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Comment by rhdunn | Hacker News Reader

The testable predictions would be at the places where QM and GR meet. Some examples:

1. interactions at the event horizon of a black hole -- could the theory describe Hawking radiation?

2. large elements -- these are where special relativity influences the electrons [1]

It's also possible (and worth checking) that a unified theory would provide explanations for phenomena and observed data we are ascribing to Dark Matter and Dark Energy.

I wonder if there are other phenomena such as effects on electronics (i.e. QM electrons) in GR environments (such as geostationary satellites). Or possibly things like testing the double slit experiment in those conditions.

[1] https://physics.stackexchange.com/questions/646114/why-do-re...

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re 2: special relativity is not general relativity - large elements will not provide testable predictions for a theory of everything that combines general relativity and quantum mechanics.

re: "GR environments (such as geostationary satellites)" - a geostationary orbit (or any orbit) is not an environment to test the interaction of GR and QM - it is a place to test GR on its own, as geostationary satellites have done. In order to test a theory of everything, the gravity needs to be strong enough to not be negligible in comparison to quantum effects, i.e. black holes, neutron stars etc. your example (1) is therefore a much better answer than (2)

Re 2 I was wondering if there may be some GR effect as well, as the element's nucleus would have some effect on spacetime curvature and the electrons would be close to that mass and moving very fast.

For geostationary orbits I was thinking of things like how you need to use both special and general relativity for GPS when accounting for the time dilation between the satellite and the Earth (ground). I was wondering if similar things would apply at a quantum level for something QM related so that you would have both QM and GR at play.

So it may be better to have e.g. entangled particles with them placed/interacting in a way that GR effects come into play and measuring that effect.

But yes, devising tests for this would be hard. However, Einstein thought that we wouldn't be able to detect gravitational waves, so who knows what would be possible.

You don't need a full fledged theory of quantum gravity to describe Hawking radiation. Quantization of the gravitational field isn't relevant for that phenomenon. Similarly you don't need quantum gravity to describe large elements. Special relativity is already integrated into quantum field theory.

In some ways saying that we don't have a theory of quantum gravity is overblown. It is perfectly possible to quantize gravity in QFT the same way we quantize the electromagnetic field. This approach is applicable in almost all circumstances. But unlike in the case of QED, the equations blow up at high energies which implies that the theory breaks down in that regime. But the only places we know of where the energies are high enough that the quantization of the gravitational field would be relevant would be near the singularity of a black hole or right at the beginning of the Big Bang.

Can't black holes explain Dark Energy? Supposedly there was an experiment showing Black Holes are growing faster than expected. If this is because they are tied to the expansion of the universe (univ. expands -> mass grows), and that tie goes both ways (mass grows -> universe expands), boom, dark energy. I also think that inside the black holes they have their own universes which are expanding (and that we're probably inside one too). If this expansion exerts a pressure on the event horizon which transfers out, it still lines up.

No.

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