[jeffreyH (OP)]

If we have a photon that is traveling on a path that takes it exactly towards the centre of gravity of a black hole how would the gravity affect its speed? When a photon is moving away from a source its wavelength is red shifted. Would we get a blue shift and an increase in energy? How much of this would be kinetic?

[Atomic-S]

When a photon is moving away from a source its wavelength is red shifted.

It depends. What is the reference frame of the photon's observer?

The speed of the photon as viewed by any observer near it will be simply c.  The speed of the photon as seen by a different observer could be calculated by noting the relationship between space and time measured by that observer vs. space and time as it applies in the vicinity of the photon.  I believe the answer to that, in the situation you propose, is that a clock near the black hole will run slower than one far away, so that in a given interval of far-away-observer time, the photon will have undergone, as seen by that observer, less time, meaning that because it is traveling at c in its own reference frame, it will have traveled a shorter distance in its frame than the clock of the observer says it should. However, we also have to take into account the difference in spatial measures. I understand that a given length near the black hole, measured radially by a local observer, will measure longer than it will appear to be to a distant observer.  That, if correct (and I am not absolutely certain), would indicate that not only does the photon travel a lesser distance in the lesser time, but the distance that it does travel will appear less to the remote observer than it will locally. both of these phenomena would result in the photon appearing, to the remote observer, to slow down as it approached the black hole, eventually approaching an apparent speed of zero.

[Atomic-S]

As pertains to the energy relationships:  An observer near the hole observes the clock far from the hole running faster than his, so that a wave emitted from far will appear to be in sync with that faster clock, and will therefore have a higher frequency than a wave emitted by a like apparatus located  near the hole. this is a blue-shift. Because the number of photons will remain unchanged by traveling, and because the quantum energy increases with frequency, the light upon arrival near the hole will have more energy as seen by the near observer than it did when it began its journey from afar as seen by the far observer.

[yor_on]

yep, it's relationships, set in an idea of conservation laws keeping count. So if we assumed that we actually could observe a photon from several positions in a SpaceTime, we would get different definitions. It's a good example of what I call using a 'container model' to describe it. In reality that 'photon' will interact just once, in its annihilation. To that you can add a 'recoil' observed as whatever it leaves react to it.

[jeffreyH (OP)]

Another thing that came to mind with regard to photons and black hole is the mass in the accretion disk and perhaps the ergosphere. Gravitational fields that are in opposition will partially cancel. This is most evident in a cavity at the centre of gravity of a massive body. Depending upon the amount of mass in the ergosphere or accretion disk there will be a gravitational field that can in effect cancel some of the gravitation of the black hole at the event horizon. This could mean that the effective horizon may shrink and that light could in effect exit the horizon due to this cancelling effect. It may be a miniscule effect but any effect should show some decrease in the radius of the horizon.

This does not mean that the black hole will necessarily lose mass but that photons generated just inside the horizon may be able to escape. I am really not sure if this is right but I can't off the top of my head think of why it shouldn't be that way. If this were true then that puts a dent in the current view of information loss. If we had two black holes orbiting each other at fairly close range then this cancellation could reduce the horizon of each by a significant amount.

[JohnDuffield]

If we have a photon that is traveling on a path that takes it exactly towards the centre of gravity of a black hole how would the gravity affect its speed?

It slows down. Yes. Check out the coordinate speed of light.

When a photon is moving away from a source its wavelength is red shifted. Would we get a blue shift and an increase in energy? How much of this would be kinetic?

People say the ascending photon is redshifted, but actually, it doesn't change. Conservation of energy applies. In similar vein people say the descending photon is blueshifted, but again, it doesn't change, and conservation of energy applies. You can work this out by sending a 511keV photon into that black hole. Ask yourself this: by how much does the black hole mass increase? The answer is 511keV/c². Not a gazillion tons. Also ask yourself this: if you accelerate towards a 511keV photon, does it get blueshifted? The answer is that actually, the photon doesn't change a jot. Your measurement of its frequency and energy changes because you moved. But again, conservation of energy applies.

If this were true then that puts a dent in the current view of information loss.

You should read about Friedwardt Winterberg's firewall.  I think it destroys the current view of information loss. Meh, I'm an IT guy, and something of an amateur relativist. I am not impressed with cosmologists talking about information as if it was some physical thing.   

what is the ctually, it doesn't change. uis

[PmbPhy]

If we have a photon that is traveling on a path that takes it exactly towards the centre of gravity of a black hole how would the gravity affect its speed?

The coordinate speed of the photon will change as it moves towards the event horozon.

When a photon is moving away from a source its wavelength is red shifted.

