Astronomers have no idea what dark matter is, but they have a few guesses. Since they can’t see the stuff directly, they’re trying to chip away at what it can’t be, peeling away theory after theory. Eventually, there should be a few theories that have withstood the most experiments, and best model what astronomers see out in the Universe. Physicists at Fermilab have made one of those steps forward, constraining the characteristics of dark matter, and overturning a recent discovery… by not seeing anything unusual.
We can’t see dark matter, but we know it’s out there. Galaxies should spin themselves apart but they don’t thanks to being inside a halo of dark matter. Amazing images from the Hubble Space Telescope show dark matter’s gravitational distortion on the light from distant galaxies. Oh, it’s out there all right.
So what is it?
Astronomers have two theories. One is that their ideas about gravity are wrong. By modifying our understanding of how gravity works over large distances, you can remove the need for dark matter entirely.
The other possibility are “weakly interacting massive particles”. These are actual particles, made of “something”, but we can’t see them or detect them in any way except through their pull of gravity.
Particle physicists have been searching for dark matter particles using powerful atom smashers, just like they discovered all the sub-atomic particles they’ve found so far.
A new experiment at the US Department of Energy’s Fermi National Accelerator Laboratory announced this week that they’ve made some headway in this search. According to theories, when dark matter particles interact with regular matter, it’s different from the way regular matter interacts. The Fermilab experiment has ruled out one of the last possible ways that the theories have predicted this should happen.
Their experiment, called COUPP, uses a glass jar filled with a litre of iodotrifluoromethane (a fire-extinguishing liquid known as CF3I. As particles strike the CF3I, it causes tiny bubbles to form in the liquid. The scientists can detect these bubbles as they reach a millimetre in size. By watching the interactions, researchers should be able to know if they’re coming from regular matter or dark matter.
So far, their results contradict another search called the Dark Matter experiment (DAMA) in Italy, who claimed to see dark matter interactions. The results for the DAMA experiment predicted that COUPP should have found hundreds of dark matter interactions, but they didn’t see any.
This research appears in the February 15th issue of the journal Science.
Original Source: Fermilab News Release
So that means MOND is in?
No, it just means there’s one aspect of WIMP that has been ruled out.
It’s good that the DAMA results, which CDMS and Edelweiss have conflicted with, have something else telling them they’ve analyzed their data wrong.
What DAMA sees is a change in its background detections, annually, as the Earth goes around the Sun. Any ideas on what’s causing this annual modulation, or only word that whatever it is, it ain’t those WIMPy particles?
It seems that scientists keep assuming that Dark Matter is a subatomic particle that they should be able to detect. The problem is that we really know nothing about it other than the fact that is probably exists. Is it not possible that it is neither a particle, nor is it present on Earth? We can’t observe a black hole, or a neutron star from Earth because they do not exist here. How do we know that dark matter isn’t some sort of framework of actual matter binding the universe together than can only be detected and studied where it actually exists? We don’t.
Does the mere presence of “Dark Matter” mean that science has to take a second look at the The standard model of particle physics, or is string theory able to explain its existence?
An experiment that should have seen hundreds of interactions, conducted at Fermilab, showed none. Published , peer reviewed, in Science.
Thank you. pete
One of the possible incarnations of dark matter are primordial black holes, although these would not really qualify as wimps.
Maybe MOND “isn’t in”, but this has to give those people hope thery’re on the right track.
The astronomical lensing that is attributed to dark matter, and the anomalous gravitational effects which we observe to be contrary to Newton in the distribution of matter in galaxies certainly says “there’s something we haven’t accounted for.
But I still consider it a leap to name the unknown something ‘dark matter” and then assert “we know it’s there.” NO WE DON’T. What we know is that our current models don’t explain the observations, and one explanation that would certainly work is: “There’s matter which we cannot see.” That’s not the only possible explanation.
Another explanation is that gravity waves have modulations like EM waves, and the modulations cause interractive interference patterns which reinforce or cancel each other, depending on their interaction. Opposed energies cancelling each other would, during their expansion, contain scalar quanta of energy, which would affect the surrounding spacetime, but would then be cancelled by an opposing modulation, leaving spacetime to snap-back to it’s original shape, dragging everything else along with it. This effect could look like a kind of “space-time” surface tension. Consider that empty space apparently has a slight negative energy (which it shouldn’t) and this explanation becomes even more intriguing.
And that’s one of hundreds of possibilities besides “unidentified, invisible particles.”
There’s something causing the effects we observe. Let’s first admit that we do not know what it is, or whether it’s dark, or matter at all. It could just be a previously uncalculated property of spacetime.
i like the first theory because it’s simplier;however,nature will have surprises.
Darrin, attempt to make sense. We can’t see what isn’t here? What does THAT mean? We see our galaxy. We see other galaxies. They aren’t “here”. Dark matter has only been detected where it may exist in rarefied, gaseous mode. And only in mass quantity. If it exists, it’s here. We can’t detect the gravitational pull of small units of gas so we simply can’t MEASURE it here.
The mystery deepens and the questions abound. I think the search is the fascinating part and I welcome all new information.
” Al Stanley Says:
February 20th, 2008 at 12:05 am
Does the mere presence of “Dark Matter” mean that science has to take a second look at the The standard model of particle physics, or is string theory able to explain its existence?”
The Standard Model does an extraordinary job of explaining the vast majority of our current observations related to particle physics, making predications that have proven to be highly accurate and precisely verified. However, it is almost universally acknowledged by physicists as being incomplete; it is not the full story. The current Standard Model may well end up being to the ultimate theory of particles as Newton’s view of gravity currently compares to Einstien’s General Relativity – it works effectively and accurately in a broad range of situations, but is only a ‘limiting case’ of a more broadly applicable and comprehensive theory. This doesn’t mean it is wrong per se, just that it isn’t quite the whole story.
The standard model does not predict dark matter, but some of the extensions to the theory that aim to go further may. For example, supersymmetry predicts that there should exist some particles that are good candidates for dark matter, specifically the neutralino. Supersymmetry has not been tested in any meaningful way as far as I know, but the Large Hadron Collider may be able to provide some more definitive answers when it fires up around mid 2008.
I’d forget, for the moment, about any dark matter predictions string theory may or may not make; even strong proponents of the theory often admit to being not quite sure what it all means. The theory is still very young, is highly untestable (for the moment, anyway), and makes a number of different predictions in any one of it’s many guises. This is not to say that it isn’t a highly worthwhile area of ongoing study – just that it isn’t mature enough yet to start taking toooo seriously.
It does not even exist, and therefore will not be found. Stop wasting time. There is
my hypothesis, explaining the reality of DM.
See my Web site:
cosmicdarkmatter.com
I can tell that this is not the first time you write about the topic. Why have you decided to write about it again?