Reddit mentions of It's About Time: Understanding Einstein's Relativity

In your scenario, you are traveling at the speed of light (speed of light is called "c" from here on out); this is impossible since you have mass and can't possibly travel at the speed of light.

Lets use your idea with a slightly different example. You would think that if you are traveling at 0.75c (aka 3/4 of the speed of light) and fire a bullet forward with a velocity of 0.75c then the bullet will be traveling 1.5c (faster than the speed of light)... but this is not how velocity addition works.

Velocities don't add like 10+10=20, but have a more complicated form called relativistic velocity addition:

vtotal=(v1+v2)/[1+(v1*v2)/c^2]

This is especially important at velocities that start to apporach the speed of light (let's say 0.2c and faster) and it is negligible at every day speeds like driving your car or flying in a plane.

With the correct formula and using the numbers in the example above;

v=(0.75c+0.75c)/[1+(0.75c*0.75c)/c^2_]
v=0.96c

You can try any combination of numbers for v1 and v2 between 0 and 1c but you will never get a result greater than c. This velocity addition equation is a result of Einstein's Special Relativity.

Relativity also affects momentum and energy giving different values than would be expected using Newtonian classical mechanics at these very high velocities. Time and the length of your moving space craft are both distorted. Furthermore, a person in the space craft and a person at rest (with respect to the spacecraft) may not even agree on the order of two events when they are observed by both people. This gif is a Minkowski diagram that shows the effect of the shifted worldline at relativistic velocities and its effect on the observation of simultaneous events.

A great resource and starting point for learning special relativity is a book called It's About Time: Understanding Einstein's Relativity.

Time to go back to my book on relativity (despite my failure, it really is a very good book). I seem to be able to understand each concept of relativity in isolation, but I always go wrong in putting them all together and analysing a real situation... never know which part of the theory is applicable. Practice makes perfect, I suppose!

Thanks for the reply!

That's right. I think theory of relativity is rarely explained well and in detail. I can recommend "It's About Time: Understanding Einstein's Relativity" by N. David Mermin as a book that helped me gain a better understanding of it.

Mermin helped me a lot.