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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.