It can look dumb, but I always had this question as a kid, what physical principles would prevent this?
this post was submitted on 11 Feb 2025
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Ok so since there's a bunch of science nerds on here and I'm sleep deprived I'm gonna ask my dumb ftl question.
If you're on a train and you walk towards the front of the train, your speed measured from outside of the train is the speed of the train (T) plus the speed of you walking (W).
So if there was a train inside of that train, and you walked inside of that, you'd go the speed of the outside train, plus the speed of the inside train, plus your own walking speed.
So what if we had a Russian nesting doll of trains, so that the inner most train was, from the outside, going as fast as light and you walked towards the front? Wouldn't you be going faster than light if you measured your speed from the outside?
Didn't come at me with how hard it would be to build a Russian nesting doll of super trains it's a hypothetical and I'm tired.
Things get really unintuitive when you go near the speed of light. Einstein's "Special Relativity" is describing that. Watch a couple of videos on the topic. It's mindbending but seriously cool.
In short: The speed light is always constant FOR EVERY OBSERVER. That means, if you would hold a flashlight in a very fast moving train, the light would travel as the same speed for you as for a stationary person that is watching your flashlight from outside the train.
But how could that be? Aren't you "adding" the trains speed to your flashlight? So shouldn't the light in your train travel faster in your train? Or maybe slower? No. Light speed is always constant - but what is NOT constant is space and time. It is relative to the observer. Time and space can stretch/dilate to make up for what seems to be a paradox. E.g. your trains would shrink in length the faster you go. But it would look different to you than it does to an outside observer.
As I said, it's mindbending, but there are a couple of cool and simple videos on the internet to get a better grasp on the matter.
That's wack af