nec209 Posted June 9 Posted June 9 In the news today major breakthrough of faster than light travel. This changes every thing. Quantum Tunnels Show How Particles Can Break the Speed of Light Recent experiments show that particles should be able to go faster than light when they quantum mechanically “tunnel” through walls. https://www.quantamagazine.org/quantum-tunnel-shows-particles-can-break-the-speed-of-light-20201020/ “Quantum tunneling” shows how profoundly particles such as electrons differ from bigger things. Throw a ball at the wall and it bounces backward; let it roll to the bottom of a valley and it stays there. But a particle will occasionally hop through the wall. It has a chance of “slipping through the mountain and escaping from the valley,” as two physicists wrote in Nature in 1928, in one of the earliest descriptions of tunneling. Physicists quickly saw that particles’ ability to tunnel through barriers solved many mysteries. It explained various chemical bonds and radioactive decays and how hydrogen nuclei in the sun are able to overcome their mutual repulsion and fuse, producing sunlight.
Genady Posted June 9 Posted June 9 1 hour ago, nec209 said: In the news today ... Today is October 20, 2020?
iNow Posted June 10 Posted June 10 1 hour ago, Genady said: Today is October 20, 2020? If he’s moving faster than light then that’s not unreasonable 3
Genady Posted June 10 Posted June 10 1 hour ago, iNow said: If he’s moving faster than light then that’s not unreasonable lol +1
exchemist Posted June 10 Posted June 10 (edited) 10 hours ago, nec209 said: In the news today major breakthrough of faster than light travel. This changes every thing. Quantum Tunnels Show How Particles Can Break the Speed of Light Recent experiments show that particles should be able to go faster than light when they quantum mechanically “tunnel” through walls. https://www.quantamagazine.org/quantum-tunnel-shows-particles-can-break-the-speed-of-light-20201020/ “Quantum tunneling” shows how profoundly particles such as electrons differ from bigger things. Throw a ball at the wall and it bounces backward; let it roll to the bottom of a valley and it stays there. But a particle will occasionally hop through the wall. It has a chance of “slipping through the mountain and escaping from the valley,” as two physicists wrote in Nature in 1928, in one of the earliest descriptions of tunneling. Physicists quickly saw that particles’ ability to tunnel through barriers solved many mysteries. It explained various chemical bonds and radioactive decays and how hydrogen nuclei in the sun are able to overcome their mutual repulsion and fuse, producing sunlight. Must admit I don't follow this. My understanding of tunnelling is that the wave function of the state in question extends through the potential barrier and out the other side to a small extent. In other words, the barrier is not high enough and/or thick enough to damp it out to zero on the far side. That would seem to me to mean that a particle in such a state has a finite probability of being found on the far side when an interaction collapses the wave function. So there is no faster than light travel: in fact there is no "travel" at all. The particle is already on the far side of the barrier, for part of the time, if you like. It's just a matter of there being a low, but non zero, probability of detecting it there as a result of an interaction. Is my picture of this wrong, or is it perhaps the article that has got it wrong in the search for an eye-catching headline? Edited June 10 by exchemist
MigL Posted June 10 Posted June 10 3 hours ago, exchemist said: Is my picture of this wrong, Not at all; but saying probability densities can manifest faster than c just isn't 'sensational' enough.
joigus Posted June 10 Posted June 10 (edited) 11 hours ago, iNow said: If he’s moving faster than light then that’s not unreasonable Good one. Here's the catch: Quote But quantum theory teaches us that precise knowledge of both distance and speed is forbidden. (my emphasis on OP's source) Nearly a 100 years in the books. And still people, when in doubt between reality and causality, would rather sacrifice the latter. It is reality that is dead as a sharp concept, even though it is a very good approximate one. This goes to show how adhesive the concept of classical reality is: "It's either this or not this" is harder to give up than smoking. Edited June 10 by joigus minor addition 2
geordief Posted June 10 Posted June 10 1 hour ago, joigus said: Good one. Here's the catch: (my emphasis on OP's source) Nearly a 100 years in the books. And still people, when in doubt between reality and causality, would rather sacrifice the latter. It is reality that is dead as a sharp concept, even though it is a very good approximate one. This goes to show how adhesive the concept of classical reality is: "It's either this or not this" is harder to give up than smoking. Is this another way of looking at it? Anything that we try to describe as a reality is always in motion. So by the time we examine the situation it is in the past. That is anthropocentric but if we acknowledge that we are part of the system being interrogated then it applies to the apparently exterior world.
