Why would'nt this work?
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Ok so since there's a bunch of science nerds on here and I'm sleep deprived I'm gonna ask my dumb ftl question.
If you're on a train and you walk towards the front of the train, your speed measured from outside of the train is the speed of the train (T) plus the speed of you walking (W).
So if there was a train inside of that train, and you walked inside of that, you'd go the speed of the outside train, plus the speed of the inside train, plus your own walking speed.
So what if we had a Russian nesting doll of trains, so that the inner most train was, from the outside, going as fast as light and you walked towards the front? Wouldn't you be going faster than light if you measured your speed from the outside?
Didn't come at me with how hard it would be to build a Russian nesting doll of super trains it's a hypothetical and I'm tired.
That's where time dilation will kick in
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Long winded video about it:
'Are solid objects really “solid”?' (go-to 7:30)
Thank you for sharing--that was a really neat demonstration, and I enjoyed seeing all the troubleshooting as well. Will definitely be subscribing and checking out more of their videos!
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Relativity would prevent this. If the train moves at the speed of light, then nothing inside it will move because time will stop. The amount of trains inside trains doesn't really change much except the effect of time dilation (slowdown) on each train. You can't actually accelerate to the speed of light.
as a software engineer that watches too much youtube, this is the first time it’s clicked for me:
If the train moves at the speed of light, then nothing inside it will move because time will stop.
the pieces of information:
- time moves slower the faster you travel, and
- nothing can travel faster than the speed of light
have never been concretely connected in my head, but this makes a lot of sense now: time moves slower (for you) the faster you travel BECAUSE that’s the thing that stops you from moving faster than the speed of light… AND that holds true from all perspectives because it’s like… a trade-off?
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Ok so since there's a bunch of science nerds on here and I'm sleep deprived I'm gonna ask my dumb ftl question.
If you're on a train and you walk towards the front of the train, your speed measured from outside of the train is the speed of the train (T) plus the speed of you walking (W).
So if there was a train inside of that train, and you walked inside of that, you'd go the speed of the outside train, plus the speed of the inside train, plus your own walking speed.
So what if we had a Russian nesting doll of trains, so that the inner most train was, from the outside, going as fast as light and you walked towards the front? Wouldn't you be going faster than light if you measured your speed from the outside?
Didn't come at me with how hard it would be to build a Russian nesting doll of super trains it's a hypothetical and I'm tired.
The idea that the velocity of a person walking forward on a train is simply the velocity of the train plus the velocity of the person walking with respect to the train is called “Galilean relativity”.
Einstein realized that Galilean relativity has a big problem if you take for granted the idea that the speed of light is the same for all observers, regardless of reference frame, and people had a lot of reasons at the time to suspect this to be true.
In particular, he imagined something like watching a train passing by him, but on board the train is a special clock which works by shooting a pulse of light at a mirror directly overhead which reflects back down and hits a sensor. Every time the light pulse hits the sensor. The clock ticks up by one and another light pulse is sent out. People usually call this the “light clock thought experiment” if you want to learn more about it.
Anyway, Einstein realized if he was watching the light clock as the train passed by him while he’s standing on the station, the path the light beam traces out will take the form of a zigzag. Meanwhile, for a person standing on the train, it will just be going straight up and down. If you know anything about triangles, you will realize that the zigzag path is longer than the straight up and down path. So if everyone observes the speed of light to be the same exact thing, it must be the case that it will take the light a longer amount of time to reverse the zigzag path. And so the person standing on the platform will see that clock ticking slower than the person on the train will. This phenomenon is called “time dilation”.
From this point, you can apply some simple trigonometry to figure out just how much slower things would be appearing to move on the train. And it turns out that the velocity the person watching the train observes the person walking on the train to have is not the velocity of the train plus the velocity of the person walking on the train. But rather, it’s something like that velocity, but divided by 1 + (train velocity)•(walking velocity)/c^2, where c is the speed of light (and this is called “Lorentzian relativity” if you want to read more about it).
It’s important to notice that since trains and walking come nowhere close to the speed of light, the value you’re adding to one is very small in these kinds of situations, and so what you’re left with is almost exactly the same thing you would get with Galilean relativity, which is why it still is useful and works. But when you want to consider the physics of objects that are moving much much faster. All of this is extremely important to take into account.
