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'm going to say that the speed of the train (relative to earth) and the speed of earth (relative to the sun) and the speed of our solar system (relative to the milky way) and the speed of the milky way (relative to space), though it seems immense to you or I, is almost trivial compared to c.
Likely less than 5% of the speed of c, and probably less than 1% of it. It's unlikely to be anything we can reasonably measure and certainly far less than we would observe without scientific equipment to assist us, it becomes little more than a rounding error.
I agree that it's probably not significant (I don't think, we can actually measure it, but if it were anywhere in the realm of c, reality would be very weird).
However, even if it's at just 0.1% of c, that's going to have an influence on GPS, where precise timing is crucial.
There's a lot of factors that affect the timing of GPS... It's built to be robust enough to handle it, and those factors are a lot more notable and common to be able to detect. Also, if there's an inaccuracy in the speed of light, where it's biased in one direction or another, it's something we've experienced for our entire existence, and it's not something we have detected as of yet, at least not in any measurable way by the current technology...
People smarter that you and I combined have worked on this, to great depth, already, and they haven't found a significant enough issue to even mention it, nevermind publish something about it, and if they had, systems like GPS would have taken that inconsistency into account when designing the system..... If they hadn't, then it's extremely likely that someone would have noticed when GPS was being made.
With all the intelligent people thinking about problems exactly like this and trying to figure things out for humanity already, I find it's best to just take c at it's value, and try not to think about it too much.
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...
Yep, nobody has come up with a way to do it, very very smart physisicts have not solved the problem, there's no hope you or I could.
We can speculate all day about it, but it won't really go further than that. So in lieu of an actual solid scientific answer, we just have to assume that's it's too small of a difference to matter in our current level of technology.
Here's what bakes my noodle though.... The speed of light, c, is a universal constant of speed. Well, speed is relative. It is always relative, but the speed of light being a constant and upper limit of speed, I have to ask, relative to what? If light is moving at this constant speed, what, compared to light, is stationary? The universe is a swirling mass of matter in various shapes, sizes and forms.... Everything is constantly in motion, so what static/stationary thing are we basing that speed off of? Space itself is a vacuum, so there's no real way to tell what the relative "not moving" speed is, and everything in the universe is moving relative to anything and everything else, at varying rates.... Is it the galactic core or the middle of the universe? How do we know that the observable universe isn't moving at incredible speeds?
But I don't want to derail the conversation too much. I know that most of this either delves into deep quantum physics, or is simply outside the realm of the current human understanding of everything, and again, we're left to only speculate about it, which doesn't actually get us anywhere.
IDK, it's fascinating to think about but ultimately, not beneficial to spend significant time on.