So, for me, in a vehicle moving at 90% of the speed of light, the time itself slows down such that I observe the photons coming out of my lightbulb still at the speed of light, right? Basically, it would adjust the t in v=s/t because the speed and the distance are to remain constant. And because me and my spaceship or whatever have mass, there will always be a bit of difference between my speed and the speed of light to accommodate this adjustment. That's just so weirdly backwards to think about.

Now, I wonder about redshift and universe expansion deduced from it. Wavelength is a frequency, right? And frequency, by definition, is how many times something (wave period) happens per unit of time. So maybe the universe isn't expanding after all, maybe it's just that time runs faster in the parts of the universe where this light comes from, and the photons just keep oscillating with the frequency that was "correct" in whichever reference frame they were emitted? Besides, the idea that universe expands seems silly tbh. There must be a more sensible explanation. Maybe time slows down over time (?!) and it just ran faster when the universe was younger?