On 4/11/2022 12:47 AM, smitra wrote:
On 11-04-2022 09:19, Bruce Kellett wrote:
On Mon, Apr 11, 2022 at 3:58 PM smitra <smi...@zonnet.nl> wrote:

On 10-04-2022 06:15, Bruce Kellett wrote:

Not relevant, since there is no enclosing reflecting boundary.

Yes there is.

Where is it then?

One can also consider an observation inside the event
horizon of a supermassive black hole. No photons escape from there.

We are not currently inside a supermassive black hole. Besides, you
knowledge of BH physics seems somewhat faulty. Inside the horizon, all
particles move towards the singularity at r = 0 (because that is the
forward direction of time). So there is no reflection off the inside
of the horizon. That is a fanciful (and wrong) idea.

The escaping Hawking radiation is so small that it doesn't contain

And since you are attempting to promote a FAPP argument to an in
principle argument, you also have to consider that the space
is not a perfect vacuum, so photons do not travel at exactly the
of light. This means that in principle one can retrieve the escaping


I don;t think the difference between c, the speed of light in a
vacuum, and the speed of light in outer space is a relevant
consideration -- you still are not going to catch and reverse those IR

That's all FAPP, not in principle. The laws of physics are reversible, it requires a rigorous argument from the fundamental laws of physics to demonstrate that reversing a measurement is impossible. Arguing from a practical situation and pointing to immense difficulties is a FAPP argument.

You seem to think the purpose of physics is to study the consequences of equations.  If something is impossible to observe, I think the purpose of physics is to explain why it's impossible.


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