B Total % of Photons Redshifted While Moving Away From a Black Hole?

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Suppose a black hole with a radius equal to the radius of the observable universe exists and a fleet of coasting spacecraft are moving directly away from the black hole (along a similar vector) at very close to the speed of light with an amount of kinetic energy A with respect to the singularity that is very much greater than is necessary for escape velocity. Each spacecraft is emitting flashes of light evenly in all directions at regular intervals at a pre-agreed frequency.

As the value of A = kinetic energy per craft increases to arbitrarily higher values in various scenarios, will a greater % of photons become redshifted by gravitational redshift in transit between spacecraft as a result of the relativistic aberration, compared to scenarios where the value of A is much lower or in fact 0?
 
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A black hole with such a large radius cannot exist in the current universe. You first have to specify how your hypothetical universe that can have such a large black hole is supposed to look before the question can be answered.

Even if we assume a smaller black hole your question is unclear. A sketch might help.
 
A black hole with such a large radius cannot exist in the current universe. You first have to specify how your hypothetical universe that can have such a large black hole is supposed to look before the question can be answered.
The craft are at a distance 2 times the radius of the event horizon.
 
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You should show some effort here. This is essentially a homework problem, so you should make your own attempt and post it.
 
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an amount of kinetic energy A with respect to the singularity
There is no such thing. The singularity is not a place in space. This error by you has been corrected in previous threads.

gravitational redshift in transit between spacecraft as a result of the relativistic aberration
Relativistic aberration has nothing to do with redshift.
 
Relativistic aberration has nothing to do with redshift.
If I understand this correctly you are saying additional v won't cause additional % intercepted photons redshift.
 
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If I understand this correctly you are saying additional v won't cause additional % intercepted photons redshift.
No, I'm saying that aberration has nothing to do with redshift. Aberration has to do with the direction of light, not its frequency.
 
Aberration has to do with the direction of light, not its frequency.
Are you saying if additional v causes additional aberration (away from the black hole), a higher % of photons will be redshifted upon interception or not?
 
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As the value of A = kinetic energy per craft increases to arbitrarily higher values in various scenarios, will a greater % of photons become redshifted by gravitational redshift
Gravitational redshift is a property of the spacetime geometry. Since the spacetime geometry is independent of how your spacecraft move, it would seem like the answer to this is "no".

However, gravitational redshift is not the only kind of redshift. But you have given no information that would allow you to assess any other kinds of redshift.
 
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Are you saying if additional v causes additional aberration (away from the black hole), a higher % of photons will be redshifted upon interception or not?
I don't understand why you keep asking about aberration when I've said twice now that aberration has nothing to do with redshift.
 
I don't understand why you keep asking about aberration when I've said twice now that aberration has nothing to do with redshift.
https://en.wikipedia.org/wiki/Relativistic_aberration
"the rays of light from the source which reach the observer are tilted towards the direction of the source's motion (relative to the observer)"
\cos \theta_o=\frac{\cos \theta_s-\frac{v}{c}}{1-\frac{v}{c} \cos \theta_s} \,


^If I understand this passage correctly, If the observer is farther away from the black hole than the fleet of ships, this excerpt means that when the ships travel with faster v away from the black hole, a greater % of photons which were initially emitted equally in all directions in the rest frame of a craft, will be directed away from the black hole by the aberration, and since a greater proportion of photons will be directed away from the black hole when the craft are moving faster, a greater % of photons will become redshifted when the craft move faster due to the gravitational doppler effect, unless I'm mistaken.

Similar reasoning why in a collision between a 20gev positron followed by a 20gev + 1ev electron* from the same gun in the same direction gives 2 photons traveling in almost the same direction from the lab frame.

*edit
 
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when the ships travel with faster v away from the black hole
Ok, so here ##v## is relative to an observer who is "hovering" at a constant altitude above the hole's horizon.

a greater % of photons which were initially emitted equally in all directions in the rest frame of a craft, will be directed away from the black hole by the aberration
If ##v## is interpreted as above, yes, this is true.

a greater % of photons will become redshifted when the craft move faster due to the gravitational doppler effect
There is no such thing as "gravitational doppler effect". There is gravitational redshift, but it has nothing to do with relative motion, which is what "doppler effect" refers to.

There will be gravitational redshift in this scenario, but there will also be doppler blueshift because the light source (the spaceship flying outward) is moving towards the observer. Which effect dominates will depend on the relative velocity and the altitude change from the spaceship to the observer.
 
There is no such thing as "gravitational doppler effect".
Sorry I thought I had originally typed "gravitational redshift..." either my memory is fuzzy or someone had edited it for me...
 
There will be gravitational redshift in this scenario, but there will also be doppler blueshift because the light source (the spaceship flying outward) is moving towards the observer.
I had intended for the only observers in the scenario to be the almost-comoving fleet of craft. Some at higher or lower altitudes above the black hole, some at similar altitudes, and a variety of separation distances between them. I wondered if the "common comoving" velocity upwards is arbitrarily high enough, if it could lead to a scenario where nearly all the flashes observed between ships could be redshifted, even if they are slightly moving towards each other, and especially as the separation distance between them increases...
 
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I had intended for the only observers in the scenario to be the almost-comoving fleet of craft.
Then there is no aberration or doppler shift because the observers are not moving relative to the source.

I wondered if the "common comoving" velocity upwards is arbitrarily high enough, if it could lead to a scenario where nearly all the flashes observed between ships could be redshifted
As I said before, gravitational redshift is a property of the spacetime geometry, which is unaffected by the motion of the ships.
 
Then there is no aberration or doppler shift because the observers are not moving relative to the source.
I thought I had read somewhere that unlike the velocity redshift where the observed redshift depends on the observers velocity, that the gravitational redshift was different somehow in that (in plain language) "all observers agree the photon is losing energy" as it climbs out of a gravity well, but after a quick search I couldn't find the reference.
 