swansont Posted June 10 Posted June 10 2 hours ago, MigL said: Not at all; but saying probability densities can manifest faster than c just isn't 'sensational' enough. Agree. There were articles years ago about FTL signals through an atomic vapor (Lene Hau was one of the researchers) when all it was was the light pulse shape was changed; the peak of the pulse moved FTL but you couldn't say that any photon did. This sounds similar in nature.
exchemist Posted June 10 Posted June 10 (edited) 33 minutes ago, geordief said: Is this another way of looking at it? Anything that we try to describe as a reality is always in motion. So by the time we examine the situation it is in the past. That is anthropocentric but if we acknowledge that we are part of the system being interrogated then it applies to the apparently exterior world. No, I don't think thinking about passage of time is helpful. No change takes place - apart from the detection event that determines where the QM entity is. The problem here, it seems to me, is that what is called "tunnelling" is a rather misleading metaphor. There is no motion from inside to outside. The wave function of a QM entity will extend a bit on the far side of a potential barrier, if the barrier is narrow enough and low enough. So a detection event - which resolves the "probability cloud" into a definite position, may occasionally find the entity outside instead of inside. Edited June 10 by exchemist
joigus Posted June 10 Posted June 10 34 minutes ago, geordief said: Is this another way of looking at it? Anything that we try to describe as a reality is always in motion. So by the time we examine the situation it is in the past. That is anthropocentric but if we acknowledge that we are part of the system being interrogated then it applies to the apparently exterior world. The mathematics and the rules to apply them are very precise. How to swallow the metaphysical pill is another matter. I was in the process of answering you when exchemist's answer blinked on my screen. I don't think it's about a subtle way of motion, or measuring "things" from a recent past, or something of the kind. I think it's about this beneath-reality physical variable that we call the probability amplitude. I carries energy and momentum and is coupled to currents. It's as physical as it can be. But it only gives you potentialities, what can happen, not what does happen.
geordief Posted June 10 Posted June 10 27 minutes ago, exchemist said: No, I don't think thinking about passage of time is helpful. No change takes place - apart from the detection event that determines where the QM entity is. The problem here, it seems to me, is that what is called "tunnelling" is a rather misleading metaphor. There is no motion from inside to outside. The wave function of a QM entity will extend a bit on the far side of a potential barrier, if the barrier is narrow enough and low enough. So a detection event - which resolves the "probability cloud" into a definite position, may occasionally find the entity outside instead of inside. I went a bit off topic and was thinking about @joigus 's disginction btw reality and causality and probably got the wrong end of the stick. I think "realism" (local realism?) has a defined meaning and use in physics (quantum physics?) that I have not been able to get my head around so far and perhaps I confused it with "reality" As for the OP it seems there are time lapses that can be measured as well as distances but ,perhaps you are saying it that the field is in both places and it is just the measurements of two particles in that field that are separated by time and space giving the illusion that one particle travels to the position of the second particle -and at a speed above c.
exchemist Posted June 10 Posted June 10 13 minutes ago, geordief said: I went a bit off topic and was thinking about @joigus 's disginction btw reality and causality and probably got the wrong end of the stick. I think "realism" (local realism?) has a defined meaning and use in physics (quantum physics?) that I have not been able to get my head around so far and perhaps I confused it with "reality" As for the OP it seems there are time lapses that can be measured as well as distances but ,perhaps you are saying it that the field is in both places and it is just the measurements of two particles in that field that are separated by time and space giving the illusion that one particle travels to the position of the second particle -and at a speed above c. Not a field, just a wave function. The suggestion of time lapses is what I don't follow. To me, that makes no sense.
