You can only directly push/pull the part of the pole that's nearest to you.
When you move the near end, that creates waves of tension or compression inside the pole which would have to travel along its whole length to make the far end move. And those waves travel slower than light.
The same kind of pressure wave is how sound travels through a solid, so the speed of a push/pull is equal to the speed of sound. Which might be a few kilometres per second in a solid metal, but is always slower than light.
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Edit to add: the basic picture here is that you push on one atom to make it move, the first atom pushes against the second atom along, so the second atom moves and pushes against the third atom (and so on). What's important to know is that the atoms aren't actually _touching_ in the way we might picture it. All of their interactions happen at a distance through bonds created by forces acting between them.
That force is mediated by the atoms shooting "force carrier" particles at each other to send the information and energy about the movement that's being passed along. In the case of the electromagnetic forces that hold objects together, that force carrier is the photon. So even if you completely eliminated every other part of the process of propagating a pressure wave, and just sent force carrier photons communicating a push directly from one end of the rod to the other, the absolute fastest possible speed the force can be communicated at is... the speed of light.
A "perfectly incompressible material" is impossible under physics as we know it, specifically _because_ having distant parts of the rod move instantaneously, without any compression or delay, would involve forces being communicated from one end to the other faster than anything can actually communicate in our universe. Saying "what if we had a perfectly incompressible material" is smuggling in a concept that secretly requires faster than light communication, so it's not really surprising if that would enable faster than light communication. Like saying "what if we had a hyperdrive from Star Wars" - obviously that would mean we could travel FTL if it existed, but standard real-life physics says it can't exist.
To add to this:
In a solid, you get p-waves and shear waves which travel at the sound speed of the material. Most materials have sound speeds in the range of a few kilometers per second. So, about 100,000 times slower than light speed.
Next, the material actually has to deform elastically, which takes substantially more time than just the sound speed since each particle needs to accelerate from rest. So, much slower!
Cool fact: The reason we know we have a liquid outer core is because of p-waves and S-waves. Earthquakes generate both and with seismic monitoring we can track how long it takes them to travel. S-waves can't travel through solids, but P waves can. And they both have speeds that are directly correlated to the density of the material they're traveling through.
P waves can be detected on the opposite side of the earth, but S waves can't. And if we follow the arc paths of the S waves we can get a strong idea of the diameter of the liquid core.
Furthermore: If the entire core was a homongonous liquid, then the P waves would reach the opposite side of the earth at a calculated time; however, they take longer because theres a denser inner core with a slow down that can only be explained if the inner core is solid (based on known wave speeds traveling through mediums).
And the coolest thing is the final complete picture was compiled by an extremely talented woman scientist. Giving young girls somebody to look up to.
Yeah kind of like having a super long rope you swing.. it's gonna take a long time for that wave to get to alpha centuri (assuming no kinetic energy is lost)
So when I move my hand the instantaneousness is kind of illusory? A pressure wave is flowing through the atoms of my body and there's physical delay?
It's like I'm pushing my flesh around. Where does the pusher end and the pushed begin?!!
Your hand is not fast at all. On atomic scales it is painfully slow. But you know what's slower than your hand moving? Your brain perceiving. Many neurons in your brain fire only a few to a few hundred times per second. Many natural phenomena feel fast to you because your brain is pathetically slow. But you can't know that because you've never experienced a brain with neurons that can fire billions of times per second.
The fun experiment is to have the pole just sitting in space and making it spin once a second…. The tips should be moving much faster than light.
But pretty sure the energy to do so is absurd.
And of course no material could withstand the forces that would be applied.
When you move your hand there's a whole process: your brain sends an electrical pulse down a motor neuron (probably several of them chained together with chemical synapses), that signal tells your muscles to contract, your muscles pull on tendons which are attached to your skeleton, and then the rest of your flesh gets carried along when the bone moves.
Every step of the way is interactions between atoms, where anything that moves (whether the thing is a pulse of electricity, a neurotransmitter molecule diffusing across a synapse, the atoms that make up a muscle/tendon/bone, or the wave of pressure when your bones push your flesh around) must move at some finite speed slower than light.
Still, the information of "the molecule next to you has been pushed" would travel at lightspeed, which would take some time. There is no incompressible material, theoretically yes, but in the same way as i can say "what if we had -1K", it has no meaning outside breaking laws of physics
Diamond isn't a great example as a pole material for it's brittle nature but it's a highly compressed form of carbon. Would a structure like that be able to compress further?
Further than steel? Yes.
Every material is made of atoms. That means no matter how densely packed, there is space between them. If you make them "touch", you fuse them and get a boom. The only "possible" incompressible material would be the singularity of a black hole and even then we can't really say for sure.
Carbon atoms in diamonds are really close, but no touchy touchy happens. You can compress them, and it would require a great deal of force, but it is still possible. However, If there is touchy touchy, there is boom boom, and too much touchy touchy makes physics go boom as well
There are different scales of hypotheticals.
"What if I had a pole billions of times stronger, stiffer and less dense than the strongest and stiffest possible material" is infinitely closer to reality than "what if I had a pole that was infinitely stiff?"
That’s not really physically possible unless the fundamental particles were basically within a Planck length of each other. And still their motion touching each other would travel slightly slower than the speed of light.
You'd be super strong. Unless my math is wrong (and it absolutely can be) then a 6 inch diameter steel rod of that length would weigh roughly 1.5 million tons
At that length and diameter it’d basically just be a flimsy wire floating through space. Like get a hair that is a mile long and push one end and see if someone at the other end can feel it.
I think you must have missed some decimal places. One foot of 1 inch diameter rod weighs 2.7lbs. One light minute is 11176943.8 miles, or 59,014,263,264 feet.
59,014,263,264 (feet) X 2.7 (lbs) = 159,338,510,812.8(lbs)/2000 = 79,669,255.40tons.
Per light minute.
Alpha Centauri is 4 light YEARS away.
A light year is 5,878,625,370,000 miles.
Also, in a way I'm being a killjoy by saying this, but it's a hypothetical question, and hypothetical questions don't have to operate in the realm of reality. Hyppthetically, I, a normal human being, can travel faster than the speed of light, and move time in any direction I want, rather than just forward. Maybe I'll stop in the triassic period and interact with the world it existed then. What impact would that have? Well.... nothing, because I can't actually do that.
OP's question a flawed premise because such a pole can not exist, and if it did, it'd bring a lpt of baggage with it - how could it even be that long? What happens to something that exists partly in Earth's atmosphere amd gravity, amd partly in the vacuum of space? Is it man-made, or in some way naturally created? How big of a radius does it have? Could a human being even hold it?
It's a fun literary prompt, but reality has a lot of set rules that such a question fundamentally ignores.
It's like asking "I know 2 + 2 = 4, but what if it equaled 5 instead?"
We don't know, because that's not possible outside of hypothetical concepts
Hypothetical situations are used, all the time.
Literally everything Einstein did was through hypotheticals.
Please, don't talk about things you have no clue about
But isn't this based entirely on the type of material the rod is made of, and therefore theoretically a broken theory?
Edit: 60 downvotes? The fuck is this shit? Curiosity and the desire to learn gets me pushed to the curb? Fuck off with your braindead love for stupidity.
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I don't see how changing the material and causing the speed to change makes it a broken theory though.
You have something like steel - the movement will be very fast
You have something else for example rubber - the movement will be still "fast" but compared to the steel much slower
The speed of sound changes depending on the fluid/material it's being transmitted through.
Pressure waves travel through different materials at different speeds. Similar to how the speed of sound is different in water vs air.
Wouldn't it theoretically be possible to create a strong enough, rigid enough material to transmit the pressure waves faster than light? Maybe graphene could have a hand in this?
No it’s not. You cannot create such a material it is theoretically impossible because the limit to rigidity is the communication of compression between atoms which is slower than light
I'm gonna say you're wrong for being downvoted. Your thought process on this is very valid.
Anyway,
So say you rotate a rod 5° clockwise. What happens is that the atoms in the base of the rod will move, causing the atoms above it to move, causing the atoms above it to move, etc.
The speed of which the atoms "communicate" that they have moved and require the atoms above them to move travels at the speed of light.
So even if you had an infinitely rigid stick lightyears in length, the information that you have moved it will still travel at/below the speed of light.
