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Dark Matter Discovered Near Solar System?
Posted by
Soulskill
on Fri Nov 21, 2008 08:09 PM
from the near-being-a-relative-term dept.
from the near-being-a-relative-term dept.
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.
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In Soviet Russia (Score:3, Funny)
Dark Matter sees evidence of YOU.
zomg (Score:5, Funny)
ZOMG, Mom, is that you?
Re:zomg (Score:5, Informative)
see http://www.xkcd.com/502/ [xkcd.com] for the joke
Parent
close ? (Score:5, Funny)
This must be some meaning of 'close' that I was previously unaware of.
Close to our Solar System (Score:2)
We must have very different notions of close. I personally cannot begin to imagine how one could consider 190 million AU to be close.
Re:Close to our Solar System (Score:5, Insightful)
Parent
Re: (Score:2)
If my calculations are correct - that would be like finding out that a random person from somewhere on earth - actually lived 27 feet away from you!
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.
Parent
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.
Parent
Re: (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: (Score:2)
(I forgot about diameter vs. Radius though)
So revising my initial estimate - maybe more like 13ft.
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.
Parent
Re: (Score:2)
the next logical question... (Score:5, Insightful)
where is the dark antimatter?
Re: (Score:3, Funny)
Re: (Score:3, Informative)
It seems that at least some dark matter particles are their own antiparticles since they can annihilate into gamma photons.
Common doublespeak! (Score:5, Insightful)
If this would be the first evidence how can we already have a little evidence of it?
Re:Common doublespeak! (Score:4, Informative)
Parent
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.
Parent
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.
Parent
Re: (Score:3, Interesting)
OK, so scientists look at how galaxies behave and notice that they are behaving as if they had more mass than we can observe them having. Now there are two options: either 1. galaxies contain mass that hasn't been observed or 2. the theories of how the gravity works need to be revised. Both of these options are being studie
Re: (Score:3, Interesting)
Scientists looked at the data and saw it didn't fit, so they made up some goofy theories that "explained" why their calculations didn't match reality.
Yeah, uh, DUH. That's what science IS. You make up a theory to describe what you observe. If it doesn't fit, it's wrong, so you make up a new one and see if that works.
As another poster said, you seem to have some kind of ideological prejudice against the particular theory they came up with. But it's foolish to criticize them merely for coming up with a new theory in the first place. That's what they're SUPPOSED to do.
No! My theory isn't WRONG! It's ... err... invisible matter that can't be detected in any manner!! Yeah! That's the ticket!
So you're mocking the idea that there can be particles out there which don't interact
Re: (Score:2)
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: (Score:2)
There is no such thing (Score:2, Insightful)
I still believe that 'dark matter' is only a temporary constant inserted into an equation modern scientists don't truly understand.
In time they will discover what is causing the effects of this 'dark matter' - it will not be super strange matter, nor another form of matter, but will be either a change in the overall calculations of our universe's energy or it will be some type of substance that was not accounted for.
Theorists throw in some offbeat number to the calculation every 30 years or so to account f
Re: (Score:3, Interesting)
Well *something* is warping spacetime this way and that, and that's what they call dark matter and dark energy respectively. Now the question is what does the warping.
Big whoopie (Score:2)
Big deal. I find dark matter every time I turn out the lights.
This is science?
I know where all the dark matter is (Score:3, Funny)
Re: (Score:2, Funny)
wow, on behalf of the winners committee on /. (because of course none of us here are losers), I'd like to present you with this ribbon and a fucking cookie.
Enjoy, and thank you for you contribution to the conversation!!
Re:Holy crap. (Score:4, Funny)
'fucking cookies' are unpleasantly ambiguous.
Parent
Re:Holy crap. (Score:5, Funny)
Over there, next to your regular one.
Parent
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.
Parent
Re: (Score:3, Interesting)
I can't get past the paywall to see how many sigmas they put on the detection event, but I seriously doubt the situation is as simple as you claim. I personally find it unlikely they would get published in Nature with a signal that is statistically indistinguishable from background noise. Unfortunately, I can't read the paper to see what they did. I'm not a particle astrophysicist, but you don't mention at all what the error bars are; a 150 GeV difference can be big or small depending on how precise the
Re: (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: (Score:3, Informative)
They have an energy dependent signal.
Re: (Score:3, Interesting)
...They have an energy dependent signal....
So there is a signal, but what produces it is still only a conjectural speculative interpretation of an observation. From experiments here at home, such radiation is ONLY and ALWAYS produced by charged particles. Instead of dark matter, the radiation could be produced by naturally occurring interstellar or intergalactic particle acceleration. It could even be some space alien's giant version of the LHC. All we observe is lots of radiation, but then they are guessin
Re: (Score:2)
I think I've seen you make this comment before.
As before, this radiation is not solely produced by charged particles.
Re:math hosers. (Score:4, Insightful)
Dude, seriously, read up on electroweak theory. You're so 1960's.
Parent
Re:math hosers. (Score:4, Interesting)
http://en.wikipedia.org/wiki/Technetium-99m [wikipedia.org]
There are lots of reactions that produce EM radiation. This one is used in medical imaging. Positron-electron annihilation also creates gamma rays. Yes, those are charged particles, but the gammas are not produced by the charges moving. That reaction is also used every day in medical imaging.
All these resources available on the Internet and you can't even educate yourself. Such a waste.
Parent
Re: (Score:2)
. You are assuming that the numbers were the range of the observations not the domain. that's why is said at 650 GeV not to 650 GeV.
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
Parent
Re: (Score:2, Interesting)
I believe you're thinking of dark energy - it's currently thought to be about 74% of the universe's mass/energy. Roughly 22% is guesstimated to be dark matter, and about 4% is "normal" matter.
Re:Kinda Reminds Me of the Face on Mars (Score:5, Insightful)
Unless and until physicists can fully explain the true mechanism of movement in language that the layperson can understand, I'll remain highly skeptical of their more outlandish conclusions (black holes, wormholes, dark matter, dark energy, big bang, parallel universes, etc.), sorry.
How do you expect the explanations in layman's terms to be any different than what we use now (what goes up must come down, at equilibrium every action has an equal and opposite reaction, object at rest stays at rest until acted upon, etc. etc. etc.)? These are extremely complex phenomena that, if described in layman's terms, cannot be accurately portrayed.
Parent
Re: (Score:2)
These are extremely complex phenomena that, if described in layman's terms, cannot be accurately portrayed.
Unless you had an Etch A Sketch handy. In which case, so accurate, you have created a new, carbon copy universe on the screen.
Re: (Score:2, Interesting)
I bet you believe in creationism too, huh?
I understand the argument you're making, it's the old 'if it's a horse, it's a horse; not a zebra' argument. However, physicists are not willy-nilly declaring stuff dark matter because that's what they want to find. There is actually a lot of hard-core science to support what you call
outlandish conclusions(black holes, wormholes, dark matter, dark energy, big bang, parallel universes, etc.)
The fact that YOU don't understand it is more a statement about yourself, not the science.
Re: (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 rant
Re: (Score:2)
Re: (Score:2)
No, no, and the last question is probably a no, but you could elaborate on what "it" refers to for a more definite answer.
Information cannot propagate faster than the speed of light. The speed of light is an absolute limit.
Re: (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 tha