I've been reading a bit of physics lately (mostly pop-sci books) trying to get a handle on the whole relativity thing. For a long time all I really knew about relativity was E=mc². So the energy of something (E) is equal to the mass of it (m) times the speed of light (c) times the speed of light (c) again.
Now, that doesn't make a lot of sense on its own, and how is that proved, and why is that relative, and what's the point of it anyway?
Well you can forget E=mc² if you want a totally non-technical version of relativity. What relativity comes down to is that all distances and even how fast time travels are all relative to the observer; the only thing that is constant is the speed of light which is 299,792,458 meters per second or 186,000 miles per second (which is pretty damn quick).
Everyone always sees light travelling at that speed, no matter what they’re doing or how fast they’re going they can’t catch up with light or run away from it. If you are driving along in your car at 180,000 miles per second (do not try this at home) do you know how fast the light around you will be travelling? 186,000 miles per second. If someone is waiting at the bus stop as you drive by and they measure the speed of the same light you did from your car they’ll still measure the speed as 186,000 miles per second. That’s relativity.
Now, because light is travelling at the same speed for everyone, no matter how fast they’re going, everything else has to be a bit more flexible to fit around this. Distances change depending on how fast you’re going when you measure them and time goes at a different speed depending on how fast things are travelling. Specifically the person at the bus stop as you drove past would see your car as shorter than you would see it from the driver’s seat and it would look like time was travelling more slowly for you from their point of view.
From this idea Einstein managed to come up with some new equations for how the universe works including the famous E=mc².
We don’t really ever get to see the affects of relativity in everyday life because we’re all stuck to the same big rock (Earth) so we all travel pretty much the same speed all the time. In fact the fastest you’re ever likely to travel is on a passenger jet and even if you flew on Concorde it only goes at 1,330 miles per hour, which is about 0.37 miles per second, and that’s no-where near the speed of light.
There are practical situations where relativity is needed and used though, so it’s not all theory and no proof. Global positioning satellites have to take relativity into account because time is travelling at a different speed for them than it is for us.
Hmm, that turned out a bit longer than I expected. Please let me know if I’ve made any errors above or if the whole thing is an unintelligible mess.