Gravitational redshift is only observed when local observers at different positions compare their measurements. The wavelength as measured by  Schwarzschild observers remains unchanged.

For details on potential and kinetic energy of a photon see
http://home.comcast.net/~peter.m.brown/gr/grav_red_shift.htm

[jeffreyH (OP)]

If we have a photon that is traveling on a path that takes it exactly towards the centre of gravity of a black hole how would the gravity affect its speed?

The coordinate speed of the photon will change as it moves towards the event horozon.

When a photon is moving away from a source its wavelength is red shifted.

Gravitational redshift is only observed when local observers at different positions compare their measurements. The wavelength as measured by  Schwarzschild observers remains unchanged.

For details on potential and kinetic energy of a photon see
http://home.comcast.net/~peter.m.brown/gr/grav_red_shift.htm

Thanks Pete. I asked this because I really don't know. I haven't had time to look at your page but I will later and respond.

[jeffreyH (OP)]

I have just read the first part of your page and I noted the two time axes. This is actually a method I hadn't thought of. Do you believe that? I will read more later. The hour is late.

[JohnDuffield]

The coordinate speed of the photon will change as it moves towards the event horozon.

See what Einstein said:

"Second, this consequence shows that the law of the constancy of the speed of light no longer holds, according to the general theory of relativity, in spaces that have gravitational fields. As a simple geometric consideration shows, the curvature of light rays occurs only in spaces where the speed of light is spatially variable".

Rather counter-intuitively, the descending photon slows down, and the ascending photon speed up. The "modern" interpretation of general relativity says the speed doesn't change, but this is not in line with what you might call the Einstein interpretation of general relativity.

Gravitational redshift is only observed when local observers at different positions compare their measurements. The wavelength as measured by  Schwarzschild observers remains unchanged.

Good man.

For details on potential and kinetic energy of a photon see http://home.comcast.net/~peter.m.brown/gr/grav_red_shift.htm

I noticed the total energy of a photon moving through a gravitational field is constant. That's nice to see. I wish more people knew it. And that it's the same for a falling brick. 

[jeffreyH (OP)]

If we have a photon that is traveling on a path that takes it exactly towards the centre of gravity of a black hole how would the gravity affect its speed?

The coordinate speed of the photon will change as it moves towards the event horozon.

When a photon is moving away from a source its wavelength is red shifted.

Gravitational redshift is only observed when local observers at different positions compare their measurements. The wavelength as measured by  Schwarzschild observers remains unchanged.

For details on potential and kinetic energy of a photon see
http://home.comcast.net/~peter.m.brown/gr/grav_red_shift.htm

Well your page has cleared up a lot of questions for me. Especially on the conservation of energy in a gravitational field. Would you mind if I used the equations?

[dlorde]

.. This could mean that the effective horizon may shrink and that light could in effect exit the horizon due to this cancelling effect. It may be a miniscule effect but any effect should show some decrease in the radius of the horizon.
...
This does not mean that the black hole will necessarily lose mass but that photons generated just inside the horizon may be able to escape.

I can see why the horizon might shrink, but light would still not escape from it - but it would be able to escape from where the horizon would have been be if it hadn't shrunk. As I understand it, the horizon is defined as the point where light can't escape.

[jeffreyH (OP)]

.. This could mean that the effective horizon may shrink and that light could in effect exit the horizon due to this cancelling effect. It may be a miniscule effect but any effect should show some decrease in the radius of the horizon.
...
This does not mean that the black hole will necessarily lose mass but that photons generated just inside the horizon may be able to escape.

I can see why the horizon might shrink, but light would still not escape from it - but it would be able to escape from where the horizon would have been be if it hadn't shrunk. As I understand it, the horizon is defined as the point where light can't escape.

Yes that is the point. If we have two equivalent black holes that are in the process of merging the horizons of both may shrink radically, releasing tell tale gamma ray bursts. As galaxies merge it may be that gamma ray bursts are releases of trapped energy from temporarily cancelled fields inside the horizon. The cancellation allowing high energy photons to escape. How fast would this phenomena happen?

[PmbPhy]

Jeff - Take a look at the chapters of the new version of Exploring Black Holes. They're online at
http://www.eftaylor.com/exploringblackholes/

Especially the chapter GlobalLightBeams141029v2.pdf

[PmbPhy]

.. This could mean that the effective horizon may shrink and that light could in effect exit the horizon due to this cancelling effect. It may be a miniscule effect but any effect should show some decrease in the radius of the horizon.
...
This does not mean that the black hole will necessarily lose mass but that photons generated just inside the horizon may be able to escape.

