Naked Science Forum
General Science => General Science => Topic started by: Nick Allen on 13/10/2008 22:08:02
-
Nick Allen asked the Naked Scientists:
Hi! Love your website, I have a question for you:
If you built a piece of conduit with a Teflon interior coating around
the world.
And also developed a nano-thread with virtually zero weight or
elasticity, and thread it once through the entire piece of conduit.
Then inserted yourself at the begging and end of the conduit, tug one
end of the thread, see what happens to the other side and record the
time it takes for the one end to move away from you as you tug the other
end.
Would the thread INSTANTLY move away from you? And if so, what does this mean? Did the string move at near the speed of light, since it travelled around the world instantly?
What do you think?
-
It's yet another example of a mechanical wave. The speed at which the force would propagate along your thread would be governed by the density of the material and its modulus of elasticity which both affect the speed of sound (mechanical waves) through a medium.
For 'real' solid materials the speed of sound is at least ten times that of sound in air. Light, on the other hand is about a million times faster.
The force which connects an atom to the next atom travels at c but the next atom has to accelerate and pass the force to the next one and so on. This accounts for the relative slowness.
-
Well in the quantum world of non- locality and entaglement atoms seem to know what others are doing on the other side of the universe at the exact same moment
Alan
-
Well in the quantum world of non- locality and entaglement atoms seem to know what others are doing on the other side of the universe at the exact same moment
Alan
That is not the same a a force being instantly transferred from A to B though.
-
Nice question.
Nothing in 'our world' will travel faster than 'c' as far as I know.
Not if it should be seen as 'work done' or 'information'.
That includes 'vibrations' and 'mass displacement'.
So if you had a pole stretching to the moon and then by your superpowers pushed it the movement traveling inside and outside (as seen from an observer) your pole would still be limited to 'c'.
And it also has to do with the 'rigidity' of your 'pole' (awh sh*, this could be miss constructed:).
The more 'rigid' it will be the faster the force will travel, but to get an speed nearing 'c' you will need an almost infinite 'rigidity'.
------------
Although you have what's called 'tunneling' or the Josephson junction.
http://en.wikipedia.org/wiki/Josephson_junction
Where matter 'magically' moves through matter.
That's most often explained like an example of the uncertainty principle when looking at electrons as wave packets.
That this 'wave packet' extends to the other side.
But I'm not sure if that should be seen as a instantaneous traveling?
And then you have entangled particles of course, but there you won't fulfill the 'information' demand.
Other than that I don't know of anything that might be moving in time faster than 'c'.
Virtual particles?
-
So if you had a pole stretching to the moon and then by your superpowers pushed it the movement traveling inside and outside (as seen from an observer) your pole would still be limited to 'c'.
In this instance, if I read it correctly, it would be restricted to the speed of sound, wouldn't it?
-
So if you had a pole stretching to the moon and then by your superpowers pushed it the movement traveling inside and outside (as seen from an observer) your pole would still be limited to 'c'.
In this instance, if I read it correctly, it would be restricted to the speed of sound, wouldn't it?
That's correct.
-
Yep, that's definitely correct.
What I was doing was to introduce the, admittedly rather weird idea, of an infinitely 'rigid' pole to get around it.
'Elastic waves' will travel in the pole at the speed of sound which must be less than the speed of light for ordinary matter.
http://answers.google.com/answers/threadview?id=73321
-
Also, as predicted by special relativity, there isn't really any such thing as "instantaneous" over large distances. What separate (in space) events happen at the same time depends on your frame of reference.
If I could send a signal to a distant object instantaneously in my reference frame, it would for someone traveling at a high velocity appear as me sending a signal back in time - which in turn leads to all kinds of paradoxes.
-
Also, as predicted by special relativity, there isn't really any such thing as "instantaneous" over large distances. What separate (in space) events happen at the same time depends on your frame of reference.
If I could send a signal to a distant object instantaneously in my reference frame, it would for someone traveling at a high velocity appear as me sending a signal back in time - which in turn leads to all kinds of paradoxes.
I got stuck on that one:)
If you are sending something 'instantaneously' then that is traveling with the speed of an entangled particle/photon as I see it.
And to me that is 'outside' of time?
So when traveling near 'c' you wouldn't see any difference at all it seems to me.
Let us say that you send away a rocket at almost light speed to take a 'turn' around our nearest star and then come back.
You have a super telescope following that ship.
At no time:) will that ship disappear from your view even though its time as compared to you will be very 'different'.
