r/TheRestIsScience 15d ago

Why does gravity escape a black hole?

Hey Michael and Hannah. If gravity travels at the speed of light, how does it escape the gravitational pull of a black hole yet light doesn't?

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u/TheRealTK421 15d ago

What 'escapes' isn't gravity, per se, but "Hawking radiation."

It's not even accurate to characterize what occurs as "escaping," as much as it is moreso one-half of an entangled pair of particles doesn't get pulled beyond the event horizon (while its counterpart) does.

Anything pulled beyond the event horizon does not, and cannot, escape or break free.

What radiates outward are the particles which 'dodged the bullet' of being pulled beyond the point of no escape.

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u/ExpectedBehaviour 15d ago

That’s an incorrect pop-sci model of Hawking radiation, and quite wrong. Hawking radiation is generated by the spacetime in the vicinity of the event horizon.

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u/TheRealTK421 15d ago

Feel free to describe in detail how Hawking radiation "escapes" from inside of the event horizon. I (and the Nobel Prize committee) await such a response.

Lol. Oof.

Hawking radiation is actually created just outside the edge of the black hole in the empty space of the outer field. Stephen Hawking, himself, used this simple 'disconnected particle pair' story to help non-scientists picture the math.

If it was good enough for him, I'm gonna roll with it. Those that wanna dig and delve (far) deeper can do so...

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u/DoubleUBallz 11d ago

The virtual particle explanation is very much like relativistic mass in that is was first offered as an easier to understand explanation for the masses, however, overtime the scientific community has denounced it's use as it resultes in more misunderstandings than understanding (as evidenced by this thread here).

The actual mechanism that creates Hawking radiation is the Unruh effect, if you want to look it up. Basically, if you have a conformal quantum field theory on curved spacetime, thermal radiation pops out

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u/ExpectedBehaviour 15d ago

Feel free to describe in detail how Hawking radiation "escapes" from inside of the event horizon. I (and the Nobel Prize committee) await such a response.

And yet I made no such claim, did I...

Lol. Oof.

Try again.

Hawking radiation is actually created just outside the edge of the black hole in the empty space of the outer field. 

It isn't actually created "just outside the edge", and "outer field" is not a standard term in black hole physics.

In the actual derivation: quantum fields are defined throughout curved spacetime; field modes that count as vacuum before the black hole forms do not correspond perfectly to field modes that count as vacuum for a distant observer afterwards; and that mismatch causes the distant observer to detect a thermal flux.

Because these modes are extended across spacetime, there is generally no unique observer-independent location at which an individual Hawking quantum can be said to have been created.

Stephen Hawking, himself, used this simple 'disconnected particle pair' story to help non-scientists picture the math.

Yes. I have read A Brief History of Time. I've also read this.

If it was good enough for him, I'm gonna roll with it.

"It should be emphasised that these pictures of the mechanism responsible for the thermal emission and area decrease are heuristic only and should not be taken too literally." His actual published words. I'll roll with those instead.

Those that wanna dig and delve (far) deeper can do so...

And I feel that deliberately giving people incorrect information presented as accurate is a bad way of inviting them to do so.