Theory on why Time travel to the past is impossible

My first assertion is that the past simply does not exist. It only esists in your memory as a combination of neurons firing. For an object each atom only exists in the present

So for someone to travel back to the past relative to them they would have to find some way to first revert each atoms quantum state. Then they would have to do that for the entire infinite expanding universe(assuming there's only one).

Comparatively time travel to the future is very easy.