>>71864
Wormholes and Albucierre warp drive via Exotic matter or Negative energy

Circling a Kerr type black hole (rotating w/ no singularity)

Cosmic strings (bringing them close and moving through them)

Dark matter and dark energy (potentially usable for traversal)

Unobtainium (a new element of our creation)

New and undiscovered laws of science, advanced technologies, or cosmological phenomena.

If you are serious about going back you should begin looking into these rather than citing reasons why backwards time travel is impossible (mere excuses not to do the required intellectual lifting + dietary habits).