And lastly if you wanna read more about this stuff in general, this is all part of “the theory of special relativity” and there’s probably helpful YouTube videos covering every single thing that I’ve put in quotation marks.
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There was, but now I'm getting older and more tired
Have you spoken to your healthcare provider about Viagra^tm^? It may be able to help with your issue. (Please seek immediate medical help with an erection lasting more than 4 hours).
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The idea that the velocity of a person walking forward on a train is simply the velocity of the train plus the velocity of the person walking with respect to the train is called “Galilean relativity”.
Einstein realized that Galilean relativity has a big problem if you take for granted the idea that the speed of light is the same for all observers, regardless of reference frame, and people had a lot of reasons at the time to suspect this to be true.
In particular, he imagined something like watching a train passing by him, but on board the train is a special clock which works by shooting a pulse of light at a mirror directly overhead which reflects back down and hits a sensor. Every time the light pulse hits the sensor. The clock ticks up by one and another light pulse is sent out. People usually call this the “light clock thought experiment” if you want to learn more about it.
Anyway, Einstein realized if he was watching the light clock as the train passed by him while he’s standing on the station, the path the light beam traces out will take the form of a zigzag. Meanwhile, for a person standing on the train, it will just be going straight up and down. If you know anything about triangles, you will realize that the zigzag path is longer than the straight up and down path. So if everyone observes the speed of light to be the same exact thing, it must be the case that it will take the light a longer amount of time to reverse the zigzag path. And so the person standing on the platform will see that clock ticking slower than the person on the train will. This phenomenon is called “time dilation”.
From this point, you can apply some simple trigonometry to figure out just how much slower things would be appearing to move on the train. And it turns out that the velocity the person watching the train observes the person walking on the train to have is not the velocity of the train plus the velocity of the person walking on the train. But rather, it’s something like that velocity, but divided by 1 + (train velocity)•(walking velocity)/c^2, where c is the speed of light (and this is called “Lorentzian relativity” if you want to read more about it).
It’s important to notice that since trains and walking come nowhere close to the speed of light, the value you’re adding to one is very small in these kinds of situations, and so what you’re left with is almost exactly the same thing you would get with Galilean relativity, which is why it still is useful and works. But when you want to consider the physics of objects that are moving much much faster. All of this is extremely important to take into account.
And lastly if you wanna read more about this stuff in general, this is all part of “the theory of special relativity” and there’s probably helpful YouTube videos covering every single thing that I’ve put in quotation marks.
Dang there goes my patent
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It can look dumb, but I always had this question as a kid, what physical principles would prevent this?
Think of it like this. If our universe is a simulation, then the speed of light is the maximum speed at which information can propagate through reality. We know that for anything to move through space, it must move from one adjoining position to another, then another, then another, incrementally. Each one of those increments takes, at minimum, one 'tick' of the universe. That's one tick to increment each bit of information, that is, the position of something moving at light speed from position x,y,z to x+1,y,z. Light moves as fast as the universe allows; if there was a faster speed, light would be doing it, but it turns out that our universe's clock speed only supports speeds of up to 299,792,458 meters per second.
What you have here is sound. Motion propagates through material, at its fastest, at the speed of sound in that material. That's part of the reason why moving large scale objects quickly gets weird.
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It can look dumb, but I always had this question as a kid, what physical principles would prevent this?
You're pushing the atoms on your end, which in turn push the next atoms, which push the next ones and so on up to the atoms at the end of the rod which push the hand of your friend on the moon.
As it so happens the way the atoms push each other is electromagnetism, in other words sending photons (same thing light is made of) to each other but these photons are not at visible wavelengths so you don't see them as light.
So pushing the rod is just sending a wave down the rod of atoms pushing each other which the gaps between atoms being bridged using photons, so it will never be faster than the speed at which photons can travel in vacuum (it's actually slower because there's some delay since part of the movement of that wave is actual atoms moving and atoms have mass so they can't travel as fast as the speed of light).
In normal day to day life the rods are far to short for us to notice the delay between the pushing the rod on one end and the rod pushing something on the other end.
