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Q & A: Speed of photons

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Most recent answer: 03/02/2014
Q:
The speed of light from point to point is roughly 300,000,000 m/s in a vacuum, but light travels as a wave, right? Doesn't that mean the actual photon is travelling faster than that, similar to how a ship moves forward at a set speed but also up and down on waves. So does that mean the photon goes along axis x at 300,000,000 m/s and up and down axis y at 300,000,000 m/s which means from the photons perspective it is moving through space at 600,000,000 m/s?
- Martin (age 33)
Sunderland, UK
A:

Hello Martin,

So far all experiments show that single photons travel a velocity c.    Velocity is a vector quantity. That means you can project its components onto any particular set of orthogonal axes.  But if you take the squareroot of the sum of the squared value of these two projections you always wind up with the value c. 

LeeH

 

I think those pictures of a wave may have misled you. For a water wave, the up and down wiggles represent actual water moving up and down as the wave pattern goes sideways. For an electromagnetic wave, nothing is moving up and down. Those wiggly pictures represent the value of the electric field at different places. The only motion is the motion of the pattern, as Lee describes.  Mike W.


(published on 03/02/2014)

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