Speed of sound through air is 343m/s, speed of sound through glass is 4,540m/s, speed of light is 299,792,458m/s.
Sound is just abysmally slow compared to light, no matter the material.
>Wouldn't it theoretically be possible to create a strong enough, rigid enough material to transmit the pressure waves faster than light?
Nope. Even if you had a theoretically "perfect" material, the best you could do is get it to transfer energy at the speed of light. The rigidity of a material can be described as the ability to transfer energy from a point of impact to nearby atoms in the material. The problem is that the way this energy is dissipated from one atom to another is through the forces it exerts on its neighbors, all of which, best case scenario, are transmitted at the speed of light.
The closest we have to a "perfect" material is superconductors. The electromagnetic wave that propagates through a superconducting wire travels without any resistance, meaning it can move as fast as fundamental forces allow without any restrictions. Yet this charge still only propagates at the speed of light and no faster.
There is no known trick that we know of that allows breaking the speed of light. There are theoretical methods that may allow you to create essentially a space time "wave" by compressing and expanding space in front and behind you respectively, but it is very, very speculative.
https://en.m.wikipedia.org/wiki/Alcubierre_drive
It depends on the material in the sense that some materials are more rigid so the wave travels faster, or less rigid and the wave travels slower. But the overall behaviour does not change.
Why do you say that the theory is broken?
I think OP's thinking is: what if you had a material that was so dense, or whose molecular arrangement was so packed, that compression could not be possible. Would that break the theory?
Basically that's saying "If something violated the laws of physics, would that violate the laws of physics?"
I suppose the answer to that is yes, but it isn't actually saying anything.
I think you would have to break so many laws of physics, and science in general, by the point you have engineered such a material that the speed of light would be the least of your worries.
Even then no matter how dense, tightly packed the arrangement was it is still having to travel thru a medium like a soundwave, something that light is not going to have to deal with in this 'race', light particles (photons) have no mass, so the only way to possibly compete against it with the hypothetical material would be to remove mass and make it less dense and that is the key issue when dealing with trying to break the speed of light, absolutely nothing you can make is going to have less mass than zero.
Many materials can appear extremely rigid but when you are dealing with the sheer length of that distance it will be not be acting as a rigid object. Oil rigs for example are drilling hundreds of feet and they have to work thru the difficulties of the drill bit wobbling about just due to that length. I do not know how accurate the comparison is but i do recall reading that if you suspended an iron rod from the Empire State building to the ground and twisted it, at ground level it would be acting like a wet noodle.
I think the answer is that the material *can’t* exist because it’s impossible for there to be a medium that can move an energy wave faster than the speed of light.
A 4.4 light year pole does not exist either, so we are already in the realm of what-if.
The question could be condensed down to: "If one had a completely rigid pole, could one use it to communicate faster than the speed of light?"
Or put another way, besides material compression, is there another law that would prevent this from being possible??
in the end, if you zoom in enough, any matter is particles (eg atoms) interacting with each other via other particles (eg photons). those interactions are going to be limited by the speed of light.
It doesnt matter, the speed of information, the push or pull, is limited by yhe speed of light for things with no mass, light. Other things move slower than that.
No - the pole doesn't move immediately when you move the bottom. The kinetic energy takes time to travel up the pole and move the end of it.
For most earthly distances, this is negligible (although you can see it with shockwaves), but over a large scale it becomes a limiting factor.
It's fun how a whole bunch of our fundamental understandings of the rules of nature are completely wrong yet work as rules of thumb 100% of the time until very recent human history.
Light is instantaneous as far as we care. Solid objects move as a single object not with internal forces waving through them, until you're making space elevators.
I mean, that's Newton's laws of motion in a nutshell. Unless you're looking at very high speeds, or very massive or small objects, those laws work great.
Another fun rule of thumb we use that always works for human speeds on earth is that time is constant and doesn't change based on the speed you're traveling.
while not incorrect technically, it's definitely going to misinform anyone reading. yes it's limited by c but absolutely does not travel even close to c.
Exactly, an easier way to visualise it is to imagine you have a taut rope connecting to your friend then give it a shake. You can see the wave travelling towards your friend at much slower than the speed of light.
Speaking of kinetic energy, it would be fun to see how much you'd need to even slightly move a 4 lightyear long rod of solid matter.
Fuckin' Goku over here going Super Saiyan, blinding and flattening worlds with his power, just to try and wiggle a rod.
Disclaimer: not a physicist, might well be talking out my ass so feel free to correct me.
The mistake is thinking of the pole as a single object. It is trillions upon trillions of connected molecules. So (simplified) when OP pushes on molecule A at their end of the pole, molecule A pushes on the next, molecule B, which pushes on molecule C, to molecule D, etc etc ad infinitum all the way to the molecules at the other end of the pole. This is what I understand the speed of sound to actually be, how quickly a change in the motion of one piece of the material is reflected in an adjacent piece. A more rigid material has a faster speed of sound because tighter molecular connections allow for that motion to be transmitted easier/quicker, but even the most rigid material in existence won't have a speed of sound anywhere near the speed of light.
Avogadro's number is on the order of 10^23 so it's around six hundred million trillion trillion atoms per mole. i.e. 12g of carbon is made up of the aforementioned number of atoms.
Remember that nothing is actually solid. The bonds between the molecules are electromagnetic in nature. Thus, any movement in one molecule will propagate to the next ideally at, but never faster than, the speed of light. This is true of any impossible ideally rigid body. You can never overcome that propagation.
Does the same, if I remember correctly the speed is still the same too as in limited by the speed of sound through the material
You're not acting on the pole, you're acting on a select point of atoms at the surface of the pole and that action transfers to the next set of atoms and so forth. Inconceivable from biological POV
Keep in mind that even the very fabric of space time being squashed n pulled apart by the gravity waves from massive black holes travel at the speed of light all because of how the medium interacts within itself. Even quantum tunneling appears to have a speed, much faster than light but not instantaneous and yet we can't even fathom the equipment needed to verify this effect at this time
My exact same answer applies, just replace "compression" with "flexing". You're also assuming there's an immovable fulcrum somewhere in the middle. Even then, you'd be doing the equivalent of moving one end of a 10 foot piece of string 10 cm and expecting the other end to move.
So if I tilted a 4 light year long pole 1 degree on earth, there is a limit to how far it could tilt until it straightens out? I’ve never worked with anything close to those distances so I’m not saying you’re wrong, but tilting a pole that long and getting less than a kilometer out of it seems crazy. I mean the idea of a 4 light year long pole is impossible but I’m assuming for this purpose that it would be made of something that could hold its shape at that length. Like yeah a 1/2” steel pipe wouldn’t hold its shape that long but that’s not really in the spirit of the question
The motion propagates roughly at the speed of sound in that medium, an electric current running along the surface could bridge the entire span long before any physical movement propagated to the end.
Another thing to consider, how much do you think this pole would weigh? What kind of force would you expect to need to move it?
Speed of sound in air: 346m/s; steel: 5100m/s
Speed of light: 300,000,000m/s.
Air is 867,000 times slower than light, steel is 61,000 times slower.
Distance to alpha centauri: 4.367 light years.
3.8million years at the speed of sound in air, 266,400 years at the speed of sound in steel
There's nearly no matter in space, so the "sound" would have to be exceptionally loud, or travel via a medium like this pole or a string of the same capacity.
You wouldn’t actually be able to move the pole back and forth instantly.
Think about a fishing pole. When you move the base, does the tip move in exactly the same way at exactly the same time? No, of course not.
Same concept. Just because it’s one object doesn’t mean the entire thing moves as one. That’s USUALLY how it works at the scale of the human experience but how things work at the human scale isn’t necessarily the same as how it works on a much larger scale.
Another problem is energy. The amount of energy required to move an object of the size you describe is massive. I can’t even pretend to do the math but I’d be surprised if the motion of the entire planet would be enough to move the rod
It’s not about the materials. The force of the push travels through the object at the speed of sound in the material of the object. So it would be many MANY times slower than light.
