Are Photons Capable of Traveling Faster Than Light?

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Discussion Overview

The discussion centers on the concept of whether photons can travel faster than light, referencing Richard Feynman's work in quantum electrodynamics (QED). Participants explore the implications of photon speed in relation to quantum amplitudes and propagators, considering both short and long distances.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant cites Feynman's QED, suggesting that including the possibility of photons traveling faster or slower than light is necessary for accurate calculations over short distances.
  • Another participant questions the specific reference in Feynman's work regarding faster-than-light travel.
  • A different participant asserts that there exists an amplitude for photons to travel at speeds other than c, although these amplitudes are small and tend to cancel out over longer distances.
  • Another participant introduces the concept of null cone properties of different propagators, indicating a distinction in how faster-than-light possibilities are evaluated mathematically.

Areas of Agreement / Disagreement

Participants express differing interpretations of Feynman's statements and the implications of photon speed, indicating that multiple competing views remain without a consensus on the matter.

Contextual Notes

There are references to specific mathematical constructs and properties of propagators that may not be fully explained, leaving some assumptions and definitions implicit in the discussion.

anorlunda
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In Feynman's famous book QED, he repeatedly reminds us that we must include the possibilities of photons traveling faster than light and slower than light to get the right answers. At least for short distances, short times. For longer distances, longer times, those possibilities cancel and the average speed, c, is adequate.

Is this because of uncertainty, or a fluke in the math, or some other physics?
 
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Where does he say that?
 
Feynman said:
In other words, there is an amplitude for particles to travel faster than the speed of light and no arrangement of super-position (with only positive energies) can get around that.

Feynman said:
It may surprise you that there is an amplitude for a photon to go faster or slower than the conventional speed c. The amplitudes for those possibilities are very small compared to to the contribution from speed c;in fact they cancel out when light travels long distances.

He mentions the same thing several times in QED: The Strange Theory of Light and Matter .

I found my question in another PF thread here but the answers seemed contradictory and unclear.
 

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