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Suppose a black hole with a radius equal to the radius of the observable universe exists and a fleet of coasting spacecraft are moving directly away from the black hole (along a similar vector) at very close to the speed of light with an amount of kinetic energy A with respect to the singularity that is very much greater than is necessary for escape velocity. Each spacecraft is emitting flashes of light evenly in all directions at regular intervals at a pre-agreed frequency.

As the value of A = kinetic energy per craft increases to arbitrarily higher values in various scenarios, will a greater % of photons become redshifted by gravitational redshift in transit between spacecraft as a result of the relativistic aberration, compared to scenarios where the value of A is much lower or in fact 0?


If we cut off some unessential stuff and some problematic stuff, then there is a gravity field and some free-fallers that send signals to each other. For those free-fallers everything works like there was no gravity field.

So the question has been answered. Free-fallers do not observe redshifts.

Well perhaps we, "outside observers", want to even better understand why the free-fallers did not observe redshift, although we can observe a redshift occurring by dangling some measuring devices at the locations where the signals are emitted and absorbed?
 
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a greater % of photons which were initially emitted equally in all directions in the rest frame of a craft, will be directed away from the black hole by the aberration
If vvv is interpreted as above, yes, this is true.
If we cut off some unessential stuff and some problematic stuff, then there is a gravity field and some free-fallers that send signals to each other. For those free-fallers everything works like there was no gravity field.

So the question has been answered. Free-fallers do not observe redshifts.
I’m confused by this point. In the scenarios when the craft are moving faster (for example .99999999999999999995c or greater), a very high % of total photons emitted by the craft will be moving away from the black hole as a result of the relativistic aberration, and since photons moving away from black holes become redshifted, I struggle to understand how, with such a very high % of the photons traveling on vectors away from the black hole they will not be redshifted in transit between distantly separated craft, in proportion to their separation distance.
 
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I struggle to understand how, with such a very high % of the photons traveling on vectors away from the black hole they will not be redshifted in transit between distantly separated craft, in proportion to their separation distance.
If the separation distance is small enough, all of the spaceships, since they are all in free fall, can be treated as being at rest in some local inertial frame during the flight time of any particular photon. This is the case that @jartsa is describing, and in this case, there is no gravitational redshift observable. (From the viewpoint of an observer who is hovering at a fixed altitude, the ships are close enough together that their altitude does not change significantly during the flight time of any particular photon.)

If the separation distance is not so small, then the ships will cover a large enough region of spacetime during the flight time of any particular photon that they cannot be treated as all being at rest in a single inertial frame during that flight time. In that case, gravitational redshift will be observable.
 
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I’m confused by this point. In the scenarios when the craft are moving faster (for example .99999999999999999995c or greater), a very high % of total photons emitted by the craft will be moving away from the black hole as a result of the relativistic aberration, and since photons moving away from black holes become redshifted, I struggle to understand how, with such a very high % of the photons traveling on vectors away from the black hole they will not be redshifted in transit between distantly separated craft, in proportion to their separation distance.

I did not say photons do not become redshifted. I said free-fallers do not observe a redshift.


How about if we (I mean you:smile:) calculate:

1) How much is light emitted by an object moving at speed .99999999999999999995c blueshifted?

(light is emitted to the direction of the motion)

2) How much is light absorbed by an object moving at speed .99999999999999999994c redshifted?

(object and light move to parallel directions)

That last one is the same calculation as how much is light emitted by an objectct moving at speed .99999999999999999994c redshifted when the light is emitted to the direction opposite to the motion of the object.


3) The net effect of those two two shifts.

That net effect is probably quite large, like blueshift by a factor of 1.00001 or something. (Well if you expected a factor of 1.0000000000000000001 then 1.00001 is large)


(And that blueshitft might cancel out gravitational redshift)
 
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If the separation distance is not so small, then the ships will cover a large enough region of spacetime during the flight time of any particular photon that they cannot be treated as all being at rest in a single inertial frame during that flight time. In that case, gravitational redshift will be observable.
Actually, I'm not sure this is true if the ships are in free fall, since they will decelerate (relative to hovering observers) while each photon is in flight. I would have to do the math to see if this exactly cancels the gravitational redshift in the general case, but intuitively it seems like it ought to.
 
If the separation distance is not so small, then the ships will cover a large enough region of spacetime during the flight time of any particular photon that they cannot be treated as all being at rest in a single inertial frame during that flight time. In that case, gravitational redshift will be observable.
I did not say photons do not become redshifted. I said free-fallers do not observe a redshift.
Is there still some disagreement about what the outcome would be?

Let me recap. In the scenario there is a black hole with a radius of the observable universe and a fleet of coasting, co-moving ships with a variety of heights above the blackhole and a variety of separation distances between them, but they are in a region of space roughly 2 black hole radii from the geometric center of the black hole, and the co-moving velocity of the ships is on a vector directly away from the black hole at an arbitrarily high speed close to the speed of light (co-moving at 0.999999999999999995c or greater in various different scenarios) with respect to the black hole. The only observers are the co-moving astronauts on the ships, and the ships are emitting flashes at regular intervals, equally in all directions, on a pre-agreed frequency.

Questions:

Will the relativistic aberration cause a higher and higher % of total photons to travel on vectors which increase in distance from the black hole over time, as the ships co-moving velocity increases in different scenarios?

In a given scenario (for example if 99.99999999999999% of total photons are moving away from the black hole), will the photons become redshifted from gravitational redshift during their flight times between craft?

^If yes, Will the measured gravitational redshift increase (as measured by an observer on one of the craft) as the separation distance between the craft increases in different scenarios (longer flight times between craft)?
 
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