What will happen if your twin returns from a trip in which he/she was traveling near the speed of light?

What is the speed of light?

If a ship is moving toward you at 2X10^8 m/s and it shines a light in your eyes, how fast does that light appear to be moving from your point of view?

Translate E=mc^2

How could the entire mass of the universe have been the size of a softball on the day of the big bang?

Is light a wave or a particle?

What do we know about the escape velocity of a black hole?