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Dark Matter — "Alternative Gravity" Team Responds
An anonymous reader writes, "Following previous results, an international team of astronomers answers, defending the case for a modification of the theory of gravity. This article presents an alternative to dark matter and states constraints on the neutrino mass. In short, dark matter is still not a necessity, provided that neutrinos weigh 2eV. This is allowed by what we currently know and should be tested in the KATRIN experiment in 2009."
regardless of their energy potential why does dark matter have to be dark? what has been done to look at the mass of all of the photons in the universe. no matter what some people say they have to have some mass. think about it, all of the photons that have ever been created, unless they run into something will continue to travel accross the universe. since the beginning of the universe their has to be quite a few of them
Technology will default in society to its most rudimentary level:::stupid computers for stupid users:::
is too!
is not!
is too!
...
Great minds think alike; fools seldom differ.
Look at your night sky. It's a whole shitload of blackness with some stars thrown in. Now consider that there is a form of matter which is very dense and very dark. So dark, in fact, that it doesn't give off any radiation at all. All it does is exert a gravitational pull on surrounding masses, just like everything else in the universe.
It isn't difficult to look up and see all that darkness and think that maybe there's something in that blackness that just can't be seen.
But these guys would have you change the Theory of Gravitation because they can't grasp that maybe there are weird states of matter that exist just outside our physical grasp. They'd rather you believe that neutrinos have mass. These neutrinos that have for eons blasted through us at the speed of light with no interaction at all, they are the cause of the entire universe bending unpleasantly.
If you say that neutrinos have a physical manifestation greater than zero, you're going to also have to explain why these particles exhibit no interaction with anything except for being able to curve the shape of space on a galactic level.
Dark Matter is the 21st century's ether.
P226
err, neutrinos do have mass, but not as much as stated in the paper. As far as current experiments go neutrinos come in three flavours and interchanging between them is only possible if they have mass. It has been shown in experiments that they change type and hence must have mass.
Well, minor nitpick: I don't see why neutrinos would interact with other particles just because they had some small amount of mass. It's not as if they would produce more than a truly tiny amount of gravity, and they obviously don't interact electromagnetically with anything.
I have seen the future, and it is inconvenient.
I would have replied to all the inconsistencies... then I noticed the name. Not a bad troll.
Ignore this signature. By order.
For me, dark matter is like religion. Made up to explain what we can't understand, and wrong.
Well, some real testing is needed. Is their any practical use for this like FTL travel?
They do interact with matter, but because they're very small they simply pass straight through matter because the distance between particles in atoms / atoms are so great and only actually collide very rarely.
Um.
Google "electron volt in amu":
That's five whole orders of magnitude lighter than an electron. That sounds like a good reason they don't interact; it'd be like saying a dust cloud should interact with a chain-link fence.1 electron volt = 1.07354412 × 10-9 atomic mass units
110100 1101000 1101000 1100110 0 1101111 1101000 1100011 1
Thats electron Volts right? I don't get it. How does one measure weight with volts? Or does it mean it weighs as much as two electrons, in which case why not just say that?
Enh.
Neutrinos *do* have mass, and this fact is accepted by pretty much all physicists. The argument for this comes from discovery that they change states over the course of their lives, which means that they experience time, which means that they cannot travel at the speed of light, which means they must have a small mass. (This explains the apparently deficiency of solar neutrinos which was a problem in the 70s) Pinning down the exact value of this mass is more troublesome, though - for now, we know only that it's small, but positive.
What more puzzles me about this statement is that neutrinos have generally been counted as *part* of dark matter - in particular, they are proposed to constitute some of those so-called Weakly Interacting Massive Particles (WIMPs) which is one of two possible models for dark matter. I don't see how changing the details of these particles would change how neccessary they are, unless these guys are trying a bait and switch by redefining dark matter to be unneccessary. (Which would be a very dirty trick.)
Moreover recent experiments have shown they do have mass (see Wikipedia).
They know their mass is >= 0 and 2.2 eV, hence why the proposed 2eV is possible.
Wait, there might be a flaw in the logic here somewhere.
Don't blame me; I'm never given mod points.
Holy date confusion! We are receiving test results from the future. Power up the tachyon beam, Cap'n.
(of the electron variety anyway)
Comment removed based on user account deletion
I'd like to clear this up because there are very common misconception that photons are massive or that something has to be massive to feel gravity, both of which are false.
THEORY: In our current understanding, photons are forbidden from having mass because of the way quantum electrodynamics (the most precisely tested theory in the history of science) works. It's an exercise in field theory to show it, but the gist is that electromagnetism (light, charge conservation, electric and magnetic forces...) are a consequence of a symmetry of nature, and that symmetry only works if the associated carrier particle (the photon) has exactly zero mass.
EXPERIMENT: If the photon had even a very tiny mass, it would also mean that the electromagnetic interactions would become short range (just like the weak interactions, which are mediated by a massive carrier). The usual inverse square law would become an exponential falloff. This has been tested for in laboratories (and in astronomy!) very precisely, so there are ridiculously strict upper limits on the photon mass.