And the same will be for that spaceship if it watches you, so space time all will 'hang together' with an time-arrow pointing in our 'usual' direction.
That time will differ when compared is true, but I don't see how you can make it go 'backward'
If you for example used a laser sending a beam from Earth to the Moon and had the spaceship watching while it traveled at near 'c' it would still see that beam moving in our 'ordinary' time arrows direction as I understand it.
In QM you have Feynman diagrams where you can make as much sense out of them backwards as forwards, and there you might talk about time without an arrow, but not macroscopically?
How do you mean you can make time go 'backward' as observed by my reference frame?
To me that seems only possible if I was traveling past 'c'??
------------
you mean that this instantaneous signal is traveling past 'c'?
And so will travel backwards from my view if i was in that spaceship.
But if it is instantaneous it will be so symmetrically no matter how you turn your arrow.
-
You're talking about time dilation, which is one relativistic effect of traveling at close-to-speed of light.
I was referring to relativity of simultaneity , which is another consequence of special relativity (see e.g. http://en.wikipedia.org/wiki/Relativity_of_simultaneity (http://en.wikipedia.org/wiki/Relativity_of_simultaneity)). It implies that there is no such thing as "universal simultaneity": what events are simultaneous depends on your reference frame.
If you could affect a distant object "instantaneously", you first have to define with respect to what reference frame the action should be instantaneous.
To make a thought experiment, imagine I could send a signal to a distant star which would arrive instantaneously according to my "resting" reference frame. The star then sends an instantaneous signal back (again instantaneous with respect to my resting frame) and I receive it at the same time that I send it. But if the star is instead traveling towards me and sends a signal back that is instantaneous according to its resting frame, I would receive the signal before I even sent it! This is because an event at my location which is simultaneous to an event at the distant star in my reference frame occurs after the event at the distant star in its reference frame (so that sending the signal back instantaneously in the stars reference frame would imply it getting back before it was sent).
Cheers,
-Emanuel
-
To make a thought experiment, imagine I could send a signal to a distant star which would arrive instantaneously according to my "resting" reference frame. The star then sends an instantaneous signal back (again instantaneous with respect to my resting frame) and I receive it at the same time that I send it. But if the star is instead traveling towards me and sends a signal back that is instantaneous according to its resting frame, I would receive the signal before I even sent it! This is because an event at my location which is simultaneous to an event at the distant star in my reference frame occurs after the event at the distant star in its reference frame (so that sending the signal back instantaneously in the stars reference frame would imply it getting back before it was sent).
Cheers,
-Emanuel
erm... (https://www.thenakedscientists.com/forum/proxy.php?request=http%3A%2F%2Fbestsmileys.com%2Fclueless%2F1.gif&hash=ba6e884e2ac18d739c0e89967c82862b)
-
Yep, I'm used to feeling confused, but now you got me right and proper.
(Confuseder than this I haven't been in a long while said Alice:)
Is it this you are referring to?
-------------------------------Guest_carbonlife-------------------------
Einstein said that space and time really aren't the "absolutes" we imagine them to be. Simultaneity is also an illusion, said Einstein -- there's no such thing as universal 'now', because time passes at different rates depending on where you are in, say, a galactic gravity well, and how fast you're going. Two events can only be simultaneous if they happen at the exact same place and time. That's why you reset your watch when you pass a planet -- you can only be sure it's the same time if you're right there.
There is however an "invariant spacetime INTERVAL" between any two events. Suppose you place two firecrackers in space a certain distance apart, set to go off ten seconds apart. To a stationary observer in the same frame, the interval between flashes is 10 seconds -- simple. In a moving observer's frame of reference, the time interval between flashes is distorted, plus the firecrackers have moved. Yet all observers, moving or not, get the same answer for the "invariant spacetime interval" between the two flashes -- square_root ( distance-squared minus time-difference-squared ), or sqrt ( x^2 + y^2 + z^2 - t^2 ). Yhat's just the Pythagorean formula for distance, but with a timelike component. In other words spacetime is real, but space and time separately are not. Space and time only SEEM separate if you're not moving -- if you are moving, space and time shift in a coordinated way, but invariant intervals remain constant. That's why you can use intervals as a measuring tool, such as the events generated by a bouncing beam of light hitting 2 mirrors.
Invariant intervals between EVENTS are like the gold standard of special relativity -- they always work. The trick is to forget about the firecrackers themselves and just look at EVENTS that you know actually happened at a particular point in spacetime. Different observations of the same EVENTS can then be reconciled using the invariant interval. The only catch is that observers can't necessarily reconstruct a SEQUENCE of events, because in some frames of reference the 'wrong' firecracker goes off first.
