Eli5 how does a photon not experience time when zooming toward point b? Wouldn’t other photons from point b passing it appear as time happening very quickly?

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The speed of light needs to be the same for all observers. This was proven by the Michelson Morely experiment that proved there is no medium through which light travels.

This means that observers at different speeds perceive time differently to ensure that they measure the same speed of light. This is Special Relativity.

The formula for this is t = t0/sqrt(1-v^(2)/c^(2))

If v=c (velocity = speed of light, like a photon would have), then sqrt(1 – v^(2)/c^(2)) = 0, and you can’t divide by 0, so time doesn’t work st the speed of light.

Photons don’t experience anything, and they don’t have a frame of reference. This is a question that gets asked a lot, but the answer is, “You’ve asked a nonsensical question the math cannot address.”

The short answer is that there is no amount of time. The photon is created and travels to point B and no time passes from the point-of-view (not that such a thing exists) of the photon.

Things traveling faster experience time as moving slower (not just observe it going slower, actually experience time slower). At speeds people typically travel the difference is so small you wouldn’t notice. But it can be measured using incredibly accurate clocks.

The simplest way I can explain it is picture three people: one standing still (A), one on a bicycle (B), and one on a motorcycle (C). If the bike is going 5 m/s and the bike is going 10 m/s in the same direction. To person A the motorcycle looks like it’s going twice as fast as the bike, but to person B it looks like the motorcycle is only moving at 5 m/s (because *relative* to their speed, it is). Now let’s say the motorcycle is breaking the laws of physics and going the speed of light and the bike is somehow managing 100 m/s. To both persons A and C the motorcycle is going the same speed regardless of their own speed relative to it which means he experiences the same amount of time regardless of what the outside observer sees (because the relative speeds don’t change our observation of his movement).

Here’s a link to the experiment showing that faster objects experience time slower:

“Photons don’t experience time” is a consequence of something called the Lorentz Transformation, which is a consequence of Einsteinian Relativity.

The idea is that time dilates as you approach the speed of light. That means that the closer you get to c, the slower you feel time move. (in comparison to whatever clock you define as stationary.)

But this effect approaches 0 as speed approaches c, so the only logical conclusion is that things traveling *at* c perceive 0 time. We of course cannot know what photons or other massless particles perceive, but there isn’t much of an option to say that they do experience time.