunked that idea. We can now divide "gravitational effects" cleanly into 3 buckets: "normal" matter, "dark" matter, and energy. The ratio of normal/dark matter that was predicted from galactic rotation was in fact observed by the CMBR studies.

Re:But what is it?

[rknop]

Dark Matter is not like the luminiferous aether. That was the title of a podcast I made three years ago -- here it is: http://cosmoquest.org/blog/365daysofastronomy/2010/06/26/june-26th-dark-matter-not-like-the-luminiferous-ether/

The luminiferous aether was a theory developed to explain a discrepancy... as was dark matter. The difference is, there are LOTS of different lines of evidence to point towards dark matter. With the luminiferous aether, the theory was tested, and it didn't stand up. With Dark Matter, the theory has been tested, and it DID stand up.

Re:But what is it?

[Anonymous Coward]

I recall a similar justification applied to epicycles.

Re:But what is it?

[Anonymous Coward]

That seems extremely implausible, so Dark Matter is, by far, the best explanation.

What I have had a problem with is that Dark Matter is a very unscientific explanation. There's no way to falsify it, as you can't prove that it doesn't exist. You could just as easily attribute the equations being off by two orders of magnitude to invisible space unicorns.

It'd be more plausible if there simply weren't so much Dark Matter/Energy. It's like saying a medication works, but only if we add 24 hypothetical patients for every one in the actual study. Thus I'm not surprised the various equations are mathematically consistent. When you have the leeway to attribute whichever properties you like to 96% of the universe, you can probably make the math say whatever you want it to say.

Re:But what is it?

[Anonymous Coward]

For example, you can use Einstein's Theory of General Relativity to find out how much Dark Matter there is based on how much light is curved by gravitational effects.

Standing waves of gravity?

Re:But what is it?

[Anonymous Coward]

Well, epicycles aren't wrong per se. Physics has no preference for any frame of reference, and epicycles are something that arises when you look at the solar system using the Earth as the frame of reference. They were ditched because it's simpler to look at things from the Sun's POV, rather than Earth's.

Re:But what is it?

[Zorpheus]

As far as I know AMS was built to look for antimatter, not for dark matter. The antimatter is just an explanation that they came up with to explain an excess of positrons. They were looking for anti-Helium to find out if there are larger amounts of antimatter somewhere in the universe.

Re:But what is it?

[TheDarkMaster]

I think it is ordinary matter, but we can not detect because it does not emit enough radiation (for example, cold dust away from heat sources) and not be dense enough to block radiation (so you could detect the "shadow" that it causes other sources of radiation)

Re:But what is it?

[sFurbo]

It could even be existing bayronic matter that's masked by some advanced alien technology.

If there were enough baryonic matter in the universe to account for the dark matter as well, the ratios products of big bang nucleosynthesis would be different than what we observe.

Re:But what is it?

[Anonymous Coward]

General relativity already accounts for energy density of an area, but that also includes mass energy too. That has been kind of the basis of gravity for almost a hundred years now...

Re:But what is it?

[Anonymous Coward]

Unseen ordinary matter could at best, in a contrived situation that would lead to bigger questions, only explain a portion of the effects explained for by dark matter. At this point, there are several lines of evidence pointing to dark matter no being composed of ordinary matter, to the point that ordinary matter is now not considered a possible candidate for dark matter. In other words, if one of those effects that could be possibly explained by ordinary matter were found to be explained by ordinary matter, it would mean they are no longer explained by dark matter as now defined, as opposed to saying dark matter is ordinary matter.

Re:But what is it?

[TheDarkMaster]

Hum... So, what are those effects that could only be explained by a new type of matter?

Re:But what is it?

[Anonymous Coward]

Observed ratios of elements within the universe as it relates to nucleosynthesis, the spatial spectrum of the CMB, the expansion rate versus distance measurements of the universe, the galactic rotation curves (taking into account upper bounds placed on MACHOs and other ordinary matter surveys), measurements of galaxy velocities within clusters (taking into account failures to model such velocity distributions with ordinary matter alone due to additional interactions constraining ordinary matter's structure and distribution), observations of mass distribution in colliding galaxies that cannot be explained by EM interacting matter alone, attempts at simulating the development of structural properties of the universe and large scale matter distribution.

