Physicists discover that gravity can create light

In physical cosmology (and especially considering alternatives to General Relativity) it is very common to consider the possibility that some effect is strong in the very early universe and so weak as to be undetectable at present times (or even as early as the first galaxies or the surface of last scattering). Examples include auxiliary gravitational fields ("bimetric" theories, for example) that decay in the early universe, variable-speed-of-light/variable-Newton's-constant theories, and so forth.

Although one might think "hm, it's very convenient that an important effect only happens so early that we cannot use telescopes to see it", there is very good evidence for electroweak unification and cosmic inflation, both of which terminated (in different ways) in the very early universe, and are (or arguably were) too difficult to directly observe this late in the universe's history. Additionally there is ample indirect evidence that (if it exists) is within our reach.

That the hypothesized graviton-photon mechanism cannot work in vacuum makes it at least very difficult to test (or observe with telescopes) today, however the final section of the paper does suggest that if it happens in nature, where it happens is likely to become accessible to us in due course. This is not a theory that has a hard cut-off in the early universe; it is just a hypothesis that to be realized requires a configuration of e.g. binaries and molecular clouds that is not very close to what we commonly observe. (Double-binary compact objects in dusty environments might end up being commonplace though, and in those settings one could expect changes in "multimessenger" signals if the authors' ideas are correct. It's amazing how many star systems are turning out to be triples, and we know of triple-compact-star systems; there are a number of known quadruples like DI Chamaelontis; and Gamma Cassiopeiae is a system of at least seven ~stellar mass bodies.)

Some discussion here: https://physics.stackexchange.com/questions/22876/does-a-pho...

This is precisely where GR doesn't work, so using it to declare with confidence what gravity "is" is as silly as using QM to do it. They don't work on this matter. General Relativity is definitely not a complete description of how the universe works. It's a good approximation, even a very good one.. but no more than that.

We know this. It is well understood. This is not some sort of whacky Time Cube position. The whacky Time Cube position is really the one that says GR is correct so we can declare with confidence that gravity isn't a force.

In the end I don't expect gravity to be different from electromagnetism and the other forces. There's been plenty of efforts to build GUTs from nothing but geometry in which case nothing is a "force". Efforts from the QM side tend to incorporate "gravitons" as the force mediation particle just like the other forces have mediation particles. It seems very likely to me that GR's "gravity is specially not a force" will end up being an error, in that either all the other forces turn out not to be forces either, in which case we'll change the meaning, or it will be a force like every other. I don't think there's a lot of reason to expect this to be anything other than an artifact of GR being an approximation.

See also: https://www.youtube.com/watch?v=v3hd3AI2CAA