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
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Remember that when you’re talking about time (and distance) you always have to specify *whose perspective* you’re talking about. That is the very essence of relativity.
Something traveling at very near the speed of light travels a distance of roughly 670 million miles *per hour* as measured by *you*. That’s *your* hour and *your* 670 million mile measurements. To the travelers perspective those measurements of how far they traveled and how long it took are completely different. To them that same hour could be a few seconds and that 670 million miles just a few feet. Both observations are valid and correct. Two different observations of the same event are what form the basis of relativity.
The reason time and distance are relative is **because** the speed of light is invariant. The reason why you and I can’t agree on whether one hour of time has passed for my journey is because we both agree that the speed of light is moving the same speed, regardless of how fast we’re moving relative to each other.
If your standing on the side of the road and I drive past you and turn on my headlights we’ll both agree that we saw the beam of light move 186,000 miles in exactly one second. However when you think about it that doesn’t make sense because in that one second of time you saw that I moved and you didn’t. So how can the beam of light be 186,000 miles from you and 186,000 miles from me if neither of us are in the same spot by the time the clock strikes one second? The answer is time. You and I *do* see the beam of light travel for 186,000 miles from our perspective in exactly one second, we just don’t agree on what “one second” actually is. By the time you see one second tick on your clock you’ll notice that one second hasn’t yet ticked on mine.
A technically incorrect but simple layman’s way to answer your question is that light doesn’t experience time because the faster something moves (relative to you) the slower it’s clock ticks (relative to yours). The speed of light is the fastest anything can move in the universe, and it moves that speed relative to everything, so light would have a clock that doesn’t tick.
A more nuanced view is to say that it’s really not valid to say light does or doesn’t experience time because that would imply you could see the perspective of light at rest – AKA “standing still” – which is physically impossible. I don’t think this gets to the spirit of your question though. I think the answer that better addresses the spirit of your question is because *time* (and distance) is relative.
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