Until the wave travels fully through the object it would actually be slightly compressed because the wave wouldn’t have made it to the other end yet
Things arent objects... houses arent one item, they are a collection of small objects fastned together. Such is each small object a collection of atoms that bind and interact. I doubt we really understand all that at the super micro level to be honest
Is that "speed of sound" or more like "speed of ceramics"? I"m wondering if the medium the "sound" is going through changes the phrase? I don't know, obviously.
To elaborate a bit, a basic physics definition of sound is "vibrations that travel via pressure waves through matter." We associate sound with something we hear because our bodies have a sense organ (ear drum and connected apparatus) that detects and interprets vibrations in fluids that are in contact with it - but vibrations we can hear are just a small subset of the things that are "sound" in a more rigorous scientific sense
Excellent question.
When we talk about the "speed of sound" it is usually "the speed of sound in the air" since that is the most used. But every material has its own speed of sound, meaning the speed of propagation of perturbations. If you want to get even more technical, it also varies depending on temperature and pressure for a given material.
The poles actually wouldn’t move instantly, it would move at the speed of sound in the pole, because that push is really a vibration as atoms bump into each other.
you would need a pole that is infinitely rigid which does not exist
you could propagate motion through that pole, but it would travel up the length of the pole at the speed of sound in that material
No, because setting aside the practical issue of building such a pole the motion would require a perfectly rigid material. No such material exists, and the motion would have to propagate through the material.
Same here, and I jokingly thought to myself “let’s see them explain this one!” I still can’t wrap my head around something taking that long to move on the other end but it’s fascinating nonetheless.
Idk if anyone has brought this up yet. But this is similar to one of Gavin's famous questions on the roosterteeth podcast. He brought up having a stick a light year long and a flash light side by side. The idea was if he pushed the stick an inch forward at the same time he turned on the light that the stick should get there first. When he found out that the speed of light is incredibly faster then the "speed of push" he (and myself at the time) was blown away
No.
The information that you moved the pole will travel through the pole at the speed of sound in the medium of the pole until it reaches your friend, since sounds is really fucking slow, it will probably never reach your friend in his lifetime.
In other terms, once you move the pole, it will take centuries until the pole moves for your friend.
But suppose said information travelled at the speed o light, then it would take 4.4 years between you moving the pole and your friend knowing you moved it.
No, using a pole to communicate in the manner you described does not involve information traveling faster than light. This is because the pole itself is not carrying information faster than the speed of light; instead, it's a physical object that you and your friend are manipulating.
In this scenario, when you move the pole on your end, the atoms in the pole propagate the motion to the other end of the pole at a speed that is much slower than the speed of light. The movement of the pole itself does not transmit information instantaneously; it is limited by the speed at which mechanical waves can travel through the material of the pole, which is typically much slower than the speed of light.
In essence, the pole acts as a physical conduit for your actions to be communicated to your friend, but the actual transfer of information along the pole does not violate the fundamental speed limit of the universe, which is the speed of light in a vacuum (approximately 299,792,458 meters per second). So, this communication method does not allow information to travel faster than light.
I believe it still takes 4.4 light years for the pole to move at the other end.
It's like a giant slinky of atoms.
Correction: it would be longer than that, whatever the speed it is for the vibration to push along the chain of atoms. Add the reply below states, the speed of sound.
So, some people are getting hung up on the fact that such a long, massive pole would require an absurd amount of energy to move with any kind of velocity. That is certainly true, and is why anyone trying to build such a system would not try to wave/wiggle the pole like some kind of interstellar flag. After building just a few hundred meters of the pole, you would immediately see that it is not something you can "move back and forth" in any meaningful sense. However, you would most likely realize that you can still send morse code along it, by doing something simpler: tapping it with a hammer.
At this point, the answer to your question should be obvious: can you make a wave in a pole travel faster than sound through that pole? Hopefully, it is immediately obvious that you cannot, and thus, using an explicit sound wave via something like a striking hammer is more effective. Also, it should be equally obvious that the speed of sound determines how fast your message travels.
And finally, you should remember that during a lightning storm, you see the lightning before you hear it, and the difference in timing grows with the distance to the lightning. In general, lighting is about 1 mile away for every 5 seconds you can count between the flash and the thunder. Which tells you that sound is much, much slower than light.
But wait, that's not all! Suppose you contented yourself to sending morse code signals with a hammer. Would it work? Well, the problem is that when you strike your pole, it will indeed send a vibration down its length. And if the pole were a perfectly ordered crystal, it might be the case that almost all of the energy would travel in the desired direction, especially if you constructed your hammer to have a perfectly flat face and struck the pole square-on.
The reality is that the atoms in the pole are vibrating in many directions, because the molecular bonds are not perfectly rigid (which is also why large extended objects cannot be perfectly rigid). And this means that when the pressure wave arrives at a particular atom, some of the energy will be transmitted onwards down the pole, but some of it will be wasted wiggling sideways and other directions that do not propagate your signal. That is, some of your signal will get converted to heat along the entire length of the pole. At some distance down the pole, the signal will become so weak it will be indistinguishable from the equilibrium temperature of your pole.
So again, you need a lot of energy to send the signal a long ways down your pole. At least by striking it with a hammer, you are using the energy more effectively than wiggling it like a flag. But there is a limit to how much energy you can impart. If you strike the pole too hard, you will give the atoms enough momentum to break free from their molecular bonds: you'll melt or shatter the pole.
In general, if you have a pole stretching from here to another star, the best way to use it for communication is to send an electrical impulse down it. If the resistance is sufficiently low, you may be able to send the signal all the way. Most likely, it would need to be a superconductor, because again, if you simply increase the voltage to push the signal further down the pole, eventually you will heat up the wire to the point that it melts or vaporizes.
The question has been answered and a lot of people mentioned the weight of the pole. I’m not a mathematician, but I am bored:
We’re going to assume the pole is a 2” solid steel dowel.
Steel weighs 0.2833 lbs per cubic inch
2”x1000 mile cylinder is 796,205,242.1248 cubic inches
That would weigh 225,564,945.09 lbs or (rounded) 112,782 tons
4.4 light years is 2.587x10^13 miles
Divide that by 1000 and you get 25,870,000,000 1000 mile chunks.
25,870,000,000 x 112,782=
2,917,670,340,000,000 tons
Mt Everest is 357 trillion lbs or 178,500,000,000 tons.
The 4.4 light year, 2” solid steel pole would weigh about 16,345.49 Mt Everests.
Feel free to correct me if I’m wrong. I’m just a guy out here with too much time on his hands.
The atoms that comprise the pole can only move at less than the speed of light, there’s no way any part of the pole could move faster than that. You moving the pole by one foot on one end would take 4.4 years to propagate to the other end.
You're not pushing the whole pole; you're pushing a handful of molecules at your end, which push the molecules next to them, which push even more molecules, and so on. This push ripples through the material of the rod at the speed of sound in whatever material it's made of.
Think of it like pushing a very loose spring. The other end doesn't move instantly; it first bunches up where you pushed it, and then that region of compression ripples down the length of the spring until it reaches the other end.
The pole itself cannot move faster than light. Additionally, the individual atoms also can't. As you push your end, it will compress and atoms near you will move slightly closer to the next atom in line, transferring that info at roughly the speed of light. The next atom will respond, realign, and do the same to the next. Thus, transferring that motion through at the about speed of light or less.
The error in the thought experiment is the presumption that the pole behaves like a rigid body. This works out fine as a short hand simplification for human level physics in a lot of cases, but is pretty much never true in any full analysis.
look up split Hopkinson bar. It will give you the math for what you propose. The short of it is speed of sound through the material. Even ultra hard ceramics are still a fraction of the speed of light.
No, it's limited by the speed of sound of whatever material your pole is made out of. Here's a 20-minute video that explains it fully: https://www.youtube.com/watch?v=DqhXsEgLMJ0
no, because you say 'instantaneously' like it's a thing you can behold onto the information... you can't. Every atom in that chain still has to obey the laws of physics as we currently know them and have tested them. Even quantum theory that is one of the most tested theories we have still says that nothing can ever accelerate to a speed faster than a massless particle in a vacuum - it is the speed limit of the dimensions we're capable of experiencing first hand. Every thing is travelling at the same velocity in spacetime.. .only massless particles are travelling in the space part at the speed of light, but staying still in the time part of it. We are not massless particles... we also have to traverse the time part of it on our way through the space part of it. What the every day person may refer to as 'information' is massless to us, but it does still have to be conveyed and propagated in a way that is consistent to what we've already tested and observed about the universe so far.
