In school, I was taught that the speed of light is constant, in the sense that if you shoot a laser off of a train going 200 km/h, it still just goes at a speed of c=299,792,458 m/s, not at c + 200 km/h.
What confuses me about this, is that we’re constantly on a metaphorical train:
The Earth is spinning and going around the sun. The solar system is going around the Milky Way. And the Milky Way is flying through the universe, too.
Let’s call the sum of those speeds v_train.
So, presumably if you shoot a laser into the direction that we’re traveling, it would arrive at the destination as if it was going at 299,792,458 m/s - v_train.
The light is traveling at a fixed speed of c, but its target moves away at a speed of v_train.
This seems like it would have absolutely wild implications.
Do I misunderstand something? Or is v_train so small compared to c that we generally ignore it?
I fully understand anyone who does feel like that, but I’m not having it.
From what I’ve gathered in other responses, we simply cannot measure one-way speed of light.
You can’t have two clocks, at the start and end of some distance, because you can’t synchronise them. The act of moving them apart could desynchronise them. And the most precise way to synchronise them at a distance is with light, which obviously will not suffice.
So, you need to measure it with one clock, which means returning the light to its origin with mirrors (two-way measurement), therefore negating all directional effects. Well, unless those effects would change enough while the light beam is in flight, but that’s likely near-impossible to simulate.
At some point, people can be as smart as they want, they can’t defy physics to actually measure this stuff. I won’t defy those physics either, I just want to know what’s secured and what’s not…