Why can gravity escape from a black hole?

[askmathquestions]

One of the leading theories of physics is that forces are mediated by virtual particles.

Well, it seems as though these virtual particles can escape a black hole. Why is that?

 

[PeterDonis]

See this Usenet Physics FAQ article:

https://math.ucr.edu/home/baez/physics/Relativity/BlackHoles/black_gravity.html

 

[Demystifier]

Well, it seems as though these virtual particles can escape a black hole. Why is that?

Virtual particles, of course, are just a computational tool, not real measurable physical objects. That's why they are called virtual, after all. Since they are just mathematical objects, not physical ones, they can "do" many things that physical objects can't. One of the things that virtual particles can "do", which real particles can't, is traveling backwards in time. Another thing that virtual particles can "do", which real particles can't, is traveling faster than light. Both traveling backwards in time and traveling faster than light are ways to escape from a black hole. But since virtual particles are just mathematical objects, the escapes of virtual particles are escapes of mathematical objects, no physical objects escape from the black hole.

 

[DaveC426913]

...since virtual particles are just mathematical objects, the escapes of virtual particles are escapes of mathematical objects, no physical objects escape from the black hole.

Isn't this, at its essence, the antithesis of science?
It's a model ... of a phenomenon that ... poorly models the phenomenon.

We throw those out and look for better models, yes?

OK, OK, I know, that, "as a computational tool it makes the math a lot easier", and "it models the phenomenon well in a majority of cases, just not all." Right? Kind of like classical Newtonian mechanics works in most cases.

But aren't virtual particles at the core of quantum gravity? And if they're a crummy model then surely they should not be used in any modern model. It would be like someone trying to revive classical Newtonian mechanics and stretch it to describe hyper-velocities and hyper-masses.

No?

 

[PeterDonis]

aren't virtual particles at the core of quantum gravity?

We don't know, because we don't have a testable theory of quantum gravity.

It's worth noting, though, that virtual particles aren't even necessarily "at the core" of other quantum field theories. They are a calculational tool, which we use because we either (a) don't know how to do the calculation any other way, or (b) don't have the time available to do the calculation any other way.

 

[PeterDonis]

One of the leading theories of physics is that forces are mediated by virtual particles in a particular approximate calculational scheme, perturbation theory, that works for many problems but does not work for all, and has to be adjusted by schemes like renormalization even for the problems for which it works.

See the bolded qualifiers. They're very important.

 

[askmathquestions]

So what is Hawking radiation if virtual particles are a purely made-up phenomena? Why did Stephan Hawking becomes so accredited for that radiation that it's named after him? What about the Casimir effect's "vacuum fluctuations"? Did physicsts lie when they said they reported the Casimir effect? Or, instead of calling all those physicists liars, might some remote form of virtual particles be a feasible model?

 

[PeterDonis]

what is Hawking radiation if virtual particles are a purely made-up phenomena?

Not virtual particles.

What about the Casimir effect's "vacuum fluctuations"?

The experiments verifying that the Casimir effect exists did not report "vacuum fluctuations". That's a theoretical interpretation, and a very limited one. See further comments below.

Did physicsts lie when they said they reported the Casimir effect?

Of course not, and nobody is claiming they did.

Or, instead of calling all those physicists liars, might some remote form of virtual particles be a feasible model?

We have a series of Insights articles on this; this one is probably a good place to start:

https://www.physicsforums.com/insights/misconceptions-virtual-particles/

 

[PeterDonis]

The OP question has been answered. Thread closed.