Must photons have motion?

jimbunyard

These are not facetious questions. Is a photon at rest still a photon? Can a photon be at rest?

Thanks

FeynmanIsCool

No, photons only exists at the speed of light. Since the speed of light is absolute, Photons can not be at rest.

Drakkith

A frame at rest, aka an inertial frame, will measure the speed of light as c at all times. Light itself cannot have a rest frame.

Khashishi

In a vacuum, no. But in a specially prepared medium, maybe? http://www.photonics.com/Article.aspx?AID=28520

FeynmanIsCool

Very interesting, but the key phrase is " "quantum mechanical magic trick". If two high energy photons come together and create a particle, this particle has NO internal constituents relating to the two photons. So from energy comes mass, but this mass is in no way connected to the two photons. Theoretically, We can move that mass, and slow it down, but this is not the same as slowing down the two photons that created it. Fascinating though!

Menaus

From a photon's perspective, it is at rest, from ours, it is moving extremely fast. It's all about frame of reference, Einstein talks a lot about this stuff in his Special theory of Relativity.

Drakkith

This is not correct. A photon cannot have a frame of reference per SR. Try transforming a frame moving at c to a frame not moving at c. You get nonsense as an answer. It doesn't work because all inertial frames will always measure light as moving at c in a vacuum. Light, per special relativity, is never at rest and cannot have an inertial frame.

Menaus

You're right, sorry.