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

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    Photons Relative Surface
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Discussion Overview

The discussion centers around the motion of photons, particularly whether they can be considered motionless relative to the Earth's surface and if they accelerate from rest to their speed in a vacuum. The scope includes concepts from special relativity, quantum mechanics, and the behavior of photons in different media.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • Some participants question whether a photon can be motionless relative to the Earth's surface and if it accelerates from 0 mps to 186,000 mps.
  • One participant asserts that, with relative velocity defined through parallel transport, a photon cannot be considered motionless or accelerate from rest.
  • Another participant emphasizes that in special relativity, a photon is a massless particle and does not undergo acceleration from rest, suggesting that this notion is classical and not applicable in quantum mechanics.
  • A later reply notes the distinction between classical and quantum interpretations of "photon," indicating potential inconsistencies in understanding the term.
  • One participant discusses the behavior of photons in a medium, raising the question of whether a photon could be observed as motionless if the medium moves relative to the observer, referencing experimental work on indices of refraction.
  • Another participant mentions that photons in a vacuum cannot be stopped and discusses the implications of zero-frequency electromagnetic waves, which do not propagate and are not quantized into real photons.

Areas of Agreement / Disagreement

Participants express differing views on the nature of photon motion, with no consensus reached on whether photons can be considered motionless or if they accelerate from rest. The discussion reflects a mix of classical and quantum perspectives, leading to potential inconsistencies in interpretation.

Contextual Notes

The discussion highlights limitations in definitions and assumptions regarding the term "photon," as well as the unresolved nature of how classical concepts apply to quantum phenomena.

James William Hall
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TL;DR
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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James William Hall said:
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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James William Hall said:
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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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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Thank you both for your balanced explanations.
 
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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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