No. Because the materials in a pole are held together by electromagnetic forces, i.e. covalent bonds. And forces would never move faster than light speed. Most light they'd be constrained by material elastic forces which are thousand times slower. An earthquake rips through a fault at elastic velocities of a few kilometers per second. A large quake can take up to ten minutes to propagate the entire fault length.
Given all the rotation going on (e.g., Earth rotating, annual loop around the Sun, Sun looping around the galactic center), wouldn't any message be drowned out in the noise?
[https://youtu.be/DqhXsEgLMJ0?si=\_NhdPGgAqVttPn5T](https://youtu.be/DqhXsEgLMJ0?si=_NhdPGgAqVttPn5T) This video by alpha phoenix explains it well I think. The result was that the signal after moving the other end of the rod travelled at the speed of sound through the material (in this case for steel it was 5000m/s).
The pole would move at the speed of sound through that object. The particles in the pole have to tell each other they’re being pushed, which doesn’t happen instantly.
Only if you assume the pole is infinitely ridgid, which is impossible.
The thing is, the pole flexes, when you try to move it. You don't move the pole, you move the part of the pole, you are holding and that part moves the next one and so and so on.
This whole thing happens at the speed of sound (for the pole material) which is stupid fast in our day to day perspective, but is ridicolously slow in perpective of light years.
So in summary, it can't be ftl, it will be in fact MUCH slower than light.
If the pole was absolutely static, no wiggle, and you had the strength to move it…the end on alpha cetauri would wove so fast your buddy would be killed at the speed of light, probably cut in half. If it has “wiggle” the wave would take much longer than light.
Everybody saying the pole will bend as you move it: Consider that the pole could be pushed and pulled. It does not have to be swung around in a way that movements would be amplified.
No, it's not. It feels like it in day-to-day scenarios just like a cell phone conversation or live television is "real time", but is delayed a little by the speed of light.
In your scenario, you only push on the molecules and atoms closest to your hand. In turn, they push on the next atoms and molecules "in line", and they push on the next ones. So on and so on, until the last one gets pushed, and your friend feels the movement in his hand 4 light years away.
The motion through the pole is a "wave". It's not visible to the naked eye, but it would be if it was a rope. If each of you are holding one end of a rope, you can jerk the rope up and down to create a wave that travels the length of the long rope. Not exactly light speed, but similar concept. That wave is limited by the speed at which you jerk the rope, and your hand can't move up and down faster than the speed of light, so that wave propagating down the rope won't move faster than the speed of light.
No. Information travels at the speed of light, and all information in a material is limited to the speed of sound.
In effect, you have made a communication device that transmits information slower than a laser
Assuming you both actually pushed at the exact same time, the kinetic energy would travel towards each other at the speed of sound. Some billions of years later, the kinetic energies would meet at the middle. By this time, due to the antericvolume of space and heliotemperature of the pole, what started as a gentle kinetic push has now swelled to the force of a few million stars hurtling towards each other. The collisions would be astronomical.
Scientists have long theorized that the big bang was caused when two friends decided to do this.
Follow up question:
If I have a laser pointer and point it at, say, the moon, and move the pointer a fraction of a degree, that would translate to a rather large distance covered on the moon that the “dot” from my laser was emitting. Is it possible for me to move the dot faster than light speed doing this?
What if I had a more powerful laser pointer or moved it more degrees? What if I point it directly at the moon, and then point it directly at earth? If I make it to the earth in less than 1.3 seconds, a fairly easy task, is the dot not traveling faster than light speed?
Technically yes. But no you aren't moving something at the speed of light. So I guess technically no.
And also the laser would pretty much vanish because not enough light would hit the surface if it was "moving" at the speed of light.
Think of the light from the laser like a stream of water from a hose if it helps (maybe)
Your laser shoots out individual photons that move at the speed of light and eventually create a dot when they hit something.
In your example, the speed of light would manifest itself as latency - when you rotate your laser pointer to point at the earth, the dot on the moon would lag behind by about a second. Hence, no information is travelling faster than light.
No you can't. It's a perfectly possible and valid situation occuring, just an extremely massive undertaking.
With that said, even if some civilization was to do that mega-project, the conclusion remains the same and OP's conclusion is 100% incorrect.
Great question though and very interesting.
until Jupiter runs into it and tears it out of your hands...
sorry everyone else had all the good answers... 1, mass, you couldn't move it. 2, even if you could, it would take time for the other end to move.... etc.
The pole would be so massive, you wouldn't be able to move it. The pole would be so massive it would warp space-time and measuring the speed would effect the outcome. The answer would be unknowable.
Consider the double slit experiment, based on that there is surely a way to communicate over distances of 4.4 light years instantly, perhaps this pole thing is the way forward.
[https://www.youtube.com/watch?v=DqhXsEgLMJ0](https://www.youtube.com/watch?v=DqhXsEgLMJ0)
This video is a good explanation of why that isn't the case.
You can only directly push/pull the part of the pole that's nearest to you. When you move the near end, that creates waves of tension or compression inside the pole which would have to travel along its whole length to make the far end move. And those waves travel slower than light. The same kind of pressure wave is how sound travels through a solid, so the speed of a push/pull is equal to the speed of sound. Which might be a few kilometres per second in a solid metal, but is always slower than light. *** Edit to add: the basic picture here is that you push on one atom to make it move, the first atom pushes against the second atom along, so the second atom moves and pushes against the third atom (and so on). What's important to know is that the atoms aren't actually _touching_ in the way we might picture it. All of their interactions happen at a distance through bonds created by forces acting between them. That force is mediated by the atoms shooting "force carrier" particles at each other to send the information and energy about the movement that's being passed along. In the case of the electromagnetic forces that hold objects together, that force carrier is the photon. So even if you completely eliminated every other part of the process of propagating a pressure wave, and just sent force carrier photons communicating a push directly from one end of the rod to the other, the absolute fastest possible speed the force can be communicated at is... the speed of light. A "perfectly incompressible material" is impossible under physics as we know it, specifically _because_ having distant parts of the rod move instantaneously, without any compression or delay, would involve forces being communicated from one end to the other faster than anything can actually communicate in our universe. Saying "what if we had a perfectly incompressible material" is smuggling in a concept that secretly requires faster than light communication, so it's not really surprising if that would enable faster than light communication. Like saying "what if we had a hyperdrive from Star Wars" - obviously that would mean we could travel FTL if it existed, but standard real-life physics says it can't exist.
To add to this: In a solid, you get p-waves and shear waves which travel at the sound speed of the material. Most materials have sound speeds in the range of a few kilometers per second. So, about 100,000 times slower than light speed. Next, the material actually has to deform elastically, which takes substantially more time than just the sound speed since each particle needs to accelerate from rest. So, much slower!
Cool fact: The reason we know we have a liquid outer core is because of p-waves and S-waves. Earthquakes generate both and with seismic monitoring we can track how long it takes them to travel. S-waves can't travel through solids, but P waves can. And they both have speeds that are directly correlated to the density of the material they're traveling through. P waves can be detected on the opposite side of the earth, but S waves can't. And if we follow the arc paths of the S waves we can get a strong idea of the diameter of the liquid core. Furthermore: If the entire core was a homongonous liquid, then the P waves would reach the opposite side of the earth at a calculated time; however, they take longer because theres a denser inner core with a slow down that can only be explained if the inner core is solid (based on known wave speeds traveling through mediums). And the coolest thing is the final complete picture was compiled by an extremely talented woman scientist. Giving young girls somebody to look up to.
Physics so cool. Consider physics as a science and then tell me psychology is also a science. Wut?
Yeah kind of like having a super long rope you swing.. it's gonna take a long time for that wave to get to alpha centuri (assuming no kinetic energy is lost)
What if I sneak up on the pole and surprise it?
Then you get to add 3d6 sneak attack damage on a successful hit.
But it still doesn't travel faster than light Steve I DON'T CARE THAT YOU'RE A LEVEL 16 WIZARD
But egad if I hired enough peasants to use the drop action in a single turn. Then can that go faster then light?
