Boffins shine new light on dark matter The LHC may have found the Higgs Boson, but overarching theories of everything have another hole: the observable universe weighs rather less than it ought if all those equations – and all the galaxies - are to hang together. The inconvenient absence of so much matter gave rise to a theory that all the energy and matter needed …
I'm not sure where the final magnet was made, but one of the links I just clicked still said that AMS-2 uses a super-cooled, superconducting magnet and it will be tested in 2010 by the ESA at ESTEC.
Well, it was tested at ESTEC, at CERN and other places and was very nice. In reality, that magnet didn't fly because the cooling helium would've only lasted for about 3 years, and the ISS is now set to stay up for a long time. Instead it has a permanant magnet, which while lasting longer doesn't help separate the really high-energy particles, which is a shame.
The results look very nice, indicating the AMS experiment is working very well. Yet the conclusions from the results so far are not very dramatic, and, in my opinion, have been significantly over-sold in the press. Despite what you may read, we are no closer to finding dark matter than we were last week. Any claims to the contrary are due to scientists spinning their results (and to reporters who are being spun).
So, AMS-02 made some bold claims today. Dark matter is mentioned 9 times in the press release, supersymmetry twice. They say that “...over the coming months, AMS will be able to tell us conclusively whether these positrons are a signal for dark matter...”. 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 reliable evidence for dark matter: not now, and not anytime soon. We simply have no robust way of telling a dark matter signal from a boring astrophysics background in that channel, because we don't know the shape nor the normalization of the background. It doesn't mean that AMS cannot provide a tantalizing signature of dark matter in the future. The most important thing we learned today is that AMS works and exceeds in precision the previous instruments (which wasn't that obvious: it's the first time a serious experiment is performed on a space station, and besides the mission underwent a dramatic downgrade shortly before the launch). We're waiting most eagerly on the AMS measurements of the antiproton and anti-deuterium spectra. A correlated excess in several channels could give us more confidence in the dark matter origin. Until that happens, the history has taught us to be skeptical about any evidence of dark matter from astrophysics experiments.
The non-paywalled goodies are here:
http://physics.aps.org/featured-article-pdf/10.1103/PhysRevLett.110.141102 (PDF)
(In another matter entirely, if the Reg Sciencedesk decides to link to a paper on the Arxiv, please use the Arxiv abstract page (from where the PDF can be reached), do not link directly to the PDF...)
If there is "dark matter" by definition it modifies the gravitational field (otherwise it wouldn't be matter and it would only be connected with the universe in a metaphysical manner).
Light paths have to follow the shape of the gravitational field (because the gravitational field, in essence, IS spacetime), so...
Yes, "dark matter interacts gravitationally with light"
If Dark Matter does not absorb, reflect or emit light...what happens when a photon hits it?
By definition, if Dark Matter does not interact with the electromagnetic field, it cannot interact with the electromagnetic field. So no photon will ever "hit it" (a better view: there is no "spark" between the dark matter field and the electromagnetic field ever).
So what happens if you put dark matter in water? does it sink?
That's a tricky question to answer, what with it being (presumably) non-baryonic in nature. But, hazarding a guess (not being a physicist of any sort, you understand) I'd say that it would probably sink through anything on account of being unable to interact with it.
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Probably that the effects of 'dark matter' are no more than the intrusions into our space-time of several (|many) extra dimensions, which we cannot directly detect.
As a result we can see their resulting effects, but not their causes - we cannot interact with them directly and I doubt we'll be able to predictably use them either.
Else it could be that membrane theory is nearer the mark in predicting matter that exists at different energy levels, again these membranes cause an effect, but not one that we can do anything with or about.
Imagine an insect on the surface of a pond that gets a stone thrown into it - the insect is being affected by forces but has no idea what causes those forces to act on it - neither can it do anything about the causes of those forces.
Ready for the total perspective vortex? try Celestia at shatters.net/celestia/ - or find it yourself.
:-)
> no more than the intrusions into our space-time
Could also be invisible ponies. All this "extra dimensions" stuff sounds far fetched and a tad on the "play loose" side to me.
Here is another idea, not that I understand much of it or condone any of it, but there may be solutions right under our nose. Note that this is a classical theory, so you still need to cross the plateau of leng and bring back the key to "quantization" :
MATTER-ANTIMATTER ASYMMETRY AND DARK MATTER FROM TORSION
We propose a simple scenario which explains the observed matter-antimatter imbalance and the origin of dark matter in the Universe. We use the Einstein-Cartan-Sciama-Kibble theory of gravity which naturally extends general relativity to include the intrinsic spin of matter. Spacetime torsion produced by spin generates, in the classical Dirac equation, the Hehl-Datta term which is cubic in spinor fields. We show that under a charge-conjugation transformation this term changes sign relative to the mass term. A classical Dirac spinor and its charge conjugate therefore satisfy different field equations. Fermions in the presence of torsion have higher energy levels than antifermions, which leads to their decay asymmetry. Such a difference is significant only at extremely high densities that existed in the very early Universe. We propose that this difference caused a mechanism, according to which heavy fermions existing in such a Universe and carrying the baryon number decayed mostly to normal matter, whereas their antiparticles decayed mostly to hidden antimatter which forms dark matter. The conserved total baryon number of the Universe remained zero.
This will probably go unnoticed as I am a day late but I'll state this for posterity.
The more I think about it, the more I feel that this might solve the question about what state the universe has.
If 23% of the universe is dark matter and it is annihilating itself and producing positrons that will annihilate all the electrons in our 5% of the universe then the logical conclusion is that sometime in the distant future the mass loss (depending on the effect of dark energy) will allow the universe to slow in its expansion and with what's left, start to contract to a point of singularity from where we originated. Or perhaps in a perpetual 'Big Bounce' where we don't quite go singular (see discussions around second law of thermodynamics). Maybe this has been going on from one universe generation to the the next and the next ...
My conclusion is that the universe has always been here so there is no creator who needs to be created. Simple. So let's get on with living in our time slot in this phase of the 'Bounce' and try to look after this tiny speck of atoms that we are living on.
> If 23% of the universe is dark matter and it is annihilating itself and producing positrons
No, it MIGHT decay to a positron/electron pair. After all, you must keep the totals of quantum numbers as they were, so the charge total must stay zero, you can't just spit out out a positron.
So you want into speculative ideas? Start Here
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