Klaynos Posted February 25, 2011 Posted February 25, 2011 I wasn't contesting what Swansont said...I was just contributing somebody else's take on the problem of understanding it. The Jabberwocky quote was the scientist's way of saying that Quantum physics has it's own logic ,language and internal consistency. The comment was not directed at you. Sorry.
Mike Smith Cosmos Posted February 25, 2011 Author Posted February 25, 2011 Understanding Spin in a Popular Science Form. I raised a few questions on the 23 Feb 2011 09:14 Mike Smith Cosmos , hoping that this would initiate a few comments for discussion along the lines that some of the old masters undertook during the early years of atomic Physics. Its true that this resulted in the Copenhagen agreement that some were told to " shut up and calculate " while others continued to discuss, argue, debate, think , propose, experiment and think again and help move atomic physics through to its present advanced form . Although many of the breakthroughs were made by maths orientated scientists. That is not true of all breakthroughs. Even Einstein was not the best of mathematicians but he was an expert in using lateral thought processes and thought experiments. I appreciate that the Science Forum ethos is, to not let speculative thought processes run wild , or to cloud current science understanding. However there may be scientists out there who can maintain and share with us, some form of model in their mind that is not pure maths. Although I have gone through the A level Maths, University Maths , Physics , Electronics, Satellite Communications Path, and taught physics , I still like to keep my feet on the ground to some extent when explaining either to myself or others physics concepts. I, along with a few others, would appreciate having some of these models ( be that not easy in quantum mechanics ), verbally offered, if at all possible .
imatfaal Posted February 25, 2011 Posted February 25, 2011 ! Moderator Note The universe is under no obligation to be understandable by you. Having said that, just because you don't understand something doesn't mean no one does. Things are hard, sometimes you need a lot of fundamentals before the interesting stuff becomes clear. Klaynos, SwansonT, AJB etc Does it ever "become clear" - or do you just learn to work around the problems? I know that some things I understand mechanically/consciously; others I have grown so 'happy' with, that the understanding is more natural/unconscious. Do the counter-intuitive contra-logical ideas of much of modern physics become part of your foundation of understanding that is no longer questioned, or does it always remain a little bit 'out-there' and alien. Sorry if this is off-topic and too philosophical
ajb Posted February 25, 2011 Posted February 25, 2011 Does it ever "become clear" - or do you just learn to work around the problems? I don't know. What is for sure the case is that knowing a little about the mathematical framework and structure is necessary for any proper understanding of physics. The depth and sophistication will depend on what you want to know and to some degree your personal taste. Of course, physical interpretations and heuristic arguments all have a place, but really they can never replace the mathematics. To understand angular momentum classically one really needs to know a little about Lie groups and their Lie algebras. The same holds for spin.
steevey Posted February 25, 2011 Posted February 25, 2011 (edited) Discussions of virtual particle/antiparticle pairs are not discussions about electrons in an atom. I'm not talking about matter-anti matter pairs, I'm talking about the electron itself re-appearing in different locations without passing through the intervening space. I can't explain that. To or paraphrase Feynman what I can explain, I can't explain in terms you understand. (It's not a matter of simplifying the terminology, it's a matter of you taking, and passing, three years of physics at a university) I've seen lectures though and I know some of the math for it and how its quantized and that it helps avoid the exclusion principal, I just don't visually see how it would be physically operating within a particle such as an electron. I can imagine that two electrons exist in the same energy level and shell because they have opposite spins, which mathematically makes them not occupy the same exact space at the same time, but what physical thing is going on thats making them do that? What is spin doing to the electrons to make them not hit each other or occupy the same space or give them the specific shapes it gives them? It isn't necessarily directed towards you, but to anyone who can answer it. Edited February 25, 2011 by steevey
Cap'n Refsmmat Posted February 25, 2011 Posted February 25, 2011 I'm not talking about matter-anti matter pairs, I'm talking about the electron itself re-appearing in different locations without passing through the intervening space. Sure, but that doesn't make them virtual. I've seen lectures though and I know some of the math for it and how its quantized and that it helps avoid the exclusion principal, I just don't visually see how it would be physically operating within a particle such as an electron. I can sort of imagine that two electrons exist in the energy level and shell because they have opposite spins, which mathematically makes them not occupy the same exact space at the same time, but what physical thing is going on thats making them do that? What is spin doing to the electrons to make them not hit each other or occupy the same space or give them the specific shapes it gives them? I don't think you can actually think of electrons in orbits as occupying a certain space or having a certain shape. Spin is merely something an electron has. You can't consider it as a way the electron moves or orbits. Quantum physics can't be visualized in terms of discrete particles moving around in certain ways. It won't work.