This doesn't mean photons don't feel gravity!! Gravity interacts with all energy, not just mass, and so the energy of a photon is enough to cause it to bend around massive objects.
Neutrinos do have mass, that has been experimentally proven within experimental error. It was the first example my lecturer gave in Physics 101 of experimental uncertainty. We're just not sure how much mass.
I'm skeptical, but it would tidy things up nicely if it turned out right.
// MD_Update(&m,buf,j);
They're just proposing that there is no "exotic", new kind of dark matter.
Incidentally, I'd watch the Cosmic Variance blog in the coming days for a discussion of this point; Sean Carroll's post there on dark matter was linked to in the last Slashdot story.
Responding to other posters: the amount of photons in the universe can be estimated based on how many of them reach us, as well as from theoretical predictions on the emission of light from stars, the Big Bang, etc., and is woefully inadequate to produce the needed gravitational effects — not to mention it is too "hot" to be the kind of dark matter needed to explain early universe structure formation.
An eV, or electron volt, is a measure of energy: the amount of energy acquired when an electron is accelerated through a 1-volt electric potential difference. It is about 1.6 * 10^-19 joules. By E=mc^2, it also corresponds to a mass, about 1.8*10^-36 kilograms. An electron, by comparison, masses about 511,000 electron volts.
I think I'd regret responding to the complete misunderstanding of forces and neutrinos in the body of your post. That would take pages.
Let me just respond to your title. That is completely wrong as well. Now, I think the alternative gravity guys are probably wrong and at this point I think they are stretching their theories to their limits. Dark matter is the "easiest" explanation. But, what they are doing is science. They are coming up with an alternate theory that makes predictions and testing them. The are countering circumstantial evidence for DM with another theory. They are not picking just one small thing, saying "Well that can't be true because of [insert some non-science babble like you just posted] so clearly God created everything." in contradiction to vast bodies of scientific evidence. And the alternative gravity people are publishing in peer-reviewed journals.
ID can't say any of those things. While the motivations may be similar (not wanting to give up on old ways of thinking about things) the methodology is completely different.
Are you saying that Dark Matter is why we have fire?
Slashdot Burying Stories About Slashdot Media Owned
Could you explain - in that case, let's say I travelled on a spaceship to a place where this dark matter was located based on gravitational measurements. Now, I am assuming the general location that it would be in could eventually be located, rather than simply being 'everywhere else than where we currently are'.
In that case, what would happen if I attempted to land on this in my spaceship, and take a piece of this and put it in my space pants?
Would it actually be black as blackness, as in light-absorbing?
Or would it be invisible, as if it was pushing light to flow around it?
Would I just pass through it, with a feeling like walking uphill (towards a 'gravitational bulge') as I walked towards it, and downhill when going away?
Would it be possible to cut off this piece and place it in my pants, only that my equipment would be attracted to it in a gentle sucking effect?
I think until these fairly basic questions are answered, which noone seems to be able to, 'dark matter' will earn a lot of skeptics and agnostics.
How can one believe this black matter theories? The flying spaghetti monster holds the truth.s ter
http://en.wikipedia.org/wiki/Flying_Spaghetti_Mon
Stupidity is the root of all evil.
It sounds like they are going for a MMOND theory, modified modified newtonian dynamics. They admit the presence of dark matter. In fact, they reference another experiment as well as the bullet cluster observations that seems to show that MOND can't account for everything. So to save MOND, they are saying it doesn't have to account for everything. Massive neutrinos migth account for the rest.
- None can love freedom heartily, but good men; the rest love not freedom, but license. -- John Milton
I don't think anyone has a huge amount of "faith" in dark matter. The problem is that there is a conflict between theory and observation; gravity as we understand it doesn't predict the shape of the universe that we see, so we try to figure out what it is that we don't understand. That is how science progresses.
Our theories of gravity have held up well under testing many times, though it's fair to say that we don't know as much about it as we would like. Alternate gravity is also a matter of uncertainty, though, as we don't have any solid data showing that our gravity theories are wrong. Quantum physics has shown that there are many types of particles and many different interactions, suggesting that not all matter is structured the same way, so it's not unreasonable to suggest that there might be a type of matter that we don't understand.
Naturally there are physicists exploring both possibilities and they can be fans of one idea or the other, but that doesn't mean that they are acting on "faith". It's just how science has always progressed. There was a time before relativity was tested when it was controversial, and to some degree it still is.
I have seen the future, and it is inconvenient.
