I have been reading a lot of sci-fi lately with wonderful tales of faster-than-light (FTL) communication and travel, so it has been in my head a lot.

This is probably a really stupid question for those that know anything about physics, but - I was thinking about it last night and was wondering - if you had a really really long rigid object (no not your wang) like (say) a broomhandle and could move it back and forth - so that as you move one end, the other end moves immediately with it, right?

Say you have a broomhandle that is several light-years long (ignoring the logistics etc), and set it up in such a way so that as you move it forward and backward, it is completing a circuit or something in such a way that you are effectively transmitting information with it. So you're not transmitting information by electrons whizzing through space or down the wire at the speed of light - you're doing it by the (instant?) movement of this object through space.

Can a setup like this be used to communicate faster than light? I suspect there's some "obvious" part of relativity that would rule this out (aside from the other obvious fact that a broomhandle that long presents its own problems).

Yep my knowledge is probably a couple of steps down from yours, but your broomhandle analogy made me think of dark matter - things closer to the centre of galaxy should orbit quicker than stuff on the outside because the gravity is stronger, but, in fact, everything rotates at the same speed regardless of its relative position to the centre of the galaxy. Therefore, its theorised that dark matter is bind everything and makes it rotate simultaneously, like the end of a broomhandle spinning at the same speed as the broom end.

This is probably a really stupid question for those that know anything about physics

dude, I think this is a stupid question for anyone who even knows anything about VACUUM CLEANERS

ps: yes, if you could get something that long and could make it move I don't see why you couldn't use it to type on a keyboard at the other end of the universe

Or am I thinking of grey matter? I gotta watch those Steven Hawkings videos again...

trog: the end doesn't move instantaneously. think of what happens at the atomic level.

Well I don't know what happens at the atomic level, I guess that's what I'm asking! I tried to google around before asking but quickly got lost.

Would be like ripples in a pond, make a motion at one end and eventually over time the motion is sent out over this massive wang at the speed of light.

aha! Someone had already asked the exact same question. The answer appears to be:

Dear Halejrb,

Whether or not information can travel faster than light, your thought
experiment is not really a candidate for a technique. You are
apparently assuming that when the Earth end of the pole is moved, the
other end moves simultaneously; this is not so. In fact, a
longitudinal mechanical wave would travel along the pole, and it would
be this that caused the other end subsequently to move and so convey
the message. So the speed of communication would be the speed of this
wave - effectively the speed that sound travels in the material of the
pole - and this would be (very much) slower than the speed of light.
You wouldn't notice any delay with earth-bound experiments using short
poles, but only because the speed of sound is quite fast in practical
terms anyway - but nowhere near the speed of light.

Carnegie

(emphasis mine)

Interesting, also interesting because I suck at google on the first attempt. Also, interesting that the number of questions left unasked appears to be shrinking!

Bit off topic, but if I was going to cark it I always wanted to be launched into a black hole.

trog: i don't know either. but here is my guess. the atoms are arranged kind of in a lattice. when the atoms are pushed down at the start of the broom they also drag down the atoms next to them, these next atoms then drag down the atoms next to them and so forth. so the speed it takes to propagate the drop to the end of the broom is constrained.

Yeh, I had guessed that the "answer" to this would have been that that motion would have happened at the speed of light - so it wouldn't be any faster than firing other particles through space or a wire or whatever. Turns out that it's heaps heaps slower!

I think that quoted answer is mixed up actually trog, I think hast's answer is more likely

Scientists will need to have this one fixed out so that communications can go faster than the speed of light if they intend on space exploration. It's mega long trips between planets and it'd be impossible to play WoW with an 8 minute ping time.

someones been into their stash!@

Energy is causing the particles to move (newtons craddle style) that energy has a speed. You'd need to talk to Condensed Matter Physics or Solid state physics nerds.

Scientists will need to have this one fixed out so that communications can go faster than the speed of light if they intend on space exploration. It's mega long trips between planets and it'd be impossible to play WoW with an 8 minute ping time.

even more evidence that dedicated servers should be a must-have when you're choosing your games

hast and carnegie are saying the identical thing.

Trog already had his international string and two cans network planned for lightning fast gaming pings too.

so infi are you saying that a keyboard wouldn't last long enough?

wat?

in essence i do like haste's explanation better. there will be delay in the pushing of the broom and the movement at the other end.

