Does a photon curve space-time, i.e., produce a gravitational field?

[yuiop]

I have read on a number of occasions that two parallel light beams do not gravitationally attract each other while two anti-parallel light beams do gravitationally attract each other. Is that true? If it is true, why does it work one way but not the other?

 

[xantox]

It is true. One may understand it more easily in linearized general relativity, where the first case arise by cancellation of the gravitomagnetic and gravitoelectric accelerations, while in the second they do add.

 

[Antenna Guy]

I have read on a number of occasions that two parallel light beams do not gravitationally attract each other while two anti-parallel light beams do gravitationally attract each other. Is that true? If it is true, why does it work one way but not the other?

If two parallel light beams pass through a gravitational field, do they remain parallel?

[Clarification: What do you mean by "anti-parallel"? I've seen reference to opposite vs. same direction, but not the way you put it.]

Regards,

Bill

 

[yuiop]

If two parallel light beams pass through a gravitational field, do they remain parallel?

[Clarification: What do you mean by "anti-parallel"? I've seen reference to opposite vs. same direction, but not the way you put it.]

Regards,

Bill

I always assumed the references to "anti-parallel" in this context to mean parallel beams with the photons in each beam moving in opposite directions as opposed to to two parallel beams that have photons moving in the same direction. That is just my interpretation. I assume we mean the same thing?

It might be added that it can be predicted that particles with rest mass behave in a similar way, with beams of massive particles gravitationally attracting each other more weakly at higher velocites when they are comoving and more strongly when the beams of massive particles are moving in opposite directions.

 

[Antenna Guy]

I always assumed the references to "anti-parallel" in this context to mean parallel beams with the photons in each beam moving in opposite directions as opposed to to two parallel beams that have photons moving in the same direction. That is just my interpretation. I assume we mean the same thing?

I read "anti-parallel" as not in same direction, and was wondering if you were including velocity components in opposite directions (rather than just velocities - as I had seen before).

Regards,

Bill

 

[Phrak]

http://en.wikipedia.org/wiki/Electromagnetic_stress-energy_tensor

Thanks, xantox.

 

[pmb_phy]

i begin with the notion that a photon moves at C. at C, distance has no meaning - there is no distance between things. ergo, a photon is essentially everywhere at once. and of course, our old general rule - you cannot say anything about a photon in between the time it is emitted and the time it is absorbed...

again, please feel free to knock that down.

You seem to have a particular wave function in mind. A initial quantum state is a given and can take on an arbitrary shape. It can be narrow step function which means that it is definitely located within a very small volume.

Again, you can't say anything until you measure something, and a measurement of the gravitational field, which is the measureable thing or (or rather its effects on a test particle) is the measurement. What can be said between measurements is that it is located somewhere within a light sphere centered on its emission point.

Pete

 

[pmb_phy]

I have read on a number of occasions that two parallel light beams do not gravitationally attract each other while two anti-parallel light beams do gravitationally attract each other. Is that true? If it is true, why does it work one way but not the other?

Yes. All that means is that the gravitational force is velocity dependent just like the Lorentz force. It doesn't mean that the field is absent.

Pete

 

[exponent137]

I will try with questions preparing for one old unanswered question.
If a photon (or better light ray) fly toward a black hole BH, I believe that it will move it.
If a photon curves it direction close to a BH it gives also some momentum to a BH. I believe this.
(I can advocate my view).
But my questions are, when these two photons gives momentum to a BH.
I suppose: When photon is one light-second close to a BH horizon, its loss of a small difference of its momentum come to a BH after one second. And so on.
I suppose that it is similarly with a photon with fly close to black hole.
This is approximately, but how it is more precisely? what is a light second length from horizon?

And final question. On https://www.physicsforums.com/showthread.php?t=147253" I get one
infinite term which describe force on a black hole.
I do not believe that infinite wide ray gives to a BH a infinite force. Where it is a mistake?