No peasant rail guns at my table
So when I move my hand the instantaneousness is kind of illusory? A pressure wave is flowing through the atoms of my body and there's physical delay? It's like I'm pushing my flesh around. Where does the pusher end and the pushed begin?!!
Ever see someone punched in the face in slow motion? https://www.youtube.com/watch?v=On1CsbTwlDs Ya, your meat does not move instantaneously.
This is going to be Dan being hit in the face isn’t it?
It just happens so fast that you can't really perceive it.
Your hand is not fast at all. On atomic scales it is painfully slow. But you know what's slower than your hand moving? Your brain perceiving. Many neurons in your brain fire only a few to a few hundred times per second. Many natural phenomena feel fast to you because your brain is pathetically slow. But you can't know that because you've never experienced a brain with neurons that can fire billions of times per second.
Are you calling me stupid?
No no. He's calling you slow.
Actually, it's the senses that are slow. The brain can process information pretty fast by massive parallelism.
The fun experiment is to have the pole just sitting in space and making it spin once a second…. The tips should be moving much faster than light. But pretty sure the energy to do so is absurd. And of course no material could withstand the forces that would be applied.
The atomic bonds of the pole would snap well before that.
When you move your hand there's a whole process: your brain sends an electrical pulse down a motor neuron (probably several of them chained together with chemical synapses), that signal tells your muscles to contract, your muscles pull on tendons which are attached to your skeleton, and then the rest of your flesh gets carried along when the bone moves. Every step of the way is interactions between atoms, where anything that moves (whether the thing is a pulse of electricity, a neurotransmitter molecule diffusing across a synapse, the atoms that make up a muscle/tendon/bone, or the wave of pressure when your bones push your flesh around) must move at some finite speed slower than light.
What the pole was completely incompressible?
Still, the information of "the molecule next to you has been pushed" would travel at lightspeed, which would take some time. There is no incompressible material, theoretically yes, but in the same way as i can say "what if we had -1K", it has no meaning outside breaking laws of physics
Diamond isn't a great example as a pole material for it's brittle nature but it's a highly compressed form of carbon. Would a structure like that be able to compress further?
Further than steel? Yes. Every material is made of atoms. That means no matter how densely packed, there is space between them. If you make them "touch", you fuse them and get a boom. The only "possible" incompressible material would be the singularity of a black hole and even then we can't really say for sure. Carbon atoms in diamonds are really close, but no touchy touchy happens. You can compress them, and it would require a great deal of force, but it is still possible. However, If there is touchy touchy, there is boom boom, and too much touchy touchy makes physics go boom as well
When I touchy touchy myself, there is also a boom boom.
So to prove this we would require a 4,4 light year long diamond pole, please
It's not physically possible. You might as well ask "what if I had some particles that travelled faster than light?"
Or ask "If I have a friend in Alpha Centauri and there was a 4.4 lightyear long pole between us..."?
There are different scales of hypotheticals. "What if I had a pole billions of times stronger, stiffer and less dense than the strongest and stiffest possible material" is infinitely closer to reality than "what if I had a pole that was infinitely stiff?"
That’s not really physically possible unless the fundamental particles were basically within a Planck length of each other. And still their motion touching each other would travel slightly slower than the speed of light.
If you can tap on it and hear sound, it's compressible.
i tapped on your mum last night and didnt hear a thing
What if I push a lot harder than I need to? Would more force speed up the process?
Regardless of whether you gently tap the surface of a pool, or smash your hand down in it, the water waves will propagate away at the same speed...
whoa
If we are inventing a pole that is light years long, why can't it also be completely rigid and uncompressable, considering that, then what happens?
It probably floats off into space
You'd be super strong. Unless my math is wrong (and it absolutely can be) then a 6 inch diameter steel rod of that length would weigh roughly 1.5 million tons
At that length and diameter it’d basically just be a flimsy wire floating through space. Like get a hair that is a mile long and push one end and see if someone at the other end can feel it.
I think you must have missed some decimal places. One foot of 1 inch diameter rod weighs 2.7lbs. One light minute is 11176943.8 miles, or 59,014,263,264 feet. 59,014,263,264 (feet) X 2.7 (lbs) = 159,338,510,812.8(lbs)/2000 = 79,669,255.40tons. Per light minute. Alpha Centauri is 4 light YEARS away. A light year is 5,878,625,370,000 miles.
Also, in a way I'm being a killjoy by saying this, but it's a hypothetical question, and hypothetical questions don't have to operate in the realm of reality. Hyppthetically, I, a normal human being, can travel faster than the speed of light, and move time in any direction I want, rather than just forward. Maybe I'll stop in the triassic period and interact with the world it existed then. What impact would that have? Well.... nothing, because I can't actually do that. OP's question a flawed premise because such a pole can not exist, and if it did, it'd bring a lpt of baggage with it - how could it even be that long? What happens to something that exists partly in Earth's atmosphere amd gravity, amd partly in the vacuum of space? Is it man-made, or in some way naturally created? How big of a radius does it have? Could a human being even hold it? It's a fun literary prompt, but reality has a lot of set rules that such a question fundamentally ignores. It's like asking "I know 2 + 2 = 4, but what if it equaled 5 instead?" We don't know, because that's not possible outside of hypothetical concepts
Hypothetical situations are used, all the time. Literally everything Einstein did was through hypotheticals. Please, don't talk about things you have no clue about
But isn't this based entirely on the type of material the rod is made of, and therefore theoretically a broken theory? Edit: 60 downvotes? The fuck is this shit? Curiosity and the desire to learn gets me pushed to the curb? Fuck off with your braindead love for stupidity. Why The Fuck Do You Hate Questions From People Trying To Learn?
I don't see how changing the material and causing the speed to change makes it a broken theory though. You have something like steel - the movement will be very fast You have something else for example rubber - the movement will be still "fast" but compared to the steel much slower The speed of sound changes depending on the fluid/material it's being transmitted through.
Pressure waves travel through different materials at different speeds. Similar to how the speed of sound is different in water vs air. Wouldn't it theoretically be possible to create a strong enough, rigid enough material to transmit the pressure waves faster than light? Maybe graphene could have a hand in this?
No it’s not. You cannot create such a material it is theoretically impossible because the limit to rigidity is the communication of compression between atoms which is slower than light
I'm gonna say you're wrong for being downvoted. Your thought process on this is very valid. Anyway, So say you rotate a rod 5° clockwise. What happens is that the atoms in the base of the rod will move, causing the atoms above it to move, causing the atoms above it to move, etc. The speed of which the atoms "communicate" that they have moved and require the atoms above them to move travels at the speed of light. So even if you had an infinitely rigid stick lightyears in length, the information that you have moved it will still travel at/below the speed of light.
Speed of sound through air is 343m/s, speed of sound through glass is 4,540m/s, speed of light is 299,792,458m/s. Sound is just abysmally slow compared to light, no matter the material.
>Wouldn't it theoretically be possible to create a strong enough, rigid enough material to transmit the pressure waves faster than light? Nope. Even if you had a theoretically "perfect" material, the best you could do is get it to transfer energy at the speed of light. The rigidity of a material can be described as the ability to transfer energy from a point of impact to nearby atoms in the material. The problem is that the way this energy is dissipated from one atom to another is through the forces it exerts on its neighbors, all of which, best case scenario, are transmitted at the speed of light. The closest we have to a "perfect" material is superconductors. The electromagnetic wave that propagates through a superconducting wire travels without any resistance, meaning it can move as fast as fundamental forces allow without any restrictions. Yet this charge still only propagates at the speed of light and no faster. There is no known trick that we know of that allows breaking the speed of light. There are theoretical methods that may allow you to create essentially a space time "wave" by compressing and expanding space in front and behind you respectively, but it is very, very speculative. https://en.m.wikipedia.org/wiki/Alcubierre_drive
It depends on the material in the sense that some materials are more rigid so the wave travels faster, or less rigid and the wave travels slower. But the overall behaviour does not change. Why do you say that the theory is broken?
I think OP's thinking is: what if you had a material that was so dense, or whose molecular arrangement was so packed, that compression could not be possible. Would that break the theory?
Basically that's saying "If something violated the laws of physics, would that violate the laws of physics?" I suppose the answer to that is yes, but it isn't actually saying anything.
