Dark Matter — "Alternative Gravity" Team Responds 215
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."
So We Must Wait. (Score:4, Insightful)
is too!
is not!
is too!
...
It's the Ether (Score:4, Insightful)
Re:why would matter be dark (Score:2, Insightful)
Of course relitivity could be wrong, or light could travel slower than the 'speed of light', if that makes any sense.
Re:Anti-dark-matter scientists are like ID scienti (Score:5, Insightful)
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.)
Re:religeon of dark matter (Score:3, Insightful)
Interesting observation, if a bit off. The difference being, of course, that we will eventually have a factual basis for dark matter ( whether it exists or not ), where as we will never know if $deity exists.
This is true for all supernatural values of $deity.
Re:Anti-dark-matter scientists are like ID scienti (Score:5, Insightful)
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.
Re:Technically, neutrinos are dark matter (Score:2, Insightful)
Re:It's the Ether (Score:5, Insightful)
A perfectly valid scientific theory, as it was also falsifiable - as demonstrated by Michelson and Morley. When it was falsified, it required a major change in how the scientific communtiy thought about light. It is entirely possible that we'll see something similar with dark matter. Sure, an unobserved WIMP could explain things like the rotation of galaxies at their current rates. But, what happens when we get out there and don't find any? What then? Well, maybe it will require a major change in how we think about gravity. Maybe there's an entirely new force out there, that's weak enough that we can't see it on terrestrial or even solar scales. Who knows?
Re:No, YOU'RE like an ID scientist (Score:3, Insightful)
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.
Re:No, YOU'RE like an ID scientist (Score:2, Insightful)
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).
Re:Useful research (Score:5, Insightful)
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.
Re:why would matter be dark (Score:2, Insightful)
Re:why would matter be dark (Score:4, Insightful)
http://en.wikipedia.org/wiki/Light_sail [wikipedia.org]
There, see? He was right about solar sails.
You were thinking of a magnetic sail:
http://en.wikipedia.org/wiki/Magnetic_sail [wikipedia.org]
Which is something completely different. Magnetic sails do use solar wind; solar sails use sunlight. Big big difference between the two.
Re:why would matter be dark (Score:4, Insightful)
Except that solar sails do not depend on "solar wind", ie. particles. The main thrust (when above a certain distance form the sun at least) is delivered by massless photons, ie. light. Hence the more correct term "light sail".