Why would'nt this work?
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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.
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It's why de Laval nozzles have their shape
I don't get it. Care to explain?
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What about using c++ or rust?
That'll anger the universe's devs who will then bully you.
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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.
I'm not sure.
The beam of light would bend as it travels to the moon, delaying the projected dot on the moons surface. -
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.
Sure, the time between detections is faster than the time it takes light to travel from one detector to the other. Nothing is actually traveling faster than light and no physical laws are broken.
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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.
this isn't at all what this example depicts, here there is actual information transfer.
this depiction is actually just false, the light would send information faster than the stick, because in the stick information only travels as fast as speed of sound in the stick, which is why completely rigid objects don't exist
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I don't think gravitational waves traveling at the speed of light is the same as the gravitational attraction being apparently felt faster than light travels. Similarly, electric attraction between + and - charges is different from electromagnetic waves being transmitted in the field. It's not light that is "communicating" that attraction.
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It can look dumb, but I always had this question as a kid, what physical principles would prevent this?
The compression on the end of the stick wouldn't travel faster than the speed of sound in the stick making it MUCH slower than light.
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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 forgetting the speed at which the shockwave from the compression travels through the stick. I guess it's around the speed of sound in that material, which might be ~2 km/s
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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 speed of the earth's rotation though, could that fuck up the stick holding?
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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.
You'd still be limited by light speed to transmit the information between the two locations to compare times or indicate they received a signal.
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What about the speed of the earth's rotation though, could that fuck up the stick holding?
It'll knock the moon and earth out of orbit!
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The compression on the end of the stick wouldn't travel faster than the speed of sound in the stick making it MUCH slower than light.
But.. But.. The stick is unfoldable!
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I don't think gravitational waves traveling at the speed of light is the same as the gravitational attraction being apparently felt faster than light travels. Similarly, electric attraction between + and - charges is different from electromagnetic waves being transmitted in the field. It's not light that is "communicating" that attraction.
I don't think gravitational waves traveling at the speed of light is the same as the gravitational attraction being apparently felt faster than light travels.
I donât know how you would measure gravitational waves without measuring gravitational attraction.
It's not light that is "communicating" that attraction.
Nobody said it was. The âspeed of lightâ isnât about âlightâ. Gravity propagates at the same speed, aka âc.â
This Reddit discussion on r/AskPhysics might help clear up your misconceptions. Notably:
Just to clarify: when people talk about the speed of gravity, they mean the speed at which changes propagate. It's the answer to questions like: if I take the Sun and wiggle it around, how long does it take for the Earth to feel the varitation in the force of gravity? And the answer is that changes in gravity travel at the speed of light.
But that's not what you're asking about. Whenever you're close to the Earth, gravity is always acting on you: it's not waiting until you step off a cliff, like in the Coyote and the Roadrunner. The very instant your foot is no longer on the ground, gravity will start to move it downwards. The only detail is that it takes some time for it to build up an appreciable speed, and this is what allows us to do stuff like jump over pits: if you're fast enough, gravity won't be able to accelerate you enough - but gravity is still there.
I get the sense that youâre thinking about the second scenario when objecting to the concept that gravity travels at the speed of light.
