Physics question

[lewblue83]

I find this an interesting question.

the conditions set down are good, completely solid, non elastic, so we're ignoring bending and flexing.

in theory the answer is yes, you communicate faster than the speed of light.

in practice, it seems as though it should be impossible,

I'm guessing that the real problem is that it's impossible because if you push on one end or the rod all the molecules in the rod also have to move, you've not pushing the rod, you're pushing the atoms at the end of the rod, which in turn are pushing other atoms, so you actually send a wave of compression up the rod rather than moving it as a solid object.

in practise, with the materials that we have today this is impossible.

but in theory, the completely solid, non elastic rod that doesn't bend or flex.
it seems like it should be possible...


I guess the question here is, can a force be transmitted faster than the speed of light? we're asking if electromagnetic radiation can travel faster that a molecule can transmit a compressive force...

the principal being that you're sending a really simple 1 bit of information with a push, and that 1 bit gets there very quickly because the rod is solid, faster than the few minutes it would take radiation to get there.

but the wave of compression still has to travel up the rod, we don't know how long that takes, (because we don't have this infinitely stiff material).

we're not talking about the rod moving faster than light though, it's just got to be able to move backwards and forwards at a rate of a couple of shoves a second and it beats radio communication to the moon.

I guess the answer is, in principal, if you add some conditions that are impossible to meet, yes. you can communicate faster with a solid medium than using radio transmissions,
in practice, it's probably going to be impossible.

it still doesnt "beat" anything. its already there! its in both spots at once so it is not traveling. it needs to travel a few inches back and forth, while radio transmissions need to travel a full 238,000 miles.

so in theory, YES there was no delay in getting the astronaut the message. and you got it done FASTER than a radio transmission. BUT you did not travel the same "distance" the radio waves had to. so no you did not move faster than the speed of light.

 

[Luke_Uk_Baggy]

Quote from Lew:

''
so in theory, YES there was no delay in getting the astronaut the message. and you got it done FASTER than a radio transmission. BUT you did not travel the same "distance" the radio waves had to. so no you did not move faster than the speed of light.

''



You didnt 'MOVE' anything faster than the speed of light, but the OP Question was 'Have I just communicated with bob faster than the speed of light'

I suppose this brings up a few slight ambiguties with the question. As I read that question, I would say yes, because the individual messages get from A to B quicker than light could...

Then again you could say 'OMFG IT WOULD TAKE YOU AGES TO WRITE ALL THAT IN MORSE'... So it really depends how you are, in this instance, defining 'faster', and also defining 'Communicate'

(I.E. is communicating with him as soon as he sees the stick move? (again instantaneously) or when he has got the whole message?)

REALLY Strict conditions need to be imposed, and defined, in order to answer the question, otherwise you can argue for ages.


BTW these sort of questions are great ty berry

 

[root]

it still doesnt "beat" anything. its already there! its in both spots at once so it is not traveling. it needs to travel a few inches back and forth, while radio transmissions need to travel a full 238,000 miles.

so in theory, YES there was no delay in getting the astronaut the message. and you got it done FASTER than a radio transmission. BUT you did not travel the same "distance" the radio waves had to. so no you did not move faster than the speed of light.

nobody said anything about travelling faster than the speed of light.

SO the big question - have I just communicated with Bob faster than the speed of light?

just communicating faster than radio waves, (which travel at the speed of light).

it's not exactly talking about the speed that the rod travels, or the speed that light travels, it's the baud rate of the two medium which is really being questioned. (i.e how long to communicate a single bit of information).

the trouble is this, if you look at a single bit of information, it's going to take a little while for a radio wave to cover the distance, on the other hand, the solid rod only takes as much time as it takes to lift the rod.

so the rod appears to transmit information instantly, whilst the radio waves, have a distance to travel (thousands of miles) and are not instant.

say the rod is only moving an inch.

so your single bit of information is transmitted faster on your push rod assembly than on your microwave transmitter. you've communicated faster than radio, radio travels at the speed of light.

(that's the bit that we agree on right)?


the question I was posing as to how effective this may be revolved around the way in which objects are built with structures of atoms arranged as molecules, how they interact and support each other, and how they can move with relation to each other.

i.e do you move the first molecule, and that first molecule moves the second, or do you move an entire structure as one?
if the molecules are responding to the pressure of their adjacent molecules, in order to move, then the question becomes how fast does the pressure wave move up the rod, and is this faster than the speed of light.

