Has dark matter finally been detected?
guardian.co.uk
guardian.co.uk
How?
Besides confirming theoretical predictions and presumably improving our understanding of cosmology, are there any potential applications for this knowledge at an earthly scale?
One idea is to use dark matter as fuel for interstellar travel:
http://www.newscientist.com/article/mg20427361.000-dark-powe...
in broad terms, it's unlikely that any new physics has applications at an earthly scale. the argument is quite simple - if there are significant differences between whatever is "new" and what we currently know at the kinds of scales that are appropriate for applications then it would be easy to do the experiments. the very fact that physics is reduced to using astronomy or the lhc to explore extreme conditions indicates that anything new applies only at scales that are largely irrelevant to us here and now.
"To detect dark matter, scientists have to wait for the extremely rare occasion when a dark matter particle knocks into an atomic nucleus in the detector and makes it vibrate"
Why? If dark matter is 90+% of the mass of 'everything', then surely many more anomalies would occur without us having to be hit by a chunk of dark matter. It would simply have to be anywhere near us (or a nearby body we could observe carefully) to observe weird gravitational effects. Nearby ones, not 'out there in other galaxies' ones.
Assuming it's not near us, why would that be? Our star isn't much affected by it. We can't see nearby stars being pulled willy-nilly. How far out must we search before we could reasonably assume it doesn't exist and there might be another explanation?
[edit] And if it's a weird non-localised 'blanket' that can't hit you in the foot, then it'd be great to have some guesses as to the structure so we can test for it. Does it exist inside all galaxies? Is it in the middle, or does it rotate like normal 'matter'? If it exists in the perimeter, is much heavier, and spins like visible matter, do we have to invent a super-ultra-dark matter to explain why common-or-garden dark matter doesn't fly off into space? If it's in the middle and clumpy, could it collapse into a dark-matter black hole, especially since there's no radiation to force particles apart? Is it only one particle type, or a family like visible matter? Since it has mass, is there another form it can convert to as visible mass does? Since it doesn't radiate (being dark) what happens to the energy when (if) it converts?
If it's clumpy, stop worrying about visible asteroids. It's the invisible ones that can really hurt you :)
Well, if the dark matter is ~90% of the mass of everything, that doesn't necessarily mean that 90% of the mass of every thing is dark matter. As far as I understand it, we see the effects of the large amount of extra matter but we don't really know where it is or how it's distributed. That could mean that there isn't any dark matter clustered in large enough quantities close by for us to detect.
Assuming it's not near us, why would that be? Our star isn't much affected by it. We can't see nearby stars being pulled willy-nilly.
Well, a really spread out distribution across the universe would explain that.
And if it's a weird non-localised 'blanket' that can't hit you in the foot, then it'd be great to have some guesses as to the structure so we can test for it.
Well we have a prediction for what the particle would look like (/act like). That's what the detector is there for. Well, not just dark matter. Think neutrinos and Cherenkov radiation.
As far as the other questions go, I'm not sure enough to answer and I'm pretty sure that some of those questions are open.
Well, a really spread out distribution across the universe would explain that.
It would, but then there's the 'why' it's spread out. Maybe that's answered in the particle predictions but something is keeping it apart, but doesn't affect visible matter in the same way. It's obviously spread out just enough to not be clumpy, but not so much that it can't pull a galaxy together. If it were everywhere it wouldn't have the effect we think we see.
Two dark-matter particles in the void will be attracted to each other (slightly) by gravity, but when they meet they'll just sail straight on through one another without colliding. This prevents the formation of small-scale (ie sub-galactic scale) dark matter clumps.
two reasons.
1 - dark matter doesn't interact much with normal matter. so even though there's lots of it, most of the time it doesn't actually collide with anything.
2 - the "clumps" of dark matter are at much larger scales than our local system. variations are spread out at something like the size of galaxies; locally it is very smooth / uniform. if you're inside a uniform distribution of mass then you don't feel the gravitational effects (for example, at the centre of the earth you would weigh nothing).
disclaimer: i was an astronomer, but have been doing real work for many years now.
"18:20 Summarizing, no discovery. Just a hint of a signal but with a very low statistical significance. Was fun anyway."
As the newspaper article said, a 75% chance of finding new particles.
http://blogs.discovermagazine.com/cosmicvariance/2009/12/17/...
2:50: Bottom line: “The results cannot be interpreted as significant evidence for WIMP interactions, but we cannot reject the possibility that either event is signal.” –Risa
To which I reply "Hang on, so you made a big deal out of this for what? Wake me when you have something which _can_ be interpreted as significant evidence for something"
EDIT: Not to imply that it wouldn't be a huge deal anyway.
What I didn't understand until just now was this: if WIMPs interact by gravity why don't they fall into stars and planets, or even form stars and planets of their own? The answer is that they do fall into stars and planets, but just keep going through the middle (since they are not subject to any ordinary interactions) and out the other side. And they can't form dark-matter planets of their own since they don't interact strongly with each other either, so they won't stick together. Neato!
Boy, Newton Totally Responded To Our Planet?
Basically, Nobody Trusts RMS To Out-think PG?
This is amusing: http://www.google.ca/search?q=BNTRTOP
Also amusing is that if you refresh it, you see from the "x minutes ago" part just how often the crawler is picking it up.
This can be dismissed until they get to 3-5 sigma.