steevey Posted February 25, 2011 Posted February 25, 2011 (edited) Sure, but that doesn't make them virtual. I don't think you can actually think of electrons in orbits as occupying a certain space or having a certain shape. Spin is merely something an electron has. You can't consider it as a way the electron moves or orbits. Quantum physics can't be visualized in terms of discrete particles moving around in certain ways. It won't work. But when I'm picturing an electron, I'm not picturing it as this particle, I'm picturing it as a wave which is the undetirmination of an electron with relative shapes. They have regions, but the regions get weaker or "less probable" as the distance increases from its most probable place, which is more or less where on a wave, it would be the crest, just like in the double slit experiment where the most probable place corresponded to being hit on a wall as a wave on the wave crest or top of the wave. How exactly do scientists know "spin" exists if there is no determined path for an electron and it pops up in different random places? Is it that classically, an electron still does have a physical spin or physical movements, but because of quantum mechanics, an electron is also undetermined and follows mathematical probability? It would make a lot more sense for electrons exist in the same state but still avoid each other as waves. Edited February 25, 2011 by steevey
Mike Smith Cosmos Posted February 25, 2011 Author Posted February 25, 2011 But when I'm picturing an electron, I'm not picturing it as this particle, I'm picturing it as a wave which is the undetirmination of an electron with relative shapes. They have regions, but the regions get weaker or "less probable" as the distance increases from its most probable place, which is more or less where on a wave, it would be the crest, just like in the double slit experiment where the most probable place corresponded to being hit on a wall as a wave on the wave crest or top of the wave. How exactly do scientists know "spin" exists if there is no determined path for an electron and it pops up in different random places? Is it that classically, an electron still does have a physical spin or physical movements, but because of quantum mechanics, an electron is also undetermined and follows mathematical probability? It would make a lot more sense for electrons exist in the same state but still avoid each other as waves.
Cap'n Refsmmat Posted February 25, 2011 Posted February 25, 2011 How exactly do scientists know "spin" exists if there is no determined path for an electron and it pops up in different random places?Is it that classically, an electron still does have a physical spin or physical movements, but because of quantum mechanics, an electron is also undetermined and follows mathematical probability? It would make a lot more sense for electrons exist in the same state but still avoid each other as waves. They know it exists because of experiment: http://en.wikipedia.org/wiki/Stern-Gerlach_experiment Classically, an electron does not have physical spin. Physical spin cannot account for spin angular momentum. Physical spin has nothing to do with spin angular momentum. Electrons do not spin. The only way you can think of spin angular momentum is that it is "some property an electron has that behaves like angular momentum." You cannot visualize it, because it is not spinning. You cannot liken it to any motion of the electron because it has nothing to do with how the electron moves. It's just a property an electron has. It acts like angular momentum.
steevey Posted February 25, 2011 Posted February 25, 2011 (edited) They know it exists because of experiment: http://en.wikipedia....lach_experiment Classically, an electron does not have physical spin. Physical spin cannot account for spin angular momentum. Physical spin has nothing to do with spin angular momentum. Electrons do not spin. The only way you can think of spin angular momentum is that it is "some property an electron has that behaves like angular momentum." You cannot visualize it, because it is not spinning. You cannot liken it to any motion of the electron because it has nothing to do with how the electron moves. It's just a property an electron has. It acts like angular momentum. I don't think an electron is actually spinning like a top, but doesn't there have to be some explanation or physical thing for it? Or do scientists not yet know that? Scientists don't know whats physically going on with spin, but they know there's some property of it? Edited February 25, 2011 by steevey
Cap'n Refsmmat Posted February 25, 2011 Posted February 25, 2011 I don't think an electron is actually spinning like a top, but doesn't there have to be some explanation or physical thing for it? Or do scientists not yet know that? Why should there be a physical explanation? What matters is that we can use our mathematical understanding to predict real-world phenomena like the Stern-Gerlach experiment. It doesn't matter what the electron does in its spare time unless that affects experimental results.
