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blaksheep423
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Do photons produce gravitational fields, even though they are massless? In other words, can a photon's gravity affect other photons or elementary particles?
Only if the photon were emitting gravitytional waves - which it can't, as it cannot change with time.causing a "gravity boom"
Do photons accelerate in the weak-field approximation when their path is bent by a massive body? If so why wouldn't this result in gravitational waves?Ich said:Only if the photon were emitting gravitytional waves - which it can't, as it cannot change with time.
Would a single electron emit http://en.wikipedia.org/wiki/Cherenkov_radiation" if it moves exactly at the speed of light in the surrounding medium? Is this a valid analogy to a photon causing a "gravity boom"?Ich said:Only if the photon were emitting gravitational waves - which it can't, as it cannot change with time.
A.T. said:Would a single electron emit http://en.wikipedia.org/wiki/Cherenkov_radiation" if it moves exactly at the speed of light in the surrounding medium?
A.T. said:Is this a valid analogy to a photon causing a "gravity boom"?
So a photon whose path was bent by a gravitational source, or which could even be in orbit around a black hole, would not emit gravitational radiation? But a massive object orbiting or having its path bent by a gravitational source would emit gravitational radiation, correct?Vanadium 50 said:A photon bends spacetime. It does not, by itself, emit gravitational radiation, although it might be part of a system that does.
If you had a point particle orbiting a large gravitational source, could the combined system emit gravitational waves even if the point particle's mass was negligible compared to the source, so that the source itself was not being affected in any appreciable way by the point particle?Vanadium 50 said:No single particle can emit gravitational radiation. You need a changing gravitational quadrupole moment, and that means you need multiple particles.
blaksheep423 said:ok, then the next question I've been wondering about is this:
if gravity propagates at c, and photons move at the exact same velocity, could a photon traveling in a straight line be constantly affected by it's own gravity at any single point? if so, wouldn't the gravity of each point of the photon's path add up continuously, causing a "gravity boom" ...
Why do you say it doesn't bend space? Anything with energy should contribute to the curvature of spacetime, no?Phrak said:Take your question and ask about pulsed lasers instead. With this, there is a particle-like region that is not a massive particle. Since it's light and not a 'massive particle' it doesn't bend space like electrons, protons, and atoms 'n stuff. Massive particles travel less than the speed of light. All massless particles travel at the speed of light.
JesseM said:Why do you say it doesn't bend space? Anything with energy should contribute to the curvature of spacetime, no?
edit: this thread has a short discussion of how light can curve spacetime...
My mistake, when you said "it doesn't bend space like electrons, protons, and atoms 'n stuff" I thought you were saying it was unlike those other particles in that it didn't bend space, but I guess you were saying it bends space in a different manner than massive particles (I should have noticed that you went on to say 'Light is not massive so we need someone who has some idea of how light bends space and time to answer this').Phrak said:But I didn't sat that... Or didn't mean to. Light doesn't bend space and time the same as massive particles. Good of you to bring it up.
JesseM said:My mistake, when you said "it doesn't bend space like electrons, protons, and atoms 'n stuff" I thought you were saying it was unlike those other particles in that it didn't bend space, but I guess you were saying it bends space in a different manner than massive particles (I should have noticed that you went on to say 'Light is not massive so we need someone who has some idea of how light bends space and time to answer this').
If you look into it a little more the Wikipedia description is actually an incorrect description of the AS Ultraboost, which is why I did not post a link to it:Phrak said:Wikipedia: "In general relativity, the Aichelburg-Sexl ultraboost is an exact solution which models the physical experience of an observer moving past a spherically symmetric gravitating object at nearly the speed of light."
I'm not sure this counts?? The object is massive so has a different stress-energy tensor...
DaleSpam said:If you look into it a little more the Wikipedia description is actually an incorrect description of the AS Ultraboost, which is why I did not post a link to it
DaleSpam said:If you look into it a little more the Wikipedia description is actually an incorrect description of the AS Ultraboost, which is why I did not post a link to it:
First, the spherically symmetric gravitating object is not moving at "nearly" the speed of light, but actually at the speed of light. This is not possible for a massive object but is possible for light. Second, there is no event horizon which is different from the spacetime for spherically symmetric massive objects, but is correct for light. Third, the AS Ultraboost is one of a general class of solutions to the EFE called pp-waves all of which model radiation moving at the speed of light.
To be fair to Wikipedia, they are not the only ones who say that, but it is incorrect when you look into the details. Of course to a first-order approximation it is good as long as the mass is really close to c and far from the event horizon.
According to the theory of general relativity, photons produce gravitational fields because they have energy and momentum. This energy and momentum can cause a curvature in space-time, which is what we perceive as gravity.
Yes, all photons produce gravitational fields. However, the strength of the gravitational field produced by a photon depends on its energy and momentum. Higher energy photons will produce a stronger gravitational field than lower energy photons.
Yes, photons can be affected by their own gravitational fields. This is known as self-gravitation and it is a consequence of the theory of general relativity. However, the effect is very small and is usually only observed in extreme situations such as near a black hole.
We can indirectly detect the gravitational fields produced by photons through their effects on other objects or particles. For example, we can observe the bending of light around massive objects, which is caused by the gravitational field of the photons. We can also detect the gravitational redshift of light, which is another consequence of the interaction between photons and gravity.
Yes, there are several experiments and observations that support the idea of photons producing gravitational fields. One of the most famous examples is the observation of the bending of starlight during a solar eclipse, which was predicted by Einstein's theory of general relativity. Other observations, such as the gravitational redshift of light from distant objects, also support the concept of photons producing gravitational fields.