• xionzui@lemmy.world
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    11 months ago

    To be pedantic, photons never accelerate. They only ever travel at one speed in one direction

    • Subverb@lemmy.world
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      11 months ago

      And as they’re massless, photons do not experience time. Regardless of how far a photon travels, from its perspective, the journey takes no time.

      • Pseu@kbin.social
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        11 months ago

        It also does not experience space, as the entire universe has been length contracted in its direction of motion into a 2d plane. It is simultaneously occupying every point along its path. So it doesn’t need to experience time.

            • DreamButt@lemmy.world
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              11 months ago

              Are we? Like even if you believe in the sliding scale it feels preposterous to assert there isn’t some breakpoint (even a fuzzy one) between inorganic thing that doesn’t experience and organic thing that does

              • 0ops@lemm.ee
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                11 months ago

                My stance is that if we can define, measure, and test experience, then it’s science. But “experience” is a pretty vague term, and the way it’s used is pretty human-centric. To me “experience” isn’t so much a sliding scale thing that’s actually measurable in nature as much as it’s a human construct. If you ask me, if there’s a fuzzy breakpoint, it’s due to the word’s ambiguous definition, not reality.

      • stebo@lemmy.dbzer0.com
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        11 months ago

        A photon would somehow experience the big bang, the heath death of the universe and everything in-between all at the same time.

    • spacesweedkid27 @lemmy.world
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      11 months ago

      They don’t accelerate, but can travel at different velocities in different mediums.

      For example light travels faster in air than in water and fastest in a perfect vacuum.

      • xionzui@lemmy.world
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        11 months ago

        In aggregate, yes, but any individual wave of light is still traveling at c. You get the appearance of a slower wave because secondary waves are generated that cancel the original one in such a way that it makes a combined wave that appears to be slower.

        • peopleproblems@lemmy.world
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          11 months ago

          Not quite.c is the speed of light in a vacuum. It’s more accurate to say c is the speed of causality.

          Velocity/speed isn’t very useful with photons either - its a wave-particle.

          Light in changing mediums is a separate but related phenomenon. The photon essentially doesn’t continue on its same path, it gets absorbed by the particles in the medium. This leads to changing states (of usually an electron in an atom) which may emit another photon, remain stable but increase the atom’s kinetic energy (I can’t remember how likely that is, if at all), or it may eject the electron, ionizing the atom. In any case, the state changes, because the whole system (the atom, electron, and photon) can’t have net energy gain or loss.

      • Pennomi@lemmy.world
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        11 months ago

        I believe they still travel at the speed of light, but are regularly absorbed and re-emitted in a way that makes the effective speed less than c.

    • yewler@lemmygrad.ml
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      11 months ago

      How do reflections work? Aren’t changes in direction caused by acceleration? Also aren’t photons affected by the gravity of black holes? How does that work?

      • xionzui@lemmy.world
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        11 months ago

        Reflections involve the material absorbing and re-emitting photons back the other direction.

        The curvature of light from gravity is actually space-time itself being curved by mass. The light continues on a straight path through a curved space-time. It looks like it changes direction from the outside, but that’s just the shape of the universe in that area.

        That’s why we feel gravity. The space-time around earth is curved inward, so going forward in time would actually mean falling towards the center if we were stationary in space. The ground is constantly accelerating us upwards. Light does not get accelerated that way, so it follows the curvature.

        If you want to get really deep into the reflection topic: https://youtu.be/rYLzxcU6ROM