Physicists generally agree that in theory time travel to the future is possible, but
travel to the past is another matter. Some speculate that the distance we can travel
backwards through time may be limited. The moment the first time machine is
activated may be the furthest into the past we can go. This would explain why we
haven't yet met any time travelers from the future. The first time machine has not
been activated yet.
Assume someone activates a time machine tomorrow at breakfast. According to
this hypothesis, how far could that person travel into the past?
The person could not travel back at all until some time had passed.
The person could travel back to the day he or she was born.
The person could never travel to the past, only to the future.