Eli5: How can light not experience the passage of time if it travels at 670 million MPH – a measurement of time (and space)

Question

If light travels at 670 million miles per hour, then that means in one hour it will travel 670 million miles. At 2 hours it will travel 1214 million miles etc. This to me sounds like a measurement of time, just on such a huge scale that we can’t comprehend it. But in the grand scheme of the cosmos this is not that crazy of a scale. I would think it’s just saying light doesn’t experience time *relative* to us. But Einstein says no- no matter what, light’s speed doesn’t change and, what, relativity just doesn’t matter? It feels like a paradox

In: 222

Answer 1

Ok, this is really going to be a stretch, but let’s take a stab at it.

Imagine for a second that you’re a fish sitting still at the bottom of a river. The river has a constant flow rate of, let’s say, 100 gallons a second, and from your frame of reference, this is how you define a second; the time it takes for 100 gallons to pass by you. As long as you’re sitting still, a second is what you would expect it to be.

If you hop into the current and start moving with the river, however, to an outside observer, you’re simply moving along with the river, and one second is one second. You’re not an outside observer, though, and to you, one second has passed only once 100 gallons of water have passed you. If you’re going half as fast as the river is flowing, then one second for you would be two seconds for the observer. To both of you, though, in that time frame, 100 gallons of water have passed you by. So you’re both correct.

Obviously, there are limitations to the analogy, but if we assumed that your biological processes (heartbeat, respiration, other fish stuff) were connected to the rate of water (time) passing you up, then those processes would depend on how quickly you were moving. The closer you get to the speed of the river, the slower your heart appears to beat to the observer, but for you, it’s still beating normally (once per second or what-have-you). If you were capable of going as fast as the river goes, then no water is passing by you, and one second for you will take, to the outside observer, an infinite amount of time to pass.

Sorry, I tried.