# Im not too clever, but faster than light?

im not too clever, but "faster than light???"

Hi,

I have no real background in physics, but got to thinking of something.

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Let’s say light travels at around 670,616,629.384 miles per hour

Then lets say I have a imaginary rod 134123326 miles long (double the number above) (size must be bigger than the distant lights travels in a given time).

This rod is not affected by heat (no shrinking of expanding) and is straight, no bending takes place.

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If I also set up a electrical circuit at the other end, with rod acting a switch. (Electric is not transferred via the rod)

a race take place between two people, sending information from the same point, here at one side of the rod to the other side of the rod, 134123326 mile away

The first person uses radio waves the second Morse code.

The message is "hello", Morse code ".... . .-.. .-.. ---"

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Now here is what I was thinking.

The radio waves are sent and travel at 670,616,629.384 miles / hour. Taking two hours to reach the end point.

But if the Morse coder could type out the message, complete / cutting the circuit at the other end, by pulling on the rod. Would the information travel instantly?

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HallsofIvy
Homework Helper
You don't need to make it that long! Imagine a rod from here to the moon. As long as the rod is perfectly rigid, a push on the rod on the earth will result in an instantaneous motion at the moon, thus resulting in instantaneous communication as you say.

Consequence? In relativity, there cannot be "perfectly rigid" materials, even theoretically.

DaveC426913
Gold Member
To further HoI's post:

The rod is made of matter. The atoms and electrons in the matter cannot interact any faster than the speed of light. Whatever mechanism you propose to transmit along it will be constrained by this limit.

I cannot see why the system in question falls into the area of GR. The rod would be modelled best using classical mechanics as the atoms are only moving a small distance at a very slow velocity in comparison to c. Time dillation and length contraction shouldn't be even noticable in the example stated. An observer in the inertial frame of the Earth or moon were to measure the rods speed during the experiment it would be very slow, maybe 3-4 cm/s. I would simplify the experiment to a hose wrapped around the equator a hundred times with an observer holding both ends. If the observer pushes a bung down one end of the hose to move the fluid in that end the fluid in the other end will rise with no delay as the pressure in all points of the hose is equal. This is not a question of a particle have a velocity faster than light, it's simply a large object moving a very small distance.

HallsofIvy
Homework Helper
David Burke said:
I cannot see why the system in question falls into the area of GR. The rod would be modelled best using classical mechanics as the atoms are only moving a small distance at a very slow velocity in comparison to c. Time dillation and length contraction shouldn't be even noticable in the example stated. An observer in the inertial frame of the Earth or moon were to measure the rods speed during the experiment it would be very slow, maybe 3-4 cm/s. I would simplify the experiment to a hose wrapped around the equator a hundred times with an observer holding both ends. If the observer pushes a bung down one end of the hose to move the fluid in that end the fluid in the other end will rise with no delay as the pressure in all points of the hose is equal. This is not a question of a particle have a velocity faster than light, it's simply a large object moving a very small distance.
So you would argue that you could send a signal faster than the speed of light?

DaveC426913
Gold Member
David Burke said:
I cannot see why the system in question falls into the area of GR. The rod would be modelled best using classical mechanics as the atoms are only moving a small distance at a very slow velocity in comparison to c. Time dillation and length contraction shouldn't be even noticable in the example stated. An observer in the inertial frame of the Earth or moon were to measure the rods speed during the experiment it would be very slow, maybe 3-4 cm/s.
Yes, the rod travels a 3-4cm/s, no one's arging that. You're missing the point. It has nothing to do with time dilation and everything to do with the speed with which atoms can interact.

Question: when you push on the near end, how fast does the push get transmitted through the rod? How fast can one atom bump its neighbour? Faster than c? The rod cannot be perfectly rigid; there is no such thing, even theoretically.

The pulse of the push will take 4s to reach the other end of the rod.
Thus, no superluminal transmission.