In pretty much all of these cases, the first thing done was to assume observations were not just seeing everything and to use models to try and determine what missing matter would be needed to produce what we do observe. MACHOs were still considered a prime candidate for dark matter up until about 5-10 years ago, so between those and the known difficulties of observing gas clouds and such, so the idea that some junk is just not being seen has been around and used (if not just from laziness too, of not wanting to add yet layer of stuff to models).

Re:But what is it?

[TheDarkMaster]

Ahhh... So, in resume the answer to my question is "Already attempted this but little is reported about the attempt", thanks. And yes, what I thought would be forgetting is the hypothesis that the missing matter was in the form of gas

Re:But what is it?

[Anonymous Coward]

It could even be existing bayronic matter that's masked by some advanced alien technology.

If there were enough baryonic matter in the universe to account for the dark matter as well, the ratios products of big bang nucleosynthesis would be different than what we observe.

The alien technology used to mask all that baryonic matter might also have modified the matter we do see, at least everywhere where there is this masked baryonic matter (which seems to be everywhere). So I don't think this ratio problem can make the "masked baryonic matter" hypothesis any less plausible.

Re:But what is it?

[ceoyoyo]

That's not even the real story. There were lots of different aether theories (and lots of dark matter theories). Some predicted Michelson and Morely's result, some the opposite. The latter were disproved. The former weren't, but kind of got ignored when everyone got distracted by shiny relativity (never mind that general relativity is most commonly explained in terms of gravitonic aether - i.e. distorted spacetime). Then quantum field theory came along and now we all believe in many kinds of aether, but we call it something different.

does it exist?

[Anonymous Coward]

Yes, it exists. There really is no serious question about whether it exists. Its characteristics (hot, cold, individual mass, etc) are less certain, although it seems like there are some reasonably established constraints on some of those things too.

Anyway, there's also apparently not anything like a clear indication that this signal is a DM interaction => http://resonaances.blogspot.com/2013/04/first-results-of-ams-02.html

"However this is just a lot of smoke without fire. There's absolutely no way that measurements of the positron spectrum may give us a robust evidence for dark matter, not now, and not anytime soon. We simply have no robust way of telling dark matter from boring astrophysics in that channel, because we don't know the shape nor the normalization of the background. "

interesting first results...we'll see

[ganv]

That is a very interesting result. Their first measurements of the positron energy spectrum are consistent with super-symmetry ideas about dark matter collisions creating positron-electron pairs. If it turns out to be right, it will be the first non-gravitational detection of dark matter. But there is not much experimental support for the super-symmetry ideas being used to connect dark matter with positrons, and there are other possible sources of the positron spectrum at the current accuracy. So we'll see. It is great to see they have some results...this experiment has taken a long time and a lot of money. But when you introduce a much more precise way to measure, it usually turns out to be worth the cost and effort in the end.

Re: interesting first results...we'll see

[Anonymous Coward]

I wonder if the discovery of electron/positron pairs emitted could possibly change the idea of the big bang... A sizable percent of the mass of the universe converting itself from what is essentially 'virtual' mass to real particles could suggest a slower, steadier creation.

Re:interesting first results...we'll see

[TheRealMindChild]

The Large Hadron Collider has more or less proved that Supersymmetry doesn't exist

Re:interesting first results...we'll see

[Anonymous Coward]

Correction- the LHC has shown that supersymmetry does not likely exist at the energy scales tested.

Re:interesting first results...we'll see

[DMUTPeregrine]

Not even close to true. The LHC has shown that certain variants of supersymmetry can't exist, and shown nothing at all about other variants. Just because I didn't find my keys on my desk doesn't mean they haven't fallen between the couch cushions.

Spin? Not that type...

[Anonymous Coward]

A contrary opinion: http://profmattstrassler.com/2013/04/03/ams-presents-some-first-results/

It's always good to exercise caution with these sorts of things. You all remember the FTL particles a couple years back yes?

Re:Spin? Not that type...

[Anonymous Coward]

Don't remember much caution with regard to the FTL particles. There was skepticism from the outset.

Obligatory xkcd

[Anonymous Coward]

http://xkcd.com/1132/

Re:Where did they find it?

[DougOtto]

No. Those are Klingons.

bad=best

[globaljustin]

It seems you have a decent command of the subject, but your conclusion is wrong.

So if you want to claim that we being confused by bad theories, you would have to be able to explain why multiple, completely independent theories are not only all wrong, but all wrong in a way such that they return the same wrong answer.

