21 February 2007

Grave theories

After having not been observed for a very long time, it seems that Dark Matter may not be getting a green light.

By carefully re-examining conventional gravity theory Fermlab scientists have decided that if gravity “differs from general relativity on large scales”, it can fill Dark Matter’s role without adding any new particles or otherwise over-exciting the physicists.

Favourite quote:

the case of dark energy also hinges on the assumption that general relativity describes gravity on larger scales. Dark energy is even more difficult to explain than dark matter, so it seems almost natural to look at gravity as the culprit in both cases

By borrowing Jacob Bekenstein’s TeVeS (relativistic covariant) theory of gravity — a theory which usefully generalises MOND (modified Newtonian dynamics) — they can “test TeVeS’ predictions in detail & compare them to the standard dark matter paradigm to see if TeVeS can be a viable alternative”. It seems to fit:

while Bekenstein’s theory has three functions which characterize space-time — a tensor, vector and scalar (TeVeS) — it’s the perturbations in the vector field that are key to the enhanced growth. General relativity describes space-time with only a tensor (the metric), so it does not include these vector perturbation

It seems that the vector changes corellate with gravity-induced changes to the curvature of space (-: if that’s weird enough for you :-) quite well.

Interestingly, Bekenstein introduced the vector factor for completely unrelated reasons, commenting that “Sometimes theories are smarter than their creators”.

It’ll be interesting to follow this as it develops, as it’s not so usual for physics theories to get simpler with time. (-:

No comments: