[Marxism] Gravitational waves & testing String theory

Jeff meisner at xs4all.nl
Thu Feb 11 07:18:56 MST 2016


Later today (15:30 GMT) we expect the official announcement of the direct detection of gravitational waves by the LIGO interferometers: this is a huge experimental confirmation of a prediction of Einstein's theory of general relativity 100 years ago. That theory several of whose predictions have already been confirmed (most famously the 1918 Eddington solar eclipse expedition) is barely controversial since hardly any other theory can explain the evidence.

On the other hand, I've been meaning to respond to some of the numerous articles on cosmology that Louis regularly posts. I appreciate him posting these, but of course they are invariably from the popular press (or else none of us would be able to understand them!) and often include numerous errors. Moreover it seems that Louis' choices for these articles have been intended to make a vague point which I'd find hard to articulate but appears to me to be an expression of jealousy from all the other sciences (thus including Marxism) of Physics being the most concise and complete science which is able to predict (at least given sufficient computing power) the outcome of almost any experiment within its scope, outside of a very small number of unsolved problems. So those rather esoteric problems (in the sense that they don't affect any experiment you could possibly perform using materials you'd find around the house, or even most laboratories) become the target of those other scientist
s and pundits.

IN PARTICULAR the extremely promising developments of string theory and theory of the multiverse are gleefully attacked on supposedly methodological or philosophical grounds. Especially in the very last article Louis posted:

https://www.quantamagazine.org/20151216-physicists-and-philosophers-debate-the-boundaries-of-science/
     
This article had so many problems with it that I didn't have time to deal with them individually when he posted it. Nor do I have so much time now, but I will call your attention to the following key statement in that article which I suspect was one of the very points Louis was hoping to make:

"However string theory, which has its roots in ideas developed in the late 1960s, has made no testable predictions about the observable universe."

That statement (which the author also applies to the theories of inflation and the multiverse) follows a philosophical discussion in which "testability" is advanced as the criterion for a proposition being within the bounds of science. I'd largely agree with that though it's not so clear and simple. But regardless I wanted to mention one important thing I learned from an interesting talk (though I couldn't understand most of it!) we had last week by a cosmologist named Robert Brandenberger.

He named one testable prediction of superstring theory, involving measurements of gravitational waves (which have now been directly detected, as we are about to be told). According to that, the spectrum of gravitational waves should rise toward high frequencies, whereas the prediction of standard inflation has a higher power at lower frequencies. So this is absolutely a testable prediction (at least in principle) on which the theory could be disproved (or not disproved, in which case there probably won't be other theories that had made the same experimental prediction, especially in advance!).

Given that, I felt encouraged given today's announcement that I might indeed see such a confirmation in my lifetime. But on further reflection I realize today's announcement will be for detection of gravitational waves from a cataclysmic event (such as the merging of two black holes) whereas the prediction of string theory involves the background of gravitational waves requiring a much more sensitive instrument. Nevertheless given what I already know, I will die with the near-assurance (as I have now) of the validity of the multiverse, given an extremely compelling piece of evidence: the existence of life in at least one universe. Plus I suspect there will be further predictions (which are testable through new experiments or observations) of these powerful theories beyond the one that I just happened to hear about last week. But I don't expect that to happen soon enough to shut up these pundits who want to use philosophy to berate the latest advances in physics.

- Jeff







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