Physics near the event horizon

[PAllen]

"Crossing" was a poor choice of words on my part because it implies the observer having knowledge of the object being on the inside of the EH, which is impossible... "reaching" or "arriving at" is what I intended.

So I am to understand that being the observer, there will be a measurable length of time that it takes for me to see the object reach the EH, which can be predicted/calculated?

Thanks

No, again. Seeing has nothing to do with what is happening 'now'. We see galaxies as they were e.g. a billion years ago. We assume they still exist and can compute things about their current (now) state under reasonable assumptions for some choice of simultaneity convention (cosmologists actually have a 'standard' one they mean if nothing else is specified).

You never see an object reaching the event horizon. You definitely can compute when it is no longer in your causal future, and it becomes plausible to say the crossing has happened. There is an earliest such time (the time after which any signal you send reaches the test body inside the horizon), but there is no latest such time.

 

[Staticboson]

No, again. Seeing has nothing to do with what is happening 'now'. We see galaxies as they were e.g. a billion years ago. We assume they still exist and can compute things about their current (now) state under reasonable assumptions for some choice of simultaneity convention (cosmologists actually have a 'standard' one they mean if nothing else is specified).

You never see an object reaching the event horizon. You definitely can compute when it is no longer in your causal future, and it becomes plausible to say the crossing has happened. There is an earliest such time (the time after which any signal you send reaches the test body inside the horizon), but there is no latest such time.

I understand that the far galaxies I see are as they were billions of years ago and not where they are now. The information about where they are now is not accessible to me because it will take billions of years for the light of where they are "now" to reach me, and by that time they will be billions of light years farther away.

But my specific wondering was exactly about about what I see, purely the perception of the observer. Imagine the observer (me) is a caveman with no idea of what is actually happening out there (not far from the truth), he just sees the object falling into the black hole. Regardless of the fact that the object will fall into the black hole in "t" time... when will the caveman see it crossing the event horizon?

 

[PAllen]

I understand that the far galaxies I see are as they were billions of years ago and not where they are now. The information about where they are now is not accessible to me because it will take billions of years for the light of where they are "now" to reach me, and by that time they will be billions of light years farther away.

But my specific wondering was exactly about about what I see, purely the perception of the observer. Imagine the observer (me) is a caveman with no idea of what is actually happening out there (not far from the truth), he just sees the object falling into the black hole. Regardless of the fact that the object will fall into the black hole in "t" time... when will the caveman see it crossing the event horizon?

But you keep confusing and changing terms with every post. If you are talking about seeing, you are not talking about 'now'. Seeing is about something being in your causal past, not about something happening 'now'. It is trivially true that horizon crossing event will never be in your causal past, and thus will never be seen, because this is what defines a horizon.

There is a relevant example for cosmological horizons. I believe the numbers I am going to use are ballpark correct per current models, but if not, the example can be changed to be correct.

We currently see galaxies that are 3 billion light years away, and others that are 4 billion light years away (per standard cosmological conventions). For both, we can compute their 'now' state under reasonable assumptions and conventions. For the 3 billion light year away galaxies, we will, in many billions of years, see this 'now' state. For the 4 billion light year away galaxies, we will never see this now state (due to cosmological horizon created by expansion). Is it meaningful to say that the current now for 4 billion light year away galaxies never happens because we will never see it?

 

[PeterDonis]

when will the caveman see it crossing the event horizon?

He never sees it in the sense of receiving light rays from the event where it crosses the horizon. That's already been explained multiple times now.

 

[PeterDonis]

The OP question has been thoroughly addressed. Thread closed.