9 ms·

This made me curious how long a photon lives. "according to the photons frame of reference, Heeck found that its lifetime would be a rather short three years;

• pdonis 7y ago
  Note that this article is assuming, for purposes of argument, that photons actually have mass, equal to the current upper limit for possible photon mass based on experiments. But the experiments are all consistent with the current theoretical belief that photons have zero mass; and if they have zero mass, the concept of "lifetime" for a photon (and indeed the concept of "photons frame of reference") is not even well-defined.
  • tinus_hn 7y ago
    If they are moving with the speed of light no time passes for photons so ‘lifetime’ has no real meaning either.
    • pdonis 7y ago
      > If they are moving with the speed of light no time passes for photons No, the concept of "time passing" for an object moving at the speed of light has no meaning. That's why "lifetime" has no meaning for a photon if it has zero mass.
      • omarchowdhury 7y ago
        Wouldn't c have to be infinite for "no time to pass", since light is still traversing space at a finite speed?
        • ben_w 7y ago
          No, because the rules of Lorenz invariant field theories mean that the infinity you’re (presumably) expecting is mapped, via the joy of hyperbolic geometry, onto the propagation speed of that field. Or, to put it another way, the speed of light is where time dilation and length contraction run into each other and it all goes zero-divided-by-zero.
        • Yajirobe 7y ago
          No, outside observer will measure clocks of photon run slower by a factor of γ (Lorentz factor), which (in scalar form) is equal to 1/sqrt(1 - v^2 / c^2 ). It diverges at v = c.
          • pdonis 7y ago
            > outside observer will measure clocks of photon run slower by a factor of γ This is not correct since "clocks of photon" is a meaningless concept (at least if photons have zero mass, which they do according to our best current models).
            • Yajirobe 7y ago
              Obviously, I did not mean to imply that you can attach a clock on a photon. I thought this goes without saying.
              • pdonis 7y ago
                > I did not mean to imply that you can attach a clock on a photon. The issue isn't that you can't attach a clock to a photon in a practical sense. The issue is that even in principle, the concept of "the clock of a photon" is not well-defined. For it to be well-defined, there would need to be an inertial frame in which a photon was at rest. But that is impossible.
        • Florin_Andrei 7y ago
          Speed of light is for-all-practical-purposes infinite in the reference frame of the moving object (i.e. photon), thanks to special relativity.
    • misnome 7y ago
      This conversation sounds like it's running into the linguistic barrier that we tend to think of "speed of light" in terms of, well, light, so becomes recursive when talking about photons with mass, which naturally travel slower than what should be thought as "the speed of massless particles".
• peteradio 7y ago
  This according to measured upper limits on photon mass. Strong theory postulates absolute zero mass for the fundamental particle and in this case it will have an infinite lifetime.
  • sbmassey 7y ago
    Or zero lifetime from its own perspective, I suppose
    • deleted 7y ago
      [deleted]