If the wave of pressure is not faster than the speed of light then the start of the rod will have moved to it highest, (or lowest) extreme, whilst the structure of the rod is still transmitting the compressive force through it's structure...


which is why the rod need to be completely stiff and non-elastic...
and there isn't such a material... (i.e it doesn't exist).

so as I said, in theory, possibly yes, you can communicate with push rod technology faster than using radio technology, (which travels at the speed of light).
but in practice, it's never going to happen.

we're not talking about the rod moving faster than light though, it's just got to be able to move backwards and forwards at a rate of a couple of shoves a second and it beats radio communication to the moon.

what I meant is that it beats radio as the fastest way to transmit information, there is a lot lower transmission time for a single bit.

but since we've only one rod there is very little bandwidth.

since we've looking at a physical movement I'm also thinking that the baud rate would be astonishingly low.

thus the speed of the connection would be astonishingly poor!

 

[berry120]

Glad this has sparked off some discussion!

Just to lay a few things down (root's already picked up on them but just to confirm it!)

- I'm not saying this is practically possible; we're talking theoretical physics here! No, no such materials exist at present and even if they did, it's hardly a practical suggestion

- As I stated in the original post, we're ignoring bending and flexing; we're assuming the rod is completely inelastic.

- To those saying it'd take ages to type out instructions in morse code; of course it would. But what I'm concerned about here is not the bandwidth but the latency. Latency in communication is the thing restricted by the speed of light, and so is the issue I'm addressing here. Communication could just be as simple as telling the astronaut to "go" when the rod is pushed - ignoring the distance it's pushed entirely. Even with this simple message, a radio wave would still take ~2 seconds to reach the astronaut.

- Faster than light travel is pretty much universally accepted as impossible given our laws of physics. However, faster than light communication isn't; have a dig up around quantum entanglement (though don't expect to understand it...)

 

[connchri]

He wouldn't have got the message faster than light.

In some way or fashion, the information would take the few seconds needed to get their.

There's no such thing as a perfectly incompressable object. Everything does even to a minute degree. And that includes your pole. This would result in the "wave" of information traveling up the pole.

You cannot transmit information, in any shape or form, faster then the speed of light. Your talking about a situation that can never be engineered to exist, simply because the laws of physics won't allow it to happen.

Plus, you've everything else to take into account, it would fall apart under it's own weight, you'd need an awful strong hand to 'poke' your mate on the moon, etc etc. Just wouldn't happen.

 

[berry120]

You cannot transmit information, in any shape or form, faster then the speed of light. Your talking about a situation that can never be engineered to exist, simply because the laws of physics won't allow it to happen.

Did you read my above post?

Quantum entanglement could be used for such a purpose, have a look here for the results of the experiment they did a couple of years back. It's a common myth that faster than light communication is prohibited by laws of physics - classical physics yes, but classical physics was proved incorrect for situations like this decades ago (hence the rise of quantum physics.)

There's no such thing as a perfectly incompressable object. Everything does even to a minute degree. And that includes your pole. This would result in the "wave" of information traveling up the pole.

I'd be interested to read any material you could point me to backing up your claim that a "wave" of information would travel up the pole and this would be slower than the speed of light (that's not a sarcastic comment, I'm genuinely interested because I've looked and found nothing.)

Plus, you've everything else to take into account, it would fall apart under it's own weight, you'd need an awful strong hand to 'poke' your mate on the moon, etc etc. Just wouldn't happen.

Of course it wouldn't, practically - I'm talking theoretically here. I'm all up for my thoughts being debunked by genuine evidence, but just saying it won't happen because you can't travel faster than the speed of light (which I'm not doing in this example) and because you can't get a big enough stick isn't brilliantly conclusive!

 

[Calibound88]

inertia. do we assume it is easy to push and pull. the weight of the rod is negligible?

 

[connchri]

I did read your post. But I never read the rest of the thread. As someone who has studied Quantum mechanics (albeit, I find it an extremely difficult subject!), I can tell you right here an now that the link you have included is a gross simplification of what you think is faster than light comunication.

If you even read the PDF that it is introducting you, the authours clearly state "the author stress that the existence of a universally privileged framewould not contradict relativity".

QM is a very difficult subject to grasp. And I admit I don't understand it fully, even though I've studied it and passed the module. But I do remember some fundamental points. Even though Quantum Entaglement allows two observers at a distance to observe an event simulatenously, it doesn't allow that event, or information from one observer to another to be transmitted faster than the speed of light.