Because they are trying to 'fill' the same gap in observed matter! Please, you must see the fallacy of your argument here. They start with the problem: we observe X but our *really good* calculations say it should be Y. Y-X=ammount any theory will have to account for.

so Dark Matter is, by far, the best explanation.

Is this your scientific opinion? Yes/No...doesn't matter. Thanks for sharing. It's doesn't mean anything or contribute to the discussion in any way.

In science, the 'best fit' theory is shorthand for saying the theory that doesn't solve a problem completely, but by consensus represents the best our human ability can offer in solving that problem at that time in history.

Dark Matter theories are, IMSO, dumb. It doesn't matter why I say that for the purposes of my comment. What matters is, dumb as they are, they are the 'best fit'

Stop defending 'dark matter' theories like they are your children. They don't work, and will be replaced one day. I agree they are the 'best' but let's not confuse everyone over your need to be right with terminology ;)

Re:bad=best

[sFurbo]

Because they are trying to 'fill' the same gap in observed matter! Please, you must see the fallacy of your argument here. They start with the problem: we observe X but our *really good* calculations say it should be Y. Y-X=ammount any theory will have to account for.

No, the start is a step back from that: Starting with very different theories whose effects we can observe on earth, and expanding the theories to the galaxy or universe domain, they all give the same roughly/exactly the same Y. The simplest answer is that they all fail to take into account the same amount of matter, not that they all just happen to be wrong in just the right way to trick us.

In science, the 'best fit' theory is shorthand for saying the theory that doesn't solve a problem completely, but by consensus represents the best our human ability can offer in solving that problem at that time in history.

That is a description of all of science. It never gives us ultimate answers, just better and better approximations of the correct answer. All scientific theories are likely to be replace some day, but not by throwing them out. In stead, a new theory will be made, that contains the old theory as a special case, just like Newtonian mechanics is a special case of relativity.

Wrong questions!

[Forty Two Tenfold]

It doesn't really, in strict sense, although one might by an honest mistake simplify it thus, exist, but rather, in a word, it is not non-existent. So to understand it better you have to exclude things it's not supposed to be diffrent from. I hope that clarifies things.

worth it, if...

[globaljustin]

the data can disprove 'Dark Matter' theories...

that's worth $2 Billion in my mind...

Loop Quantum Gravity is by far a more elegant theory. The only problem is Cambridge really...they like their multi-verse theory a little too much over there...

Re:worth it, if...

[Anonymous Coward]

they like their multi-verse theory a little too much over there...

Try LSD, and you'll understand why. (If you actually want to understand that.)

Re:worth it, if...

[Anonymous Coward]

You're thinking of bath salts, probably what someone told you was LSD.

Re:worth it, if...

[painandgreed]

the data can disprove 'Dark Matter' theories...

that's worth $2 Billion in my mind...

Loop Quantum Gravity is by far a more elegant theory. The only problem is Cambridge really...they like their multi-verse theory a little too much over there...

If only LQG said anything about dark matter then you might get your wish.

Explanation

[Roger W Moore]

First the energy limit on interstellar travel is not getting out of the gravitational well of the sun it is getting up to a large fraction of the speed of light. If your intention was achieve that sort of velocity with a gravitational field then please try this is someone else's solar system because a gravitational field of that magnitude - think black hole - will do nasty things to planetary orbits.

Second Dark Matter is incredibly diffuse, far more so than normal matter because it only interacts via gravity and - possibly - the weak force. So there it no way to make small, dense concentrations of it like you can with normal matter.

Finally, the AMS results does not yet show any evidence for Dark Matter. They need to extend their energy by a few bins to see whether the spectrum starts to drop - the current spectrum could be explained by pulsars - the positron excess has been known to be there for some years already thanks to PAMELA and Fermi/Glast(for a slightly more technical announcement with plots see here). So it is a very interesting result but not yet evidence of Dark Matter. However, if it is Dark Matter, it should have a low enough mass to be created in the LHC so we may get a shot at finding whatever it is in 2015 when we turn back on with ~twice the energy. In fact my grad student and I worked on the ATLAS search for Dark Matter models associated with this type of positron-only signature but found no evidence. It's now being repeated with the 2012 data so stay tuned...

Re:Explanation

[Intrepid imaginaut]

First the energy limit on interstellar travel is not getting out of the gravitational well of the sun it is getting up to a large fraction of the speed of light. If your intention was achieve that sort of velocity with a gravitational field then please try this is someone else's solar system because a gravitational field of that magnitude - think black hole - will do nasty things to planetary orbits.

