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From: robert bristow-johnson on 29 Mar 2010 12:35 On Mar 28, 4:13 pm, Eric Jacobsen <eric.jacob...(a)ieee.org> wrote: > On 3/28/2010 11:40 AM, WWalker wrote: > > > I am sorry to insist, but it does not matter what the reason is. If I have > > a communication link that allows me to transmit a pulse over a distance > > faster than a light propagated pulse, then the pulse propagates faster than > > light. > > I suppose you can argue semantics here about what defines the "pulse", > but understand that "information" is not propagating faster than light > in any of the examples, and neither is energy. This seems to be the key > point that must be understood. A simple small phase advance of a > signal is NOT indicative of information exceeding the speed of light. > > If you just want to claim that the signal has phase advanced and appears > to arrive earlier than expected, that's fine, I don't think anyone will > argue with you there. That's what has led to discussion and study on > this topic in many places. > > > If I use the pulse to denonate a bomb located a distance away, the > > bomb will explode sooner than if the pulse propagated at the speed of > > light. This is absolutely true and cannot be argued. well, it *is* argued. this is funny, because i have been in similar discussions but on sci.physics.research or sci.physics.foundations or, in the past, the Physics Forums site. i haven't seen it here on comp.dsp. sometimes the discussion is about the speed of gravity (in comparison to the speed of electromagnetic propagation a.k.a. "speed of light"). now, i *do* seem to remember reading something about the group velocity of some modulated light source exceeding the phase velocity in some medium. i don't usually concern myself with non-vacuum propagation since, at the atomic level, it's a vacuum between the atoms and when epsilon differs from epsilon_0 it's a macroscopic *aggregate* effect of the polarization of molecules in the medium. same with mu and mu_0. the speed of light (or of EM) in a vacuum, what we call "c", is not a property of E&M, but is a property of space and time. it doesn't matter what the "instantaneous" force or interaction is. could be EM, gravity, strong (turns out weak is mediated by particles with mass, so it ain't as instantaneous). suppose you are standing there and i am standing here, some distance away. now suppose you are holding a big negative charge and i am holding a big positive charge and we are both restricting the movement of our charges to a plane that is perpendicular to the line connecting the two of us. since our charges are attracted to each other, when i move my charge up, your charge follows it up. if i move it down, your charge follows it down. if i move it to my right, your charge follows it to your left (assuming we are facing each other). similarly if i move my charge to my left, your charge follows to your right. if i move my charge up and down repeatedly, yours will follow it up and down repeatedly. i am literally a "transmitting antenna" and you are a "receiving antenna". if i move my charge up and down a million times per second, you could tune it in with an AM radio. if i move it left and right 100 million times per second, you can tune it in with an FM radio. if i move it back and forth 500 trillion times per second, you would see it as a blur of orange color. that's what EM radiation is, at a fundamental level. now imagine there is a third party observing us at a distance and is equidistant from us both. and suppose this third party knows, from some other means, what the distance is between us. no matter what i do with the charge, when the observer sees the perturbation of position on my end and then observes a perturbation at your end, the time differential between the cause and effect will always be that distance between us divided by c. i don't care what you read or what you think W, that's what it is. it would be the same if you and i were the size of gods and, instead of charges, i was holding a planet and you were holding a planet. i perturb the position of my planet and your planet will get disturbed by that change of gravitational field and the time differential between the disturber and disturbed will be the distance between the two of us divided by the *same* c. so, even if we tried to use gravity waves to communicate information, we would still be limited by the speed c. now, despite what we sometimes read, it isn't that Nature is imposing a fundamental limit to the speed of propagation of information, it's that Nature, namely the fundamental nature of space and time, imposes a finite limit of speed of the fundamental interactions, of which all of physical reality is built upon. *that* is what imposes a limit of speed of conveyance of information since information is conveyed by a physical interaction. there is nothing magical about that speed "c". all the physics needs is that c is real, positive, and finite. it could be *any* speed (as observed by a god-like observer who is not himself affected by the physics). for those of us who are mortal and are governed by the interactions of Nature, all of the rest of reality would be scaled in such a way that the speed of propagation, c, would appear to be the same, *unless* some *dimensionless* fundamental physical constant (like alpha) changes. and then, the salient fact is that this dimensionless "constant" changed (not c). we don't measure or perceive dimensionful quantities directly, but we *always* measure or perceive such as a ratio against a reference quantity of the same dimension. there is always a reference voltage in our DVM, there are always pre-existing tick marks on our ruler. the dimensionful quantity we call "c" is more of an expression of the anthropometric units we happen to be using to measure length and time. WWalker, i might suggest that you take this up at sci.physic.foundations or maybe sci.physics.research (both are moderated) or go to the PhysicsForums.com site. r b-j
