Einstein’s theory of relativity is a very profound knowledge. If someone can explain it in a few words, don’t believe it! The person in front said so many things, but he didn't get to the point, and some of them were even wrong.

In fact, the most essential thing is E=mc squared, because Einstein also said: "c (the speed of light remains unchanged)". Therefore, the greater m (mass), the greater E (energy)! Haha, keep it simple! But this solves the problem of whether motion is relative or absolute. In the past, people thought that there was an absolute "ether". If you know this, it will be used throughout your life!

The later general theory of relativity only introduced the concept of space and time (that is, matter exists in time, and time is the fourth dimension). The theory of relativity is actually very simple, haha.