>>9664546Let’s rerun the experiment and synchronize clocks as the ship passes Earth at D. However, instead of turning around (and changing inertial frames), the pilot turns on the near-hyperdrive at E. It carries him along the dashed line at 0.9 cee.
But 0.9 cee measured in which reference frame? Relative to the Earth? Why should Earth matter? Relative to his motion at the instant before he turned the near-hyperdrive on? Maybe. At least as likely as any other possibility.
Whichever, his “hyper-motion” is directed opposite the way he’d been cruising. We can argue about whether an Earth observer would see him going 0.9 or 0.4 cee, but he's definitely going towards F. When he reaches there, he turns off the near-hyperdrive and resumes his "kinetic" velocity -- which takes him past Earth again, at G, still at 0.5 cee. Clocks can be compared for a 2nd time.
How much has the pilot aged? If he's younger than his stay-at-home counterpart that means he's changed inertial frames at both E and F and undergone time-dilation. Relativity (Special and General) still work even in hyperspace! And if you can’t evade Relativity through some sort of SF motion-without-acceleration, then FTL remains impossible even if we’ve sidestepped the “infinite energy” difficulty.
But what if he’s the same age as his sibling back on Earth? That’s how “Star Trek” works. He never accelerated (or did something like diving deep into a gravity field) to change his time-rate. Yet we’ve been able to compare side-by-side clocks on two separate occasions. We’re right back to the Twin Paradox. Clocks, which were observed to run differently during the first pass, are still right in step when we make the 2nd comparison. We have a logical inconsistency!!
So I don't see the Alcubierre Drive (or hyperspace or subspace or whatever) enabling us to ignore the consequences of superlight travel.