From: Jerry Avins on 29 Mar 2010 12:38 WWalker wrote: > Jerry, > > The speed of light is a corner stone in physics and if it is not a constant > then many of our theories in physics will be affected. There may be direct > practical uses as well, but I just guessing: improving accuracy of high > speed doppler radar, speeding up communication to spacecraft where time > delays are problematic, increasing speed of computers when they are > eventually limited by light speed delays etc. As I said, these are only > guesses, the main effect would be a change in many of our theories in > physics, which would eventually lead to new practical uses and > technologies. > > William How much Doppler radar is done within half a wavelength of the antenna? One might as well use a tape measure for distance, and if the Doppler shift amounts to anything, duck! Jerry -- Discovery consists of seeing what everybody has seen, and thinking what nobody has thought. .. Albert Szent-Gyorgi
From: Jerry Avins on 29 Mar 2010 12:46 WWalker wrote: > Steve, > > Clearly energy is also propagating faster than light in the dipole system. > If the pulsed carrier is propagating faster than light, as shown in my > simulaton, then the energy of this signal is just the signal squared and > low pass filtered. This is exactly how I detected the signal in my > simulation. So the detected pulse I showed in my simulation is also > proportional to the energy. I once did a titration simulation for a chemistry class. In most respects, it was as real as I could make it. As neutrality was approached, each drop of reagent flashed before it expanded and faded. The time to fading was a good clue to the pH. To remind the students that a simulation may be made to show whatever the author wants it to, the simulation differed in one very obvious way: the phenolphthalein turned green, not red. How do you know that you aren't looking at green phenolphthalein? Jerry -- Discovery consists of seeing what everybody has seen, and thinking what nobody has thought. .. Albert Szent-Gyorgi �����������������������������������������������������������������������
From: Eric Jacobsen on 29 Mar 2010 14:32 On 3/29/2010 8:42 AM, WWalker wrote: > Eric, > > Could you elaboate on your comment below. I think we need to agree on the > definition of information in regards to the LPF pulsed carrier simulation. > How does your comment refute my argument presented again below? > >> I suppose you can argue semantics here about what defines the "pulse", > > Again I claim: > > "Refering to the Low Pass Filtered Pulse > simulation I posted, the simulation clearly shows that if I transmit a > pulse, the pulse edge arrives sooner than if it had propagated faster than > light. If my detector at the receiving end is a threshold detector which > is > set to look for anything above the noise level, it will fire earlier than > if the pulse had propagated at light speed. In other words, it shows that > if I push a button launching the narrowband pulse signal and propagate it > via a dipole to a nearfield receiver with the threshold detector, the > pressed button will be detected sooner than a light propagated signal. > This > clearly shows that an action (informaton) in this nearfield dipole system > can be detected faster than light. If this is true than I have proven my > point that information propagtes faster than light in the nearfield of a > dipole." > > "it does not matter what the reason is. If I have > a communication link that allows me to transmit a pulse over a distance > faster than a light propagated pulse, then the pulse propagates faster > than > light. If I use the pulse to denonate a bomb located a distance away, the > bomb will explode sooner than if the pulse propagated at the speed of > light. This is absolutly true and cannot be argued. The only question is > if > the dipole simulation demonstrates that a pulse can be detected over a > distance faster than light. I think it has. > " > > So if press a button with the same signal characteristics as the LPF pulse, > and if I use the above setup to detect the pulse and explode a bomb, the > bomb will explode earlier than if the pulse propagated at the speed of > light. The pressing of the button (Action) results in the exploding of a > bomb (Reaction) faster than light speed. This is clear cause and effect > (information) which propagtes faster than light. > > > William How did the input "pulse" get bandlimited in the first place? This is key to understanding how this works. It's not magic, information is not accelerated. Imagine this and you might be able to see what's going on: Start with an ideal impulse, a dirac delta, or some suitable equivalent. Pass that impulse through your bandlimiting filter, see how long it takes to come out. Since the bandlimiting filter is causal, the bottom of the leading edge of the pulse doesn't happen until the instantaneous impulse has arrived. The entire width of the output pulse is then a delay from the incidence of the impulse. Consider the dirac delta the "information". So, it is easy to see that the peak of the output pulse has, at minimum, the delay from the bottom of the leading edge of the bandlimited output pulse. If you closely examine the output of the predictive filters, whether it's a filter with a negative group delay or the near field of an antenna or whatever, it does NOT begin to ramp up the output pulse values until the input pulse values have actually arrived. In other words, as we know, or at least most of us know, such a filter is still causal and does NOT predict the onset of the leading edge of the pulse. So, what you are seeing is, for example, because I don't know the actual numbers from the simulations, the distance from the initial dirac delta to the bandlimited output pulse peak being X, and the "accelerated", predicted pulse output is X-delta, where delta is the small advance achieved by the prediction. NOTE THAT X-delta IS STILL A POSITIVE NUMBER, and delta is going to be small compared to X. All filters have delay. What you are seeing is that the predictive filter has a little less delay than the signal being compared to it. The "information" arrival, as compared to the actual incidence of the initial dirac delta, will not violate causality or c. Observers can be fooled, however, as you are demonstrating. -- Eric Jacobsen Minister of Algorithms Abineau Communications http://www.abineau.com
