Dark Matter Discovered Near Solar System? 179
gpronger writes "The ATIC (Advanced Thin Ionization Calorimeter) has potentially discovered the presence of dark matter close (only 3000 light-years) to our solar system. The system detected a large-amount of high energy cosmic rays which match the theoretical signature of dark matter annihilating itself. The universe is believed to be composed of about 25% dark matter, but there has been little evidence of it. This discovery, if correct, would be the first."
The paper was published in Nature , but it requires a subscription to see beyond the abstract.
Re:zomg (Score:5, Informative)
see http://www.xkcd.com/502/ [xkcd.com] for the joke
Re:math hosers. (Score:5, Informative)
You have a background intensity that is a function of energy, B(E).
Signal intensity is also a function of energy, S(E).
The observed intensity I(E) is B(E) + S(E). The signal portion (observed intensity above background level) peaks at E = 650 GeV. At 800 GeV (and, one would assume, higher), the signal is small enough that the observed intensity is adequately explained only by background.
Re:math hosers. (Score:3, Informative)
They have an energy dependent signal.
Re:Common doublespeak! (Score:4, Informative)
Re:Common doublespeak! (Score:5, Informative)
So, the evidence that points towards dark matter could also point towards other conflicting models of our universe, essentially being evidence for many different models at once. The reason discoveries of this kind of evidence is exciting is because it gives us something to look at and test so that we might select or eliminate from the groups of conflicting models.
Bad summary. (Score:5, Informative)
The summary misinterprets the results.
The instrument detects high-energy electrons. They found an excess (only 70, but statistically significant) with a particular energy, which if they come from a galactic source (like a pulsar), that source must be within 3000 light years. However, the researchers can't find an appropriate source.
Alternatively, this could be due to annihilating dark matter---the energy spectrum matches some models---but that's not necessarily coming from a particular source.
Re:math hosers. (Score:5, Informative)
No, their math is just peachy.
A figure like 650 GeV is the energy of ONE cosmic ray. Think of a graph of the number of rays arriving per second versus the energy of the individual rays. You're getting this many 400 GeV rays per second, this many 500 GeV rays, and so on.
What TFA says is that LOTS of 650 GeV rays were arriving from the newly observed source, and hardly any 800 GeV rays except for the background rate that you get from everywhere in the sky.
rj
Re:Close to our Solar System (Score:5, Informative)
Interestingly enough, the universe is almost certainly much bigger than you believe.
Honestly, we have no idea and probably no real way of determining how big the universe really is. Nonetheless, the observable universe seems to be at least 90 billion light years [wikipedia.org] in diameter. So, it'd be more like finding that random person in the same room.
Re:Close to our Solar System (Score:1, Informative)
What? Wild leap of faith, my friend.
You are assuming that the universe is finite, and has been expanding at the speed of light from 15 billion years ago.
Actually, the big bang occurred about 13.73 billion years ago, and from that you can calculate the radius of the visible universe, which is about 13.8 billion light years.
The actual radius is unknown, as we don't know if the universe is finite or infinite, but it's at least 46 billion light years.
But yeah, it's pretty close.
Re:Close to our Solar System (Score:3, Informative)
While not very close, it is a heck of a lot closer than if we were able to see it nearer the \edge\ of the observable portion of our universe.
Re:FTL Particles (Score:2, Informative)
Re:Common doublespeak! (Score:5, Informative)
Heck, you don't think that we scientists got together one day and said "I know, lets make up some goofy theory and then fudge the data to fit it!" do you? You do realize multiple theories were purposed, predictions were created, new data was taken, and conclusions drawn about which theories were supported by the new evidence, right? And that LCDM is the one that survived all the vetting? And that this process is still on going, yet LCDM still remains as the best theory?
Just checking... See, that's sort of how science is supposed (and in this case does) work.
Re:the next logical question... (Score:3, Informative)
It seems that at least some dark matter particles are their own antiparticles since they can annihilate into gamma photons.
Re:FTL Particles (Score:3, Informative)
Being stoned is pretty good.
The short answer is that that tachyons can't transmit information. The short explanation is that Einstein's theories prevent it.
Anything with mass cannot reach the speed of light; it would require an infinite amount of energy. Anything without mass travels at the speed of light. Tachyons are obtained by throwing imaginary numbers into the mix.
Dark matter is thought to be matter that does not interact with other matter except gravitationally. We don't have much of an idea what that would look like, but it would obey the rest of the physical laws as we understand them.
If you have any other questions I can try to answer them. Wikipedia has a good article on faster-than-light [wikipedia.org].
Also, I hope that you don't mind me correcting you, but the the word is 'piqued'.
Re:Kinda Reminds Me of the Face on Mars (Score:3, Informative)
Savain isn't a creationist, but he is a well-known physics crackpot. He's been promoting his B.S. for over a decade; just search the 1990s archives of the Usenet sci.physics.* groups. He emotionally can't accept the mathematical notion of spacetime, because he claims that "nothing can move in spacetime", which only proves that he misunderstands the whole concept. (Thus his claim above that physicists have been unable to explain the concept of "movement".) He usually then proceeds with long, profane rants against various respected physicists. You know you're on the receiving end of a classic Savain rant when he starts raving about "chickenshit voodoo physicists".
Re:Close to our Solar System (Score:4, Informative)
So shouldn't the longest distance to the far "edge" be 13.8 billion light years
No, because spacetime is curved and the expansion rate is neither constant nor equal to the speed of light.
The misconception is that the Big Bang was an explosion of matter into space, and there is some volume of space with matter in it and some volume outside of which no matter has yet reached.
In modern cosmology, the Big Bang is an expansion of space. There is no center or edge of the universe (although there is an edge of the universe we can see, because light hasn't yet reaches us from farther), and matter is distributed more or less uniformly everywhere in space. More details in this FAQ [ucla.edu].
Anyway, how can we go from that size to estimate how old it is? Because they expect it to expand at light speed?
They look at the relationship between how far away objects are and how fast they're moving (via Doppler shift). This gives them the expansion history of the universe. Farther objects are older. Also, the structure of fluctuations in the cosmic microwave background radiation left over from the early universe depends on how the universe has expanded between then and now. When combined with the general relativity theory of cosmology and how the universe expands, you can back out an age estimate.
Re:Close to our Solar System (Score:5, Informative)
Space can expand at any rate, including faster than light. The FTL restriction is on matter/energy moving through space. It is not a restriction on the geometry of space itself.
As for where the estimated age comes from, your own link answers that.
Re:math hosers. (Score:3, Informative)
Correct. That's what the article is saying -- it peaks at 650 GeV, and by 800 GeV is indistinguishable from background.
Re:FTL Particles (Score:1, Informative)
Not really. The speed of light should been seen not as the speed that light happens to travel at, but a fundamental universal constant.
From wikipedia:
Special relativity reveals that c is not just the velocity of a certain phenomenon, namely the propagation of electromagnetic radiation (light)--but rather a fundamental feature of the way space and time are unified as spacetime. A consequence of this is that it is impossible for any particle that has mass to be accelerated to the speed of light.