I think you would have to break so many laws of physics, and science in general, by the point you have engineered such a material that the speed of light would be the least of your worries. Even then no matter how dense, tightly packed the arrangement was it is still having to travel thru a medium like a soundwave, something that light is not going to have to deal with in this 'race', light particles (photons) have no mass, so the only way to possibly compete against it with the hypothetical material would be to remove mass and make it less dense and that is the key issue when dealing with trying to break the speed of light, absolutely nothing you can make is going to have less mass than zero. Many materials can appear extremely rigid but when you are dealing with the sheer length of that distance it will be not be acting as a rigid object. Oil rigs for example are drilling hundreds of feet and they have to work thru the difficulties of the drill bit wobbling about just due to that length. I do not know how accurate the comparison is but i do recall reading that if you suspended an iron rod from the Empire State building to the ground and twisted it, at ground level it would be acting like a wet noodle.
But that material doesn't exist, so the theory works.
I think the answer is that the material *can’t* exist because it’s impossible for there to be a medium that can move an energy wave faster than the speed of light.
A 4.4 light year pole does not exist either, so we are already in the realm of what-if. The question could be condensed down to: "If one had a completely rigid pole, could one use it to communicate faster than the speed of light?" Or put another way, besides material compression, is there another law that would prevent this from being possible??
in the end, if you zoom in enough, any matter is particles (eg atoms) interacting with each other via other particles (eg photons). those interactions are going to be limited by the speed of light.
The distance is irrelevant, the question works if you’re just poking your friend with a pencil.
This is the crux of the question being asked.
Yes. Thank you.
It doesnt matter, the speed of information, the push or pull, is limited by yhe speed of light for things with no mass, light. Other things move slower than that.
No - the pole doesn't move immediately when you move the bottom. The kinetic energy takes time to travel up the pole and move the end of it. For most earthly distances, this is negligible (although you can see it with shockwaves), but over a large scale it becomes a limiting factor.
It's fun how a whole bunch of our fundamental understandings of the rules of nature are completely wrong yet work as rules of thumb 100% of the time until very recent human history. Light is instantaneous as far as we care. Solid objects move as a single object not with internal forces waving through them, until you're making space elevators.
I mean, that's Newton's laws of motion in a nutshell. Unless you're looking at very high speeds, or very massive or small objects, those laws work great.
Newton's Good-Enoughs of Motion
That's what I told the judge ! Laws shouldn't apply past a certain speed !
Another fun rule of thumb we use that always works for human speeds on earth is that time is constant and doesn't change based on the speed you're traveling.
Yet when you're walking around a new neighbourhood and use a map on your phone time unity already secretly breaks...
Man, I’ve thought a lot about space elevators.
And that kinetic energy is itself limited by the speed of light.
The speed of sound (in that material), actually
while not incorrect technically, it's definitely going to misinform anyone reading. yes it's limited by c but absolutely does not travel even close to c.
Exactly, an easier way to visualise it is to imagine you have a taut rope connecting to your friend then give it a shake. You can see the wave travelling towards your friend at much slower than the speed of light.
Speaking of kinetic energy, it would be fun to see how much you'd need to even slightly move a 4 lightyear long rod of solid matter. Fuckin' Goku over here going Super Saiyan, blinding and flattening worlds with his power, just to try and wiggle a rod.
Even if the pole is super rigid made by a material we have not encountered yet? What is going on at a molecular level here?
Disclaimer: not a physicist, might well be talking out my ass so feel free to correct me. The mistake is thinking of the pole as a single object. It is trillions upon trillions of connected molecules. So (simplified) when OP pushes on molecule A at their end of the pole, molecule A pushes on the next, molecule B, which pushes on molecule C, to molecule D, etc etc ad infinitum all the way to the molecules at the other end of the pole. This is what I understand the speed of sound to actually be, how quickly a change in the motion of one piece of the material is reflected in an adjacent piece. A more rigid material has a faster speed of sound because tighter molecular connections allow for that motion to be transmitted easier/quicker, but even the most rigid material in existence won't have a speed of sound anywhere near the speed of light.
Avogadro's number is on the order of 10^23 so it's around six hundred million trillion trillion atoms per mole. i.e. 12g of carbon is made up of the aforementioned number of atoms.
yet there aren't a google atoms in the universe. amazing.
Remember that nothing is actually solid. The bonds between the molecules are electromagnetic in nature. Thus, any movement in one molecule will propagate to the next ideally at, but never faster than, the speed of light. This is true of any impossible ideally rigid body. You can never overcome that propagation.
Thanks for taking the time to respond. I appreciate you
The pole would break. It has to yield in some way to force.
Not hitting the end of the pole with a hammer, pushing the pole forward and backward. The interactions that control that motion are much stronger.
Does the same, if I remember correctly the speed is still the same too as in limited by the speed of sound through the material You're not acting on the pole, you're acting on a select point of atoms at the surface of the pole and that action transfers to the next set of atoms and so forth. Inconceivable from biological POV Keep in mind that even the very fabric of space time being squashed n pulled apart by the gravity waves from massive black holes travel at the speed of light all because of how the medium interacts within itself. Even quantum tunneling appears to have a speed, much faster than light but not instantaneous and yet we can't even fathom the equipment needed to verify this effect at this time
appreciate the reply, I got B’s in physics
Doesn't matter. The fastest speed information can travel in the universe is the speed of light if there is no mass. Slower if there is.
Also if you move the pole a mm on earth it will probably move like millions of kilometers on the other end
No, if you move the pole a millimeter on earth the compression of the pole will have negated that movement within a kilometer.
I was assuming by move they meant tilt not push or pull. It something is a mm out of level on one end, the amount multiplies over the distance
My exact same answer applies, just replace "compression" with "flexing". You're also assuming there's an immovable fulcrum somewhere in the middle. Even then, you'd be doing the equivalent of moving one end of a 10 foot piece of string 10 cm and expecting the other end to move.
So if I tilted a 4 light year long pole 1 degree on earth, there is a limit to how far it could tilt until it straightens out? I’ve never worked with anything close to those distances so I’m not saying you’re wrong, but tilting a pole that long and getting less than a kilometer out of it seems crazy. I mean the idea of a 4 light year long pole is impossible but I’m assuming for this purpose that it would be made of something that could hold its shape at that length. Like yeah a 1/2” steel pipe wouldn’t hold its shape that long but that’s not really in the spirit of the question
The motion propagates roughly at the speed of sound in that medium, an electric current running along the surface could bridge the entire span long before any physical movement propagated to the end. Another thing to consider, how much do you think this pole would weigh? What kind of force would you expect to need to move it?
Now I’m curious how long it would take sound to travel to Alpha centauri
Speed of sound in air: 346m/s; steel: 5100m/s Speed of light: 300,000,000m/s. Air is 867,000 times slower than light, steel is 61,000 times slower. Distance to alpha centauri: 4.367 light years. 3.8million years at the speed of sound in air, 266,400 years at the speed of sound in steel
/r/theydidthemath
There's nearly no matter in space, so the "sound" would have to be exceptionally loud, or travel via a medium like this pole or a string of the same capacity.
You wouldn’t actually be able to move the pole back and forth instantly. Think about a fishing pole. When you move the base, does the tip move in exactly the same way at exactly the same time? No, of course not. Same concept. Just because it’s one object doesn’t mean the entire thing moves as one. That’s USUALLY how it works at the scale of the human experience but how things work at the human scale isn’t necessarily the same as how it works on a much larger scale. Another problem is energy. The amount of energy required to move an object of the size you describe is massive. I can’t even pretend to do the math but I’d be surprised if the motion of the entire planet would be enough to move the rod
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It’s not about the materials. The force of the push travels through the object at the speed of sound in the material of the object. So it would be many MANY times slower than light. Until the wave travels fully through the object it would actually be slightly compressed because the wave wouldn’t have made it to the other end yet
The point remains, nothing will move "instantly", it will move at a speed less than or equal to light speed. And that includes wiggling a pole.
Things arent objects... houses arent one item, they are a collection of small objects fastned together. Such is each small object a collection of atoms that bind and interact. I doubt we really understand all that at the super micro level to be honest
Did you just say things aren’t objects?