geordief Posted June 10 Posted June 10 19 minutes ago, exchemist said: Not a field, just a wave function. The suggestion of time lapses is what I don't follow. To me, that makes no sense. There are two measurements ,aren't there?(I assumed that the pre tunnel particle was measured and then the post tunneling particle was measured and the interval measured) (Well I might be wrong as my knowledge is so patchy) Is the wave function applied to the field?(I thought particles were excitations of the field -in qft)
MigL Posted June 10 Posted June 10 57 minutes ago, geordief said: I think "realism" (local realism?) has a defined meaning and use in physics (quantum physics?) that I have not been able to get my head around so far and perhaps I confused it with "reality" In very simple terms, 'reality' is ( as close as we can tell ) what we measure. The act of measurement collapses the wave function and ( sort of ) establishes 'reality'. In between the two measurements, what we have is a mathematical expression called a wave function that describes all possible states of the particle we will measure. This is not a 'wave' of the particle's field ( QFT ), as you ask in your other post. The square of the absolute value of the magnitude of the wave function, describes the probability of locating the particle, so the wave function is simply a probability amplitude or density ( not sure of the appropriate term ), rather than the 'waving' of a field. ( although I'm sure someone has used a 'probability field' to help their calculations; any field is a value associated with each point ) The term 'no local realism' simply references the fact that one of the most accurate models we have to describe 'reality', tells us that , between measurements, 'reality' is simply a mathematical expression devoid of any reality.
tylers100 Posted June 10 Posted June 10 Maybe can suggest interdisciplinary discussion between these threads and this one: link: Other comment: Also maybe factor into understanding spacetime related thread(s) in other physics categories. It occurs to me that trying to understanding spacetime thread(s) between and this one and warp thread might help.
joigus Posted June 10 Posted June 10 27 minutes ago, geordief said: I went a bit off topic and was thinking about @joigus 's disginction btw reality and causality and probably got the wrong end of the stick. I think "realism" (local realism?) has a defined meaning and use in physics (quantum physics?) that I have not been able to get my head around so far and perhaps I confused it with "reality" As for the OP it seems there are time lapses that can be measured as well as distances but ,perhaps you are saying it that the field is in both places and it is just the measurements of two particles in that field that are separated by time and space giving the illusion that one particle travels to the position of the second particle -and at a speed above c. Just to clarify, I meant reality according to Einstein: Quote "If, without in any way disturbing a system, we can predict with certainty (i.e., with probability equal to unity) the value of a physical quantity, then there exists an element of reality corresponding to that quantity." (from the famous EPR paper) Quantum mechanics does not necessarily deny reality (in this sense) for a wide range of system properties (energy, momentum, spin, orbital angular momentum...) Position is not one of them because position is not a conserved quantity. What it does is deny reality for certain property-pairings that are classified as incompatible, at the same time. See how naturally the question of causality pops up when one examines this question of reality?: At the same time. There's the relativistic rub. What if a system has spatial extension and one measures one property here and another (incompatible) property there? In QM there is a tension between reality and causality, you see. This 'tension' is more clearly perhaps expressed by way of Bell's theorem. And, as MigL says, every time you measure, this reality is 'updated'. I prefer this term to 'established'. But I have no objection to 'established'.
exchemist Posted June 10 Posted June 10 (edited) 17 minutes ago, tylers100 said: Maybe can suggest interdisciplinary discussion between these threads and this one: link: Other comment: Also maybe factor into understanding spacetime related thread(s) in other physics categories. It occurs to me that trying to understanding spacetime thread(s) between and this one and warp thread might help. You’ve lost me. Why should there be a connection between QM tunnelling, which involves no motion, and a warp drive? Edited June 10 by exchemist
joigus Posted June 10 Posted June 10 49 minutes ago, joigus said: I prefer this term to 'established'. But I have no objection to 'established'. I suppose that's what @MigL meant when he said 'sort of'. Here: 1 hour ago, MigL said: The act of measurement collapses the wave function and ( sort of ) establishes 'reality'. 43 minutes ago, exchemist said: You’ve lost me. Why should there be a connection between QM tunnelling, which involves no motion, and a warp drive? Just for the record, I don't see the connection either. Not to mention nobody mentioned space-time curvature here. And nobody should.
swansont Posted June 10 Posted June 10 4 hours ago, geordief said: There are two measurements ,aren't there?(I assumed that the pre tunnel particle was measured and then the post tunneling particle was measured and the interval measured) (Well I might be wrong as my knowledge is so patchy) Is the wave function applied to the field?(I thought particles were excitations of the field -in qft) From what I read: The time is inferred from the Larmor precession of the spin in the magnetic field of the barrier, which is inferred from the spin measurement after tunneling. IOW the particles going in are prepared in a spin state (up) and the spin precesses in the barrier, which puts them in a mixed state of up and down. You measure the spins, and the ratio of up/down tells you how much precession occurred, which depends on how long they were in the barrier region. Without seeing the paper itself I don’t know more. Since only a fraction of particles tunnel, there might be some systematic effect in play. I don’t know if they looked at the reflected particles. How far does the particle penetrate before it’s reflected? Does the precession effectively change the barrier height? Steinberg has a good reputation in the AMO community, but I know that not everyone is convinced that Larmor time is a measurement of the tunneling time.
