Idle Photons (motionless relative to the Earth's surface?)

  • #1
James William Hall
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TL;DR Summary
Photon Motion
Can a photon ever be motionless relative to the earth's surface? Did it accelerate from 0 mps to 186,000 mps?
 

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  • #2
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TL;DR Summary: Photon Motion

Can a photon ever be motionless relative to the earth's surface? Did it accelerate from 0 mps to 186,000 mps?
No* and no*.

*With relative velocity being defined through parallel transport along any arbitrary but given path rather than as a coordinate speed.
 
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  • #3
PeroK
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TL;DR Summary: Photon Motion

Can a photon ever be motionless relative to the earth's surface? Did it accelerate from 0 mps to 186,000 mps?
This is really a Quantum Mechanics question. In SR the photon is simply a massless particle that may take part in particle collisions. But, the theory does not go any deeper that that and there is no theory on how the photon appears and no implication that it accelerates from rest.

In Quantum Electrodynamics, the photon is the quantum of the Electromagnetic field. It's not a point particle at all and a concept like "acceleration from rest" is a classical notion that has no place in the theory.
 
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  • #4
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Note: my response in #2 was classical, basically interpreting "photon" to mean "pulse of light". @PeroK 's post #3 was quantum interpreting "photon" to actually mean "photon". So there will be some inconsistencies, just pick the answer that uses the meaning of "photon" that you intended.
 
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  • #5
James William Hall
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Thank you both for your balanced explanations.
 
  • #6
snorkack
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Photon in vacuum clearly cannot be stopped. If you Doppler shift it, its frequency changes... but you will find its speed unchanged.
How about photon in medium? Could you observe a photon in a medium such that the medium is moving relative to the observer/Earth surface in direction and with velocity opposite and equal to the speed of photon relative to the medium?
Lene Vestergaard Hau achieved some impressively big indices of refraction in media such as Bose condensate.
Also, photon cannot really "accelerate from rest". Indeed consider the basic limiting case of electromagnetic "waves" with zero frequency. On that limit, what we get is electrostatic and magnetostatic fields... which do not propagate, do not carry energy, momentum or angular momentum and are not quantized into real photons, only virtual ones. (Precisely how is electrostatic field expressed through the virtual photons, though?)
 

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