Yes, if you read the rest of the comments the concept isn't within the solar system nor is it a single large gravitational field.

Second Dark Matter is incredibly diffuse, far more so than normal matter because it only interacts via gravity and - possibly - the weak force. So there it no way to make small, dense concentrations of it like you can with normal matter.

It does form structures, so I'd say it's too early to make definitive statements about what can and can't be done with it.

It's now being repeated with the 2012 data so stay tuned...

Will do.

Re:Explanation

[Anonymous Coward]

Why would Dark Matter be more diffuse? If it only interacts via gravity, shouldn't it be more compact than ordinary matter, with the only exception being black holes.

Re:Explanation

[50000BTU_barbecue]

Well, without ionic or covalent chemical bonds (electromagnetics!), what do you think will happen? Gravity is a very weak force; you can charge up a party balloon with static electricity and it will stick on the ceiling, against the gravity of the entire planet.

Re:Explanation

[Roger W Moore]

It does form structures, so I'd say it's too early to make definitive statements about what can and can't be done with it.

That it does - huge, massive structures on a galactic and cosmic scale. The reason for this is that it interacts via gravity and, perhaps, the weak force. I agree that we can say very little about it at all at the moment but I do think that we can say that it will not form structures on a stellar scale which can generate a large enough gravitational field to accelerate an object to close to light speed in a reasonable length of time.

Yes, if you read the rest of the comments the concept isn't within the solar system nor is it a single large gravitational field.

You cannot stop a gravitational field at the edge of the solar system - gravitational fields are infinite in extent. In order to have feasible interstellar travel you would need to have a reasonably rapid acceleration. Any gravitational field capable of generating that would disrupt planetary orbits.

Re:Explanation

[Intrepid imaginaut]

That it does - huge, massive structures on a galactic and cosmic scale. The reason for this is that it interacts via gravity and, perhaps, the weak force. I agree that we can say very little about it at all at the moment but I do think that we can say that it will not form structures on a stellar scale which can generate a large enough gravitational field to accelerate an object to close to light speed in a reasonable length of time.

People are good at taking otherwise inoffensive substances and concentrating them into all sorts of volatile configurations. I'm not making any assertions, just blue skying it, but it's too early to say yea or nay at this point.

You cannot stop a gravitational field at the edge of the solar system - gravitational fields are infinite in extent. In order to have feasible interstellar travel you would need to have a reasonably rapid acceleration. Any gravitational field capable of generating that would disrupt planetary orbits.

Gravity gets stronger the closer you are to its source. A chain of dark matter 'planetoids' stretching between stars wouldn't have much of an effect on the endpoints, particularly since they wouldn't be in a straight line, or at least not that straight. The idea relies on small pushes over the length of the gargantuan distances between stars, even those closest to us.

Physics!

[benjfowler]

There's nothing like physics articles to bring out all the morons who think that because something is complex and counterintuitive, it's a license to make up any old bullshit they want.

And it's amazing how indignant the drooling retards get when they get called out on their bullshit by people who actually know what they're talking about (because they busted their arses at college for years, rather than just pulling shit out of their arses).

Re:Physics!

[Anonymous Coward]

Are you referring to someone in this thread, or Space Nutters that think we'll colonize the universe based on nothing more than wishful thinking and dog-eared paperbacks from the '70s?

This is bullshit

[iris-n]

As usual, this is just a press release full of hype.

They didn't discover dark matter. They measured, with higher precision than ever, the excess in the positron fraction coming from cosmic rays. The existence of this effect, however, was already well-established. The question that was open, and still is, is which is the origin of this effect. One of the possible answers is dark matter. The problem with this answer is that we have to assume a discredited theory -- supersymmetry, and even within this theory a very artificial model of dark matter annihilation. The higher precision of the current measurements does not credence to this answer, nor does it discard more boring answers (i.e. coming from astrophysical processes that do not involve new physics). If you want to understand more about it, please read it from an actual particle physicist. I am a physicist, but not an astrophysicist nor a particle physicist.

Please keep in mind that I'm not criticising the AMS experiment itself: its job was to measure this excess with high precision, and this it did quite well. What I'm criticising is the people who have published this irresponsible press release.

Re:This is bullshit

[Kongming]

While I'm not a physicist of any variety, the following text from the article also caused me to call its reliability into question:

"As the moniker suggests, dark matter is dark; it doesn’t interact with electromagnetic radiation."

