2018-11-26 11:42:20 UTC
Time travel to the future is only possible if Einstein's 1905 conclusion
"the clock moved from A to B lags behind the other which has remained at B" http://www.fourmilab.ch/etexts/einstein/specrel/www/
is true. The conclusion is non sequitur - it doesn't follow VALIDLY from Einstein's 1905 postulates. This means that, even if the postulates were true (actually the second one is false), the conclusion remains unjustified.
The following two conclusions VALIDLY follow from the postulates:
Conclusion 1: The clock moved from A to B lags behind the other which has remained at B, as judged from the stationary system.
Conclusion 2: The clock which has remained at B lags behind the clock moved from A to B, as judged from the moving system.
Conclusions 1 and 2, in their combination, give no prediction for the readings of the two clocks as they meet at B. That is, although conclusions 1 and 2 are logically correct (do follow from the postulates), their combination amounts to nonsense.
In contrast, Einstein's INVALIDLY deduced conclusion
"the clock moved from A to B lags behind the other which has remained at B"
provides a straightforward prediction: The moving clock is slow and accordingly its (moving) owner can remain virtually unchanged while sixty million years are passing for the stationary system (travel into the future par excellence):
Thibault Damour: "The paradigm of the special relativistic upheaval of the usual concept of time is the twin paradox. Let us emphasize that this striking example of time dilation proves that time travel (towards the future) is possible. As a gedanken experiment (if we neglect practicalities such as the technology needed for reaching velocities comparable to the velocity of light, the cost of the fuel and the capacity of the traveller to sustain high accelerations), it shows that a sentient being can jump, "within a minute" (of his experienced time) arbitrarily far in the future, say sixty million years ahead, and see, and be part of, what (will) happen then on Earth. This is a clear way of realizing that the future "already exists" (as we can experience it "in a minute")." http://www.bourbaphy.fr/damourtemps.pdf