Entanglement inside a black hole

In summary, the paradox is that Assistant #1 can measure + and also see the Assistant #2 measure +. Hence, he observes that the entanglement was severed by the BH event horizon.
  • #1
Kostik
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TL;DR Summary
A thought experiment involving measuring the spins of entangled electrons.
Suppose two electrons are entangled with opposite spins. Electron #1 passes through the event horizon of a black hole, together with Laboratory Assistant #1. Suppose the assistant measures electron #1's spin after they pass through the event horizon (according to #1's [proper] time) and measures a + spin.

Another laboratory assistant, #2, outside the black hole, watches the Assistant #1 falling into the black hole, but #2 never sees #1 cross the event horizon. After a time, suppose Assistance #2 measure the spin of electron #2. He measures + or −.
If Assistant #2 measures +, then electron #1 must be −. And yet, Assistant #1 (in his proper time) already measured +!

It seems to me the "answer" is probably that when #1 makes his measurement inside the BH, he is no longer within the same spacetime as #2. He is not in #2's universe. Hence, the entanglement is effectively severed once #1 enters the BH (which #2 never sees), since #2 has no access to #1's spacetime.

Therefore, both electrons can have a spin measurement of +.

Assistant #2 never sees #1's measurement, so the issue here is meaningless to him. The interior of the BH is not in #1's spacetime.

HOWEVER, Assistant #1 can see #2's measurement, especially if he has a long time to relax and wait before reaching the BH singularity. #1 can measure +, and then after a while he can observe that #2 also measured +. Therefore, #1 can witness that the entanglement was broken.
 
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  • #2
Kostik said:
How to understand this?
Your black hole is just a more complicated way of setting up an experiment which has been done many times: the two measurements are spacelike-separated so there is no unambiguous way of saying which one happened first. The resolution of your apparent paradox is also the same: Entanglement doesn’t work the way you’re thinking.

Measuring the spin of one particle does not somehow set the spin of the other particle. When I measure one particle and get spin up, that just means that I know that when and if the other particle is measured (and for all I know that’s already happened) it will be spin down. It doesn’t matter which measurement is first.
 
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  • #3
Nugatory said:
Your black hole is just a more complicated way of setting up an experiment in which has been done many times: the two measurements are spacelike-separated so there is no unambiguous way of saying which one happened first. The resolution of your apparent paradox is also the same: Entanglement doesn’t work the way you’re thinking.

Measuring the spin of one particle does not somehow set the spin of the other particle. When I measure one particle and get spin up, that just means that I know that when and if the other particle is measured (and for all I know that’s already happened) it will be spin down. It doesn’t matter which measurement is first.
It’s not just a spacelike separation scenario. I outlined a scenario where both spins are measured with the same direction. Observer #2 never sees #1 make a measurement.
 
  • #4
Kostik said:
It’s not just a spacelike separation scenario. I outlined a scenario where both spins are measured with the same direction. Observer #2 never sees #1 make a measurement.
It is still just a spacelike separation scenario.

Kostik said:
If assistant #2 measures +, then electron #1 must be -. And yet, assistant #1 (in his proper time) already measured +.
This cannot happen according to our current theories. And we don’t have any experimental evidence contradicting the theory for this scenario
 
  • #5
But it can easily happen. It seems to me the "answer" is probably that when #1 makes his measurement, he is no longer within the same spacetime as #2. He is not in #2's universe. Hence, the entanglement is effectively severed once #1 is inside the BH, since #2 has no access to #1's spacetime.
 
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  • #6
Kostik said:
It’s not just a spacelike separation scenario. I outlined a scenario where both spins are measured with the same direction. Observer #2 never sees #1 make a measurement.
You are just repeating your original misunderstanding. In all of these entanglement situations, it is does not matter whether either observer sees the other’s measurement.
 
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  • #7
Of course it does not matter, except if both spins turns out to be the same.
 
  • #8
Why did you ask the question if you don't want to know the answer? Seems like you just want to argue, not learn.
 
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  • #9
The paradox seems to be how Assistant #1 can measure + and also see the Assistant #2 measure +. Hence, he observes that the entanglement was severed by the BH event horizon.
 
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  • #10
Kostik said:
The paradox
is all in your head
 
  • #11
Hoping for a more useful reply.
 
  • #12
Kostik said:
Hoping for a more useful reply.
What could be more useful than being told where the mistake is?
 
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  • #13
Vanadium 50 said:
What could be more useful than being told where the mistake is?
Read the answers you've already gotten.
 
  • #14
Kostik said:
But it can easily happen.
As said above, this has never been observed. Our current best understanding of the universe says it can't happen.

Kostik said:
It seems to me the "answer" is probably that when #1 makes his measurement, he is no longer within the same spacetime as #2. He is not in #2's universe. Hence, the entanglement is effectively severed once #1 is inside the BH, since #2 has no access to #1's spacetime.
We do not allow personal speculation. Thread closed.
 
  • #15
Kostik said:
when #1 makes his measurement, he is no longer within the same spacetime as #2
This is wrong. The entire black hole, interior and exterior, is a single spacetime.
 

1. What is entanglement inside a black hole?

Entanglement inside a black hole refers to the phenomenon where two or more particles become connected in such a way that the state of one particle is dependent on the state of the other, even at great distances. This occurs within the event horizon of a black hole, where the intense gravitational forces cause particles to become entangled.

2. How does entanglement inside a black hole occur?

Entanglement inside a black hole occurs when particles are pulled into the black hole's event horizon. The intense gravitational forces cause the particles to become entangled, meaning their states are intrinsically linked. This is due to the fact that the particles are so close together and are subject to the same gravitational forces.

3. What is the significance of entanglement inside a black hole?

The significance of entanglement inside a black hole is still a topic of ongoing research and debate. Some theories suggest that it could play a role in the information paradox of black holes, where information is seemingly lost after entering a black hole. Others propose that it may have implications for quantum gravity and the unification of quantum mechanics and general relativity.

4. Can entanglement inside a black hole be observed?

Currently, it is not possible to directly observe entanglement inside a black hole. This is due to the fact that the intense gravitational forces within the event horizon make it impossible for any information to escape. However, scientists have been able to indirectly observe entanglement through experiments and simulations.

5. How does entanglement inside a black hole affect the outside world?

The effects of entanglement inside a black hole on the outside world are still not fully understood. Some theories suggest that it could have implications for quantum teleportation, where information is transferred between entangled particles instantaneously. Others propose that it may have a role in the behavior of Hawking radiation, the radiation emitted by black holes.

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