Isn't one theory that dark matter is normal baryonic matter, just not baryonic matter that is concentrated or luminous enough to have a measurable effect on any light getting to us?

Re:This is bullshit

[PvtVoid]

Wish I had some mod points to mod parent up. It's bang on.

AMS confirmed (to much higher precision) the excess already observed by PAMELA and Fermi. This is interesting. It is also a long way from even an indirect detection of dark matter. Meanwhile, there is no evidence for SUSY. None. Nada.

Re:This is bullshit

[marcosdumay]

Isn't one theory that dark matter is normal baryonic matter, just not baryonic matter that is concentrated or luminous enough to have a measurable effect on any light getting to us?

Yes, there is an old theory that can't explain a lot of recent observations.

Re:This is bullshit

[iris-n]

Sorry, this is not the case. Again, I'm not an expert on this, but the best evidence I now that dark matter isn't just normal matter that happens to be dark is the Bullet Cluster. The thing is that, even if we can't see the normal matter, we know that it interacts with normal matter, well, normally. So in a collision of galactical clusters, we expect even this dark gas to interact a bit and get left behind, while the interactionless dark matter passes straight throught, and this is what we have observed in th Bullet Cluster.

If the effects we attribute to dark matter could be explained by known matter I don't think anybody would be excited about it =)

The sentences that could have given you warning were "An excess of antimatter within the cosmic ray flux was first observed around two decades ago.", i.e., the effect was already well-known, and "the AMS measurement can not yet rule out the alternative explanation that the positrons originate from pulsars distributed around the galactic plane. Supersymmetry theories also predict a cut-off at higher energies above the mass range of dark matter particles, and this has not yet been observed.", i.e., boring explanations were not ruled out, and the "smoking gun" evidence for dark matter was not yet found.

Re:This is bullshit

[sFurbo]

If there were enough baryonic matter in the universe to account for the dark matter as well, the ratios products of big bang nucleosynthesis would be different than what we observe. Furthermore, the study of the variations in the cosmic microwave background tells use that around five-sixths of the total matter is in a form which does not interact significantly with ordinary matter or photons. Both facts are mentioned in the WP article on dark matter.

New Age idea

[Anonymous Coward]

I have a great idea for a new religion or spiritual movement, following the concept that God lives in the gaps of our understanding.
Scientists will say that we don't meaningfully interact with dark matter, but one can just deny that and use it as the "explanation" for whatever mystical phenomena one wants to claim are out there. This will be hard (or even impossible, I believe) to disprove.
Auras? Dark energy. Souls? Dark matter. Et caetera.
I am too lazy, but this is Scientology-grade material and I think religious charlatans won't let it go to waste.
I'm just surprised they haven't done it already --- or maybe they have and I'm just not aware of it. In any case, the pathway to profit seems rather clear.
I have one firm prediction --- when they catch up with it, they'll claim that they knew about it all along, but they were just using a different language.
The same sort of claims are currently being made regarding the privileged role of the observer in quantum mechanics.

next to last

[Anonymous Coward]

the penultimate shuttle mission to the orbital outpost.

Excellent Question!

[Roger W Moore]

Why would Dark Matter be more diffuse? If it only interacts via gravity, shouldn't it be more compact than ordinary matter

That's a very intelligent question! That's exactly what you might expect but you need to go a little deeper. Think about a planet forming from a cloud of dust and rocks. Once a clump of a few rocks has formed it starts to pull in more dust and rocks from the surrounding cloud and a planet starts to form because rocks in the cloud are pulled in my the gravitational field of the clump until they smash into it and stop. This increases the mass of the clump so it pulls in more rocks and grows.

The critical part is that the only reason that the rocks stop when they hit the clump of material is because of the electromagnetic repulsion between the atoms in the rock and the atoms in the clump. This is the same reason that you do not fall to the centre of the Earth - the atoms on the soles of your feet are repelled by the atoms of whatever you are standing on.

Now lets think about Dark Matter. It has no electrical charge and so feels no electromagnetic force. So when a Dark Matter particle is attracted towards a clump of other Dark Matter particles it simply passes right through them without any interaction! It then starts to slow down under their gravitational field until it, eventually, turns around and flies back through the centre. Effectively all a "clump" of Dark Matter is is a group of particles oscillating back and forth in their shared gravitational well. This is why Dark Matter is so diffuse - it can form structures but only on a very large scale.

