Don’t misunderstand, I’m not questioning the truth of relativity. I know the necessity of it for GPS to work. This is more of a fundamental understanding issue. I also don’t have a problem with C being a constant, or in understanding that two beams of light heading towards each other still won’t exceed C. I accept relativity as established fact, so I’m not trying to be “clever” and disprove it.

All of this I “get”, as well as someone who’s bad at math CAN get it anyway. I get that it’s not intuitive too. I “get” time dilation too. I get that since C must stay the same, something has to give, and that’s time.

The ONE detail that eludes me is how it picks which one get the slower reference frame compared to the other. I don’t get why the earth wouldn’t be the one to have massively slowed time relative to the space ship, since from the ship’s perspective, isn’t it the earth that goes away, turns around, and comes back? Apparently it isn’t the motion so much as the acceleration that does it, which confuses me even more, since I know a photon experiences zero time, but ALWAYS travels at the speed of light out of necessity, so it never accelerates at all.

I know my question is probably so basic that it’s hard to believe I’d get all that other stuff and still struggle with this one detail, but there it is.