1. David exists at time T = 2pm PST August 1, 2021.
2. David travels back in time to before time T.
3. Now there is the original David-O and a "copy" David-C.
4. David-C goes up to David-O and kills him.
5. Therefore, David-O is not alive at time 2pm PST August 1, 2021.
6. Therefore, David-O does not exist at time T.
7. And therefore, David-O does not travel back in time at all.
The Theory of Time Travel leads to a logical contradiction. Therefore, it is a bad and invalid theory.
The Dirac Equation is Relativistically Invariant.
Proof attached.
Proving the Relativistic Energy-Momentum relation, the hard way and the easier way.