Evaporating black holes, a kind of flux of space?

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Discussion Overview

The discussion revolves around the concept of evaporating black holes and the implications of Hawking radiation on the nature of space and energy. Participants explore theoretical aspects related to the measurement of space in the context of black hole evaporation and the effects of surrounding regions.

Discussion Character

  • Exploratory
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • One participant suggests that if a black hole evaporates via Hawking radiation, there may be a radial flux of energy from the black hole, questioning whether the space within a hypothetical box around the black hole decreases as it evaporates.
  • Another participant seeks clarification on the nature of the hypothetical box, expressing uncertainty about how to quantify the amount of space within it.
  • A different participant references General Relativity, proposing that it allows for the measurement of volumes in regions with and without mass, suggesting that mass affects the volume of a region.
  • In response, another participant argues that General Relativity does not directly address volumes, introducing the concept of a universe with a black hole and a positive cosmological constant, and discussing the implications of a future horizon on measurements of space.

Areas of Agreement / Disagreement

Participants express differing views on the relationship between mass, space, and volume in the context of General Relativity, indicating that there is no consensus on how to interpret these concepts in relation to evaporating black holes.

Contextual Notes

There are limitations in the discussion regarding the assumptions made about the nature of the box and the definitions of space and volume in the context of General Relativity, which remain unresolved.

Spinnor
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If a black hole can "evaporate" via Hawking radiation then there is a radial flux of energy from the black hole? Put a box around on such evaporating black hole. When the black hole is gone there is less space in the box? If so is that space carried away by the Hawking particles?

Thanks for any help!
 
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Spinnor said:
If a black hole can "evaporate" via Hawking radiation then there is a radial flux of energy from the black hole? Put a box around on such evaporating black hole. When the black hole is gone there is less space in the box? If so is that space carried away by the Hawking particles?

Thanks for any help!
I assume you're talking about a perfectly transparent box, just a hypothetical region around the black hole? I don't really know how you would go about making any sort of statement about how much space there is within the box in the first place.
 
Chalnoth said:
I assume you're talking about a perfectly transparent box, just a hypothetical region around the black hole? I don't really know how you would go about making any sort of statement about how much space there is within the box in the first place.

I thought General Relativity allowed us to measure volumes of regions with and without mass inside? The ratio the the radius to the circumference of some region gives a measure of the mass inside that region? A region with more mass has a greater volume then the same region with no mass?

Thanks for your time!
 
Last edited:
Spinnor said:
I thought General Relativity allowed us to measure volumes of regions with and without mass inside?
No, General Relativity really doesn't talk about volumes directly.

Perhaps you were thinking about an entire universe? If we take a universe with a black hole and a positive cosmological constant, that universe has a future horizon. Anything that happens beyond this horizon "now" will never reach us (a global now is a bit arbitrary, but if we say that "now" is the time at which different places see the same CMB temperature we currently see, we can talk sensibly about it). Similarly, anything we release now (whether light rays or something else) will never reach anything that lies beyond that horizon.

After the black hole evaporates and the radiation all redshifts away, the horizon is larger than it was with the black hole there.
 

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