-------------------------------------On the Other Tentacle----------------------
What am I missing?
I'm not questioning this, just the thought that 'instantaneous' action, when seen from a object in 'fast' motion would be shown as going backwards.
Isn't that almost an oxymoron 'instantaneous backward':)
If time was made out of chained events creating our 'movie'.
Instantaneous to me would be just one of those 'events' and nothing more.
-
Einstein said that space and time really aren't the "absolutes" we imagine them to be. Simultaneity is also an illusion, said Einstein -- there's no such thing as universal 'now', because time passes at different rates depending on where you are in, say, a galactic gravity well, and how fast you're going. Two events can only be simultaneous if they happen at the exact same place and time. That's why you reset your watch when you pass a planet -- you can only be sure it's the same time if you're right there.
There is however an "invariant spacetime INTERVAL" between any two events. Suppose you place two firecrackers in space a certain distance apart, set to go off ten seconds apart. To a stationary observer in the same frame, the interval between flashes is 10 seconds -- simple. In a moving observer's frame of reference, the time interval between flashes is distorted, plus the firecrackers have moved. Yet all observers, moving or not, get the same answer for the "invariant spacetime interval" between the two flashes -- square_root ( distance-squared minus time-difference-squared ), or sqrt ( x^2 + y^2 + z^2 - t^2 ). Yhat's just the Pythagorean formula for distance, but with a timelike component. In other words spacetime is real, but space and time separately are not. Space and time only SEEM separate if you're not moving -- if you are moving, space and time shift in a coordinated way, but invariant intervals remain constant. That's why you can use intervals as a measuring tool, such as the events generated by a bouncing beam of light hitting 2 mirrors.
Invariant intervals between EVENTS are like the gold standard of special relativity -- they always work. The trick is to forget about the firecrackers themselves and just look at EVENTS that you know actually happened at a particular point in spacetime. Different observations of the same EVENTS can then be reconciled using the invariant interval. The only catch is that observers can't necessarily reconstruct a SEQUENCE of events, because in some frames of reference the 'wrong' firecracker goes off first.
Nope. Still as clear as mud to me. [???]
-
What I was trying to say is that if you accept that what intersection of space-time is "now" depends on your frame of reference (velocity), two distant events that is simultaneous for one observer might not be simultaneous for another.
If a signal could be sent "instantaneously" from a source to a receiver according to one reference frame, the reception event could come before the emission in another reference frame (e.g. one traveling in the same direction as the signal).
The only way of avoiding such violations of the principle of cause and action is to postulate that no signals (forces etc.) can travel faster than light.
-Emanuel
-
Ah, now I get it... I think... sort of... ish
-
Emanuel, can you give me an example of such an reference frame?
where from some other's transmission would be perceived as 'instantaneous'?
Or are you using it from its 'original frame' so to speak
Wherein it 'really' do happen instantly?
Either 'instantaneously' have a 'time period' to it?
Or it has no time at all.
And to me that word implies 'no time'.
just so i get you right:)
And if it is so, then it will be a 'symmetry' to me.
like a 'point particle', taking up no space.
And times arrow won't do it a thing, I say::))
I would love to see a good example on how this works.
"If I could send a signal to a distant object instantaneously in my reference frame, it would for someone traveling at a high velocity appear as me sending a signal back in time"
When transmitting something 'inside/taking' time I don't see how it could be received as being before the transmission?
No matter your velocity?
I agree that it's all relative, but times arrow will be unbroken macroscopically up to 'c'.
After 'c' its a different thing, then there will be thygers:)
But if you can give me a good example, maybe I will have to change my mind (again:)
-
Most esteemed colleagues:)
The land of relativity hails you.
Like a mighty shower of, ah, hails?
Allow me to describe Relativity of simultaneity as seen from a light-bulb.
Not a provincial bumbling lightbulb either, no Sires and Ladys..
A most real and existing one, ahh, that one yes, or was it that one?
And yes..
The story begins a sunny day with you meeting a most benevolent and accommodating man inviting you to witness his new innovation.
And you being such a young and trustful thing naturally follows his lead.
(Btw: Could i get your number afterwards:)
'Now, please follow me inside this room' he says.
'In the roofs exact middle I have placed that circumstantial and not so provincial light bulb, as you can see my Lady'?