Mike Smith Cosmos Posted February 25, 2011 Author Posted February 25, 2011 Steevey, I may have something for you to visualize . I am working on some research at this very moment concerning WHY the pauli exclusion principle is invoked by two electrons in the same orbit or energy band. My area of research is to an extent looking for analogue models in the classical world where two tightly coupled particles behave in both an attractive/ repulsive coupling yet behave in opposite modes exactly. One such analogue is the tuning fork, where two similar prongs of a tuning fork vibrate in opposite directions IE one going exactly west when the other prong is going exactly east. This is irrelevant of initial striking of one prong of the tuning fork. Although this may sound crude as an equivalence of quantum mechanics , however ref:The new Quantum Universe Hey and walters 2009 edition page 58,59 shows violins bodies and drum surfaces as analogues to quantum mechanics wave functions , standing waves etc. So if we find electrons coupled in pairs as they appear to be in orbitals the equivalence of coupling and movement ( angular momentum ) may yet become evident. It is unreasonable to think of some formula or rule (pauli exclusion principle ) floating about in space , so as to impose a rule on two electrons in proximity, rather the fabric of space time and all particles and forces that such space consists of, having within itself the coupling necessary to facilitate the orientation we find happening with two coupled electrons in a given energy band or orbital. Prof Lee Smolin of Princetown University Institute in Canada, has been proposing for years that space time is not a backdrop on which thing playout thier lives (particles , forces etc) but rather Space time comes out of / or is indemically part of the particles and forces themselves. ( Quantum Gravity the road to reality By Lee Smolin). Hope this is of some help . ! Sorry Steevey I seem to have no got the method of attaching postings of mine to the members questions. Its there somewhere in the overall listing of postings
steevey Posted February 25, 2011 Posted February 25, 2011 (edited) Steevey, I may have something for you to visualize . I am working on some research at this very moment concerning WHY the pauli exclusion principle is invoked by two electrons in the same orbit or energy band. My area of research is to an extent looking for analogue models in the classical world where two tightly coupled particles behave in both an attractive/ repulsive coupling yet behave in opposite modes exactly. One such analogue is the tuning fork, where two similar prongs of a tuning fork vibrate in opposite directions IE one going exactly west when the other prong is going exactly east. This is irrelevant of initial striking of one prong of the tuning fork. Although this may sound crude as an equivalence of quantum mechanics , however ref:The new Quantum Universe Hey and walters 2009 edition page 58,59 shows violins bodies and drum surfaces as analogues to quantum mechanics wave functions , standing waves etc. So if we find electrons coupled in pairs as they appear to be in orbitals the equivalence of coupling and movement ( angular momentum ) may yet become evident. It is unreasonable to think of some formula or rule (pauli exclusion principle ) floating about in space , so as to impose a rule on two electrons in proximity, rather the fabric of space time and all particles and forces that such space consists of, having within itself the coupling necessary to facilitate the orientation we find happening with two coupled electrons in a given energy band or orbital. Prof Lee Smolin of Princetown University Institute in Canada, has been proposing for years that space time is not a backdrop on which thing playout thier lives (particles , forces etc) but rather Space time comes out of / or is indemically part of the particles and forces themselves. ( Quantum Gravity the road to reality By Lee Smolin). Hope this is of some help . ! Sorry Steevey I seem to have no got the method of attaching postings of mine to the members questions. Its there somewhere in the overall listing of postings I don't know what your trying to tell me exactly, but there is no "proof" for a fabric of space-time, since no particle has been discovered which comprises it or acts as a medium for light and forces, so I suppose its possible that space being infinite and all is a composite of the waves of particles which, a wave function also extends indefinitely through space. The Pauli exclusion principal though seems to come second; If I start with one electron is the lowest energy orbital then add one more electron, the other electron is already there and repels the other electron, so the added electron will have something different about it such as its spin. If your trying to ask "why two objects can't occupy the same space", its because forces such as the electro-magnetic force prevent it. One electron will repel the other, and without extensive research on things like neutronium, the matter in neutron stars comprised only of neutrons, that's the best we can do it seems. When trying to visualize the quantum mechanical world, I can't rely just on real-world objects, I have to use my imagination too combined with the understanding of how it works. I can't really visualize the fact that an electron is undetermined, so I just have to realize that as I'm imagining it as a wave and that it results in this spherical shape which is the electron in an undetirmed state of existence. Usually, real-world objects are only good for the mathematic portions, such as what you said with the tuning fork. If I have a double p orbital or dumbbell, then one is + while the other is -. Or its also good because we can't distinguish two different electrons at that level, so we have to use math to make it as though their wave functions are combined to form a single one, which the warp-able surface or a drum might be good for as well, although you can just use cosine/sine substitution and see the same effects on a wave. Edited February 25, 2011 by steevey
