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Message: <blockquote data-quote="freyar" data-source="post: 6257269" data-attributes="member: 40227">A photon is infinitely long-lived (it can't decay into anything), which is perfectly consistent with having time stopped. <img src="https://cdn.jsdelivr.net/joypixels/assets/8.0/png/unicode/64/1f609.png" class="smilie smilie--emoji" loading="lazy" width="64" height="64" alt=";)" title="Wink    ;)"  data-smilie="2"data-shortname=";)" />It's a bit trickier than that.  According to general relativity, if you are falling into a black hole, you don't notice that there's anything unusual about the horizon at all.  So, other than tidal forces, which might or might not be noticeable outside the horizon (depending on the size of the black hole), you don't notice anything weird at all until you hit the singularity.  This is part of the difficulty understanding Hawking radiation in black holes.That's one way of thinking about quantum mechanics (whether of light or not), but you actually have to compute all possible paths between the two events.This is a common and pretty good way of explaining things.  However, a more accurate way of explaining it in simple language has been put forward by Matthew Strassler (I recommend his blog very highly if you are interested in particle physics).  Virtual particles aren't really particles.  The idea of particle/wave duality has come up in this thread already.  Virtual particles are better describe as packets of wave rather than particles, so it's more like a photon goes along, dissolves into a lump of electron wave, and then reforms.  And it does this constantly.Just to add about something weird.  Umbran is perfectly correct for anything with real mass.  It is perfectly mathematically consistent to have a particle with imaginary mass (as in square root of -1) that can only travel faster than light.  These are called tachyons.  However, in our current understanding of particle physics, tachyons are not stable particles but instead represent an instability, like sitting on the top of a hill is unstable to falling down the hill.Spot on.The time traveler would always think that he/she is traveling forward in time, despite ending up in the past of when he/she left.  It is a continuous process.  That's the weird bit.All I can say is that the mathematics work perfectly if there are no forces acting on the photons.  You're precisely right that it is their masslessness that makes them move at speed c at all times, including as soon as they are created.Morrus, I can't tell you how much I, as a physicist, appreciate that you understand this and wrote it in this thread.  I (and many many physicists) deal with this kind of logic all the time, and it is sometimes very difficult to get people to understand that mathematics is required.  It's the same thing with the new paper by Hawking that has been a big deal in the press recently.  It's a nice idea (which is actually very similar in some ways to what other people have done), but it's right now impossible to evaluate because there is no math (though other people's similar ideas are fleshed out mathematically).  Physics can only be properly understood with a grasp of the mathematics involved.  That's why Newton had to invent (or co-invent) calculus to describe planetary motion.  I think it's possible to get an idea of what's happening with an explanation in words, but a full understanding and the ability to do physics simply requires a lot of math.</blockquote>

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