-essentially says that the laws of physics don’t change when we switch between different reference frames.
For the past century there have been two incompatible theories on how the universe works: Gravity (courtesy of Einstein’s general theory of relativity) and Quantum Theory (used for the other three fundamental forces of nature: electromagnetism and the strong and weak nuclear forces ). Both work ok, except in extreme environments (like inside a black hole). So, scientists are looking for a good theory of Quantum Gravity. The problem is that relativity wants gravity to be continuous, while quantum theory wants it grainy.
The French mathematician Pierre de Fermat died in 1665. A note found in the margin of his textbook Arithmetica declared he had found a proof for his theorem that xn + yn = zn has no solutions where n is a whole number greater than 2, but did not have room to write it down. The proof was finally found by the Cambridge mathematician Andrew Wiles in 1993.