It's a common myth that faster than light communication is prohibited by laws of physics - classical physics yes, but classical physics was proved incorrect for situations like this decades ago (hence the rise of quantum physics.)

You clearly have zero understanding of Quantum Mechanics. And it certianly didn't arise due to anyone finding out how to transmit information faster than the speed of light. It came about after newton mechanics (classical physics) could not explain systems at microscopic sizes or the photo-electrical effect on metals.

It is a common myth that QM allows faster than light imformation transmittion, NOT the otherway about!

read here for a quick wiki
http://en.wikipedia.org/wiki/Faster-than-light#Quantum_mechanics

As for the "wave traveling up the pole", it's quite simple. Using relativity, the end of the pole is at a different time frame than the other end, albeit by seconds, but still significantly enough to prevent the "wave" from traveling instantanously to the end of the pole.

The same reason why if the sun dispeared, it would take 8 minutes for earth to notice, as it's not only 8 light minutes away, but also 8 minutes away in time! ie, the earth would still orbit it for 8 minutes even though it is no longer there.

 

[berry120]

inertia. do we assume it is easy to push and pull. the weight of the rod is negligible?

It's irrelevant in this instance, the point is more that whatever force you put behind the rod at one end, it'll move at the other; even if it takes a lot of energy to do so!

connchri - No need to get worked up! It's a moot point I was wondering about, I too have studied quantum mechanics (albeit some years ago) and I'm afraid you seem to have taken a lot of what I said out of context - at least not in the way I intended it. This could well be because of me not putting things across as clearly as I could however, so I'll try and explain.

If you even read the PDF that it is introducting you, the authours clearly state "the author stress that the existence of a universally privileged framewould not contradict relativity".

I have read the PDF, and I'm aware it doesn't contradict relativity - I don't recall claiming it did? Special relativity doesn't outlaw "apparent" faster than light communication - which is how I'd classify entanglement.

Even though Quantum Entaglement allows two observers at a distance to observe an event simulatenously, it doesn't allow that event, or information from one observer to another to be transmitted faster than the speed of light.

Or does it? Whilst you're 100% correct in pointing out the no-communication theorem holds up in the instance you've described, I was taught this isn't an altogether uncontested "theorem".

Another experiment, also done a couple of years back is where I'm coming from on this one. From the report given there:

By doing so, the research team was able to conserve up to 20 percent of the original entanglement after the release of the photon back into the surrounding environment.

No, it's not a lot, and it was observed over a 1mm gap - but it's arguably something could well be seen as violating the no communication theorem.

I've had a look at the wikipedia articles on the subject, but in these sorts of fields they're really not the most reliable (anyone writing said articles is going to be an expert in the field, and therefore will most likely have a strong view on the matter one way or another.)

You clearly have zero understanding of Quantum Mechanics. And it certianly didn't arise due to anyone finding out how to transmit information faster than the speed of light. It came about after newton mechanics (classical physics) could not explain systems at microscopic sizes or the photo-electrical effect on metals.

I never said it did. By "situations like these" I was referring to any situation where classical physics simply doesn't hold up - the infamous double slit experiment being the obvious choice (and the experiment that I believe sparked it all off!)

It is a common myth that QM allows faster than light imformation transmittion, NOT the otherway about!

Agreed to an extent - perhaps I put my point too definitively. I still maintain though it's a common myth that faster than light transmission has been proven impossible. I'm not saying it is - but with the no communication "theorem" not accepted by all for reasons I've outlined above, I'm not jumping to the conclusion that it isn't either.

As for the "wave traveling up the pole", it's quite simple. Using relativity, the end of the pole is at a different time frame than the other end, albeit by seconds, but still significantly enough to prevent the "wave" from traveling instantanously to the end of the pole.

That I do accept as a decent argument - probably the best put forward as of yet I'm still not 100% convinced but I'll have more of a think in the morning...

I'll admit I'm at the edge of my knowledge here - but please don't assume I'm blindly throwing things out there I've randomly heard in science fiction films. Time travel (to the past at least), actual faster than light travel, and using tachyons for faster than light communication I all think are complete nonsense. After reading around though I'm not convinced it's the same for faster than light communication just yet.

 

[sniperviper21]

As for the "wave traveling up the pole", it's quite simple. Using relativity, the end of the pole is at a different time frame than the other end, albeit by seconds, but still significantly enough to prevent the "wave" from traveling instantanously to the end of the pole.

Ex:
the wave of energy in a slinky...

for the less edgimecated.