Mordred Posted June 10 Posted June 10 (edited) Here is a paper discussing the Hartman effect which the article of the OP describes. In this paper it shows that the Hartman effect is in point of detail subliminal https://arxiv.org/abs/2208.09742 The gist of the paper is that the probability distribution function (wavefunction ) is larger with a leading tail that precedes the peak of the amplitude. The illusion occurs in examinations that focus strictly on the amplitude peak. Most of the answer given in this thread was in the right ballpark in recognizing the distinction due to the probability function. QFT for example the probability functions are Fourier transforms which provide a Delta function. That Delta function has both a leading edge and a following edge. The peak of the function is somewhere in the middle. This is the region of highest probability current. (This region also has number density terms describing the probable density of particles.) In QM with position and momentum operators the Schrodinger equation the above applies as well albeit single particle states the probability current is still used. As well as Fourier transforms. Edited June 11 by Mordred
tylers100 Posted June 11 Posted June 11 14 hours ago, exchemist said: You’ve lost me. Why should there be a connection between QM tunnelling, which involves no motion, and a warp drive? Perhaps I was jumping a bit too much without really knowing in detail or depth about QM, but it just occurs to me that QM tunnelling (you said no motion) seems to involve 1st travel distance as in "jump or instantaneous" QM tunnelling ("no motion"). If so, that would seem to enable a "pathway" for spaceship have a warp drive capability to travel in it. 13 hours ago, joigus said: I suppose that's what @MigL meant when he said 'sort of'. Here: Just for the record, I don't see the connection either. Not to mention nobody mentioned space-time curvature here. And nobody should. I think gotta have to know or understand spacetime stuff better first in order to as precede QM tunnelling and warp drive, if that make sense. I just want to interject myself into this discussion due to fact that I like Star Trek stuff and this may open up a possibility about warp drive for spaceflight exploration, but I'm aware that I may be a bit far-fetched with what I said.. but still, if there is a chance that it could be possible.
joigus Posted June 11 Posted June 11 1 hour ago, tylers100 said: I just want to interject myself into this discussion due to fact that I like Star Trek stuff and this may open up a possibility about warp drive for spaceflight exploration, but I'm aware that I may be a bit far-fetched with what I said.. but still, if there is a chance that it could be possible. Tunneling is about one particle going through a barrier a few angstroms thick --I'm thinking Josephson junctions and the like. Star Trek stuff is about sending 1025 atoms many miles away, and these atoms remembering who you where and what exactly you were thinking on the other side. Quite a feat in comparison. For the dark side of teleportation you might want to consider The Fly. Either the 1986 film, or perhaps the classic, 1958.
exchemist Posted June 11 Posted June 11 1 hour ago, tylers100 said: Perhaps I was jumping a bit too much without really knowing in detail or depth about QM, but it just occurs to me that QM tunnelling (you said no motion) seems to involve 1st travel distance as in "jump or instantaneous" QM tunnelling ("no motion"). If so, that would seem to enable a "pathway" for spaceship have a warp drive capability to travel in it. I think gotta have to know or understand spacetime stuff better first in order to as precede QM tunnelling and warp drive, if that make sense. I just want to interject myself into this discussion due to fact that I like Star Trek stuff and this may open up a possibility about warp drive for spaceflight exploration, but I'm aware that I may be a bit far-fetched with what I said.. but still, if there is a chance that it could be possible. No, QM tunnelling offers no such possibility, I'm afraid. For a start it is only significant at the scale at which the wavelike nature of matter become important - in practice, objects the size of an atom or a subatomic particle. And then, as I've been saying it's a statistical effect from the way a probability cloud is resolved into a measurement.
swansont Posted June 11 Posted June 11 3 hours ago, tylers100 said: I just want to interject myself into this discussion due to fact that I like Star Trek stuff and this may open up a possibility about warp drive for spaceflight exploration, but I'm aware that I may be a bit far-fetched with what I said.. but still, if there is a chance that it could be possible. Star Trek shares a similarity with AI - not based in facts, but generating vaguely plausible-sounding jargon. It’s fiction.
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