Here's Newton's law of gravity:
d mV/dt = - G M m/R^2 R_hat
It doesn't work for galaxies, it doesn't work for the big bang, it is broken for almost anything BIG. It also has a tiny bit of error that GR corrects, but that is minor. The problems with this law are HUGE. So we have two schools of thought. One wants to stuff the big M box with dark matter:
d mV/dt = - G (M + Dark_M) m/R^2 R_hat
These folks get to put Dark_M wherever it needs to go to get the answer right. Then there the MOND folks who want to mess with the R:
d mV/dt = - G (M + Dark_M) m/R^2 or if dV/dt is small, d m V/dt = - a_0 sqrt(G M/R^2) m R_hat
where a_0 is a new constant in nature that changes the form of gravity's law if tiny. I got my own proposal. Remember the chain rule from calculus?
d mV/dt = m dV/dt + V dm/dt
That V dm/dt is the stuff of rocket science. We know it is not relevant for stars cause those big star things and galaxies don't change. But we could, just for the fun of it, do a relativistic swap-out, and consider:
d mV/dt = m dV/dt + V dm/dt + V c dm/dR
Force is a change in momentum, which can be seen either as the usual acceleration, the rocket-ship effect, or as where stuff is distributed in space. That sounds like what is going on. So my proposed modification is this one:
d mV/dt = m dV/dt + V dm/dt + V c dm/dR = - G M m/R^2 (R_hat + V_hat)
Too bad I suck at numerical integration or I'd try and see if it could match real data sets. I like it because it uses stuff we know is true (the chain rule) with a fun twist to make an old law point in a new direction.
doug
Working on new views of old physics at http://VisualPhysics.org
From reading the summary, this is my understanding of what these guys are saying, too. Call it modified MOND.
- None can love freedom heartily, but good men; the rest love not freedom, but license. -- John Milton
There's a some evidence (see? gravity! DARK MATTER!) but it's theoretical,
IANAP (I am not a physicist), but isn't the The Great Attractor more than theoretical proof of something dark that is attracting all those galaxies? Also, why do stars on the outer rim of galaxies revolve so fast around the core? Spiral galaxies do not seem to spin around their core like expected.
Dismissing dark matter as purely theoretical is shortsighted IMO.
People should NOT take the impression from this article that there is doubt that dark matter exists. The only doubt being raised is over what form the dark matter takes. Let me clarify:
(Note: Baryons are protons and neutrons. "Non-baryonic" means not made up of the building blocks of ordinary atoms.)
The beauty of the Clowes work (the "proof that dark matter exists" from a couple of weeks ago) is that the colliding clusters they worked on give simple, clean evidence that galaxy clusters are really dominated by invisible, non-baryonic dark matter. At it's core, it's a very simple argument. Two clusters collided, and the baryonic clouds (hot gas, seen with X-rays) experienced drag and got a bit hung-up passing through one another. Most of the mass, however (seen with gravitational lensing), passed straight through with no drag. We see the X-rays and lensing in two different places on the sky - they really are two different kinds of stuff. This is VERY direct proof that most of the mass in galaxy clusters is not the ordinary matter we see on earth - it's something non-baryonic that does not interact with light and does not interact much with ordinary matter. In other words, dark matter is real, physical stuff!
This article argues only about what that dark matter might actually be. It's generally believed that it can't be neutrinos, because neutrinos are so light that they would mess up galaxy formation, and so must be some new, exotic kind of particle. The logic here is that very light particles move so fast that they don't clump together well under their own gravity, which would disrupt the formation of galaxies and smaller clusters of galaxies. All this paper argues is that the dark matter might not be a truly new particle - the combination of modified gravity and neutrinos can be made to work. They still conclude that the invisible neutrinos must outmass the baryons in the clusters by a factor of at least 2.5.
Many people (particularly those who do not understand the evidence) dislike the idea of dark matter, thinking it sounds too much like epicycles. That's understandable, and it's good to be very skeptical of such a weird idea (I know I was). The truth is that there is now enough evidence to say that it really does exist, no matter how strange it may seem to us. The future lies is figuring out what the dark matter is actually made of, not bland assertions that "that just can't be right...".
The sweaty fat kid at college had loads of mass and no one interacted with him. :-)
Perhaps neutinos are similar.
If you were to take a spaceship to the place where dark matter exists, your ship would be obliterated by the tidal forces generated by the dark matter. Spacetime would physcially change as you approached and like a black hole, you would be sucked in.
Though to answer your question, yes, though your equipment may in fact be microscopic, the fact that you have any equipment at all would mean that you would be attracted to the dark matter. It would be the siren's song for your dong, so to speak.
As has been explained before, and will doubtless be explained again, ID is not a scientific theory, and does not hold the same value as the scientific theory of the existence of dark matter.
If dark matter exists (ie, the theory), it can explain certain observed phenomena. However, where it differs from ID is that the theory can be used to make falsifiable predictions about things we have not yet measured. Using the theory as a base point, we can predict what will happen in certain regions of space if there are WIMPs there. We can predict how the universe is going to expand or contract. If any of these predictions are wrong, then the theory that there is dark matter is also wrong.
On the other hand, intelligent design does not offer any falsifiable predictions. There is no way to test the "theory" (in this case, non-scientific) to determine if it is false. If you can devise a test that would prove ID to be false, then that would elevate it to the status of a scientific theory. It still wouldn't be a useful theory, however, as it does not offer any predictions as to how unobserved phenomena will react when we do get a chance to observe them.
