this post was submitted on 27 May 2025
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Explain Like I'm Five
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The light takes the same amount of time to get there from an external point of view. It's more like time slows down for you the faster you go, which from an external perspective would look like you moving and acting slower than normal. So in the time it would take light to travel 1 light year, it always takes one year. However, you would be slowed down so much that it would appear to you that much less time had passed, maybe only a few days. If you travel at the speed of light you slow down so much that no time passes for you at all at that speed. So you instantly arrive, from your point of view. However, from the point of view of an external observer, it still took one year.
Essentially, it slows down the amount of time you experience, but the amount of time that actually passes externally doesn't change. If you go to the moon, it will take only 1 second at light speed, so you wouldn't really notice whether it felt instant or to take a second. However, if you go somewhere further like Proxima Centauri, which is 4 light years away, you will arrive back on Earth at least 8 years later (there and back). If you go at light speed, it would appear to be instant, suddenly you're at Proxima Centauri 4 years later, suddenly you're back at Earth 8 years later. If you go just below light speed, you'll see the world outside go past like it's being fast forwarded, and when you return, 8 years will have been compressed into something that seems much shorter to you.
Perhaps a stupid follow up but what would this mean for things necessary for survival like food and water? Would I theoretically starve on that 4 year trip before I even realized I needed water?
No. Let's say you and I start each one a stopwatch at the same time here on earth. Then you get in your spaceship and travel the 8 years at light speed, get back to earth and land your ship. When you get out and we put the watches side by side mine shows 70000+ hours while yours the couple minutes it took you to get on and off of the ship.
Just want to add that what the person on the ship observes is length contraction. When their ship is at near light speed, the distance to their destination contracts to nearly zero (because it is moving at near light speed relative to them); this is why the trip seems short to them.
It’s not just your perception - your actual atoms slow down in “time”. This is because any movement they make, from their vibration alll the way up through chemical reactions and physical movements, from your metabolism to your thoughts being transmitted through your neurons, will require acceleration towards light speed from their already high speed.
The faster you move through space, time literally moves slower- you sacrifice one for the other, like a ratio.
No, you would physiologically age at the same fast-forwarded time rate. Essentially, for you, less time would pass at the same time that more time passes for the outside world.