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?

  • Knusper@feddit.deOPEnglish
    2·
    1 year ago

    Man, I hate how it sounds like you’re contradicting yourself. As if you’ve somehow gotten extremely confused by my questions or hit your head or something.

    Someone else posted this video: https://www.pbs.org/video/pbs-space-time-speed-light-not-about-light/
    At least for me personally, that explanation made it click better that we’re not talking about traditional speed, but rather about a general propagation speed limit for causality.

    I certainly don’t understand the implications yet, but I feel like I just have to think about it and re-read everyone’s responses a few times over.

    Thanks a ton for your help!