This is not quite the entire picture - there may be a very small chance of an interaction when Dark Matter particles pass by each other. This will help the particles to clump more but it will be a very, very slow process - and this is only the case if Dark Matter feels the weak force which is not certain. These interactions might also involve two Dark Matter particles annihilating which, if true, may give the positron signal which AMS sees. However to confirm this they need to look at a sightly higher energy which they claim they already have the data for.

Re:Excellent Question!

[Anonymous Coward]

So when a Dark Matter particle is attracted

What makes us believe dark matter is particulate?

Re:Excellent Question!

[Roger W Moore]

What makes us believe dark matter is particulate?

It has a mass because it exerts a gravitational field and the distribution of the mass is non-uniform. This means it is a particle, unlike Dark Energy which is the energy of the vacuum.

Re:Excellent Question!

[Anonymous Coward]

Thanks for the posts. They've been informative. So is dark matter essentially like a bunch of Neutrino's going really slow and just being pulled back and forth by gravity?

Re:Excellent Question!

[Roger W Moore]

Yes...but it is not neutrinos. Neutrinos have tiny masses - so low in fact that we have not been able to measure them yet but we know that they are not zero because the oscillate which means there are mass differences between them. This means that when they were created they were moving at close to the speed of light so they would travel a huge distance before gravity would pull them back into the clump.

This would result in huge sized, very diffuse clumps of Dark Matter. However all the data suggest that Dark Matter is more clumped than that i.e. the clumps are far smaller than they would be for a particle travelling nearly at the speed of light. So the result is that we need something that interacts somewhat like a neutrino but which has a huge mass - probably heavier than any particle we have yet discovered. If we can find it then this would be a bigger discovery than even the Higgs!

Re:Excellent Question!

[strikethree]

Now lets think about Dark Matter. It has no electrical charge and so feels no electromagnetic force. So when a Dark Matter particle is attracted towards a clump of other Dark Matter particles it simply passes right through them without any interaction! It then starts to slow down under their gravitational field until it, eventually, turns around and flies back through the centre. Effectively all a "clump" of Dark Matter is is a group of particles oscillating back and forth in their shared gravitational well. This is why Dark Matter is so diffuse - it can form structures but only on a very large scale.

Another question then: How can Dark Matter be a particle if the particles do not interact except through gravity? Wouldn't all of these particles keep piling up at the same point and eventually become black holes? Wouldn't these "clumps" of Dark Matter suck in regular matter too?

Re:Excellent Question!

[Roger W Moore]

I'll answer these in reverse order!

Wouldn't these "clumps" of Dark Matter suck in regular matter too?

Yes they would...and in fact did: this is how galaxies formed! Dark Matter far outweighs normal matter the gravitational field of its clumps pulled in normal matter which then formed the galaxies we see today.

Wouldn't all of these particles keep piling up at the same point and eventually become black holes?

No because for particles to "pile up at a point" they all have to have the same position AND velocity. If they have the same position but different velocities then they just move apart - like two water waves travelling in different directions they would just pass through each other. To get particles to pile up should have to have an interaction when they get close which will cause them to exchange momentum so that, given time, all the particles end up with the same velocity. Whether they can have the same position depends on what type of particle they are. Particles called "bosons" (which give us forces) can pile up in the same position and velocity state. Particles called "fermions" (which give us matter) cannot. So overall, while it is possible, I would say it is unlikely that you would get a dense enough collection of Dark Matter to make a black hole without normal matter helping out...but I'm a particle physicist not an astronomer!

How can Dark Matter be a particle if the particles do not interact except through gravity?

Neutrinos are particles even though they are electrically neutral and so not feel the EM force. Electrons are particles even though they do not feel the strong (nuclear binding) force. If DM particles only interact through gravity it just means that they carry no charge of any of the other forces of nature (weak, strong or EM). However it is possible that they do carry a weak charge and so will feel the weak force...we just don't yet know.

Re:Excellent Question!

[strikethree]

First, thank you for your response. I greatly appreciate it.

No because for particles to "pile up at a point" they all have to have the same position AND velocity. If they have the same position but different velocities then they just move apart - like two water waves travelling in different directions they would just pass through each other.

Hm. But they attract gravitationally. But if they can not hit each other... Hm. Tough one.

However it is possible that they do carry a weak charge and so will feel the weak force...we just don't yet know.