And here he smiles at you evincing his darkly red, fully stained, slightly bloodied teeth in a sunny smile.
'Do we all see it'? (He looks around, and as you do the same you, to your everlasting surprise, notice that you're not alone any more)
'Good' he continoues.
'Please, will all notice that the walls are painted in a very thoughtful and reflective manner, that as when the light-ray from the light-bulb strikes those walls they will light up'.
'The wall at the back of me we will call 'A' ladies and gentlemen.
And the wall to the front of just before that', pointing to a shiny pointy thing, vaguely seen outside the window 'just for fun ladies and gentlemen, just for fun, why don't we call that thing ohh, what do I know, ah well, a nn noosecone'.
'Well.' He harrumphes. 'Furthermore the wall in front of me just before that, and here he gives you a deep meaningful look, 'we will for simplicity's sake call 'B''.
So 'A'<--'o'-->'B' (and --> nosecone.) oh oh...
(where 'o' = light-bulb)
'Good', (combing his beard nervously while smiling fiendishly)
'Now if you all will be so kind to put on your light retarding goggles thank you'.
'Those goggles'. (looking around most proudly while twirling his mustaches in an agitated manner)'Thooose Gooogles, are an invention of mine to better show you the Relativity of simultaneity in motion'.
And 'yes' he whispers to you in confidentiality. 'We are talking full panavision color moving pictures here, no less lass'.
'With them on you will be able to notice the exact time when the light strike the walls'.
All said and done he turns the light-switch and you see the light-bulbs rays strike the both walls at exactly the same time.
And you were there to see it, with those amazing goggles too, no less.
But what you didn't know was that it was all a trick....
He was a inter galactic slave trader planning to sell you all.
And that room was no room!!!
It was a spaceship, ever so imperceptible moving, and that at a rather respectable speed too if I may say so.
In fact at almost seventy percent of the speed of light and raising.
But you were very lucky, yes you were, because on Jupiter ranger Jim was ranging, him and his trusty telescope.
And through that same instrument he had followed the experiment, oh yes he had.
Ahh, did I forget to mention the panorama window that the inter galactic Rover-reapers had installed into that same room?
Well they had, and through that Jim could view the experiment as the rocket was passing Jupiter.
But mystery of mystery's, when he watched those light rays he saw something different happening with the walls.
What he witnessed was the light first hitting the back of the room, namely 'A' and needing an awful long time to reach the 'front wall' of the room, namely 'B'.
Why???
Well he was on Jupiter, right.
Not on the ship at all.
And that ship was traveling, was it not?
Very fast it was (Yoda)
So those light quanta's (rays) running with the ships motion found themselves needing to catch up with the ships motion before they could reach that front wall 'B' as seen from our stationary friend Jim.
And the ones running against that ships motion towards the back, found the back wall 'A' ever so rudely coming to meet them.
All according to what Jim was witnessing.
So why didn't you see the same then?
Well, you was traveling aside those rays weren't you?
In the same room, right, so compared to that light-bulb in the roof you was at rest,wasn't you..Huh, you lazy son of a .., well, not moving at least, right.
But that mystery couldn't stop our brave hero Jim.
Jumping on his jolly spacebuckaroo he rode out the spaceway's to rescue and whilst in the midst of it freeing you too.
But there is still a mystery to it. Namely that the speed of light always, no matter from where you measure, always, will have a defined speed of ... 'c'.
Ahaa, explain that if you can, can you, huh, you can can you..:)
And how could he see that light move 'slower' to the front and 'faster' towards the back.
Also, what do you think happened with the waves from that light-bulb as they traveled, seen from Jim's perspective?
If Jim (still being on Jupiter) had been looking at the spaceship from behind instead.
Would those light-waves have changed 'character' as seen from Jims 'stationary' planet.
Ah, I forgot to tell you did I?
Yes they had a floor of glass to, the solid kind of glass, bless you:)
Well, they were after all stockbrokers gone bad, you know, trying to relive the eighties and all...
Ah well. And the waves, if Jim had been in front of the Spaceship then?
Looking in???
Would they had changed in any way as compared to what you saw inside that room?
For Jim on his --->stationary<--- Jupiter.
Think of those meandering looping curly waves pressing them self out from that -> --> moving ---> object, ah, light-bulb, sorry..
And yesss, the whole phreaking ship was made of glass, satisfied!!!
(Cinderella never got the chance to try it on though, due to relativistic chance and circumstance..)
Sorry, got carried away here:)
Had to write it..
Compulsive, I know:)