Why light beams attract or repel each other even when they don't have charge

[SunRay-dvsh]

Hi,

Can someone please explain as to why light beams attract or repel each other even when they don't have charge. Seems like it behaves like two current carrying parallel wires. There is very little material about this which goes completely above the head.

Thanks

 

[BvU]

There is very little material about this which goes completely above the head

Is that good or bad ?
Can you indicate where you got this idea about light beams that attract or repel each other ?

 

[Demystifier]

Perhaps he is talking about bunching and anti-bunching in quantum optics. If so, it is caused by specific entanglement between photons in a light beam.

 

[Mentz114]

Hi,

Can someone please explain as to why light beams attract or repel each other even when they don't have charge. Seems like it behaves like two current carrying parallel wires. There is very little material about this which goes completely above the head.

Thanks

There is a gravitational effect see
(https://www.physicsforums.com/threads/parallel-light-beams-converge.473694/)

 

[vanhees71]

...and there is Delbrück scattering, recently observed for the first time by the ATLAS collaboration at the LHC, but it's of course not about light beams in the visible spectrum but for high-energy photons in ultraperipheral heavy-ion (Pb-Pb) collisions:

https://home.cern/about/updates/2017/08/atlas-observes-direct-evidence-light-light-scattering

 

[pervect]

Parallel light beams going in the same direction don't attract each other gravitationally. Parallel light beams going in the opposite direction do attract gravitationally, about 4x as strong as one gets by a naive calculation.

 

[Vanadium 50]

There is very little material about this which goes completely above the head.

Before we determine why something is true, we need to determine if it is true.

 

[SunRay-dvsh]

+Bvu

Thank you all for your replies. Please see this article:

https://en.wikipedia.org/wiki/Optical_force

 

[SunRay-dvsh]

Perhaps he is talking about bunching and anti-bunching in quantum optics. If so, it is caused by specific entanglement between photons in a light beam.

Hello,
I couldn't find any reference to bunching or anti-bunching. I hope this article helps: http://discovermagazine.com/2010/jan-feb/083

Thank You

 

[vanhees71]

Well, you should refer to the true "story", which in this case can be found here:

https://www.nature.com/articles/nature07545
https://www.researchgate.net/publication/23501103_Harnessing_optical_forces_in_integrated_photonic_circuits

All this has nothing to do with gravitational interaction between light beams of course but is about the forces of electromagnetic fields on charged particles/matter.

 

[Demystifier]

Thank you all for your replies. Please see this article:
https://en.wikipedia.org/wiki/Optical_force

Now I get it. This is not a force between light beams as such, but a force between waveguides of the light beams. The light beams induce the dipole moments in the guides, and those dipole moments cause the force. The effect is very similar to the Casimir effect. For more details see http://lanl.arxiv.org/abs/physics/0509073

 

[SunRay-dvsh]

Well, you should refer to the true "story", which in this case can be found here:

https://www.nature.com/articles/nature07545
https://www.researchgate.net/publication/23501103_Harnessing_optical_forces_in_integrated_photonic_circuits

All this has nothing to do with gravitational interaction between light beams of course but is about the forces of electromagnetic fields on charged particles/matter.

THANK YOU VERY MUCH FOR THESE REFERENCES ! Its easier to understand, though i still don't get how the transverse force is measured.

 

[SunRay-dvsh]

Now I get it. This is not a force between light beams as such, but a force between waveguides of the light beams. The light beams induce the dipole moments in the guides, and those dipole moments cause the force. The effect is very similar to the Casimir effect. For more details see http://lanl.arxiv.org/abs/physics/0509073

Thanks,
They have explained it very well, the original research paper in nature didn't really explain it nicely.

 

[SunRay-dvsh]

Basically, if someone is shooting a Really powerful laser at you, you can use a tiny weak laser to deflect it ?!

 

[Demystifier]

Basically, if someone is shooting a Really powerful laser at you, you can use a tiny weak laser to deflect it ?!

No.

 

[Demystifier]

Thanks,
They have explained it very well, the original research paper in nature didn't really explain it nicely.

That's why you need to read theoretical papers, not experimental ones.

 

[SunRay-dvsh]

That's why you need to read theoretical papers, not experimental ones.

 

[Zafa Pi]

That's why you need to read theoretical papers, not experimental ones.

Expository articles about old experiments can be fun and informative. It's a shame modern experimentalists can't do the same with their own work.

 

[Demystifier]

Expository articles about old experiments can be fun and informative. It's a shame modern experimentalists can't do the same with their own work.

It's also a shame that there are single books covering all branches of theoretical physics but no single books covering all branches of experimental physics.
https://www.physicsforums.com/threads/experimental-physics-for-theoreticians.883789/

 

[vanhees71]

Hm, the introductory textbooks for the experimental-physics course do not too bad a job. Of course, theoreticians, sometimes have problems to understand these books due to a lack of math in these books ;-)).

 

[Demystifier]

Hm, the introductory textbooks for the experimental-physics course do not too bad a job. Of course, theoreticians, sometimes have problems to understand these books due to a lack of math in these books ;-)).

To avoid repeating, see your post #21 and my reply #24 in the old thread above.