Mike Smith Cosmos Posted February 25, 2011 Author Posted February 25, 2011 STEEVEY Not all lines of scientific research are following the same approach to the fabric of space time. Some view it as a blank canvass others a void seething with activity. Frank Wilczek a Nobel prize winner and professor involved with the Large Hadron Collider, calls it Grid The which has several layers of activity including the virtual particles commented on earlier. However these are separate to the particles such as the electron pairs we were discussing . Professor Frank Close also involved with the large hadron collider speaks of it as the Void. The idea that space is empty seems to be fading fast. Neutrinos also seem to be teeming across space; from the sun ; from power stations ; through the earth ; through you by the billion; even from the Big bang. So the small though not tiny electron with its SPIN whatever that is , is quite a significant happening in amongst all this other stuff. I can visualize these pairs of electrons in some way being coupled and being particularly comfortable doing their angular momentum bit in some form of balancing "up" and "down" opposite direction. This is exactly how tuning fork prongs move. Touch one the other stops. Tap one the other moves but in an opposite direction. Try to make one vibrate on its own. It will but not as balanced and comfortable as the pair. This has striking resemblance to the electron pairs. Also if you try to bring in a third prong. No deal. Exclusion. This is only a model, but as I mentioned in a previous posting Prof Frank Wilczec says its good to have toy models untill you knock them down for something better.
steevey Posted February 26, 2011 Posted February 26, 2011 (edited) STEEVEY Not all lines of scientific research are following the same approach to the fabric of space time. Some view it as a blank canvass others a void seething with activity. Frank Wilczek a Nobel prize winner and professor involved with the Large Hadron Collider, calls it Grid The which has several layers of activity including the virtual particles commented on earlier. However these are separate to the particles such as the electron pairs we were discussing . Professor Frank Close also involved with the large hadron collider speaks of it as the Void. The idea that space is empty seems to be fading fast. Neutrinos also seem to be teeming across space; from the sun ; from power stations ; through the earth ; through you by the billion; even from the Big bang. So the small though not tiny electron with its SPIN whatever that is , is quite a significant happening in amongst all this other stuff. Matter, energy, momentum, spin, orbitals, and just about anything else on the atomic and sub-atomic level are all quantized, so therefore, there has to be an end somewhere since infinitesimal and infinite amounts of matter and energy couldn't exist. There might be a lot of activity that we don't notice, but the fabric of space itself hasn't been proven to exist. Although, what seems promising is that thing about space being a composite of all the indefinite waves since it would explain why an electron could pop all the way on the other side of the universe: Not because there's some hole poking through the 4th dimension to the 3rd dimension at two points, but because the electron's existence itself extends all the way to the other side of the universe. I can visualize these pairs of electrons in some way being coupled and being particularly comfortable doing their angular momentum bit in some form of balancing "up" and "down" opposite direction. This is exactly how tuning fork prongs move. Touch one the other stops. Tap one the other moves but in an opposite direction. Try to make one vibrate on its own. It will but not as balanced and comfortable as the pair. This has striking resemblance to the electron pairs. Also if you try to bring in a third prong. No deal. Exclusion. This is only a model, but as I mentioned in a previous posting Prof Frank Wilczec says its good to have toy models untill you knock them down for something better. Are we talking about the same electron pairs? I'm talking about two electrons at the first energy state, but you seem to be talking about an electron and positron appearing out of the nothingness of space then annihilating each other and then trying to explain a medium using it. But also, isn't the energy released from that type of collision suppose to be very big? Why aren't there explosions everywhere when in the Hadron Collider one particle and its anti-particle release huge amounts of measurable energy when collided? Edited February 26, 2011 by steevey
imatfaal Posted February 26, 2011 Posted February 26, 2011 Are we talking about the same electron pairs? I'm talking about two electrons at the first energy state, but you seem to be talking about an electron and positron appearing out of the nothingness of space then annihilating each other and then trying to explain a medium using it. But also, isn't the energy released from that type of collision suppose to be very big? Why aren't there explosions everywhere when in the Hadron Collider one particle and its anti-particle release huge amounts of measurable energy when collided? Low energy annihilations will produce two gamma rays with 511 KeV. The lhc operates with particles at much higher energies - the lead nuclei will eventually have c 500 TeV so 511 KeV won't be a problem. PET scans work by detecting those two gamma rays that are given off when a positron annihilates with an electron in the body.