Dark matter is there because the math behind it explains the current set of observations, and because there is a way to prove that the current set of observations is not due to dark matter. Intelligent design is there because Christians are upset about the removal of their god from the science classroom.
It may look like I'm doing nothing, but I'm actively waiting for my problems to go away.
--Scott Adams
KATRIN experiment homepage URL
http://www-ik.fzk.de/~katrin/
Even if dark matter exists, there is no reason why it all would add up to (nearly) zero.
2 0Gravity would stand a chance.
For example, if dark matter exists, what if there is just a little more of it than expected? Then the theory of "pushing gravity" http://www.everything2.com/index.pl?node=Pushing%
Hey don't blame me, IANAB
I try to be conservative, but not closed minded, in my accepting of new ideas. Concerning a concept as heavy as gravity, I think that scientists are just throwing us around, and i'm not falling for it.
Look at the sun. Look at how bright it is.
It isn't difficult to look up at all the brightness from the sun and think that maybe there is something there that we cannot see.
That thing in the sun that we cannot see is the planet Vulcan (not to be confused with the planet from Star Trek.) It is clear that this planet is the reason why the orbit of Mercury is not what we would expect using Newtonian physics. All we need to do is find that planet and newton's laws will be validated
But now this Einstein guy would have us believe that we should change Newton's law of gravity just because he couldn't grasp that there is a strange planet out there that exists just outside our ability to measure it.
My point is that any theory may seem insane until it is validated using physical measurements.
Those who push a theory that is eventually proven wrong are doing an important job. They are helping the theory that will be proven right to become that much stronger. So no matter which side is eventually proven right we really need to thank both sides!
Is there dark matter or do we need to change our ideas about the laws of gravity? I for one am going to wait until all the measurements are in before I make up my mind!
They want you to accept this unseen unobservable force that explains the things we don't understand, because it's more comfortable than acknowledging that we don't have all the answers. ...
Ok, but seriously: Major scientific theories are always subject to change. As experiments disagree with accepted theory, there's always a choice between "tweaking" the theory while holding onto its core assumptions, vs. introducing a new theory.
As a matter of scientific philosophy, we replace more complex theories with simpler ones if they predict reality with the same accuracy. As a matter of history, the simpler theory often ends up proving to be more accurate as experiments are refined. "Simple" doesn't mean "easy for a lay-person to understand", though; maybe elegant is a better term than simple.
One camp wants to add a new concept (dark matter) to existing theory; the other wants a new theory that dosen't require the same new concept. Both can use their method to explain what we see today. Most importantly (and distinguishing both groups form ID scientists), it is conceivable to test the theories. Real observation may (probably will) eventually favor one or the other.
Frankly, I have my opinion, but it's based more on history of science than on details of the two theories. The only fact in this debate is, until experimentation can tell the difference between a reality obeying one theory vs. the other, anyone saying 'this way is Right and the other is Wrong' has failed to understand science.
This is incorrect. Theory exists regardless of the existance of any one theorist who believes that the theory must be true or is the only explanation available.
To re-state: dark matter is a theory becuase it was a hypothesis which has endured the gathering of some experimental data, but there is not yet enough experimental data to exclude other possibilities. This is, in no way, a matter of faith. It's certainly a matter of speculation and experimentation, and anyone who tells you "dark matter exists" is over-simplifying to the point of error.
Now, this hypothesis that we're discussing is a different beast. It's a mathematical model that may or may not preclude dark matter by chaning the rules slightly. Changing the rules of gravity isn't that much of a big deal (we assume that the unification of gravity with the other forces will probably come with some surprises), but one does not speculate about those changes lightly. To wit, this theory is being greated with skepticism, not because it offends some faith in dark matter, but because it requires some heavy thinking about existing mechanics.
This is what science is all about. You build a model, and then you tear it down. You repeat this process until you have a model for which the difference between "sturdy" and "unassailable" is indistiguishable. At that point, you refer to the model as a "law". That is, "a very sturdy model". Then you move on to the implications of that model, and start building new models.
I am fine with the possibility that there is a lot of normal matter which is not detectable from earth. I am also fine with the idea that more exotic forms of matter and energy might exist. The current dark energy models are the best matches for astronomical observations thus far. And when it is all said and done, if dark energy continues to be the best description, it will prevail, but that doesn't mean we shouldn't stop testing it.
At one time, all the scientists thought there was this stuff called ether, and it was the best explanation for the observations we had. Then people did more tests, and discovered incongruities. In the end it was proven an incorrect idea, and was supplanted with a better model.
Einstein spent many years trying to find a deterministic alternative to quantum mechanics. There were many respectable scientists that felt that QM was merely a useful approximation, but after years of testing, a the consensus finally turned, and the community accepted that the non-deterministic aspects of QM were real.
