Ever wondered what it would be like to see your friend fly by in a spaceship at half the speed of light? Well, according to Einstein’s theory of relativity, when you observe someone flying by in a spaceship at speeds close to that of light, as you move towards them and they move away from you, time slows down. And if they’re going really fast – say 550 kilometers per second (that’s about 310 miles per second) – then for every one-second interval on their spacecraft clocks, there are two seconds passing back here on Earth. So when your friend flies out in their spaceship moving at 550 km/s (310 mph), for you the event will last three seconds.
This is a discrepancy of two seconds from when it actually took place, but for your friend, the event will have taken only one second. Weird? Yes! But this is what relativity tells us about how time moves differently depending on an observer’s velocity relative to another object (like in our case).
So if you saw your friend fly by at half the speed of light and thought that three seconds had passed, then they could never be going more than 299 million meters per second because that would make their spaceship appear stationary. And if somehow their ship was moving even faster – say 800 km/s – then you would observe them flying by as if someone were standing still just ahead of you. You would see them pass by like a blur with your eyes following them as they went by.
And if you were to start moving at half the speed of light when your friend passed you, then for him it would seem like he just saw a stationary ship that was standing still ahead of him – but now we are talking about what this person’s frame of reference is and not yours! That difference in perspective would be nicely illustrated using some animations which will show how time moves differently depending on an observer’s velocity relative to another object.
So let me explain:
Doing something else instead? Okay, so here is why relativity tells us that time passes more slowly when objects move faster than 300 000 km/s- or close enough together such as two cars traveling at 100 km/s (about twice the speed limit).
In short, when objects move close to the speed of light they will experience what is called time dilation. The faster something moves, the more its clocks are running slower relative to an observer who just stays put on Earth. And no matter how fast you may think you’re moving in your car or spaceship, remember that there’s always someone out there traveling even faster than you!
A perfect example can be seen with a photon that has zero mass and travels at 300 000 km/s- and therefore sees everything as happening in slow motion because it takes longer for signals from events to reach it. In fact, this means we need not only one but two animations – one showing things as being sped up when seen from the perspective of a photon and one as being slowed down when observed by someone standing on Earth.
“You can’t be too fast or you will die, but at least it would take an infinite amount of time for that to happen!”
Albert Einstein
The faster anything moves relative to us, the more stretched out its light appears due to what is called ‘time dilation’. The closer an object gets to the speed of light, the slower their clocks run in relation with other objects which just stay put on earth. And no matter how fast you may think your traveling in a car or spaceship, remember there’s always someone who travels even faster than you!
A perfect example can be seen when you see a plane flying by. Planes move at very high speeds when they fly over us, but they are not speeding up; it is just that we are much slower because of the Earth’s gravity and time dilation.
You can see this in reverse as well when someone moves past you or your friends on foot or in a car: notice how their clocks run faster with respect to yours? They seem to be moving more slowly!
We experience these effects intuitively because our bodies respond differently to acceleration-a low g force makes us feel heavy, while an even higher one feels light enough for flight. It’s all about relativity!
