Black Hole Event Horizon: Is There a Physical Boundary?

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Discussion Overview

The discussion revolves around the nature of the event horizon in black holes, specifically whether it constitutes a physical boundary or is merely a result of coordinate choice in the Schwarzschild metric. Participants explore the implications of different coordinate systems on the understanding of the event horizon and its singularity.

Discussion Character

  • Debate/contested
  • Technical explanation
  • Conceptual clarification

Main Points Raised

  • Some participants question whether the event horizon is a physical boundary or if it is dependent on the choice of coordinates, citing that it may disappear with different coordinate systems.
  • Others argue that while the singularity at the event horizon can be a result of coordinate choice, the event horizon itself is a well-defined surface that retains physical significance in certain coordinate systems.
  • A participant mentions that the event horizon is a light-like surface and suggests that the term "physical boundary" may not be the most appropriate for describing it.
  • Some participants express uncertainty about the existence of texts that support the idea that the event horizon is solely a coordinate artifact.
  • There is a clarification that while a coordinate singularity can be resolved with appropriate coordinates, the event horizon itself remains a coordinate-independent surface.

Areas of Agreement / Disagreement

Participants generally disagree on the characterization of the event horizon, with some viewing it as a coordinate-dependent feature and others asserting its physical significance regardless of coordinate choice. The discussion remains unresolved.

Contextual Notes

Limitations include the dependence on specific coordinate systems and the ambiguity surrounding the definition of "physical boundary" in the context of the event horizon.

ChrisVer
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Is there a physical boundary that is the event horizon? Or is there not?
The reason I'm asking is because texts say that the event horizon that appears in Schwarzschild's metric is a result of the coordinate choice, and it disappears by choosing some other coordinates.
 
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ChrisVer said:
The reason I'm asking is because texts say that the event horizon that appears in Schwarzschild's metric is a result of the coordinate choice, and it disappears by choosing some other coordinates.
I think what they say is that the singularity at the EH exists only in some coordinates.
 
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ChrisVer said:
Is there a physical boundary that is the event horizon? Or is there not?
The reason I'm asking is because texts say that the event horizon that appears in Schwarzschild's metric is a result of the coordinate choice, and it disappears by choosing some other coordinates.

The singularity at the horizon is a result of coordinate choice (you can make it go away by choosing, for example, Kruskal coordinates) but the physical significance of the event horizon is not. The event horizon is a light-like surface, and "physical boundary" is not an especially natural term for describing it, but it is a well-defined surface in the Schwarzschild spacetime as long as you use coordinates that aren't singular there.
 
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ChrisVer said:
The reason I'm asking is because texts say that the event horizon that appears in Schwarzschild's metric is a result of the coordinate choice, and it disappears by choosing some other coordinates.

I have never encountered a text that says this.
 
George Jones said:
I have never encountered a text that says this.

That's a coordinate singularity. It exists due to the choice of coordinates, and can be resolved by a more appropriate choice of coords.
 
At risk of putting words in George's mouth, I think he's pointing out that a coordinate choice doesn't remove the event horizon, which is a co-ordinate independent surface. You can remove the coordinate singularity at the event horizon by careful choice of coordinates, but the horizon remains.
 

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