# The idea that travelling at the speed of lìght makes one age at a different rate to those of their home planet.

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I need someone to make sense of it for me. I appreciate the clock scenario where it stays at 12 o’clock if you move away from it at the speed of lìght, but regardless of how fast someone travels, their body will still age just as fast as anyone else (roughly). I don’t understand how just putting distance between someone’s self and the rest of Earth would somehow make them age at a slower rate? You’re aging, just further away..

Hope this makes sense!

In: Physics

More like “time slows down for people who move really fast”. Obviously you’ll age. This is some of the weird stuff that the theory of relativity says will happen as you approach light speed, along with things like effectively becoming heavier.

If you took some kind of space ship capable of nearly light speed and went to visit a planet 1000 light years away it will take 1000 years to get there. However on the ship you might experience only 1 year of time for the trip depending on your speed. Obviously you age that year, need to be put in some kind of sleep/stasis or have a year’s worth of food for you, and all that science fiction stuff. But time for you is slowed down because of the high speed.

The time dilation of special relativity is not an optical result of light taking longer to catch up. It is an objective fact – if I move relative to you near the speed of light, time will in actual fact be moving slower for me. This has been experimentally confirmed with extremely accurate clocks.

There is an additional observational factor that has to do with light’s finite speed of travel, but as you suspect that doesn’t affect how much time passes for us, it just affects how we see something. If you take all the light you see and put it through the calculations to correct for the mere finite speed effects, you will still see time dilation happening.

Also to clarify, distance doesn’t matter.
I could move at near the speed of light round and round in circles right next to the earth and a lot more time would pass on earth than for me, from my relative perspective.

Before I can explain this, there is an assumption we must make: the speed of light is constant for everyone. That is, if I’m moving at a certain spzed relative to you, and we both measure the speed of light, we both will get the same result.

Now, with that out of the way, let’s simplify everything down to you and me. Both of us sitting in a spaceship out in space, and nothing else is near. At some point , you see me passing with some speed. And I see you passing with the same speed, but in the other direction. So far nothing special.
Now, let’s imagine we have a clock on board. But not just any clock. A special one. Two parallel mirrors, with a beam of light going between them. It takes a certain amount of time for the light to move between the mirrors.

Here’s where it gets interesting. When you look at my clock, the beam of light is going diagonally. If it weren’t, then the light wouldn’t hit the mirror for you, but it would for me. Which can’t be. And since we have already established that the speed of light is constant, the beam on my end must take longer to get to the mirror. [This image](https://upload.wikimedia.org/wikipedia/commons/8/8e/Time-dilation-002-mod.svg) shows it well. On the left is my clock as I see it, on the right as you see it.

But there’s more! I see the same effect for your clock. To me, your clock is ticking slower. At firdt glance, this is weird, but the thing is, there is nothing special about my spaceship, or yours. An anaology to this symmetry of weirdness is perspective. If we’re fzr away from each other, each will see the other as smaller.

And as a final note, I leave with the cavezt that this only works for constant linear motion. In other words, there are no forces involved, no changing of direction or whatever. As soon as you get to that, you’ll need general relativity. Which is a lot more complex, and I’m not privvy to its secrets.

It’s not distance that makes time go slower, but speed. The closer you get to the speed of light, the slower time passes for you. Of course, you don’t *feel* like time is going slower, it’s not like you’re stuck going in slow motion or anything. *Everything* slows down at the same rate, your thoughts, clocks, aging, etc.

I think the distance thing comes in because examples tend to use travelling in straight line off into space on a rocket. Going 90% speed of light for 10 years, you’ll travel 9 light-years. But, the same effect will happen if you just go in a small circle at 90% the speed of light for 10 years (nevermind the extreme g-forces that you’ll experience) and effectively go nowhere.

It’s really weird and counter-intuitive because for everyday life it seems like time ticks by at a steady rate, but ultimately that’s how the universe really works.