If they interact through the weak nuclear force, wouldn't there be some sort of evidence such as light or heat? Even if just in very small amounts... Very odd stuff.

Again. Thank you.

What caused the price tag?

[daffy951]

What caused the 2 billion price tag? Is alot of research included? Extremely difficult to create the device or what? (Not meant as criticism, just curious because $2 billions sounds like a lot of money..)

Re:What caused the price tag?

[Anonymous Coward]

Last I heard, the project was closer to $1.5 billion, so maybe 25% of that is round up? At the time though, part of the cost was just launching it via space shuttle and getting it attached to the ISS. But the project also had several technical difficulties and dead ends that resulted in going over budget just on design and construction. For example, they had to redo the magnet design after problems with a cooling system meant use of superconducting magnets would make the project lifetime too short. The device itself is pretty expensive to make too, and I've heard estimates of it being equivalent to a couple hundred million dollars to make an equivalent device for use on the ground, while this one had to be mostly self contained and be space worthy.

Re:What caused the price tag?

[ceoyoyo]

Well, it required a shuttle launch to get it up there. That's a good part of the price tag. Usually these things include the science for a few years as well. And it is a complicated piece of high precision electromechanical hardware. In orbit.

A Better Explanation

[Anonymous Coward]

I am sorry but the scientific community seems hell bent on finding "Dark Matter" etc. There is a simple and obvious source for positrons etc and we found it already. NASA turned their gama ray satellite at the earth and to their amazement thunderstorms emit positrons from "red sprites" and "blue jets" associated with lightning discharge. Nearly every body in the solar system emits this stuff. It would be stunningly surprising if it wasn't emitted from every significant body in the universe. That pretty much closes the case on another example of "BAD SCIENCE" brought to you by people still trying to drive the universe with the weakest force (gravity) and ignore the dominant force. (Electromagnetic!)

Re:A Better Explanation

[careysub]

Gosh. Another AC who - without reading the article - knows the true obvious answer that all those Nobel laureate were to dense to see.

If you bothered to read it you would see that the fact that positrons can be emitted by other sources is precisely why they are not calling this a signature of dark matter yet. You would also see that your "explanation" holds not a single drop of water - the positron flux detected is omnidirectional and does not vary with time ruling out any sources local to the solar system, much less the Earth, as a significant contributor.

You should move on to explaining other great mysteries of science, but of course without reading anything about them first.

Bullshit

[gr8_phk]

These results are consistent with the positrons originating from the annihilation of dark matter particles in space, but not yet sufficiently conclusive to rule out other explanations.

What widely accepted model of particle physics predicts this? Right, NONE.

Theory?

[gr8_phk]

Isn't one theory that dark matter is normal baryonic matter, just not baryonic matter that is concentrated or luminous enough to have a measurable effect on any light getting to us?

I think you mean "hypothesis". Yes, scientists get carried away with calling their wacky unsupported ideas "theories".

Ridiculous

[slashmydots]

So dark matter touches itself and explodes into positrons and electrons. It's 4x more common mass-wise than regular matter, both have gravity, but only dark matter didn't manage to coalesce into planets and starts? Is there some sort of huge gravity differential or more spread out distribution are they just making things up again?

P.S. I still think dark matter is a fantasy created from bad math.

Re:Ridiculous

[Anonymous Coward]

It's 4x more common mass-wise than regular matter, both have gravity, but only dark matter didn't manage to coalesce into planets and starts

Without things like electromagnetic interactions it is rather difficult to coalesce. Whether dark matter has no such interactions or is weakly interacting compared to normal matter, large clouds of dark matter would not collapse into a body on timescales of the universe's age due to limited to no way to radiate away heat or cool. The result is large clouds that are gravitationally bound to things like galaxies, but with individual particles having too much energy to settle into something smaller than the halo. It would be analogous to having a satellite that could pass through the Earth and putting it in orbit or even just dropping it. Such a satellite would just continue on an orbit/trajectory that passes through Earth and comes out the other side, and never settle within Earth without some sort of interaction that removes some of its energy.

mixing up proof and evidence again

[slashmydots]

Look up "proof" in the dictionary. There has never been proof of dark matter existing at all. There's pretty pictures and self-serving, biased, one-sided studies, and sketchy math equations, and really specific experiments that don't consider other possibilities, but zero proof.

Re:pertamax

[datavirtue]

Yep, after 2Billion is spent you HAVE to find something!

