Posted on 08/09/2010 7:25:58 AM PDT by LibWhacker
Physicists struggling to reconcile gravity with quantum mechanics have hailed a theory inspired by pencil lead that could make it all very simple
IT WAS a speech that changed the way we think of space and time. The year was 1908, and the German mathematician Hermann Minkowski had been trying to make sense of Albert Einstein's hot new idea - what we now know as special relativity - describing how things shrink as they move faster and time becomes distorted. "Henceforth space by itself and time by itself are doomed to fade into the mere shadows," Minkowski proclaimed, "and only a union of the two will preserve an independent reality."
And so space-time - the malleable fabric whose geometry can be changed by the gravity of stars, planets and matter - was born. It is a concept that has served us well, but if physicist Petr Horava is right, it may be no more than a mirage. Horava, who is at the University of California, Berkeley, wants to rip this fabric apart and set time and space free from one another in order to come up with a unified theory that reconciles the disparate worlds of quantum mechanics and gravity - one the most pressing challenges to modern physics.
Since Horava published his work in January 2009, it has received an astonishing amount of attention. Already, more than 250 papers have been written about it. Some researchers have started using it to explain away the twin cosmological mysteries of dark matter and dark energy. Others are finding that black holes might not behave as we thought. If Horava's idea is right, it could forever change our conception of space and time and lead us to a "theory of everything", applicable to all matter and the forces that act on...
(Excerpt) Read more at newscientist.com ...
It really is not whimsical. What Petr did in his initial paper is justified, and, in retrospect, it is suprising that none of us thought of doing it earlier. It is not really possible to go into the full details of this in a forum such as a blog, but the main point is that, at “finite temperature” (this the jargon we use to refer to physical systems at temperatures above zero), Lorentz invariance (”Lorentz symmetry,” as it is referred to in the article) is automatically violated. The reason is that the mere statement that there is a finite temperature at all implies that there is present in the problem a large number of particles in the “background” that together make up what is referred to as a “heat bath.” The word “temperature” actually refers to a statistical measure associated to this background heat bath. However, this is the reason that Lorentz invariance is broken: the aggregate properties of the large number of particles that, together, make up the heat bath, among many other things, implicitly pick out a so-called “preferred direction” in spacetime. This “preferred direction” (technically, this is the direction in spacetme towards which the velocity 4-vector of the heat bath points) intrinsically breaks Lorentz invariance. What Petr did in his paper is technically justified. Other physicists later showed (as described in the article) that the original paper didn’t properly reduce to general realtivity (whcih DOES exhibit Lorent invariance) at low temperatures, but that defect of the original Horava idea has since been fixed. This is all still very much research in progress.
Thanks for the explanation. “E8” — I’ve seen that before! (Lisi)
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