There’s a race on to find the first direct evidence of cold dark matter. And it ain’t pretty. There’s probably a Nobel at stake for the winner which means the leading groups are at each other’s throats, like alleycats over chicken bones.

For any of ya’ll who wanna know who’s who in this backstreet brawl, Laura Baudis at the University of Zurich has compiled a card of the main fighters. All these guys are lookin’ for Weakly Interacting Massive Particles and she gives a good summary of all the contenders looking to be crowned king of  WIMPs.

The basic idea is that WIMPs sit around in space twiddling their thumbs until a great big lump of ordinary stuff like the Earth comes along and smashes into them. When this happens physicists should be able to see the impact in their labs as atoms get pranged.

Laura takes the rather optimistic view that “the major questions have shifted from ’how
to detect a WIMP’ to ’how can we identify its nature in case of a signal’”.

She neatly avoids the biggest question which is whether WIMPs exist at all.

They’ve been imagineered to explain the observation that many galaxies are spinning so fast that the matter they contain ought to be thrown outwards.  Something has to be holding these galaxies together and so astrobods have hypothesised that particles called WIMPs provide the extra gravitational ooomph to hold galaxies together.

But plenty of theorists think other explanations are just as feasible, modified newtonian gravity, for example. And if they’re right, then the hundreds of millions of dollars being spent in this area might as well have been dumped at the bottom of a dirty great mine shaft. Which, as fate would have it, is where most of the WIMP detectors happen to have ended up anyway.

Ref: arxiv.org/abs/0711.3788: Direct Detection of Cold Dark Matter

Yer only have to go back to Plank to find a pretty detailed argument that there are three fundamental dimensional constants from which all others can be derived. They are length, time and mass. Plank argues that as long as you got a tape measure, a clock and set of scales you can measure anything in the universe.

Seems reasonable but various philosophers have argued over the details sayin’ maybe there are no constants or perhaps two or God knows how many. But being philosphers, they ain’t interested in actually provin’ anything only arguin’ about it.

Now a group of Brazilian eggheads this week say they have proven the result objectively and that Plank is wrong. They reckon there are only two of fundamental dimensional constants and that these correspond to length and time. They argue that all ya need is a tape measure and a clock.

A key to their thinkin is that they assume that all that can be measured are intervals in space and time. This leads to the idea that gravitational mass is the same as inertial mass, which is a big leap but one they say they prove. Given that, mass is simply the acceleration produced on a test particle at a certain distance. Ya don’t need no scales to measure that.

Interesting approach. When it comes to fundamental dimensional constants, two is a big improvement on three.

Ref: arxiv.org/abs/0711.4276: The Number of Dimensional Fundamental Constants