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wave function (something that does not travel) collapses (something that does not move either) faster than light (themselves?)
this word soup does not make sense
I used wave function as a bad form of shorthand for the general properties of the photon, such as the theoretically infinitely extending magnetic and electric fields. Those associated fields stop existing when the photon is absorbed onto a screen. They collapse faster than light can travel. This doesn't ruin much of modern theories, because there doesn't seem to be a way to transfer usable information through this phenomenon.
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When you push something you push the atoms in the thing. This in turn pushes the adjacent atoms, when push the adjacent atoms all the way down the line. Very much like pushing water in the bathtub, it ripples down the line.
The speed at which atoms propogate this ripple is the speed of sound.
In air this is roughly 700mph, but as the substance gets harder* it gets faster. For example, aluminum and steel it is about 11,000mph.
That's why there's a movie trope about putting your ear to the railroad line to hear the train.If you are talking about something magically hard then I suppose the speed of sound in that material could approach the speed of light, but still not surpass it. Nothing with mass may travel the speed of light, not even an electron, let alone nuclei.
*generalizing
Best answer
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It can look dumb, but I always had this question as a kid, what physical principles would prevent this?
What about the mass of that stick? Inertial doesn't care for your little silly games.
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Is it instantaneous though?
It depends on the person who's holding it and pushing it. For me it takes at least three minutes!
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It can look dumb, but I always had this question as a kid, what physical principles would prevent this?
I don't see this mentioned in any of the other comments: the repulsion between atoms that causes the movement to propagate through the stick is actually communicated via photons. So your push really generates the same kind of particles that your light torch is generating, and they travel at the same speed (except slowed down by repeated absorption and excitation by the electrons in the atoms of the stick).
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Things get really unintuitive when you go near the speed of light. Einstein's "Special Relativity" is describing that. Watch a couple of videos on the topic. It's mindbending but seriously cool.
In short: The speed light is always constant FOR EVERY OBSERVER. That means, if you would hold a flashlight in a very fast moving train, the light would travel as the same speed for you as for a stationary person that is watching your flashlight from outside the train.
But how could that be? Aren't you "adding" the trains speed to your flashlight? So shouldn't the light in your train travel faster in your train? Or maybe slower? No. Light speed is always constant - but what is NOT constant is space and time. It is relative to the observer. Time and space can stretch/dilate to make up for what seems to be a paradox. E.g. your trains would shrink in length the faster you go. But it would look different to you than it does to an outside observer.
As I said, it's mindbending, but there are a couple of cool and simple videos on the internet to get a better grasp on the matter.
That's wack af
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What about the mass of that stick? Inertial doesn't care for your little silly games.
Neither do the two gravity wells the stick spans. And the earth and moon are moving relative to each other, someone would probably get their head knocked off by that stick. Before it eventually falls to the earth with quite a bit of force because earth's gravity well will win. Then it'll eventually settle into a giant teeter totter, assuming it is rigid enough to survive the impact.
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It can look dumb, but I always had this question as a kid, what physical principles would prevent this?
Putting it on the moon is just a distraction. It doesn't matter if the rod is 1m long or 100,000km.
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It can look dumb, but I always had this question as a kid, what physical principles would prevent this?
because...
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It can look dumb, but I always had this question as a kid, what physical principles would prevent this?
So folks have already explained the stick, but you're actually somewhat close to one of the ways you can sort of bend the rules of FTL, at least when it comes to a group of photons.
Instead of a stick, imagine a laser on earth pointed at one edge of the moon. Now suddenly shift the laser to the other side of the moon. What happens to the laser point on the moon's surface?
Well, it still takes light speed (1.3 seconds to the moon) for the movement to take effect, but once it starts, the "point" will "travel" to the other side faster than light. It's not the same photons; and if you could trace the path of the laser, you'd find that the photons space out so much that there are gaps like a dotted line; but if you had a set of sensors on each side of the moon set up to detect the laser, they would find that the time between the first and second sensor detecting the beam would be faster than what light speed would typically allow.
It's not exactly practical, and such an edge case that I doubt we can find a good way to use it, but yeah; FTL through arc lengths can kind of be a thing.
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It can look dumb, but I always had this question as a kid, what physical principles would prevent this?
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You think its instantaneous because you never held such a long stick.
Speak for yourself!
Alas, the longer the stick is, the floppier it gets.
