From Dan Falk at Cosmos:
A century ago Einstein sweated blood to give us his mind-bending theory of gravity. As technology caught up, his predictions were verified, one by one. Now only gravitational waves remain.
Yet for all its triumphs, general relativity faces a couple of big challenges. Einstein wrestled unsuccessfully with one of them: reconciling the theory with its great nemesis, quantum mechanics. Each theory has been outstanding in its own domain – relativity in the cosmos, quantum mechanics in the subatomic world. But occasionally the domains overlap. To understand the Universe’s earliest moments, as well as the insides of black holes, we still need a theory that bridges the very large and the very small.
No one knows what the resulting theory might look like. One candidate is string theory, based on the premise that the fundamental building blocks of the Universe are tiny strings. An alternative, “loop quantum gravity” views space-time as granular. As with string theory, however, its proponents have yet to come up with an experiment to test it.
And then there’s the problem of dark energy. Discovered in the late 1990s it appears to be a force that acts in opposition to gravity, causing our Universe to expand at an accelerating rate. The Universe, it seems, obeys two masters – gravity and dark energy – and it may take another Einstein to make sense of the latter.
Yes, it will.
Meanwhile, as friends of ours argue whether beauty is a fundamental quality of our universe, it’s interesting to note a key reason Falk uncovers why people stick with Einstein (when there gotta be fifty ways to leave him):
No, says Clifford Will. Fiddling with general relativity, he believes, would be tantamount to changing the Fifth Symphony. “General relativity is so unbelievably beautiful and simple – it’s in some ways the most perfect gravitational theory that you could possibly imagine,” he says. All of the alternatives he’s seen so far are “horrendously ugly by comparison”. More.
Hmmm. If the universe itself is ultimately beautiful, wouldn’t an ugly theory attract suspicion in principle?
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