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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Think of it like this. If our universe is a simulation, then the speed of light is the maximum speed at which information can propagate through reality. We know that for anything to move through space, it must move from one adjoining position to another, then another, then another, incrementally. Each one of those increments takes, at minimum, one 'tick' of the universe. That's one tick to increment each bit of information, that is, the position of something moving at light speed from position x,y,z to x+1,y,z. Light moves as fast as the universe allows; if there was a faster speed, light would be doing it, but it turns out that our universe's clock speed only supports speeds of up to 299,792,458 meters per second.
What you have here is sound. Motion propagates through material at the speed of sound in that material. That's part of the reason why moving large scale objects quickly gets weird.
Edit: to be clear, I am not making the case that we're in a simulation. I'm only trying to use computers to make it relatable.
The speed of 'push' is effectivly the speed of sound in a medium. So your shove would be the same as propagating a soundwave through whatever that rod is made of.
Veritassium covers this https://www.youtube.com/watch?v=EPsG8td7C5k&t=61s
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.
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This is actually a great example for why that stick must not exist.
You can also do this with a unbreakable stick and an unbreakable shorter tube. Throw the stick at a high velocity through the tube and it contracts for the point of view of the tube. Then close it shut. Now you have a stick that's longer than the tube fully contained in it.
Putting it on the moon is just a distraction. It doesn't matter if the rod is 1m long or 100,000km.
The whole poll does not move as end entire unit instantaneously. You send a sort of shock-wave through the poll, when you push it from your end. That shockwave has a travel time that's much slower than light. I suspect that the speed of that shockwave probably proportional to the speed of sound in the material that the poll is made of.
Long winded video about it:
'Are solid objects really βsolidβ?' (go-to 7:30)
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Nah, I prefer using quantum spookiness for that. Send a steady stream of entangled particles to the other person on the moon first. Any time you do something to the particles on Earth, the ones on the Moon are affected also. The catch is that this disentangles them, so you have only a few limited uses. This is why you want a constant stream of them being entangled.
You also cannot choose the spins of entangled particles, they collapse randomly in either direction when interacted with, meaning you cannot send messages. If you can figure out how to directly influence the spin of generated subatomic particles then BAM you have FTL communication.
But you would be amazed how many obstacles the universe throws in front of you when you try to break the speed of causality. Faster than light communication isn't possible because it makes no sense when you understand it. It's like "getting answers faster than questions." It's nonsense.
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There's a bunch of these thought experiments that try to posit scenarios where C is violated.
Here's one I remember from uni involving scissors. Similar to what OP was thinking, but really really big scissors.