I just liked carnegie putting it into context:

You wouldn't notice any delay with earth-bound experiments using short
poles, but only because the speed of sound is quite fast in practical
terms anyway - but nowhere near the speed of light.

the question put was that it would be able to convey instructions or information faster than the speed of light but the minute fractions of delay in the movement of atoms of the "broom" would prevent it from being faster than the speed of light.

While we're at it, here's a quiz. I already hold the answer (it's within my research area at uni), just curious as to the responses here:

QUESTION:

Does a signal travel down an optical fibre faster, slower or roughly the same speed as in a twisted-pair copper cable or coax?

(Try to answer this without googling)

I would have imagined the optical fibre is marginally faster given the signal is a light impulse vs. an electrical pulse travelling inside a solid material (this would have friction i guess).

(but i'm no scientist)

Does a signal travel down an optical fibre faster, slower or *roughly* the same speed as a signal in a twisted-pair copper cable or coax?

i would guess at roughly the same speed coz it's just electromagnetic energy that is doing the moving.

as for the solid pole communications... well that's just silly.. i can't ignore the logistics :P how do you anchor the ends !@?! :P

the ends aren't anchored - you need to be able to move the ends to other keyboards. that's right, english isn't the only language in the universe

I would have imagined the optical fibre is marginally faster given the signal is a light impulse vs. an electrical pulse travelling inside a solid material (this would have friction i guess).

But the light has to bounce off the walls in a fibre optic cable, right? does that slow it down?

Does a signal travel down an optical fibre faster, slower or roughly the same speed as in a twisted-pair copper cable or coax?

isnt electrical pulse around 2/3 the speed of light?

But the light has to bounce off the walls in a fibre optic cable, right? does that slow it down?

I don't think it slows it down. But it expends energy so you need to repeat the signal to boost it. Has to travel a further distance as well I guess while it refracts around in the cables.

last edited by Twisted at 13:58:43 12/Jun/08

I vote slower for the reasons trog said

if you had a really really long rigid object (no not your wang) like (say) a broomhandle and could move it back and forth - so that as you move one end, the other end moves immediately with it, right?

No.

This is kinda how particle accelerators work - throw enough matter into a decide designed to accelerate it to such a speed that it:
a) No longer remains a solid
b) Allows particles to colide creating new solids, both at molecular and atomic levels. Note that most of the interest here is at the atomic level, they rerely give a stuff at anything created at any level above that.

At some point an abject could be made to move at a speed so fast that the covalent bonds of the atoms within would either break, or fail, thus breaking apart the object.

Does a signal travel down an optical fibre faster, slower or *roughly* the same speed as a signal in a twisted-pair copper cable or coax?

Light travels down the glass of fibre optic at, from memory, around 67% the speed of light. In copper it's reduced to between half and one third the speed of light.
In air light is from memory 90% the speed of light. Again I'm just going off the top of my head, but I'm sure a quick look at wackypedia would give reasonably accurate results.

But the light has to bounce off the walls in a fibre optic cable, right? does that slow it down?

This ia *a* factor which slows it down, yes.

Do the electrons of a twisted pair copper cable travel along the outside of the wire and not the inside and this makes it faster then what you would think?

I would say at roughly the same speed.

Also, Faster then light travel isn't possible is it? Instead you would have to take a different path that is shorter by bending the crap out of space/time or doing some funky uber dimensional travel?

last edited by Tollaz0r! at 14:09:04 12/Jun/08

i would guess at roughly the same speed coz it's just electromagnetic energy that is doing the moving.

Yep, that's the key point. Off the top of my head I think electrons travel at an average speed in the direction of propagation about a trillion times slower than the EM wave, but they're not the signal-carrying component of the system (the EM wave is).

Do the electrons of a twisted pair copper cable travel along the outside of the wire and not the inside and this makes it faster then what you would think?

Read my previous sentence. Basically it's not the slow jiggling/pressure/movement of the electrons that makes them move down the line, but a VERY FAST electromagnetic wave traveling down the line, rapidly telling all the electrons to start moving. That's a simplification, but good enough.

I don't think it slows it down. But it expends energy so you need to repeat the signal to boost it.

