Does time dilation require acceleration? In her latest video, Sabine Hossenfelder seems to get this wrong!
https://www.youtube.com/watch?v=ZdrZf4lQTSg
In the twin paradox, Alice stays at home, while Bob departs to a rapid but long-winded journey, and when he comes back, he's younger than alice. But the time measurement which says that Bob experienced less time than Alice can be done without turning Bob around!
We let Bob meet Carl at a distance who then does the traveling back instead of him. None of our three friends need to accelerate, they just have to meet at three events which form a causal triangle, and be able to compare clocks when that happens!
Alice waits for t years, Bob takes some u years to meet Carl, and Carl needs v more years to get back to Alice, where they learn that t > u+v. That's the triangle inequality with the compare operator flipped! This is caused by the sign flip in Einstein's metric!