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I’m trying to understand how that reference frame works when you just just bounce a photon off a mirror and time how long it takes to come back? Like, light must have a non-infinite speed to the stationary observer, or it wouldn’t take time to traverse the distance.

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FiskFisk33@startrek.website ⁨5⁩ ⁨weeks⁩ ago
thats the thing, thats from your reference frame. From the photons perspective time stands still and everything happens at once

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vithigar@lemmy.ca ⁨5⁩ ⁨weeks⁩ ago
The observable effect is the same either way. If light is infinitely fast and causality propagates at c then it’s still going to take (distance to the mirror / c) for the fact that you turned on the light to reach the mirror, and that same amount of time for the fact that the light reflected to propagate back to you.

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- Liz@midwest.social ⁨5⁩ ⁨weeks⁩ ago
  Those two things don’t square. If you’re moving relative to the mirror when your fire the photon, it would hit in a different place than if you were stationary. The photon can’t be moving infinitely fast in your reference frame for that to happen.
  
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  - Zink@programming.dev ⁨5⁩ ⁨weeks⁩ ago
    Yeah I think infinite is the wrong word for them to use there. Maybe call it maximally fast? Like it goes as fast as possible no matter your reference frame, but that speed is limited by the speed of causality. The photon has 100% of its skill points in speed through space and 0% on speed through time.
    
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  - vithigar@lemmy.ca ⁨5⁩ ⁨weeks⁩ ago
    Would it? What does “stationary” mean when discussing relative velocities? The mirror being stationary and the person firing the photon moving at a constant velocity is literally an indistinguishable scenario from a stationary person firing the photon at a moving mirror.
    
    If I am moving relative to a mirror when I fire the photon, then the mirror is moving relative to me, and will be in a different relative position by the time the “event” of my firing that photon reaches it.
    
    Also, the photon isn’t moving infinitely fast in my (the firer’s) reference frame. It’s moving infinitely fast in it’s own reference frame.
    
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    Liz@midwest.social ⁨5⁩ ⁨weeks⁩ ago
    Yeah I eventually picked up that that’s what you meant in your original comment, not that photons move instantaneously and that causality somehow catches up later.
    
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