# Does light bend light?

1. Aug 22, 2008

### Tomtom

E=mc^2. Mass warps spacetime. From use of the aforementioned equation, light can have a hypothetical mass (can't it?). So, does light bend spacetime, and consequently, bend light?

Does light have a gravitational pull is another way of phrasing my question.

2. Aug 22, 2008

### ZapperZ

Staff Emeritus
3. Aug 22, 2008

### Tomtom

That was a good read! Thanks a lot. However, it still doesn't answer my question ;)

I guess what I am looking for, is serious discussion on the subject, or any papers written on it. I've searched a bit, but only found forum discussions with too many "I think"s.

I've just found two threads on this forum concerning the topic, but there are no clear answers.

4. Aug 22, 2008

### George Jones

Staff Emeritus
From page 427 of Quantum Field Theory in a Nutshell by A. Zee:
Zee then uses quantum field theory to show this, but I'm sure that Tolman, Ehrenfest, and Podolsky used only classical relativity to deduce the result.

Last edited: Aug 22, 2008
5. Aug 22, 2008

### Tomtom

George Jones: Thanks you very much! It's not often I get an affirmative on a theory here ;) Is there more info on exactly that in your book? I've considered buying that one myself.

6. Aug 22, 2008

### MeJennifer

7. Aug 22, 2008

### Tomtom

Very interesting MeJennifer! Great to find that there exists understandable research on the subject! My mathematics (and physics) are only slightly above A-level-equivalent, so I didn't understand most of the math, but the conclusion was "readable". =)

8. Aug 22, 2008

### MeJennifer

Even in special relativity one can make some inferences about the directions of two photons. For instance a system of two photons moving in the same direction has no rest mass while a system of two photons moving in opposite directions has a rest mass.

9. Aug 23, 2008

### coelho

Is it because we could define a "center of mass" of the systems of two photons, and in the case of the photons moving in opposite directions this center of mass would be moving at v<c (what allows a rest mass), while in the case of the photons moving in the same direction the center of mass would moving at v=c, what doesnt allow a rest mass?

10. Aug 23, 2008

### Antenna Guy

By the same token, what does the velocity of a phase center say about the rest mass of a spherical wave?

(n.b. In antenna terms - "phase center" is where r=0 in $e^{-jkr}$)

Regards,

Bill