Physics

[Roger W Moore]

People are good at taking otherwise inoffensive substances and concentrating them into all sorts of volatile configurations.

Dark Matter is not made of atoms nor does it have any electrical charges. You cannot do chemistry with it - it is fundamentally different from any normal form of matter. What you propose is in direct contradiction to the know properties of Dark Matter.

Gravity gets stronger the closer you are to its source. A chain of dark matter 'planetoids' ...

Take a high school physics course and then do the maths. To get up to 10% of light speed (30,000 km/s), assuming your planetoid was Earth-sized and neglecting relativistic effects you would need a mass 22 times that of the sun. Now explain to me again how sticking a mass 22 times larger than the sun anywhere near our solar system would not severely impair the orbits of the planets?

If you include relativity the mass you need will increase and, even if you get to 10% of c we are still talking 30-40 years to get to the nearest star. Although this travel time will soon decrease as the line of 22 solar mass planetoids you'll need to sustain this speed will rapidly collapse into a blackhole with a mass so large that us and all the nearby stars will get pulled into it. Technically at this point travel to the matter which used to be Alpha Centauri might be possible but since we will all be being ripped to shreds by the tidal forces in the black hole's accretion disc I doubt anyone will appreciate it.

So, as I said, please don't try this anywhere near out solar system.

Re:Physics

[Intrepid imaginaut]

Dark Matter is not made of atoms nor does it have any electrical charges. You cannot do chemistry with it - it is fundamentally different from any normal form of matter. What you propose is in direct contradiction to the know properties of Dark Matter.

So you're saying it's impossible that science will ever be able to create the conditions to cause dark matter to come into being? It's a strange substance, not magical.

Take a high school physics course and then do the maths. To get up to 10% of light speed (30,000 km/s), assuming your planetoid was Earth-sized and neglecting relativistic effects you would need a mass 22 times that of the sun. Now explain to me again how sticking a mass 22 times larger than the sun anywhere near our solar system would not severely impair the orbits of the planets?

Twice as many would be needed because you have to slow down too. You don't aggregate the gravity on a single point because it's not in a single point, it is stretched over a half dozen light years. This is not a new concept, one variation is the Dyson Slingshot. The only question I'm wondering about is whether or not dark matter offers advantages in this regard. The unique properties of dark matter strike me as something that could have many uses. And keep in mind I'm just wondering, not making assertions, despite the entertaining hysterics it appears to have caused some anonymous posters.

If you include relativity the mass you need will increase and, even if you get to 10% of c we are still talking 30-40 years to get to the nearest star. Although this travel time will soon decrease as the line of 22 solar mass planetoids you'll need to sustain this speed will rapidly collapse into a blackhole with a mass so large that us and all the nearby stars will get pulled into it. Technically at this point travel to the matter which used to be Alpha Centauri might be possible but since we will all be being ripped to shreds by the tidal forces in the black hole's accretion disc I doubt anyone will appreciate it.

Stars many times larger than 22 solar masses exist, if it were even relevant.

Re:Physics

[Roger W Moore]

So you're saying it's impossible that science will ever be able to create the conditions to cause dark matter to come into being?

No, I'm personally working on a large, international experiment which hopes to do exactly that and we certainly aren't using chemistry! Once DM is made it is stable and does not interact easily with matter and we know this from astronomy.

Twice as many would be needed because you have to slow down too.

Please, please, please take a high school physics course - you seem to be very interested in physics but also seem to lack even the most basic understanding of it and I can't correct that in a few posts. However in this case after you have fallen into the planetoids gravity well and zoomed by the surface at 10% fo c you will then start to move away from it on the other side and slow down automatically due to the gravitational field.

Re:Physics

[saveferrousoxide]

Please, please, please take a high school physics course

I think it's just a simple and common enough misconception about "sling-shotting" in space. I believe the thought is that gravity somehow accelerates you more than it decelerates you (even though, obviously, the deceleration is exactly the same acceleration with a '-' in front). What's missing is the understanding that the "sling-shot" is using the orbital velocity to accelerate, not the gravity itself. The gravity is just there acting like the pouch of the sling. In fact, XKCD recently likened it to bouncing a ball off a moving truck, which is illustrative, if not overly accurate.

Is this the "Blast from the past"

[niftymitch]

So how many light millennia back in time does this measurement depend on?

Anyhow this may be interesting enough to go and read the initial article.

I think I will tune into "Big Bang Theory" tonight for an update.