Should we have blindly accepted Ether or QM, just because preliminary results showed promise with the ideas? No - we continued to question them and test them until they were disproved or time had shown them to be solid ideas. Dark Matter is in the same place as these theories once were. I don't know whether it will turn out to be correct or not, but I do know we should continue to challenge it, to think of new ways to test it, and to think of alternative explanations, because that is what science is about and that is how we take good ideas and turn them into a rigorous and well-established understanding of the universe.
You would call these people pseudo-scientists, and yet your only argument an application of Occam's Razor (and as others pointed out, faulty understanding of principles). But that's the funny thing about Occam's Razor - it is dependant on one's personal opinion of what is the most likely, or most simple explanation. Some would consider making up new particles that we have never observed a real stretch, others consider tweaking the existing rules a hack. That someone has a different view of what is elegant than you, does not make their ideas pseudo-science. What matters is if they are predictive and falsifiable, which these are.
Honestly, if you can't tell the difference between people that present testable alternative hypothesis, and people whose best "theory" that they could present amounts to "does this not appear irreducible", then you are the one that needs a refresher on what is and is not science.
Only if your black magic comes from the dark side of the Force.
(Got a female illusionist of African descent?)
Can we get a -1, Laypersonspeakify mod?
Edward@Tomato - /home/Edward/ man woman
man: no entry for woman in the manual.
"Qua!?"
"Dark matter": an invisible attractive force operating on galaxy-level distances (at million light years). Size: about 23% of the energy-mass of the observed universe. Evidence: Galaxies spinning faster than the number of visible stars justify. Gravitational lenses stronger than visible stars justify. Suspects: known low mass particles like neutrinos; unknown low or high mass particles like strings, wimps; a new phsyical force; non-r-squared term in Newton's equation of gravitation, observational error ...
...
"Dark energy": an invisible repulsive force operating on universe-size distances (at billion light years). Size: about 73% of the energy-mass of the observed universe. Evidence: Hubble expansion is accelerating over time when gravity would suggest eventual deceleration or collapse. Suspects: energy in fabric of space-time, unknown force, observational error
"Observed matter": stars, galaxies, gas clouds, neutrinos; Size: about 4% of the energy-mass of the universe.
The real result of Clowe et al's fascinating work was to show that the missing mass in the bullet cluster must be COLLISIONLESS, whatever gravity looks like (a purely baryonic bullet cluster has been *falsified*). However, a big misconception about it was to think it was a direct *confirmation* of the Lambda-CDM concordance model that everybody is supposed to believe (may I recall that real science is about *falsifying* things, not "proving" them right), or that it was falsifying MOND. Actually, it is known for years that MOND is UNABLE to fit the temperature profiles of X-ray emitting clusters from their pure baryonic content. The fix, for MOND to stay in the game, was to propose that neutrinos have a 2eV mass and can then make up for the missing mass, in clusters ONLY, because they are too light to cluster on the galaxy scales (incidentally they are also too light to form structure in GR, but this is not a problem for structure formation in MOND). However, if dark matter is indeed cold as the lambda-CDM guys tend to take for granted, and even more since Clowe's work, why does the 2eV neutrino combined with MOND seem to work in ALL clusters??? The bullet cluster being a totally new kind of constraint for MOND on the galaxy cluster scale (constraint coming from gravitational lensing instead of temperature profiles), it was mandatory to check if 2eV neutrinos were excluded even in MOND, which would have *falsified* MOND indeed! This is what those guys wanted to do, to *falsify* MOND once and for all, but the surprising result is that they didn't manage to do so, because the SAME neutrino mass as the one needed to fit temperature profiles of other clusters ACTUALLY WORKS in the bullet cluster too. Their conclusion is thus just that MOND is *not excluded* by Clowe's data. One will thus have to wait for particle physics experiments to rule out massive neutrinos to rule out MOND. Until then, place your bets...
I don't think there's anything approaching reasonable in that statement. This is a theory. It is either a good theory or a bad theory on its own merits, and you don't introduce a theory because you feel that no other competing theory could be correct, you introduce a theory because you can demonstrate that it could be correct.
Science is the process of breaking existing theory, and there is nothing wrong with attacking the existing model for gravitation. In fact, attacking existing theory is one of the most important tasks in the scientific method. How correct this theory turns out to be is still anyone's guess, and our speculation without either mathematical proof or experimentation is moot.
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You're trying to draw a binary distinction where none exists - that if we "catch" some dark matter that would mean we know for sure it exists, but until then it has the same status as ID.
That's simply nonsense - a direct detection of DM would mean you built a detector and it registered some hits. Assuming the particles detected had the correct properties, that would be taken by most as confirmation of the existence of DM - but you could assail it on precisely the same grounds, that scientists interpreted that as evidence for DM only because the can't imagine other explanations, etc.
The point is, all you can ever do is accumulate evidence for or against theories. At some point the evidence becomes convincing and the theory generally accepted, but it's not an either/or situation - it's gradual. There is massive evidence for DM, from all sorts of different observations. Direct detection would be additional very strong evidence, but the theory is already on a pretty firm foundation (and people have thought of MANY other possibilities, by the way - it's just that none of them are consistent with the data).
