Why would'nt this work?
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You are slightly and temporarily increasing the spacing between atoms/compounds in the stick. This spacing will effectively travel like a shockwave of "pull" down the stick.
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Well no. As others have said the force in the pole will travel at the speed of sound.
Though if you were to wiggle the flashlight back and forth really fast the spotlight on the moon would travel "faster" than the speed of light.
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Like some sort of material that has a speed of sound close or equal to the speed of light? Then yeah, it would move about the same speed as the speed of light.
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Wouldn't that still be normal light speed communication from earth to two places on the moon, not FTL communication between two places on the moon?
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Reminds me of
- If you can have dinner with anyone, alive or dead, who would it be?
- No thanks, I've already eaten.
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It was Alpha Phoenix
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Objects like an unbreakable stick are still composed of atoms suspended in space and held together by the fundamental forces of nature. When you push on one end, the other end doesn't immediately move with it but rather the object experiences a wave of compression traveling through it. This wave of compression travels faster than we can perceive but still cannot travel faster than light.
Look up why arrows bend after they've been released by a bow, it's essentially the same mechanic.
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Because you put the apostrophe in the wrong place?
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It's still called the speed of sound. Your intuition is correct in that it's much higher for solid things, but it's still much slower than the speed of light.
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Move a sheet up and down rapidly
You can see the wave travel across it
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So have to ask what a solid is to answer this question.
Sticks are quite complex, so lets consider a simpler solid: an elementally pure iron rod.
You can imagine said rod as if it were a fixed array of crystalline atomic cores surrounded by a jelly-like substance. In this 'jellium' model the atomic cores have a positive charge, they are the protons and neutrons, and the jelly has a negative charge. The jelly is the wavefunction that represents the electron structure in bulk. If that makes no sense, congrats on knowing your limits.
You've probably seen the more modern model of an atom where there's a nucleus and around it is an electron fuzz with discrete energy levels. Or if you've studied at uni strange geometry representing a threshold in probability of finding the electron/s there on a given measurement (if not familiar under certain conditions reality kinda unfocuses it's eyes and things that we often think of as points become volumes of possible effect). This is a good model of a single atom, but when we bring atoms together they change each other's properties and the result is that these density functions (the weird electron cloud/shape things) start to blur together.
In our iron rod the electrons delocalize sufficiently we can kinda think of it as a weird jelly. A real stick is more complex, but can kinda be thought of as a stack of smaller jelly treats packed against each other.
When you push on the rod you're mashing the jelly of your hand into the jelly of the rod, this causes a shockwave that begins to spread, it propagates like a ripple in a skipping rope or a bounce on a trampoline. But since it's moving 'amount of electron like properties here'. That makes some areas more negatively charged which drags the positively charged atom cores slowly after it. It moves much slower than the speed of light as we aren't considering individual electrons which can move energy between them via photons, but the propagation of a disturbance in the collective arrangement of many that are tightly linked (we say coupled).
We can't imagine a stick that is perfectly rigid because we would be proposing a kind of matter that does not exist, one which isn't made of a lot of fuzzy electron jelly stuff but something else entirely. We can imagine matter where the jelly is very stiff, and consequently less energy goes into wobbling it all about and the squish moves forward very fast but that speed is still much slower than light because of this collective behaviour.
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This is an excellently written response.
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It's pretty hand wavy. The question: why is the speed of sound so slow? (which is essentially isomorphic to this one) is pretty hard to answer. I can't do the the maths to derive it anymore haha.
There are similar things about light slowdown during refraction and stuff.
It's just much easier to view certain bulk phenomena as waves in homogeneous material but it can be very unsatisfactory. Hence all the bullshit artists in this thread talking about speed limits, the standard model, and time dilation. For some reason "it just be that way ok?" feels more satisfying if the thing you're asserting seems more fundamental, but it doesn't really make stuff clearer.
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Alright now eli5? Everything is jelly?
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Not going to disagree with that, but you’re responding to somebody who obviously has no background in physics, and it strikes me as a reasonable balance between conceptual (“hand wavy”) and detailed enough.
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Everything soft and slow like your brain yes.
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I used to run physics labs at uni so I'd hope I was as alright teacher still. Never made it as a real physicist though ;_;
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Your push would travel at the speed of sound in the stick. You could think of hitting a pipe with a hammer, the sound of the hit would travel at the speed of sound, same is true for you pushing the stick.
