Question about the uncertainty principle

  • #1

Main Question or Discussion Point

The uncertainty principle says that you can't know position and velocity of particle at the same time. So particular we can not say that the particle is at rest at some point because then we would know it is not moving and we would know exactly where it is.
So my question is if we send the particle into the singularity of a black hole can we say that the particle does not move and we know exactly where it is? Оr the uncertainty still exist and we can say, we do know exactly where the particle is, but we do not know its velocity.

Thank you for your attention!
 
Last edited:

Answers and Replies

  • #2
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Well, actually the uncertainty principle says that we cannot measure position and velocity with arbitrary precision. Point is, if you send a particle in the singularity of a black hole we cannot measure anything (no way to extract information from there). So your gedanken experiment seems not very well crafted. And that even without mentioning that you must modify a theory in the regimes when singular point arise (quantum gravity theories are trying to do that).
 
  • #3
So even if i'm behind the horizon i can not measure anything about singularity?
 
  • #4
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Your question cannot be answered without a reference to a specific quantum gravity theory: there are theories who get rid of of the (classical) singularity and others that propose to modify the Heisenberg uncertainty principle.
In the first case the uncertainty principle predictions still holds. For the second case I cannot answer, I don't remember the detail of the modifications proposed.
 
  • #5
Can you tell me a literature which i can start read and i learn more about quantum gravity and why it's so difficult to unite the two theories?

Thanks for the feedback :)
 
  • #6
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Here you would probably find all of what you are asking, perhaps even too much: https://arxiv.org/archive/gr-qc (also https://arxiv.org/archive/hep-th, but only related to string theory approach).

A big warning: technical details of quantum gravity theories are really, really hard to follow without a robust knowledge on very advanced mathemathics.

In order to have some guidance over quantum gravity problems, so at least you can have some idea on this subject, I suggest you to follow the wonderful Sabine Hossenfelder blog: https://backreaction.blogspot.com/

She is not only a great expert in quantum gravity, but also very much agnostic on the specifics of the various theories.

Have fun!
 
  • #7
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The uncertainty principle says that you can't know position and velocity of particle at the same time. So particular we can not say that the particle is at rest at some point because then we would know it is not moving and we would know exactly where it is.
So my question is if we send the particle into the singularity of a black hole can we say that the particle does not move and we know exactly where it is? Оr the uncertainty still exist and we can say, we do know exactly where the particle is, but we do not know its velocity.

Thank you for your attention!
There is quite a bit of misunderstanding in this post. The uncertainty principle is not about measurement but about quantum state preparation, there are plenty of threads about this. Secondly, a singularity of a black hole is equivalent to saying no one knows what happens here because General Relativity breaks down and there is no quantum theory to replace it .

Cheers
 

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