It can look dumb, but I always had this question as a kid, what physical principles would prevent this?
There’s no such thing as a perfectly rigid object.
When you push something you push the atoms in the thing. This in turn pushes the adjacent atoms, when push the adjacent atoms all the way down the line. Very much like pushing water in the bathtub, it ripples down the line. The speed at which atoms propogate this ripple is the speed of sound. In air this is roughly 700mph, but as the substance gets harder* it gets faster. For example, aluminum and steel it is about 11,000mph. That’s why there’s a movie trope about putting your ear to the railroad line to hear the train.
If you are talking about something magically hard then I suppose the speed of sound in that material could approach the speed of light, but still not surpass it. Nothing with mass may travel the speed of light, not even an electron, let alone nuclei.
*generalizing
Perfectly rigid sticks don’t exist.
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.
Because of relativistic effects, from your point of view on the train you would just walk forward. But you would notice a strange effect while the trains were accelerating: your atomically synchronized wristwatch has slowed down and stopped counting time. So it seems that your journey to the front of the train takes no time at all.
From someone standing on the side of the tracks catching a glimpse of you and the train as you whizz by, the front of the train is moving at light speed. You’re at the back of the train completely frozen still, unable to move forward because the front of the train is moving away at light speed.
Weird things happen when you’re talking about the limits of physical reality.
your atomically synchronized wristwatch has slowed down and stopped counting time.
Wait, surely time would move at a normal speed within your own reference frame. The act of you walking to the front of the inner-most train you are in would be a normal occurence to you, but if you looked out of the window you would see a completely frozen scene.
Only once you measure time afterwards with an observer would you notice the gaping time difference.
You are correct, I should have said there was an atomic clock out the window that the walker looked out at.
Not a science nerd. But I would assume the inner trains would like to push forward, stealing some kinetic energy from the outer train because it pushes itself away from the outer train and making the outer train slower or even push back.
Even if it were perfectly rigid, supernaturally so, your push would still only transmit through the stick at the speed of light. The speed of light is the speed of time.
The push would travel at the speed of sound in the stick, much slower than the speed of light
In a “perfectly rigid” stick (a fictional invention), the speed of sound is the speed of light.
No it wouldn’t. Sound is air vibration, which has to travel from one place to the next, static atoms don’t have to actually move to a place just transfer kinetic energy to the adjacenct atom, so it would be much closer to the speed of light. Although probably still (relatively (get it??)) slower.
Sound is air vibration
Sound is not exclusive to air, it can be generalized to vibrations in any media. Whale song and dolphin echolocation are certainly sounds, and we’re almost always talking about them propagating in water rather than air.
which has to travel from one place to the next
No, that isn’t how sound works. In air this would be a description of wind, not sound.
just transfer kinetic energy to the adjacenct atom
This is actually a good description of how sound waves propagate.
Matter is made of atoms. Things are only truly rigid in the small scales we deal with usually.
I predict we’ll have FTL travel before we can invent a stick that’s “unfoldable”.
A wooden stick is pretty much unfordable in an unaltered state Or a glass stick
Glass easily bends
EDIT: It’s in Polish, but it’s still a good video.
Next, I suppose you’ll want to know about the speed of dark 🤨
Damn it even on Lemmy I can’t get to the comments before someone else has the samr idea as me ahaha
Go find a 30’ stick and let us know if you can point it at the moon.
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.
If you’re openminded enough to listen to those who disagree with the standard model,
take an elastic band and turn one end. Instead of the band turning, you’ll have a twist in your band
and it takes time to unravel the twist. That’s what will happen to the stick and this travels at lightspeed,
because this is what light does. Light works like ‘the stick’ in your example.
And if you try turning it faster the ‘elastic band’/stick/‘atom on the other end’ starts breaking.If you need FTL communication, then use gravity…somehow.
Probably quantum entanglement, which we (and certainly I) don’t fully understand yet
I think the standard model says the same thing, tbh…
Gravity waves doesn’t go faster than light though?
Iirc from the 2 YouTube videos I watched light can theoretically bend thanks to gravity, black holes anyone?
Space bends due to gravity. Light continues in a straight line through the now non-linear space, thus appearing to bend.
Gravity bends spacetime, light always goes in a straight line, bent spacetime means straight lines can be curvy. That all checks out.
But none of that helps you with FTL communication.
why wouldn’t this work
because bullets are faster than whatever the fuck speed stickman is achieving
and even bullets are slower than lightalways had this question as a kid
And then went, draw it out, and asked.
I applaud that (and the art), good for you.(And the good people already provided answers.)
The problem lies in what “unstretchable” and “unbendable” means. Its always molecules and your push takes time to reach the other end. You think its instantaneous because you never held such a long stick. The push signal is slower than the light
I would liken it to a long freight train starting to move. Once the front starts moving, it will still be a minute before the back starts moving. The space between the train couplings is like the spring effect between atoms, or something.
You think its instantaneous because you never held such a long stick.
Speak for yourself! 😏
Tbh I thought someone would make that joke when i wrote it lol
Is it instantaneous though?
Basically the speed of sound in that material
