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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."
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?
Give me Classic Slashdot or give me death!
No.
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.
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?
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.
Socialism: a lie told by totalitarians and believed by fools.
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.
systemd is Roko's Basilisk.
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.
Socialism: a lie told by totalitarians and believed by fools.
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?
Socialism: a lie told by totalitarians and believed by fools.
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...
Thank you Dave Raggett
Ahh, I see adult conversation wasn't your goal in the first place. Fair enough.
Socialism: a lie told by totalitarians and believed by fools.
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...
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.
entropy happens
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.