## Must photons have motion?

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

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

## Must photons have motion?

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

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

 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.

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 Quote by 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.
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.

 Quote by 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.
You're right, sorry.