The attractive force of photons on other photons & matter

[Pauljamestill]

Summary: massless particles (or at least photons) are attracted to other photons and to matter, but which is most attractive, and why ...

Summary: massless particles (or at least photons) are attracted to other photons and to matter, but which is most attractive, and why ...

I am really hoping someone might be able to offer a solution or at least offer guidance on something that is interesting me - are massless particles more attracted to particles with mass or other massless particles.

A good example to work with could be photons: is light more attracted to matter or to other photons...

High-power laser beams can bend other laser beams, which means that streams of light do affect each others trajectory; streams of light attract other streams of light (proved by the harvard biophotonics group, I believe)

&

In 1919, four years after Einstein fully formulated his theory of gravity, his General Theory of Relativity, it was proven that light could indeed find itself attracted to objects with mass by measuring how much a beam of light could bend in their vicinity.

I would really love to know which provides most attraction. And if so, I’d love to know why.

I’ll look forward to anyone who might be able to shed a little, eh, light.

Best wishes
James

 

[phinds]

in GR what matters is the stress-energy tensor and while photons are massless they do not have a zero stress-energy tensor value and therefore they follow geodesics in space-time, which in other words means they are "attracted" (not really the right word) to massive objects (thus "Einstein Rings").

Since two photons each have non-zero values of stress-energy tensor, they do "attract" each other but to such a trivial extent that calling it "negligible" would be grossly overstating the attractiveness.

 

[Nugatory]

One caution here: The observed phenomenon we're talking about here is the deflection of a beam of light by gravitational effects. It's not clear that this phenomenon can be understood in terms of a force on photons, or even that that notion is meaningful.

 

[Pauljamestill]

I’m so thrilled that you two have taken the time to share your thoguhts, I really appreciate it.

I have had to go away for a weeks but I’m excited to look into what you’re shared and I will respond and thank you all, hopefully soon

Best wishes
Paul

 

[Haelfix]

For the general notion of the deflection of light by gravitational effects, the effect can also be studied in the weak field limit where there is a certain notion of 'force'.

The calculations for this are quite illuminating actually and can lead to quite paradoxical results, such as for the case of two photons. It turns out that they do NOT attract each other gravitationally if they are traveling parallel to each other. On the other hand they do attract each other gravitationally if they are traveling antiparallel.

This was shown long ago by Tolman and Ehrenfest, and was shown in the context of field theory by Wheeler.

 

[chaszz]

The spacetime near a star is bent by the star’s gravity. A photon traveling through that spacetime follows the bent pathway. According to Einstein, this a more accurate way of describing it than speaking of “attraction.”