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Do Massless Particles Cause Gravitation?

by Constantin
Tags: gravitation, massless, particles
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Mar7-12, 05:57 PM
P: 95
I know physical bodies with mass cause gravitation.
But do massless particles, like photons, also cause gravitation ? I know they're affected by gravity, but would a cloud of photons bend space by itself?

Thank you
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Mar7-12, 06:06 PM
Sci Advisor
PF Gold
P: 6,024
Yes, photons have energy, and anything with energy causes gravitation.

More precisely, photons have a non-zero stress-energy tensor, which is what acts as the "source" of gravitation. See, for example, this Wikipedia page:

The stress-energy tensor of a source-free electromagnetic field, down the page, would apply to photons.

I add this qualification because there are also cases where an "energy" can be assigned to the gravitational field itself, but this "energy" is not part of the stress-energy tensor and so it does not act as a "source" of gravitation in the above sense.
Mar7-12, 06:10 PM
P: 2,766
JA Wheeler once investigated the idea of a geon. Light traveling in a self perpetuating circle due to its own gravity.

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