From: Jerry Avins on 29 Mar 2010 14:56
Eric Jacobsen wrote: > On 3/29/2010 8:42 AM, WWalker wrote: >> Eric, >> >> Could you elaboate on your comment below. I think we need to agree on the >> definition of information in regards to the LPF pulsed carrier >> simulation. >> How does your comment refute my argument presented again below? >> >>> I suppose you can argue semantics here about what defines the "pulse", >> >> Again I claim: >> >> "Refering to the Low Pass Filtered Pulse >> simulation I posted, the simulation clearly shows that if I transmit a >> pulse, the pulse edge arrives sooner than if it had propagated faster >> than >> light. If my detector at the receiving end is a threshold detector which >> is >> set to look for anything above the noise level, it will fire earlier than >> if the pulse had propagated at light speed. In other words, it shows that >> if I push a button launching the narrowband pulse signal and propagate it >> via a dipole to a nearfield receiver with the threshold detector, the >> pressed button will be detected sooner than a light propagated signal. >> This >> clearly shows that an action (informaton) in this nearfield dipole system >> can be detected faster than light. If this is true than I have proven my >> point that information propagtes faster than light in the nearfield of a >> dipole." >> >> "it does not matter what the reason is. If I have >> a communication link that allows me to transmit a pulse over a distance >> faster than a light propagated pulse, then the pulse propagates faster >> than >> light. If I use the pulse to denonate a bomb located a distance away, the >> bomb will explode sooner than if the pulse propagated at the speed of >> light. This is absolutly true and cannot be argued. The only question is >> if >> the dipole simulation demonstrates that a pulse can be detected over a >> distance faster than light. I think it has. >> " >> >> So if press a button with the same signal characteristics as the LPF >> pulse, >> and if I use the above setup to detect the pulse and explode a bomb, the >> bomb will explode earlier than if the pulse propagated at the speed of >> light. The pressing of the button (Action) results in the exploding of a >> bomb (Reaction) faster than light speed. This is clear cause and effect >> (information) which propagtes faster than light. >> >> >> William > > How did the input "pulse" get bandlimited in the first place? This is > key to understanding how this works. It's not magic, information is not > accelerated. > > Imagine this and you might be able to see what's going on: > > Start with an ideal impulse, a dirac delta, or some suitable equivalent. > Pass that impulse through your bandlimiting filter, see how long it > takes to come out. Since the bandlimiting filter is causal, the bottom > of the leading edge of the pulse doesn't happen until the instantaneous > impulse has arrived. The entire width of the output pulse is then a > delay from the incidence of the impulse. > > Consider the dirac delta the "information". > > So, it is easy to see that the peak of the output pulse has, at minimum, > the delay from the bottom of the leading edge of the bandlimited output > pulse. > > If you closely examine the output of the predictive filters, whether > it's a filter with a negative group delay or the near field of an > antenna or whatever, it does NOT begin to ramp up the output pulse > values until the input pulse values have actually arrived. In other > words, as we know, or at least most of us know, such a filter is still > causal and does NOT predict the onset of the leading edge of the pulse. > > So, what you are seeing is, for example, because I don't know the actual > numbers from the simulations, the distance from the initial dirac delta > to the bandlimited output pulse peak being X, and the "accelerated", > predicted pulse output is X-delta, where delta is the small advance > achieved by the prediction. NOTE THAT X-delta IS STILL A POSITIVE > NUMBER, and delta is going to be small compared to X. > > All filters have delay. What you are seeing is that the predictive > filter has a little less delay than the signal being compared to it. The > "information" arrival, as compared to the actual incidence of the > initial dirac delta, will not violate causality or c. Observers can be > fooled, however, as you are demonstrating. That's good analysis. Another way to show this with signals that can be more easily (at least less contentiously) constructed than an impulse is with a square pulse and an L-C delay line of the kind used at the input of many analog oscilloscopes. (Such a delay line is a low-pass filter.) Although the shape of the input pulse is quite well preserved and the delay is evident, close examination shows that "preringing" begins soon after the input pulse is applied, well before the main pulse appears at the output. Jerry -- Discovery consists of seeing what everybody has seen, and thinking what nobody has thought. .. Albert Szent-Gyorgi ����������������������������������������������������������������������� |