If time travel is possible it’ll probably be limited to the lifeline of the time machine itself. You cannot travel back in time to a point prior to the invention of the first time machine.
GR predicts “closed time-like curves,” but they require weird conditions (an infinitely dense and infinitely long rotating string) or negative energy, and you can only ever travel to the start of the loop at the earliest.
If time travel is possible it’ll probably be limited to the lifeline of the time machine itself. You cannot travel back in time to a point prior to the invention of the first time machine.
GR predicts “closed time-like curves,” but they require weird conditions (an infinitely dense and infinitely long rotating string) or negative energy, and you can only ever travel to the start of the loop at the earliest.