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Nov 28 2009

“Topples” Relativity? Really?

A physicist from University of California by the name of Petr Hořava has postulated how to unify the theory of relativity and quantum theory — by untying space from time when you start dealing with quantum-level reactions.

[T]he problem is the way that time is tied up with space in Einstein’s theory of gravity: general relativity. Einstein famously overturned the Newtonian notion that time is absolute—steadily ticking away in the background. Instead he argued that time is another dimension, woven together with space to form a malleable fabric that is distorted by matter. The snag is that in quantum mechanics, time retains its Newtonian aloofness, providing the stage against which matter dances but never being affected by its presence. These two conceptions of time don’t gel.

The solution, Hořava says, is to snip threads that bind time to space at very high energies, such as those found in the early universe where quantum gravity rules. “I’m going back to Newton’s idea that time and space are not equivalent,” Hořava says. At low energies, general relativity emerges from this underlying framework, and the fabric of spacetime restitches, he explains.

This is fascinating. Looking for a grand unified theory — or a theory that at least covers both relativistic mechanics and quantum mechanics — has been a major goal since the quantum level was discovered. In much the same way that Einsteinian relativity makes up for fundamental flaws in Newtonian mechanics — which themselves work great until you get into some wacky fringe cases — Hořava’s idea of disassociating time from space at the quantum level not only explains a lot of those fringe cases mathematically and elegantly, it also successfully pairs the two theories such that Relativity with Hořava’s modifications, if they turn out to be correct, could very well become the dominant theory in physics.

However, “topples” in the title is a strong word.

You see, Newtonian mechanics is an abstraction that explains a lot of physics very elegantly as well. It only starts producing garbage numbers at high velocities and with black holes (and other such extremes of space or time). Einstein’s realization that space and time are married, outside of the quantum scale at least, was a stroke of genius, regardless of how simple a realization it might have been. The idea that, at the quantum scale, that marriage isn’t quite as stringently enforced as it is on the macro-scale, is another one of those ideas that’s so simple, it took a genius to figure out.

As how relativity did not “topple” Newtonian mechanics so much as enhance it, Hořava’s hypothesis could enhance the theory of relativity such that it is no longer necessary to claim that “either quantum physics or relativity can be correct, but not both”. They could both be correct, for different sets of circumstances.

The pursuit of science is not a dogmatic one where one must be married to a hypothesis in the face of contravening evidence. And most scientific progress is not made by disproving the prevailing theories, so much as fixing the spots where the theories produce incorrect predictions. We are chasing a static set of rules by which this universe plays — and we are getting very close to an accurate understanding of them. But our understanding is, de facto, an abstraction of those rules — a human-imposed framework to help us understand them. The universe is what it is — it is reality. We’re just trying to describe it in as good a manner as possible, lowering the error bar on our abstractions through observation, hypothesis and experimentation.

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    Quark stars may act like hypothesized pre-Big-Bang state « Lousy Canuck

    [...] universe being unlikely in the current model of cosmology, the news from November of Petr Hořava potentially reconciling general relativity and quantum mechanics hinted at the possibility that the cyclical model could be a [...]

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