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Is it possible to have an object that is a quantum superposition of a black hole and an equivalent mass that is not a black hole?

Suppose we are adding iron atoms one at a time to a pile somewhere out in space. My understanding is that eventually, when the pile is massive enough, it will collapse under its own gravity into a black hole. But what happens just before the last atom that causes the pile to collapse is added? Could a quantum fluctuation (my apologies in case this is not the right term) cause it to enter a superposition of states where there is some likelihood that it has collapsed and some that it has not?

One could also imagine an experiment where the addition of atoms is triggered by a mechanism that depends on atomic decay as in Schrodinger's cat experiment. What then?

Daniel Genin
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    This question assumes that there is an accepted theory of quantum gravity, but there isn’t. There are no black holes in the standard mode of particle physics, and no quantum superpositions in the standard model of cosmology. This makes the question opinion-based. – Ghoster Mar 04 '23 at 21:59

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Here’s a better variation of the experiment. Say you have a mass that will almost become a black hole. All that’s needed is 1 more particle. Now you have the classic SG experiment. If a particle goes upwards, it will hit the mass and form a black hole. If it goes downwards it won’t.

The state of the particle can be written as a linear combination of spin up and spin down. If the particle is spin up, a black hole forms. If it’s spin down, well a black hole doesn’t form. So the answer to your question is yes. We can have a linear combination of “black hole forming” and “black hole not forming”.

  • Intuitively it seems that there should be the final atom that causes the pile to collapse but i wonder if that depends on how long the time interval between successive atoms is. Inevitable fluctuations may take a pile that is several atoms short of "critical" over the threshold given enough time. It is also unclear to me how kinetic energy of atoms, which after all is equivalent to mass, affects proximity to the collapse threshold. But in the end, as @Ghoster pointed out, the answer depends on the quantum nature of gravity, which is unknown. – Daniel Genin Mar 05 '23 at 18:01
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    This answer is incorrect. There are no quantum particles in General Relativity and no black holes in Quantum Mechanics. This site is for competent answers, not unsupported opinions. – safesphere Mar 07 '23 at 04:10
  • @safesphere there are particles in general relativity. QFT on curved spacetime exists. The same thing applies there. –  Mar 07 '23 at 23:43
  • QFT on curved spacetimes is neither a complete theory nor have been proven at all. See this great answer for details: https://physics.stackexchange.com/questions/492028/ - And no, there are no quantum particles in GR, as it is a purely classical theory with no quantum effects whatsoever. – safesphere Mar 09 '23 at 00:31