Question

Can someone also tell me about Einstein's theory of relativity?
Thanks :)

Answer 1

Relativity is a really big field, but the basic principals are that:
1) the speed of light is constant in all inertial reference frames (even if you're going 0.99 times the speed of light, light will still appear to be moving away at 2.998*10^8 m/s)
2) Simultaneity is dependent on the observers reference frame (2 events may appear to be simultaneous for one observer, but another observer moving towards one event and away from the other will observe the happening at different times)
3) as you approach the speed of light, time will pass more slowly for you than others moving at a slower velocities (Ie if you're moving away from earth at 3/4 the speed of light for 1 year in your time, earth time will have advanced by 551 days instead of the year you experienced) This is called Time Dialation
4) as you approach the speed of light, spacial dimensions contract. (an object at rest in your reference frame may measure 1m to you, but if you're passing it at 1/2 the speed of light it will contract to 81 cm long. called Length Contraction
5) It's not possible to differentiate between an accelerating reference frame and one under the influence of gravity, because of this, time will move more slowly for someone under the influence of a sufficient gravitational field than for someone not the presence of one (They make use of this part of relativity with GPS devices)

Theres a lot of math to go with relativity, the main mathematical element though, appears in pretty much every formula in special relativity (relativity not dealing with gravity). It's symbolized by the greek letter gamma and looks like this\[\gamma = \frac{1}{\sqrt {1-\frac{v^2}{c^2}}}\]where v is your speed and c is the speed of light. As you can see this equation prohibits travel faster than the speed of light, resulting in a negative number under the square root sign, as well as travel at the speed of light(for massive objects) which will result in 1/0 or gamma = infinity... In my personal opinion, time dilation is probably the coolest part of special relativity. the math is really simple:\[t=t_o \gamma\]where t is the time measured in a second observers reference frame, and t_o is time measured in your reference frame, when your speed (v) is measured relative to the other person.

So that's a really quick introduction to relativity.. anything you want expanded on just ask. I'm also not really very well versed in general relativity, I do know a few things though, but it starts to get much more complicated when you introduce non-intertial reference frames & gravity.