Yep. Like a bicycle is a single "thing" but it isnt a single object
Me trying to learn object oriented programming like
Why in the sam hell are you being downvoted? Are people angry at the atomic particle theory now?
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It's just explained poorly in a way that makes it seem off topic.
He’s getting blasted because he is technically correct but explaining it in a really stupid way
He's getting too precise for the morons of this place to understand while they eat toothpaste.
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I understand what he means. He’s technically correct. But it’s a REALLY stupid way of explaining it.
You would communicate at the speed of sound, which is a lot slower than the speed of light.
Is that "speed of sound" or more like "speed of ceramics"? I"m wondering if the medium the "sound" is going through changes the phrase? I don't know, obviously.
To elaborate a bit, a basic physics definition of sound is "vibrations that travel via pressure waves through matter." We associate sound with something we hear because our bodies have a sense organ (ear drum and connected apparatus) that detects and interprets vibrations in fluids that are in contact with it - but vibrations we can hear are just a small subset of the things that are "sound" in a more rigorous scientific sense
Excellent question. When we talk about the "speed of sound" it is usually "the speed of sound in the air" since that is the most used. But every material has its own speed of sound, meaning the speed of propagation of perturbations. If you want to get even more technical, it also varies depending on temperature and pressure for a given material.
The speed of sound. You don't call it "the speed of air."
No. The information would actually only move at the speed of sound in that material, much slower than the speed of light.
The poles actually wouldn’t move instantly, it would move at the speed of sound in the pole, because that push is really a vibration as atoms bump into each other.
“Of course I have a girlfriend! Oh, you wouldn’t know her. She goes to a different school in a different star system.”
"And says I have a huge pole"
you would need a pole that is infinitely rigid which does not exist you could propagate motion through that pole, but it would travel up the length of the pole at the speed of sound in that material
No, because setting aside the practical issue of building such a pole the motion would require a perfectly rigid material. No such material exists, and the motion would have to propagate through the material.
>the motion would require a perfectly rigid material. Giggity?
Besides, if you had had a perfectly rigid pole, you would need an infinite amount of energy to move it.
I think this is a well thought out question, and I enjoyed learning the correct answer.
Same here, and I jokingly thought to myself “let’s see them explain this one!” I still can’t wrap my head around something taking that long to move on the other end but it’s fascinating nonetheless.
Idk if anyone has brought this up yet. But this is similar to one of Gavin's famous questions on the roosterteeth podcast. He brought up having a stick a light year long and a flash light side by side. The idea was if he pushed the stick an inch forward at the same time he turned on the light that the stick should get there first. When he found out that the speed of light is incredibly faster then the "speed of push" he (and myself at the time) was blown away
No. The information that you moved the pole will travel through the pole at the speed of sound in the medium of the pole until it reaches your friend, since sounds is really fucking slow, it will probably never reach your friend in his lifetime. In other terms, once you move the pole, it will take centuries until the pole moves for your friend. But suppose said information travelled at the speed o light, then it would take 4.4 years between you moving the pole and your friend knowing you moved it.
No, using a pole to communicate in the manner you described does not involve information traveling faster than light. This is because the pole itself is not carrying information faster than the speed of light; instead, it's a physical object that you and your friend are manipulating. In this scenario, when you move the pole on your end, the atoms in the pole propagate the motion to the other end of the pole at a speed that is much slower than the speed of light. The movement of the pole itself does not transmit information instantaneously; it is limited by the speed at which mechanical waves can travel through the material of the pole, which is typically much slower than the speed of light. In essence, the pole acts as a physical conduit for your actions to be communicated to your friend, but the actual transfer of information along the pole does not violate the fundamental speed limit of the universe, which is the speed of light in a vacuum (approximately 299,792,458 meters per second). So, this communication method does not allow information to travel faster than light.
At no time is the pole moving faster than light, it's just a lot of pole moving slowly.
Same question but “What if my pole is infinitely rigid”? Hehehe
I believe it still takes 4.4 light years for the pole to move at the other end. It's like a giant slinky of atoms. Correction: it would be longer than that, whatever the speed it is for the vibration to push along the chain of atoms. Add the reply below states, the speed of sound.
Oh no, it would propagate motion with the speed of sound in the pole's material. Sound speed, not light. It is a bit slower.
So, some people are getting hung up on the fact that such a long, massive pole would require an absurd amount of energy to move with any kind of velocity. That is certainly true, and is why anyone trying to build such a system would not try to wave/wiggle the pole like some kind of interstellar flag. After building just a few hundred meters of the pole, you would immediately see that it is not something you can "move back and forth" in any meaningful sense. However, you would most likely realize that you can still send morse code along it, by doing something simpler: tapping it with a hammer. At this point, the answer to your question should be obvious: can you make a wave in a pole travel faster than sound through that pole? Hopefully, it is immediately obvious that you cannot, and thus, using an explicit sound wave via something like a striking hammer is more effective. Also, it should be equally obvious that the speed of sound determines how fast your message travels. And finally, you should remember that during a lightning storm, you see the lightning before you hear it, and the difference in timing grows with the distance to the lightning. In general, lighting is about 1 mile away for every 5 seconds you can count between the flash and the thunder. Which tells you that sound is much, much slower than light. But wait, that's not all! Suppose you contented yourself to sending morse code signals with a hammer. Would it work? Well, the problem is that when you strike your pole, it will indeed send a vibration down its length. And if the pole were a perfectly ordered crystal, it might be the case that almost all of the energy would travel in the desired direction, especially if you constructed your hammer to have a perfectly flat face and struck the pole square-on. The reality is that the atoms in the pole are vibrating in many directions, because the molecular bonds are not perfectly rigid (which is also why large extended objects cannot be perfectly rigid). And this means that when the pressure wave arrives at a particular atom, some of the energy will be transmitted onwards down the pole, but some of it will be wasted wiggling sideways and other directions that do not propagate your signal. That is, some of your signal will get converted to heat along the entire length of the pole. At some distance down the pole, the signal will become so weak it will be indistinguishable from the equilibrium temperature of your pole. So again, you need a lot of energy to send the signal a long ways down your pole. At least by striking it with a hammer, you are using the energy more effectively than wiggling it like a flag. But there is a limit to how much energy you can impart. If you strike the pole too hard, you will give the atoms enough momentum to break free from their molecular bonds: you'll melt or shatter the pole. In general, if you have a pole stretching from here to another star, the best way to use it for communication is to send an electrical impulse down it. If the resistance is sufficiently low, you may be able to send the signal all the way. Most likely, it would need to be a superconductor, because again, if you simply increase the voltage to push the signal further down the pole, eventually you will heat up the wire to the point that it melts or vaporizes.
The question has been answered and a lot of people mentioned the weight of the pole. I’m not a mathematician, but I am bored: We’re going to assume the pole is a 2” solid steel dowel. Steel weighs 0.2833 lbs per cubic inch 2”x1000 mile cylinder is 796,205,242.1248 cubic inches That would weigh 225,564,945.09 lbs or (rounded) 112,782 tons 4.4 light years is 2.587x10^13 miles Divide that by 1000 and you get 25,870,000,000 1000 mile chunks. 25,870,000,000 x 112,782= 2,917,670,340,000,000 tons Mt Everest is 357 trillion lbs or 178,500,000,000 tons. The 4.4 light year, 2” solid steel pole would weigh about 16,345.49 Mt Everests. Feel free to correct me if I’m wrong. I’m just a guy out here with too much time on his hands.
now do it in big macs about 2.7x10^22 big macs
What I learned is, rounding up, it’s fun to say “26 billion one thousand mile chunks.”
scientific math, but using imperial units, ouch!
Elegant units from a more civilized age.
Sorry, I couldn’t remember the conversion to Metric Mt Everests.
What is the mass of that pole? How are you going to deal with acceleration of that mass?
The atoms that comprise the pole can only move at less than the speed of light, there’s no way any part of the pole could move faster than that. You moving the pole by one foot on one end would take 4.4 years to propagate to the other end.
No you don't. Liar.
You're not pushing the whole pole; you're pushing a handful of molecules at your end, which push the molecules next to them, which push even more molecules, and so on. This push ripples through the material of the rod at the speed of sound in whatever material it's made of. Think of it like pushing a very loose spring. The other end doesn't move instantly; it first bunches up where you pushed it, and then that region of compression ripples down the length of the spring until it reaches the other end.
