Einstein's spacetime is not just the false alternative of Newton's absolute time. It is a paralyzing idiocy incapable of any prediction about clocks. Popular "predictions" - "Moving clocks run slow", "Traveling twin returns younger" - are actually non sequitur. This was clear to Einstein from the very beginning:
Albert Einstein, On the Electrodynamics of Moving Bodies, 1905: "From this there ensues the following peculiar consequence. If at the points A and B of K there are stationary clocks which, viewed in the stationary system, are synchronous; and if the clock at A is moved with the velocity v along the line AB to B, then on its arrival at B the two clocks no longer synchronize, but the clock moved from A to B lags behind the other which has remained at B by tv^2/2c^2 (up to magnitudes of fourth and higher order), t being the time occupied in the journey from A to B." http://www.fourmilab.ch/etexts/einstein/specrel/www/
"the clock moved from A to B lags behind the other which has remained at B"
does not follow from Einstein's 1905 postulates - the argument is INVALID. This means that the conclusion is unacceptable no matter whether the postulates (the principle of relativity and the constancy of the speed of light) are true or false. Today's wisdom "Moving clocks run slow" is just a generalized formulation of Einstein's 1905 non sequitur.
The following two conclusions, in contrast, VALIDLY follow from the postulates (they will be true if the postulates are true):
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 (symmetrical time dilation) in their combination give no prediction for the readings of the two clocks as they meet at B. This remains the central feature of Einstein's spacetime - without recourse to invalid arguments, it is unable to predict anything about clocks.
Unlike conclusions 1 and 2, the INVALIDLY deduced conclusion does provide a prediction - the moving clock is SLOW, the stationary one is FAST (asymmetrical time dilation). The famous "travel into the future" is a direct implication of the INVALIDLY deduced conclusion - the slowness of the moving clock means that its (moving) owner can remain virtually unchanged while sixty million years are passing for the stationary system:
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