Well it technically should achieve total internal reflection (ie, no light transmitted through the fibre interface), but from what I've been reading a heap of the loss is through scattering/absorption inside the material.

In air light is from memory 90% the speed of light.

It's very close to 100% actually. Air is usually a good enough approximation for a vacuum for most purposes.

---------------

Basically the motivation for my question was a fibre optic network adapter by Netgear:

http://www.netgear.com/Products/Adapters/WiredAdapters/PF101.aspx

Their very first marketing point/advantage was listed as:

* Stream large amounts of data at the speed of light

Yeah no s***, just like twisted pair and coaxial cables!

last edited by parabol at 14:12:02 12/Jun/08

i guess the broom handle would have to be anchored to a keyboard on one of the poles (heh) coz otherwise everyday the ~7 light year long broomhandle would swish through the sun at a very high speed n would prolly get burnt :P

7 light year long broom stick .. interstellar travel for all mother in laws!

I have a question about entangled particle , Quantum spookiness at a distance, if you have one particle here and you lugged the other particle to the end of the broomstick in such a manner that is keeps its entangled properties, would it instantly change its properties as you change its twin?

If so it isn't technically faster then light travel as the single didn't 'travel' did it?

is the cat dead or alive ??!?!?

If so it isn't technically faster then light travel as the single didn't 'travel' did it?

Yeah people generally think that at first. The physicists have said it technically can't transmit information FTL that way.

Here's something:

http://curious.astro.cornell.edu/question.php?number=612

I just like the fact you can use lasers to freeze something.

Freeze rays on your killer sharks.

Yep, that's the key point. Off the top of my head I think electrons travel at an average speed in the direction of propagation about a trillion times slower than the EM wave, but they're not the signal-carrying component of the system (the EM wave is).

Pretty much. The actually *electrons* in a current move much much slower than c because they are bouncing aruond inside the lattice of the material while being pulled down the wire by the electric potential (Voltage). The internal chaotic motion of the electrons or protons releases energy from collisions with the particles in the material (this is how heat from resistance in a material is generated).

A moving charge (i.e. an electron not bound to an atom) only produces an electromagnetic wave when it is accelerated. At rest or constant motion, a charged particle does not having a changing electromagnetic field so the field-lines radiate symmetrically outwards (but are subject to doppler effects due to velocity). When the charge is accelerated/decelerated this creates a 'kink' in the field lines and these field changes propogate with the the speed of c.

When this change in the electric field interacts with another particle in space, the particle will want to follow or be repelled by (dependnig on whether its a proton or electron) the field change so it'll in turn recieve an acceleration that tries to 'keep up' with the changing field.

The problem is that a linearly accelerated electron will create a field that is strongest at 90º to the acceleration and zero field parallel with the acceleration (such as a single pole transmitter). Thats why antennas are often positioned at a specific angle to line up with the direction of the accelerated source signal.

A vertically polarised signal will not induce any current along a horizontally positioned reciever since theres no actual length to accelerated the conductor's free electrons (only the much smaller radius of the recieving pole).

last edited by ³dee at 15:07:21 12/Jun/08

Just my 2 cents but I know different types of electricity, (different frequencies maybe) travel down different parts of a wire better than others.
For instance, radio signals travel down the outside of a wire better than the inside. My father builds crystal set radios as a hobby, and he uses special wire that contains 100 very thin individually insulated wires, to maximize surface area.

For instance, radio signals travel down the outside of a wire better than the inside.

A conducting object cannot have a charge inside the material. Since all the charge in a charged conductor is the same polarity all electrons are pushed to the outer surface away from all other free electrons. If you charge a metal bucket and touch the outside, you get a shock but if you touch the inside (say through a whole in the lid) you will not feel any charge.

This is known as electrostatic shielding and can be called a Faraday cage (if the conductor is hollow). This is why you need an antenna outside your car because the car itself shields against any external net charge being inside the cars conducting body.

P.S sorry for the thread gravedigging

is the broomhandle on a treadmill?

fyi ftl ftl imo

ftl ftl coz we cant go ftl, afaik when ftl is possible maxe will change his mind from ftl 2b ftmfw imo irkn

p.s duzz that maek sense?

Wtf are you talking about? FTL ftw.

yeah i no but its ftl atm coz we go ftl ourselves...