How Does Black Hole Entropy Increase When Starting with a Pure State?

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Discussion Overview

The discussion revolves around the increase of black hole entropy when a particle in a pure state is absorbed by a black hole. Participants explore the implications of this process on entropy, the second law of thermodynamics, and the potential conflict between quantum mechanics and general relativity.

Discussion Character

  • Debate/contested
  • Conceptual clarification
  • Exploratory

Main Points Raised

  • One participant posits that starting with a particle in a pure state, which has zero entropy, leads to a paradox when the particle is absorbed by a black hole, resulting in an increase in black hole entropy.
  • Another participant suggests that entropy generally increases in physical processes, questioning the surprise at this phenomenon.
  • A third participant references the second law of thermodynamics, asserting that entropy cannot decrease, which may imply challenges for the concept of white holes.
  • One participant raises the issue of black hole information loss, indicating that an increase in entropy from a pure state may require a violation of unitary time evolution, highlighting a conflict between quantum mechanics and general relativity.
  • There is a mention of a theory that suggests information cannot be lost or destroyed, but this is countered by the idea that information can be lost in irreversible macroscopic processes.
  • Another participant emphasizes that the principle of unitary time evolution should not be violated, suggesting that any violation indicates a flaw in the underlying theory of black holes.

Areas of Agreement / Disagreement

Participants express differing views on the implications of black hole entropy and the nature of information loss, indicating that multiple competing perspectives remain unresolved.

Contextual Notes

Participants reference various principles such as the second law of thermodynamics and unitary time evolution, but the discussion does not resolve the implications of these principles in the context of black hole entropy.

touqra
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Supposing I started off with a particle, which I know exactly the state it is in, hence, it is in a pure state. And hence also, its entropy is zero.
Now, suppose we throw the particle into the black hole and be sucked in, then, then the area of the black hole increases and hence, the entropy of the black hole also increases.
But, how can this be possible? I started off with a zero von Neumann entropy and why should the entropy/area of the black hole increase?
 
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In most physical processes entropy increase, so why are you surprised?
 
according to the 2nd law of thermodynamic, entropy cannot decrease..decreasing the chance of a white hole possiblility.
 
If you started with a pure state, entropy increase is only possible if you allow for a violation of unitary time evolution. This problem is known as black hole information loss and points out an incompatibility between QM and GR.
 
but i thought there is a theory that states that information cannot be lost or destoyed?
 
white holes said:
but i thought there is a theory that states that information cannot be lost or destoyed?
Information is lost in irreversible macroscopic processes. I think that the statement is that unitary time evolution of pure quantum states is a principle that should not be violated. In case of quantum field theory of black holes, it's violation is an indication that something is wrong in the theory. If you are interested in knowing more about this I would suggest to ask in the subforum "Beyond the Standard Model".
 

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