Why would'nt this work?
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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.
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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.
With your example, nothing is âmovingâ.
Imagine a giant wave in the ocean that is almost lined up perfectly parallel to the shore. Imagine the angle that the wave is off by is astronomically small (0.0000000001 degrees off from parallel). Also imagine the shore line is astronomically long (millions of kilometers).
One end of the wave will crash the shore slightly before the other end of the wave at the opposite end of the shore. The difference in time between the two sides of the shore is also astronomically small (so small that not even light could reach the other end in time)
Now let me ask you: did the wave travel faster than the speed of light? Of course not. I think that is a similar analogy to the laser movement concept you described.
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Gravity waves doesn't go faster than light though?
I'm going way way out against the standard model here.
No spacetime, no dark matter or dark energy, not even photons.
Just a '3D big ball of yarn single object universe'.If light is a 'turn of the "stick"', then gravity is how 'the "sticks" are binding the atoms together'.
And so there would not be any gravity waves.
And any measurement of them would then have nothing to do with gravity. -
It can look dumb, but I always had this question as a kid, what physical principles would prevent this?
There's a thought experiment about this in most intro classes on relativity, talking about "length compression". To a stationary observer a fast-moving object appears shorter in its direction of travel. For example, at 87% of the speed of light, length compression is about 50%. So if you are carrying a pole 20 meters long and you run by someone at that speed, to them the pole will only look 10 meters long.
In the thought experiment you run with this pole into a barn that's only 10 meters long. What happens?
The observer, seeing you bringing a 10-meter pole into a 10-meter barn, shuts the door behind you, closing it exactly at the point where you're entirely in the barn. What happens when you stop, and how does a 20-meter pole fit in a 10-meter barn in the first place?
First, when the pole gets in the barn and the door closes, the pole is no longer moving, so now to the observer it looks 20 meters long. As its speed drops to zero the pole appears to get longer, becoming 20 meters again. It either punches holes in the barn and sticks out, or it shatters if the barn is stronger.
Looking at the situation from the runner's point of view, since motion is relative you could say you're stationary and the barn is moving toward you at 87% of the speed of light. So to you the 10-meter barn only looks 5 meters long. So how does a 20-meter pole fit in?
The answer to both questions is compression - or saying it another way, information doesn't travel instantly. When the front end of the pole hits the inside of the barn and stops, it takes some time for that information to travel through the pole to the other end. Meanwhile, the rest of the pole keeps moving. By the time the back end knows it's supposed to stop, from the runner's point of view the 20-ft pole has been compressed down to 5 meters. From the runner's point of view the barn then stops moving, so it's length returns to 10 meters, but since the pole still won't fit it either punches holes in the barn or shatters.
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It can look dumb, but I always had this question as a kid, what physical principles would prevent this?
For anyone looking for other cool ideas or videos about speed of light etc
What Is The Speed of Dark? - Vsauce (13m:31s)
- Cool older vsauce video going over shadows and light speed etc
The Faster-Than-Light Guillotine - Because Science (w/ Kyle Hill) (14m:19s)
- Basically goes over the "FTL Scissor action" that a lot of people have covered but he does a good segment covering it.
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Long winded video about it:
'Are solid objects really âsolidâ?' (go-to 7:30)
That was a really good video!
