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Missing Matter... Still Missing
squidfrog writes "Nature.com, PhysicsWeb, and the BBC all report on the latest results from the Cryogenic Dark Matter Search. 'The most powerful search yet for the Universe's missing matter has come up empty handed, contradicting an earlier study that claimed to have seen new particles.' 'A favoured theory is that the dark matter consists of Wimps (weakly interacting massive particles) about a thousand times more massive than a proton, one of the particles found in an atom's nucleus... on the rare occasions a Wimp strikes an ordinary atom, the effect should be noticeable.' 'Writing in the Physical Review Letters, the team says that while a detection has yet to occur, there is now a better idea of how much dark matter must exist.' They 'hope to improve the sensitivity of the experiment by another factor of 20 over the next few years.' What's 20 times 0? And don't tell me zero!"
I think the answer to the dark matter problem and the quantum theory of gravity is one in the same. Our description of gravity is wrong. It has recently been discovered that dark matter is 'missing' from three elliptic galaxies. One would think that on the scale of something as big as a galaxy and with WIMPs being so massive that you ought to detect some quite major effect..
Add that to the fact that the universe's acceleration is getting quicker rather than slowing down and I think we have a strong case for our description of gravity being incorrect.
Simon.
This research, though, seems to be taking the same route: rather than questioning the model, they continue a so-far fruitless search for the "missing matter." If the model demands something the existence of which we are completely unable to verify, shouldn't we be questioning the model? Doesn't the very fact that there's all this "missing" matter indicate that perhaps our understanding is flawed?
Or am I just displaying rampant ignorance of the current state of physics and cosmology by asking this?
Reality has a conservative bias: it conserves mass, energy, momentum...
Opps. I meant, seven.
IBM may agree with you! Try this code on AIX:
#include"stdio.h"
int x,y,z;
int main() {
x=1;
y=0;
z=x/y;
printf("%d", z);
}
On most unix implementations you get floating point exception since the divide operator takes floating point operands. On AIX, when the denominator is cast to a float, it's a zero approximation rather than the official floating point zero. The result is that instead of a core dump, you get... 15.
Disconnect your television. Do your own research. Draw your own conclusions. They're probably lying. Don't be a sheep.
One of the possible outcomes of string theory is multiple universes, each separated by a fairly small distance (of course this distance is in a higher dimension so we can't notice them). If these alternate universes do exist, it is thought that the gravity from particles in our universe affects the other nearby universes. Imagine our universe as a flat sheet and another universe is a parallel flat sheet close to ours. In this model, gravity would still be three dimensional - ie, it would be able to bridge the gap between universes and affect the other universe. Perhaps this is what we're noticing - the gravity of massive particles in another universe?
BTW, I am not a physist but I have read up on this stuff. The theory of gravity carrying over to other universes actually does make sense - it explains why gravity is so much weaker than the other forces, because much of gravity's effect isn't on this universe. There's experiments going on now to test and see whether this is actually the case but I don't know the outcome. Anyway, this is just my thought on perhaps why we can't detect the dark matter - because it's not physically in our universe.
There seems to be a common sense here that all of the evidence for dark matter could be equivalently explained by changing the force law.
However, that isn't true. One unique test of dark matter is that it is dynamical; it can move. And there are a bunch of tests that have started to be made that show evidence for dynamical dark matter:
- in order to explain rotation curves without dark matter, models like MOND require force laws that would make the derived "shape" of the dark matter halo spherical at large radius. You can test this by looking at the shapes of clusters using X-ray emitting gas (eg. Buote et al. 2002, ApJ, 577, 183; Lee & Suto 2003, ApJ, 585, 151; Lee & Suto 2004, ApJ, 601, 599) or the Sunyaev-Zeldovich effect (LS03,LS04). You can also look at the shapes of dark matter halos around galaxies using weak gravitational lensing (Hoekstra et al. 2004, ApJ, 606, 67). So far all of the tests indicate that dark matter halos are not spherical, but flattened exactly as predicted by cold dark matter.
- the bars in barred spiral galaxies should slow down and disperse quickly in a spherical static halo potential, like you'd get from modifying the force law, but they can be maintained for long periods of time if they can exchange angular momentum with the dark matter (Athanassoula 2002, ApJ, 569, L83; Valenzuela & Klypin 2003, MNRAS, 234, 459).
- there's a weak gravitational lensing observation of a group that is falling into a cluster, where the mass of the infalling group is offset from the light - the gas is moving slower because it's interacting with the cluster gas, while the dark matter has kept moving (Clowe et al. 2004, ApJ, 604, 596).
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