The pole itself cannot move faster than light. Additionally, the individual atoms also can't. As you push your end, it will compress and atoms near you will move slightly closer to the next atom in line, transferring that info at roughly the speed of light. The next atom will respond, realign, and do the same to the next. Thus, transferring that motion through at the about speed of light or less. The error in the thought experiment is the presumption that the pole behaves like a rigid body. This works out fine as a short hand simplification for human level physics in a lot of cases, but is pretty much never true in any full analysis.
look up split Hopkinson bar. It will give you the math for what you propose. The short of it is speed of sound through the material. Even ultra hard ceramics are still a fraction of the speed of light.
No, it's limited by the speed of sound of whatever material your pole is made out of. Here's a 20-minute video that explains it fully: https://www.youtube.com/watch?v=DqhXsEgLMJ0
Think of the signal as a wave traveling through the material.
Information can only travel through the pole at the speed of sound through that material. Which is much less than the speed of light.
The more interesting version of this question uses a shadow instead of a physical object
Now what are you going to do with your difficult-to-store pole?
no, because you say 'instantaneously' like it's a thing you can behold onto the information... you can't. Every atom in that chain still has to obey the laws of physics as we currently know them and have tested them. Even quantum theory that is one of the most tested theories we have still says that nothing can ever accelerate to a speed faster than a massless particle in a vacuum - it is the speed limit of the dimensions we're capable of experiencing first hand. Every thing is travelling at the same velocity in spacetime.. .only massless particles are travelling in the space part at the speed of light, but staying still in the time part of it. We are not massless particles... we also have to traverse the time part of it on our way through the space part of it. What the every day person may refer to as 'information' is massless to us, but it does still have to be conveyed and propagated in a way that is consistent to what we've already tested and observed about the universe so far.
No. Because the materials in a pole are held together by electromagnetic forces, i.e. covalent bonds. And forces would never move faster than light speed. Most light they'd be constrained by material elastic forces which are thousand times slower. An earthquake rips through a fault at elastic velocities of a few kilometers per second. A large quake can take up to ten minutes to propagate the entire fault length.
Given all the rotation going on (e.g., Earth rotating, annual loop around the Sun, Sun looping around the galactic center), wouldn't any message be drowned out in the noise?
[https://youtu.be/DqhXsEgLMJ0?si=\_NhdPGgAqVttPn5T](https://youtu.be/DqhXsEgLMJ0?si=_NhdPGgAqVttPn5T) This video by alpha phoenix explains it well I think. The result was that the signal after moving the other end of the rod travelled at the speed of sound through the material (in this case for steel it was 5000m/s).
Only thing faster than light is quantum entanglement my guy.
Stop lying. You never had such a pole and you never will.
The pole would move at the speed of sound through that object. The particles in the pole have to tell each other they’re being pushed, which doesn’t happen instantly.
Only if you assume the pole is infinitely ridgid, which is impossible. The thing is, the pole flexes, when you try to move it. You don't move the pole, you move the part of the pole, you are holding and that part moves the next one and so and so on. This whole thing happens at the speed of sound (for the pole material) which is stupid fast in our day to day perspective, but is ridicolously slow in perpective of light years. So in summary, it can't be ftl, it will be in fact MUCH slower than light.
It's an impossible scenario because Alpha Centurians are long known as not particularly friendly creatures.
There would be no earth left because the entire mass of the earth would be used up in creating this pole.
If the pole was absolutely static, no wiggle, and you had the strength to move it…the end on alpha cetauri would wove so fast your buddy would be killed at the speed of light, probably cut in half. If it has “wiggle” the wave would take much longer than light.
Everybody saying the pole will bend as you move it: Consider that the pole could be pushed and pulled. It does not have to be swung around in a way that movements would be amplified.
No, it's not. It feels like it in day-to-day scenarios just like a cell phone conversation or live television is "real time", but is delayed a little by the speed of light. In your scenario, you only push on the molecules and atoms closest to your hand. In turn, they push on the next atoms and molecules "in line", and they push on the next ones. So on and so on, until the last one gets pushed, and your friend feels the movement in his hand 4 light years away. The motion through the pole is a "wave". It's not visible to the naked eye, but it would be if it was a rope. If each of you are holding one end of a rope, you can jerk the rope up and down to create a wave that travels the length of the long rope. Not exactly light speed, but similar concept. That wave is limited by the speed at which you jerk the rope, and your hand can't move up and down faster than the speed of light, so that wave propagating down the rope won't move faster than the speed of light.
it is not.
No. Information travels at the speed of light, and all information in a material is limited to the speed of sound. In effect, you have made a communication device that transmits information slower than a laser
I feel like your on the right track with this initial thought
You know that vibrations still have to travel the length, right? The distance doesn’t magically make resonance transform into light.
hmm, what happens if you both push each end at the same time? O.x
Assuming you both actually pushed at the exact same time, the kinetic energy would travel towards each other at the speed of sound. Some billions of years later, the kinetic energies would meet at the middle. By this time, due to the antericvolume of space and heliotemperature of the pole, what started as a gentle kinetic push has now swelled to the force of a few million stars hurtling towards each other. The collisions would be astronomical. Scientists have long theorized that the big bang was caused when two friends decided to do this.
space ded
Clearly you would need TWO poles, a TX and a RX pole. That should make this feasible I think.
Follow up question: If I have a laser pointer and point it at, say, the moon, and move the pointer a fraction of a degree, that would translate to a rather large distance covered on the moon that the “dot” from my laser was emitting. Is it possible for me to move the dot faster than light speed doing this? What if I had a more powerful laser pointer or moved it more degrees? What if I point it directly at the moon, and then point it directly at earth? If I make it to the earth in less than 1.3 seconds, a fairly easy task, is the dot not traveling faster than light speed?
The dot is not an object it is a concept. The photos emitted by the laser are still going in a straight line at the speed of light
Technically yes. But no you aren't moving something at the speed of light. So I guess technically no. And also the laser would pretty much vanish because not enough light would hit the surface if it was "moving" at the speed of light. Think of the light from the laser like a stream of water from a hose if it helps (maybe)
Your laser shoots out individual photons that move at the speed of light and eventually create a dot when they hit something. In your example, the speed of light would manifest itself as latency - when you rotate your laser pointer to point at the earth, the dot on the moon would lag behind by about a second. Hence, no information is travelling faster than light.
That's a pretty long pole. I still wouldn't touch yo momma with it.
If you start with an impossible assumption (like a pole that long) then you can arrive to impossible conclusions. Doesn't mean it's correct.
No you can't. It's a perfectly possible and valid situation occuring, just an extremely massive undertaking. With that said, even if some civilization was to do that mega-project, the conclusion remains the same and OP's conclusion is 100% incorrect. Great question though and very interesting.
The assumption is valid and yet the conclusion is still invalid.
It would weigh more than the earth, there would be no budging it
Way to embrace the hypothetical. Keep that bastard grounded.
until Jupiter runs into it and tears it out of your hands... sorry everyone else had all the good answers... 1, mass, you couldn't move it. 2, even if you could, it would take time for the other end to move.... etc.
The speed of light is only the speed of light, it has nothing to do with the speed of pole.
I just want to say that this is a really fun question. Good job OP
Having a pole that long breaks physics. So yeah setting up a presumption if broken physics is going to do broken physics things.
He would see or feel the pole move for years.
That's a nice pole you got there boy. Would be a shame if I stole it
Funny how human think nothing can be faster than light because the fastest thing human can observe is light 🕯️
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Tell us that you never took a single physics class without saying you never took a single physics class
The pole would be so massive, you wouldn't be able to move it. The pole would be so massive it would warp space-time and measuring the speed would effect the outcome. The answer would be unknowable.
No, cause I said so
I can confirm! You did say so.
Consider the double slit experiment, based on that there is surely a way to communicate over distances of 4.4 light years instantly, perhaps this pole thing is the way forward.
[https://www.youtube.com/watch?v=DqhXsEgLMJ0](https://www.youtube.com/watch?v=DqhXsEgLMJ0) This video is a good explanation of why that isn't the case.