4 ms·
> Notice that if you could travel exactly at light speed, time would cease to exist and you could get anywhere in the universe instantly, as light itself experi
by misja111 4y ago
> Notice that if you could travel exactly at light speed, time would cease to exist and you could get anywhere in the universe instantly, as light itself experiences no time.
This is not true. The easiest way to see why, is to realize that speed is relative: there is no difference in considering the observer to move with the speed of light towards the foton, or the foton to move with the speed of light towards the observer.
Yet as you know, we observe light all the time and still we experience time.
- tux3 4y agoNote that speed is relative, but time dilation is not. That's the twin paradox, they're both relatively moving away from each other, but only one 'ages slower'. Though I don't know what it means to say a photon doesn't experience time, and even more so for hypothetical humans travelling at the speed of light. That's outside the scope of what relativity predicts.
- heavenlyblue 4y agoYou could also say “only one ages faster” so this is not a paradox because of that.
- misja111 4y agoOk so let's say two humans pass each other by somewhere in the universe, each in their own spaceship, in opposite directions. They both travel with half the speed of light, so relative to each other with full light speed. Which one is the one aging slower?
- ubercore 4y agoThey won't see each other moving at the speed of light though. This example is covered in any class on relativity. Having an approach velocity between two objects at the speed of light or greater is different than accelerating a frame of reference to c. When an approach velocity is c, nothing is actually _moving_ at c.
- Tyr42 4y agoIn particular, it's acceleration you need to account for when talking about time dilation, not speed. And acceleration is less symmetric.
- ryandvm 4y agoLove the Fermilab series of videos. Here's the one that covers the Twin Paradox: https://www.youtube.com/watch?v=GgvajuvSpF4 https://www.youtube.com/watch?v=GgvajuvSpF4
- spywaregorilla 4y agoJust because you can describe velocity from any frame of reference doesn't mean all frames of reference are valid for describing time dilation. They're not. If you're not accelerating, you're not accelerating. Either way, supposing you were accelerating towards a photon at rest, at the speed of light, that doesn't mean you would suddenly experience time in slow mo. You're going to feel "time" normally. It means that the photon would appear to be in slo mo, which isn't something easy to imagine. Hence the preference for imagining clocks that turn slower.
- deleted 4y ago[deleted]
- ubercore 4y agoTalking about a "photon at rest" is kind of nonsensical. From any frame of reference, c is c, and you'd measure the photon moving at the same speed.
- spywaregorilla 4y agoYes, that's true. Just a contrived example to try and illustrate why it's not correct to say time dilation isn't real because you experience time despite moving at c relative to a photon's frame of reference. Probably more distracting than helpful