I like Sean Caroll’s way of explaining SpaceTime, which is different than the mainstream “length contraction, time extension” in many other lectures.

The traditional rendition is conducted by Brian Green in his series of WSF channel, using light clock (invented by Einstein maybe) he is able to deduce the equation of gamma factor to convert stationary time and moving object’s time based on his key observation/axiom that speed of light is fixed.

While with Sean Caroll, he starts with a light cone drawing,

Then pivoting on this light cone, he explains why time is shortened and the famous twin paradox that even Richard Feynman was not able to get it clear.

Using this frame he easily explains “length contraction” by looking at the head and tail of ruler respectively in light cone:

What’s more, spacetime concept is able to unify momentum and energy too.