Obviously theoretical but if I took a light year long stick and say pushed a button at the other end would that button be pushed at the same time for me as say someone standing at the button? How does the frame of reference work when physically moving something? And could that “work” as a method of instant communication?
In: Planetary Science
This is something that I thought about for a very long time before I found the answer!
Imagine the long stick was made of sponge. If you push one end, the other doesn’t move instantaneously – you’d see a “wave” of sponge travelling along it.
Turns out every material is like that – it’s just that things like metal do it so fast that we can’t detect it at normal human scales. This is why physicists say there’s no such thing as instant or simultaneity. It just appears that way to most people.
No. When you push something it doesn’t all move at the same time, the atoms push each other until they get to the end. This interaction atoms pushing each other is actually what also makes sound travel through an object. So pushing something would happen at the speed of sound in that object.
Basically, you’re talking about rudimentary FTL communication.
In theory, yes, but the rod would need a few additional properties: infinitely rigid and massless. The rigid requirement is to remove any possibility of compression which would normally happen internal to the material. The massless requirement is to overcome internal inertia and gravitational influences.
In practice, no, because ideal material properties don’t exist – hence, theoretical.
Instantaneous communication would also break causality rules as we know them – that is, the person at the receiving end would read the message before light could arrive showing the sender transmitting the message.
To piggyback off this queation, since all you smart folk are here. What if I got an indestructible, 1,000,000 mile long stick and started spinning around. Would the end of that stick go faster than the speed of sound? Why can’t it go faster than light?
I don’t understand the explanations in some of these comments. Can someone please ELI2 😅
If I have a wooden pole, from earth to the moon, and I push it toward the moon, if I see it actually move say 1 meter, why will that take so long for the other end? Wouldn’t it be instant since it’s not like the rod gets shorter. If I can see it move (let’s pretend it’s weightless) then where does it “go” while it is moving?
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Other commenters have raised the central issue that the signal travels through the rod at the speed of sound. If you want to do a practical experiment to demonstrate a similar principle, try the following. Find a slinky and dangle it from a window or the top of a flight of stairs. You want to be high enough that the slinky can fully stretch out and still have some clearance above the floor or the ground. What do you think will happen when you let go of the upper end?
>!the bottom end will stay in place until the upper end falls to meet it, and then the whole thing will fall together!<
No. c is the speed of any information. The fact that light travels at c is only because photons don’t have rest mass, so they travel at the maximum speed of information. Everything in the universe that has mass travels at a slower speed than the speed of information. Everything without mass travels at exactly the speed of information.
If you pushed a very long rod, a couple of things… First, it will be too heavy to move. Something that long would likely weigh more than the Sun.
Second, even if you could push it, you can’t push the entire thing, because you only exist at one location. You can push on the end, which would compress it slightly, starting a wave which would travel down the material at a particular speed. It would be called a compression wave. Another word for compression wave is “sound.”
Your information traveling through a rod of physical material would travel at the speed of sound, which is dependent on the material and its density.
Sound is much slower than light.
This happens because what we call the “solid” state of matter is a macro scale illusion. Molecules and atoms don’t actually touch each other. They are packed closely in what we call a solid but they are separated by the electric charge of the electons in their orbitals. *All solids are made of mostly empty space, and are squishy.*
I thought of this before but with a massive typewriter with the parts that connect the keys to the “stamp” parts being the light years long rods parts.. In other words, you could type and it would print onto the paper that’s light years away.
I know it doesn’t work but I thought that would be a cool way to move info faster than the speed of light.
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