Dark energy not needed?

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Dark energy not needed?

Post by plodder » Sat Jan 25, 2020 10:36 am

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Re: Dark energy not needed?

Post by shpalman » Sat Jan 25, 2020 11:24 am

The theory, known as massive gravity, modifies Einstein’s general relativity, positing that the hypothetical particles (gravitons) that mediate the gravitational force themselves have a mass. In Einstein’s version, gravitons are assumed to be massless.
Einstein’s general relativity doesn't have gravity carried by particles. Quantum theories of gravity have gravity carried by particles (like quantum theories of electromagnetism have the photon) but nobody has a working quantum theory of gravity. So, first you would need one of those, and then you give your gravity-carrying spin-2 boson a tiny non-zero mass. Her list of publications is here but even I'm not theoretical enough of a physicist to read it all now on a Saturday morning and form an opinion. But it can at least be said to be a mathematically consistent theory. Whether it has any bearing on reality is a completely different question.

Also, not everyone is entirely convinced that the rate of the expansion of the universe is actually accelerating which is the result which dark energy is supposed to "explain" (i.e. something is happening which you don't understand so you invent something which you don't understand to take care of it). In that case, however, I think that the expansion of the universe is actually accelerating.

Any mass of the graviton would have to be really tiny since gravity still works over very long length scales. This is probably going to be one of those parameters which will be forever set at just too small to actually measure.
molto tricky

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Re: Dark energy not needed?

Post by Gfamily » Sat Jan 25, 2020 12:14 pm

Also AIUI, the recent 'Gravitational Waves plus light' detection of the Neutron star merger demonstrated that the speed of gravity is pretty much the speed of light to parts per billion.
ETA - which suggests a non zero mass graviton is unlikely.
My avatar was a scientific result that was later found to be 'mistaken' - I rarely claim to be 100% correct
ETA 5/8/20: I've been advised that the result was correct, it was the initial interpretation that needed to be withdrawn
Meta? I'd say so!

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