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Does Light have Mass?

Does Light have Mass?

Yes. Photons have energy and thus mass. Lots of it.

But they have zero rest mass, which is kinda cute because you will never find a photon at rest.

So, saying a photon has zero rest mass is the same as saying photons travel at a constant speed relative to any reference frame. Years before Special Relativity Maxwell’s equations showed this very clearly.

Einstein must have been acutely aware of this, and in fact his first paper on what we now call Special Relativity had the title “On the Electrodynamics of Moving Bodies”.

Content written and posted by Ken Abbott
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