David Burke said:
If the observer pushes a bung down one end of the hose to move the fluid in that end the fluid in the other end will rise with no delay as the pressure in all points of the hose is equal.
No noticeable delay - over short distances. How fast can water molecules trasmit pressure?

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SF
I'd reckon the speed with which the movement is transmitted equals the speed of sound in the rod's material.

HallsofIvy
Homework Helper
SF said:
I'd reckon the speed with which the movement is transmitted equals the speed of sound in the rod's material.
Which typically is a lot less than the speed of light.:rofl:

Of course, the original post was positing a perfectly rigid material in which the "speed of sound" would be infinite.

DaveC426913
Gold Member
HallsofIvy said:
Which typically is a lot less than the speed of light.:rofl:

Of course, the original post was positing a perfectly rigid material in which the "speed of sound" would be infinite.
The best I would accept is:

"...positing a material as perfectly rigid as theoretically possible, in which the "speed of sound" would be at or near the speed of light."

This type of argument above is one of the reasons I could never accept relativity theory.

All my textbooks say take 2 reference frames measured out with light, rigid rods....

By definition of relativity theory there is no such a thing as a rigid rod, as explicitly explained above

The theory seems to contradict itself from the very beginning.
Or at least it's very difficult (impossible ?) to formulate the Lorentz transformations from Einstein's angle without immediately breaking the rules you are about to describe... ;-/

Probably the person who started this topic was influenced by the same contradictions.
Maybe somebody smarter than me can explain this ?

DaveC426913
Gold Member
The theory does not contradict itself - the explanations for laypeople often do though. Don't confuse them.

The theory does not know from 'rods', rigid or otherwise - but for us to understand it, we need to grasp the theory in bite-sized chunks. This is why we use thought experiments, usually including an array of "ideal" (physically impossible) tools, such as spaceships with unlimited fuel and acceleration, telescopes with unlimited distance, etc.

An attempt to understand relativity without any of these mental crutches, will require examination of the mathematical formulae directly. And there, you can be sure, it will have no contradictions.

P.S. Having said all that, I'd doublecheck your textbooks.
- Are you sure they were proposing a rigid rod? Or are you mashing things in your memory?
- They might have been proposing it as a sort of 'reducto ad absurdum' - i.e. showing how it is impossible.

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baywax
Gold Member
Which typically is a lot less than the speed of light.:rofl:

Of course, the original post was positing a perfectly rigid material in which the "speed of sound" would be infinite.
Can the speed of sound match c if its embedded in the light inside of a fiber optic? In this case perhaps the "sound" has been translated into binary and is then transfered as the binary "information" that is relaying the sound at the speed of light.

Is this the same thing as sending an actual "sound" at the speed of light?

The information involved in the non-local effects proposed by Bell's Theorem (and as experimentally demonstrated) travels faster than light. It appears to be instantaneous over large distances.

The information involved in the non-local effects proposed by Bell's Theorem (and as experimentally demonstrated) travels faster than light. It appears to be instantaneous over large distances.
Well, I think that in this instance, we have to be careful about distinguising the various usage of the word "information" because of its subtle and delicate nature in the EPR-Bell context. What I mean is that the influences associated with the wavefunction collapsing does not send out energy or causal "information", and that the only evidence of this influence is the correlation in the data at the two seperate locations -- data that must be examined together to find any correlation... unlike other forms of "information" transfer.

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Anyone reading this, PLEASE let me know if I got anything wrong, I'm still a student and honing out my QM skills... I'm by no means an expert like the others in here.

