head_relative
bluebar

There is no absolute, or "same," time and space. This means time and space are different for everyone! How you experience events in time and space depends on TWO important things:

rel_1

Where you're looking from.
Imagine you're sitting on a fast-moving train. You see your friend moving by you; your friend sees you moving by him.

relative_img
rel_2

How fast you're moving compared to the speed of light.
Imagine you are still on the train and two lightning bolts flash — one in front of the train, the other behind it. If your friend sees them flash at the same time, you'll see them flash at different times. Why? Because you're moving toward the light of one bolt and away from the light of the other.

relative_tag

You've just been working on a thought experiment. Einstein and others have used them to try to explain how the universe works.
To perform a thought experiment, you don't need a laboratory or machines — just your imagination! Once, when someone asked Einstein where his laboratory was, he pointed to his pen.

Image Credits:

Kid photos: courtesy of Denis Finnin, AMNH; It's All Relative: Jim Paillot; Rabbit, elephant, and ant: Francesco Santalacia; You Light Up My Life!: Cathy Sanchez Duvivier