I can see why the horizon might shrink, but light would still not escape from it - but it would be able to escape from where the horizon would have been be if it hadn't shrunk. As I understand it, the horizon is defined as the point where light can't escape.

Yes that is the point. If we have two equivalent black holes that are in the process of merging the horizons of both may shrink radically, releasing tell tale gamma ray bursts. As galaxies merge it may be that gamma ray bursts are releases of trapped energy from temporarily cancelled fields inside the horizon. The cancellation allowing high energy photons to escape. How fast would this phenomena happen?

There is a formula to determine what the value of the remaining black hole is. Obviously its a function of the two radii and is larger than either.

[jeffreyH (OP)]

.. This could mean that the effective horizon may shrink and that light could in effect exit the horizon due to this cancelling effect. It may be a miniscule effect but any effect should show some decrease in the radius of the horizon.
...
This does not mean that the black hole will necessarily lose mass but that photons generated just inside the horizon may be able to escape.

I can see why the horizon might shrink, but light would still not escape from it - but it would be able to escape from where the horizon would have been be if it hadn't shrunk. As I understand it, the horizon is defined as the point where light can't escape.

Yes that is the point. If we have two equivalent black holes that are in the process of merging the horizons of both may shrink radically, releasing tell tale gamma ray bursts. As galaxies merge it may be that gamma ray bursts are releases of trapped energy from temporarily cancelled fields inside the horizon. The cancellation allowing high energy photons to escape. How fast would this phenomena happen?

There is a formula to determine what the value of the remaining black hole is. Obviously its a function of the two radii and is larger than either.

Thanks for the information Pete I will be reading it while I wait for a new book on Lagrangians and Hamiltonians. I may be back asking question!

[PmbPhy]

Thanks for the information Pete I will be reading it while I wait for a new book on Lagrangians and Hamiltonians.

What book is that?

[JohnDuffield]

Thanks for the information Pete I will be reading it while I wait for a new book on Lagrangians and Hamiltonians. I may be back asking question!

I recommend some caution. It's a renowned text, but there are... issues. I think the best way to show this is with why doesn’t the light get out?
 
You're standing on a gedanken planet holding a laser pointer straight up. The light doesn't curve round, or slow down as it ascends, or fall down. It goes straight up. Now I wave my magic wand and make the planet denser and more massive. The light still doesn't curve round, or slow down as it ascends, or fall down. I make the planet even denser and more massive. The light still doesn't curve round, or slow down as it ascends, or fall down. I make the planet even denser and more massive, and take it to the limit such that it's a black hole. At no point did the light ever curve round, or slow down as it ascends, or fall down. So why doesn't the light get out?
 
Note that some people might answer with the waterfall analogy. It’s wrong, because a gravitational field is a region of inhomogeneous space which we model as curved spacetime. See this Einstein quote and this paper. A gravitational field alters the motion of light and matter through space, but it doesn’t suck space in. We do not live in a Chicken-Little world where the sky is falling in.

[jeffreyH (OP)]

Thanks for the information Pete I will be reading it while I wait for a new book on Lagrangians and Hamiltonians. I may be back asking question!

I recommend some caution. It's a renowned text, but there are... issues. I think the best way to show this is with why doesn’t the light get out?
 
You're standing on a gedanken planet holding a laser pointer straight up. The light doesn't curve round, or slow down as it ascends, or fall down. It goes straight up. Now I wave my magic wand and make the planet denser and more massive. The light still doesn't curve round, or slow down as it ascends, or fall down. I make the planet even denser and more massive. The light still doesn't curve round, or slow down as it ascends, or fall down. I make the planet even denser and more massive, and take it to the limit such that it's a black hole. At no point did the light ever curve round, or slow down as it ascends, or fall down. So why doesn't the light get out?
 
Note that some people might answer with the waterfall analogy. It’s wrong, because a gravitational field is a region of inhomogeneous space which we model as curved spacetime. See this Einstein quote and this paper. A gravitational field alters the motion of light and matter through space, but it doesn’t suck space in. We do not live in a Chicken-Little world where the sky is falling in.

I never take anything at face value. I will read it without reference to anything else simply because I don't want to start with a slanted view. There are real difficulties with gravitation that no one has an answer to. The main difficulty is in experimental validation for some of the more extreme macroscopic or microscopic environments.

[JohnDuffield]

I don't think there's much of a problem with gravitation myself, or that nobody has answers. But I think there is a problem wherein what's taught just doesn't square with what Einstein said. Pete wrote about it in this paper. I share his sentiment about "Einstein's general relativity" and "modern general relativity", but I think the issues are greater than he appreciates. I recommend that you understand why doesn't the light get out? IMHO it really gets to the heart of things.