Originally posted by ivan2908Ignoring the fact that the energy required to pull such a rope would be of magnitudes beyond any engine we have, there isn't a substance in existence that, if made the length between earth and moon, would remain taut so as to pull one end and the other move.
I was always wondered something which is pretty stupid but interesting. Theoretically if you connect Earth and moon with some indestructible rope (we are about 384000 km far away from the moon) and astronaut is holding one end of the rope on the moon, Earthling the second end... So lets say that man from earth pull the rope (ignore practical problems like h ...[text shortened]... he would achieve that with most primitive device imaginable...
Any hole in my assumption ??
Originally posted by ivan2908When you pull on a rope, you pull *directly* only on the portion you are in contact with. That portion, in turn, pulls on the next portion, and so forth, until finally the object at the other end is pulled. In other words, force must be transmitted, molecule by molecule, down the length of the rope. I think also that for this reason the postulation of an absolutely inflexible rope (or anything else) is an erroneous premise. All of this, of course, represents conventional assumptions which I don't agree with, but you were asking the question within a conventional framework, and so I have answered it.
I was always wondered something which is pretty stupid but interesting. Theoretically if you connect Earth and moon with some indestructible rope (we are about 384000 km far away from the moon) and astronaut is holding one end of the rope on the moon, Earthling the second end... So lets say that man from earth pull the rope (ignore practical problems like h he would achieve that with most primitive device imaginable...
Any hole in my assumption ??
Originally posted by ivan2908[reply to be replaced by a moderated post, feedback pending; our muscles do not produce transversal waves like light in a medium like rope or steel]
I was always wondered something which is pretty stupid but interesting. Theoretically if you connect Earth and moon with some indestructible rope (we are about 384000 km far away from the moon) and astronaut is holding one end of the rope on the moon, Earthling the second end... So lets say that man from earth pull the rope (ignore practical problems like h ...[text shortened]... he would achieve that with most primitive device imaginable...
Any hole in my assumption ??
Originally posted by StarrmanWell about rope it is only practical problem regarding material. Estimated length of blood vessels in one human body is 50000 to 100000 miles and we are not heavy objects at all... That is why I said in theory.
Ignoring the fact that the energy required to pull such a rope would be of magnitudes beyond any engine we have, there isn't a substance in existence that, if made the length between earth and moon, would remain taut so as to pull one end and the other move.
Originally posted by PawnokeyholeI think it would work. the only way there could be a delay is if the inflexible rope would stretch, which it by definition can't. which would make the signal speed instantaneous.
But the key question is: Does the truth of relativity theory exclude the pragmatic impossibility of such a communication device?
Originally posted by ivan2908There's an analogy for this, imagine a very long scissors or shears. When you close it very quickly, the point at which the blades meet can travel faster than the speed of light, but not a single atom of the shears is moving faster than a few metres per second.
I was always wondered something which is pretty stupid but interesting. Theoretically if you connect Earth and moon with some indestructible rope (we are about 384000 km far away from the moon) and astronaut is holding one end of the rope on the moon, Earthling the second end... So lets say that man from earth pull the rope (ignore practical problems like h ...[text shortened]... he would achieve that with most primitive device imaginable...
Any hole in my assumption ??
Originally posted by wormwoodEven if it was imperfectly rigid, as long as the rod is pulled a further distance in a shorter time than the rod can respond to, the signal would be transmitted nonetheless. Imagine a steel rod, if I pull it so fast that it accelerates to faster than the speed of sound in steel, the opposite end would have moved before the vibration as a result of steels elasticity could reach it. The same could apply to the earth/moon rod, where the vibration as a result of the elasticity of the material is still travelling to earth by the time the opposite end has already moved.
I think it would work. the only way there could be a delay is if the inflexible rope would stretch, which it by definition can't. which would make the signal speed instantaneous.
no actual point of mass nor photon would travel fast, so there's no problem with relativity.
BUT, if we think of what material is on an atomic level, a collection of atoms/wa ...[text shortened]... ves, not a rigid connection between subsequent mass points in the rope.
I think...
Originally posted by ivan2908This is similar to the stainless steel rod (inflexible) theory. If a rod extends infinitival and you move the base a slight amount the farthest end would travel faster than light.
I was always wondered something which is pretty stupid but interesting. Theoretically if you connect Earth and moon with some indestructible rope (we are about 384000 km far away from the moon) and astronaut is holding one end of the rope on the moon, Earthling the second end... So lets say that man from earth pull the rope (ignore practical problems like h ...[text shortened]... he would achieve that with most primitive device imaginable...
Any hole in my assumption ??
Originally posted by cheshirecatstevensexcept that the forces required to accelerate the distant mass would be transferred to your end of the lever, meaning that you would still have the problem of infinite energy being required to move it...
This is similar to the stainless steel rod (inflexible) theory. If a rod extends infinitival and you move the base a slight amount the farthest end would travel faster than light.
Originally posted by agrysonYou can build it in vacuum so it would be easier to move
except that the forces required to accelerate the distant mass would be transferred to your end of the lever, meaning that you would still have the problem of infinite energy being required to move it...
Originally posted by agrysoni've been thinking about this post for a while... there must something wrong in that reasoning, i think... i'll get to it later...
There's an analogy for this, imagine a very long scissors or shears. When you close it very quickly, the point at which the blades meet can travel faster than the speed of light, but not a single atom of the shears is moving faster than a few metres per second.
To come back from that analogy, assuming an inextensible (zero elasticity, this is a thought expe ...[text shortened]... rmation would be transmitted faster than the speed of light, but only the information.