Sad and ignorant. Don't you realize the grasp of how our world works defines our status of accomplishment as a species? In 1,000 years what will be more important to the race?
Nevermind, I shouln't have bothered. It IS an obvious troll.
--
Northern Virginia? Fairfax Underground!
I'd like to point out that the difference in the scientific approach 'should' be considered when comparing the conflicting theories of dark matter and redefining gravitationl mechancics. Thus far, the proponents of dark matter formed a hypothesis, experimented, and concluded. The opponents experimented, hypothesized, and then concluded. I tend to lean towards those who followed the accepted scientific method. Let's remember that it doesn't matter which is correct, it only matters that we correctly determine which is correct.
That is a failed analogy.
Mostly becuase chainlink fences do not show a discernable gravity force on dust clouds...
Neither did the Dark Matter feel compelled to be effected by gravity...
Attention, parent poster and everyone who agrees with him: please immediately cease enjoying benefits of government-funded science. That means logging off /., getting rid of your computer -- in fact, not owning any personal electrical devices whatsoever -- refusing any medical diagnostic procedure developed after the invention of X-rays, and generally living life ca. 1900.
For those who say, "that's technology, not science!" I will note that the examples I gave were based largely on previously abstract, largely government-funded scientific research whose applications were not immediately obvious, but which have since transformed the way we live. If you don't understand the research, that's fine; you don't have to in order to take advantage of it. But just because you don't give a shit about the way things work doesn't mean that you get to stand in the way of people who do, and whose work will benefit you and your children's lives, no matter how little you deserve it.
The correlation between ignorance of statistics and using "correlation is not causation" as an argument is close to 1.
Hear about those scientists doing research into this electricity thing?
Thanks God it's not my taxes that are spent on this research.
I'd rather have my artist friends make another painting using gas light. Not like this electricity thing will ever lead to anything useful!
IANAP, just a computer engineer.
But I was wondering, could it be that dark matter is just invisible to current methods of detection? Perhaps the energy it radiates is in frequencies above what our current technology can detect? Like...exohertz or something?
I also recall something from some of my signals classes that there is such a phenomenon as negative frequency. Maybe dark matter emits energy in negative frequencies?
I pulled all of the above straight out of my ass, but the point seems valid enough. Obviously we can't detect all electromagnetic phenomena at every frequency range.
:(){
True. I'm ignorant. I do not watch "Dr. Who" and "Lexx". Well, I do not have TV at all.
We have wars. We have starving people. We have sicknesses with no cure.
But all news channels are flooded with what? Right. Is Pluto a planet or not? Does black/white/red/whatever matter exists?
Who's ignorant? Me wonders.
All hope abandon ye who enter here.
> logging off /.
The networks existed before Internet. Learn facts. And Internet at large is privately owned - as communication channels concerned. As well as standards used to back it are collective effort - not affiliated with any gov't. (Though it's true that DARPA sponsored protocol is the Internet Protocol)
> getting rid of your computer
Computers and algorithms were invented about 150 years ago - when science was still considered mostly private matter and not supported by gov'ts.
Also transistor was invented again by non-gov't related companies. Check here - http://www.pbs.org/transistor/album1/index.html
> X-rays
X-rays? Check your facts - http://en.wikipedia.org/wiki/X-ray - before posting.
> applications were not immediately obvious
Well, yes. I do not understand how existence of black/dark/light/whatever mater would help anyone. As well as all the theories about Universe origin: in the beginning there was nothing and then it exploded. I really do not understand.
P.S. What was first - nuclear reactor or nuclear bomb? Bombs were first - and sponsored by government.
All hope abandon ye who enter here.
Read on. Then post. Show me were the gov't was involved there. (*)
I have seen many researchers using state funds. And honestly all there were capable - research-wise - find a ways to get another trunk of money.
On other side, I have worked a lot with research institution sponsored by Intel: they do not keep there people who do only theorize. If you can improve something - that's achievement.
When you waste bandwidth e.g. arguing Pluto is planet/not planet (underline correct answer) - to me that what it is - waste of time and resources.
(*) Reminded me of Ronald Reagan saying: "When something starts moving - tax it. If it still moves after that - regulate it. If it starts dying - fund it."
All hope abandon ye who enter here.
Alternative gravity? Alternative energy? What else are we running out of?
Don't blame me -- I voted for Roslin.
The comment: "In short, dark matter is still not a necessity, provided that neutrinos weigh 2eV." is contradicted by this statement in the abstract of the paper: "In agreement with Clowe et al. (2006) we show that a dominant component of non-baryonic matter is needed in the bullet cluster - in MOND as well as in GR."
Sound familiar? Every time someone says evolution is just a theory, they are ridiculed, and someone else points out that gravity is 'just a theory, but nobody doubts it'. Next time, please refer to this thread. The theory of gravity is subject to doubt.
