Re: Redshifted image outside event horizon

rob langley <rhlangley@xxxxxxxxxxxxx> wrote:
Would be grateful if someone could please put me right on this and/or direct
me to ArXiv references -

Alice stays outside the BH at some 'safe' distance and Bob enters. Alice
watches while Bob (apparently) slows down as he approaches the horizon, and
she also sees his image become increasingly redshifted.
1. Is this merely an image, or something more substantial?

It's merely an image. There's a nice discussion of this in
key = {Misner73},
author = {Charles W. Misner and Kip S. Thorne and John A. Wheeler},
title = {Gravitation},
publisher = {W. H. Freeman},
address = {San Francisco},
year = 1973

2. If Alice approaches the horizon herself where Bob's image 'is', what
would she find?

Just the photons which make up the image. The Misner, Thorne, and Wheeler
discussion makes this clear.

3. If she is moves WRT the BH, presumably she will see that the image is 3D?

Yes (and very distorted and very faint, too).

4. What happens to Bob's image if the BH is spinning?

I've never seen anyone work this out in quantitative detail.
Might be a nice student project...

-- Jonathan Thornburg (remove -animal to reply) <J.Thornburg@xxxxxxxxxxxxxxxxx>
School of Mathematics, U of Southampton, England
"Washing one's hands of the conflict between the powerful and the
powerless means to side with the powerful, not to be neutral."
-- quote by Freire / poster by Oxfam