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What I mean is that the influences associated with the wavefunction collapsing does not send out energy or causal "information"
I too am a bit out of my depth so lets help each other.
Indeed, the 'information' involved in the various EPR-Bell experiments must be considered as different in nature in that it transcends causality, but we cannot dismiss this information simply because it flies in the face of "conventional' expectations. It has been experimentally verified that measuring one particle of a Bell correlation instantaneously transforms the properties of the other. For the second particle to assume the correct properties I can concieve of no explanation (which probably indicates my own limitations more than anything else), other than it has received information concerning the nature of the first particle. My point - the apparent 'instantaneous' nature of this effect indicates that information has 'arrived' without travelling and even light has to travel. Causality goes out of the window, so to speak, but if we begin by assuming that information must have a causal aspect we go round in circles and the 'information' in the EPR-Bell experiments cannot be considered information because it seems to have no causal aspect.
I think

baywax
Gold Member
Cool thanks. I thought about it before I read this and figured that the sound is reduced to a binary (group of 1s and 0s) reproduction of sound.

If I try to sell a reproduction of a Rembrant I'm not selling a Rembrant. Thus, with this logic, sound is not travelling at c there is a binary group representing a sound travelling at c that will activate a device at the other end where the sound will be (partially) reproduced (when compared to the original, analog, sound).

But, about the the perfectly straight rod. Isn't there friction slowing the transmission of the sound wave?

Like, say there's a tin can on earth, a perfectly taunt string and another tin can on the moon. Communications are still limited to the speed of sound minus the density of the string. No?

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I too am a bit out of my depth so lets help each other.
Indeed, the 'information' involved in the various EPR-Bell experiments must be considered as different in nature in that it transcends causality, but we cannot dismiss this information simply because it flies in the face of "conventional' expectations. It has been experimentally verified that measuring one particle of a Bell correlation instantaneously transforms the properties of the other. For the second particle to assume the correct properties I can concieve of no explanation (which probably indicates my own limitations more than anything else), other than it has received information concerning the nature of the first particle. My point - the apparent 'instantaneous' nature of this effect indicates that information has 'arrived' without travelling and even light has to travel. Causality goes out of the window, so to speak, but if we begin by assuming that information must have a causal aspect we go round in circles and the 'information' in the EPR-Bell experiments cannot be considered information because it seems to have no causal aspect.
I think
I don't want to get off topic and I think there have been numerous discussions on this subject already, so I'll just say that the postulates of special relativity and their logical consequences are not violated in my opinion if we accept that the influences involved in the ERP-Bell experiments do not send out any sort of causal information. This way, no contradiction in our understanding of natural laws follows.

So you would argue that you could send a signal faster than the speed of light?
Don't the ERP-Bell experiments demonstrate this?

I don't want to get off topic and I think there have been numerous discussions on this subject already, so I'll just say that the postulates of special relativity and their logical consequences are not violated in my opinion if we accept that the influences involved in the ERP-Bell experiments do not send out any sort of causal information. This way, no contradiction in our understanding of natural laws follows.
I don't want to get off the subject either, which seems to be "information travelling faster than the speed of light" (but I may be mistaken).
Does the "transmission of information" involved in the EPR-Bell experiments travel faster than light (or am I missing something of fundamental importance - which is very likely )?

"faster then light" is possible.

The speed of shadow for example can be faster then the speed of light.

All which is said is that the speed of any signal / information or energy can not exceed light speed in vacuum.

Group velocity can also travel faster as the speed of light.

But like the speed of shadow, this does not involve any transfer of information or energy.

baywax
Gold Member
Did you get that?

HallsofIvy
Homework Helper
The best I would accept is:

"...positing a material as perfectly rigid as theoretically possible, in which the "speed of sound" would be at or near the speed of light."
That makes no sense. If a rod were "perfectly rigid" then the "speed of sound" in it would be infinite, not "at or near the speed of light". Do you mean you would accept that as the upper limit of "rigidity" in a material (which would NOT be "perfectly rigid").

The speed of shadow for example can be faster then the speed of light
D'oh
What about the speed of speed? Surely nothing travels faster than speed:surprised

D'ooooooh

baywax
Gold Member
"faster then light" is possible.

The speed of shadow for example can be faster then the speed of light.
Please do me the honor of proving this statement.