Dark Matter Found? $2 Billion Orbital Experiment Detects Hints 173
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."
Re:But what is it? (Score:5, Informative)
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.
Spin? Not that type... (Score:2, Informative)
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:Dark matter (Score:4, Informative)
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.
Explanation (Score:5, Informative)
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 [web.cern.ch]). 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...
This is bullshit (Score:5, Informative)
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 [blogspot.co.at]. 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.