I love how all the dumb ass kids on slashdot think they are experts in everything. Just because you watch the sci fi channel and occasionally read a popular physics book doesn't mean you know squat about relativity or quantum mechanics. All the dumb kids are mindlessly repeating stuff they heard others say 100 times like "space is curved" without actually understanding WTF this means. Just know-it-all kids trying to look smart but contributing nothing. Oh wait, all slashdot articles are like this.
I've got a theory: the more popular a site becomes, the more it becomes crap.
If photons had no mass, how much energy would they have? (Hint: consider "m * c^2" for m = 0.)
And what is momentum without mass anyways? Pixie fairies twirling? The intents never acteds on?
Despite what the "Dark Matter Folks" would have you believe, most* modern day scientists** don't believe Dark Matter exists.
Heres the part about it...Dark Matter exists if a certain sub theory of a certain sub theory of String Theory is true...and for 50 years, scientists have been working to prove a SINGLE point about String Theory, and have failed. Modern Particle Science has been put on hold for 50 years so that the "New Kids" of science can test their ideas, and yet still, nothing has been proven***.
*They would have you believe, "all the smart ones"
** This includes university professors
*** Nothing has been proven because String Theory has yet to predict something in an experiment. If Dark Matter is in fact true, it will be the first.
That doesn't answer my questions.
You are saying that the existence of dark matter would obliterate any spaceship nearby. But how come NASA recently 'proved' the existence of dark matter in the galaxy collison study? Obviously these galaxies must have dark matter in them - why isn't the dark matter simply obliterating the galaxies alltogether? Are every planet in them made of rubble, as they are constantly washed with gravitic tidal waves from the dark matter permeating them? And why would such 'waves' even exist - why wouldn't the gravitic effect be stable, much like for regular matter, only inverse?
'Like a black hole'? Wasn't dark matter exercising _ANTI_ gravity? How would that 'suck someone in'?
I can accept that if you had a clod of dark matter the mass of the sun, at a good distance from regular matter, then travelling towards it would take an equal amount of force as if taking off from the sun's surface - is that correct? But that still does not preclude that dark matter may be in smaller quantities that are actually reachable. Surely you cannot say that a bit of dark matter the size of a football would cause the instant destruction of everything in a mile radius from _gravitic waves_ - if made out of antimatter then the resulting explosion might - but gravity? If the antigravity is enormously strong for even a small amount, wouldn't you essentially get an inverse black hole effect, as the innerside of spacetime ruptures outwards? And again, does dark matter absorb light and give resistance to a spade, or do these go directly past it?
I was going to say 'if you have aren't sure about any of this then please say so' - but considering what I've read, I don't really think many people are.
One pound of dark matter or one pound of photons?
It's all done with mirrors. We just don't understand the mirrors yet.
One will thus have to wait for particle physics experiments to rule out massive neutrinos to rule out MOND. Until then, place your bets...
Actually, my understanding is that we need only wait until experiments rule out 2 eV neutrinos - they can still be massive.
Of course I agree with you, by massive I meant "as massive as 2eV", and not e.g. 0.1 eV. We already know for sure that they have a non-zero mass, that's why I didn't foresee the potential misunderstanding there
Look, GP was from BadAnalogyGuy. It was a bad analogy, OK? It's what the boy does. You might as well get annoyed at the Pope for being Catholic.
And the brethren went away edified.
P.S. What was first - nuclear reactor or nuclear bomb? Bombs were first - and sponsored by government.
Actually, the reactors came first. Remember Fermi's pile under the squash court?
And then there was the natural reactor in Africa a couple of million years ago...
If it weren't for DARPA you would still have to worry about 30 different TCP-type protocols.
Please, for the good of Humanity, vote Obama.
Ether
by the Gang of Four
Trapped in heaven life style (locked in Lock Kesh)
Now looking out for pleasure (H-block torture)
It's at the end of the rainbow (White noise in)
The happy ever after (a white room)
Dirt behind the daydream
Dirt behind the daydream
The happy ever after
It's at the end of the rainbow
Dig at the root of the problem (Fly the flag on foreign soil)
It breaks your new dreams daily (H-block Lock Kesh)
Fathers contradictions (Censor six countries news)
And breaks your new dreams daily (each day more deaths)
Dirt behind the daydream
Dirt behind the daydream
The happy ever after
It's at the end of the rainbow
White noise in a white room
There may be oil under Rockall
The happy ever after
There may be oil under Rockall
It's corked up with the ether
RS
Shoes for Industry. Shoes for the Dead.
You ignore opportunity costs in your assertions.
If the government didn't fund this research, then the tax dollars would be left in the pockets of the private individuals. What would the private individuals have done with this money instead of the government? That's what you're missing here. In very many scenarios, the private individuals can allocate this money more efficiently than a government.
Example: X-prize vs. NASA
My assertion: We'd have BETTER technology if we got rid of all of these government programs due to the more efficient allocation of dollars by the private sector. Governments have very little incentive to be efficient with capital. Their only incentive is to get re-elected.
