The theory of special relativity was created and discovered by Albert Einstein which was developed between 1907-1915. The theory of special relativity explains what happens to energy, matter, space, and time when it reaches certain speeds close to light.
Space near the speed of light
If a person is traveling near the speed of light, Space will become smaller for them.
Mass near the speed of light
The more Mass reaches the speed of light the more it will increase.
Dilation of Time
Dilation of Time is when times moves slowly for an object that is in motion.
The Twin Paradox
A Twin Paradox is when one of the twins (of the paradox) travels to space near the speed of light but that twin’s other twin stays on Earth. After 20 years have passed that twin travels back to Earth and she has aged only 2 years while her twin has aged 20 years. The reason this is caused is because of Dilation of Time.