The networks existed before Internet. Learn facts. And Internet at large is privately owned - as communication channels concerned. As well as standards used to back it are collective effort - not affiliated with any gov't. (Though it's true that DARPA sponsored protocol is the Internet Protocol)
... it wasn't until home internet access became widely available that any of them even tried to adapt by increasing access and lowering prices. And now they've almost all died a well-deserved death, with AOL marching steadily toward the grave shared by its forebears.
... until computers came along. Bernoulli's law? Great for explaining how birds fly, but not terribly practical until the invention of the internal combustion engine and this little thing called "the airplane." Quantum physics? Neat but useless stuff for the first fifty years or so ... Look, astrophysics doesn't exist in isolation; it's simply the study of how the universe works on the grand scale, and a great deal of our understanding of how the universe works at our scale stems quite directly from it.
Strictly speaking, of course, you're correct -- there were plenty of computer networks before anything that could reasonably be called "the internet" started to come into existence in the 1960's. But none of those networks became the internet; ARPAnet did. And more recently, we have perfectly good examples of what commercial networks for general use look like. Compuserve, GEnie, Prodigy, Delphi, AOL -- any of these ring a bell? Closed systems, not extensible by private users, refusing to communicate with each other, insanely expensive
Computers and algorithms were invented about 150 years ago - when science was still considered mostly private matter and not supported by gov'ts.
Babbage received a mix of private and government funding (the Crown has been funding science on a large scale a lot longer than the US government has -- actually, longer than the US government has been in existence.) And modern electronic computers were almost entirely developed, for the first critical decades of their existence, with government money.
> X-rays
X-rays? Check your facts - http://en.wikipedia.org/wiki/X-ray - before posting.
Nice one -- leave out four crucial words and completely change the meaning of what I wrote. I wrote "after the invention of X-rays," by which I meant newer imaging methods such as CT, MRI, and PET. Also, of course, modern genetic diagnostics, which depend almost entirely on research funded by the NIH and similar institutions.
Well, yes. I do not understand how existence of black/dark/light/whatever mater would help anyone. As well as all the theories about Universe origin: in the beginning there was nothing and then it exploded. I really do not understand.
You don't have to understand, and I don't have to understand, as long as someone, at some point down the line, somewhere, understands; we'll all benefit regardless. Linear algebra and numerical analysis? Mildly entertaining but utterly abstract branches of mathematics
P.S. What was first - nuclear reactor or nuclear bomb? Bombs were first - and sponsored by government.
No, Fermi's reactor came first. And IIRC, the Manhattan Project had to build several reactors (and thus lay the foundation for the nuclear power industry) in order to accomplish their primary mission.
In any case, this may not be an opinion with which you have much sympathy, but I'm inclined to say that on the whole, the existence of the Bomb is a good thing. Yes, it's a terrible weapon, the worst weapon ever made, in fact. But it is also the thing which kept the US and the USSR from fighting WW3 on a scale that would have dwarfed WW1 and WW2 combined, and which continues to hold the dreams of would-be Caesars and Napoleons and Hitlers in check. No one will ever try to conquer the world ag
The correlation between ignorance of statistics and using "correlation is not causation" as an argument is close to 1.
A great deal of teh darkness you see has nothing to do with dark matter -- it's light polution. In most Western countries, there are relatively few stars at night - say 200 - 500. But get out to a third world country where there is no light polution and you will see the entire sky lit up with 20,000-50,000 stars. Everyone knows that in between these stars is emptiness. There may be dark matter somewhere, but it certainly isn't between stars. Dark Matter would pull a galaxy appart. Therefore, if there is Dark Matter, it is speculated that it surrounds a galaxy.
Mike www.sharecube.com
After that, the two differ greatly. The ether was the transmission medium for light; dark matter (obviously) isn't. The ether provided an absolute inertial frame of reference; dark matter doesn't. The ether was almost perfectly uniform throughout space; dark matter very much isn't. I could go on, but you get the point.
Basically what I'm trying to say is that statement seems true at first glance, but don't think it's that simple.
Comment removed based on user account deletion
So, ..., where's the follow-up paper estimating the temperatures of the baryonic and non-baryonic components as they "relax" out into the shallower gravitational wells left after being separated?
I am not sure that photons 'have' to have mass.
Everything in the universe that exists, has mass. Einstein discovered this. The gravitational field of the sun has mass, and this mass exerts its own, secondary gravitational field. Although this secondary gravitational field is small, it is large enough to have a detectable effect on the orbit of Mercury. When this effect was experimentally verified, it was a huge win for the theory of relativity.
The mass of a photon can be computed by taking the photon's energy, E, plugging it into E = MC**2, and solving for M.
It is true that photons do not have a "rest mass", as they can never be at rest, as they always travel at the speed of light. If we replace the terms "mass" and "instrinsic mass" in your posting by "rest mass", then your posting becomes correct.
Doug Moen
I have written a truly remarkable program which this sig is too small to contain.