steevey Posted February 26, 2011 Posted February 26, 2011 (edited) Low energy annihilations will produce two gamma rays with 511 KeV. The lhc operates with particles at much higher energies - the lead nuclei will eventually have c 500 TeV so 511 KeV won't be a problem. PET scans work by detecting those two gamma rays that are given off when a positron annihilates with an electron in the body. So if I take one electron and one positron and put them together, they will generate two low energy gamma rays, and according to theoretical physics, this is happening everywhere all the time. But, whats the frequency of this happening? If my entire room was filled with these gamma-rays forming from matter-anti matter pairs, why wouldn't I get some kind of cancer easily? One of those low energy gamma rays would certainly be enough to accidentally ionize something. And since this phenomena produces energy which doesn't disappear, doesn't that violate the conservation of matter and energy? I have two particles which are creating out of the nothingness of space, but then they annihilate each other and they get converted into energy which then goes about the universe...that doesn't seem right. Edited February 26, 2011 by steevey
swansont Posted February 26, 2011 Posted February 26, 2011 I'm not talking about matter-anti matter pairs, I'm talking about the electron itself re-appearing in different locations without passing through the intervening space. Those are not virtual particles. Not having a well-defined trajectory is part and parcel of quantum mechanics. what physical thing is going on thats making them do that? That's unanswerable. The physical things ones would use as analogies are classical, and spin is not classical. It's not a physical object spinning. It really doesn't matter how many times you ask the question. The answer isn't going to change.
lemur Posted February 26, 2011 Posted February 26, 2011 That's unanswerable. The physical things ones would use as analogies are classical, and spin is not classical. It's not a physical object spinning. It really doesn't matter how many times you ask the question. The answer isn't going to change. Doesn't it depend on what you mean by "physical object." If physical objects are made of particle-fields, then why aren't those particle-fields themselves physical objects that constitute the larger object?
steevey Posted February 26, 2011 Posted February 26, 2011 (edited) Those are not virtual particles. Not having a well-defined trajectory is part and parcel of quantum mechanics. It's not that its not a well defined trajectory, its that electrons literally appear and disappear in and to different locations. That's unanswerable. The physical things ones would use as analogies are classical, and spin is not classical. It's not a physical object spinning. It really doesn't matter how many times you ask the question. The answer isn't going to change. I'm not picturing an electron as actually spinning, which I keep telling you, but I am also visualizing an electron as a wave which isn't classical either. I'm only see spin as a physical thing thats going on, but I want to know what that physical thing is. But if we can't answer that, then thats fine for now, but since we don't know what it is exactly, its not fair to say it can't possibly be a physical thing. Doesn't it depend on what you mean by "physical object." If physical objects are made of particle-fields, then why aren't those particle-fields themselves physical objects that constitute the larger object? Your trying to say how you can make something physical from something thats not physical? Edited February 26, 2011 by steevey
swansont Posted February 26, 2011 Posted February 26, 2011 It's not that its not a well defined trajectory, its that electrons literally appear and disappear in and to different locations. No, that's not "literally" what happens. Doesn't it depend on what you mean by "physical object." If physical objects are made of particle-fields, then why aren't those particle-fields themselves physical objects that constitute the larger object? I don't know what you mean by objects being made of particle-fields.
steevey Posted February 26, 2011 Posted February 26, 2011 No, that's not "literally" what happens. Well thats the way I've heard it from multiple sources, and if thats not whats happening, what is? Why else would scientists say "the electrons appears at another location without traveling through the intervening space"?
Cap'n Refsmmat Posted February 26, 2011 Posted February 26, 2011 Doesn't it depend on what you mean by "physical object." If physical objects are made of particle-fields, then why aren't those particle-fields themselves physical objects that constitute the larger object? The electron may be a physical object, depending on your interpretation, but it's still not spinning. It's not that its not a well defined trajectory, its that electrons literally appear and disappear in and to different locations. That's still not a virtual particle. The point of quantum mechanics is that the electron, for most of the time, has no defined location. It is merely somewhere, with the probability of finding it at a given point given by the square of the wavefunction. It's not that it's a small particle that pops from one place to the next -- it has no single location. I'm not picturing an electron as actually spinning, which I keep telling you, but I am also visualizing an electron as a wave which isn't classical either. I'm only see spin as a physical thing thats going on, but I want to know what that physical thing is. But if we can't answer that, then thats fine for now, but since we don't know what it is exactly, its not fair to say it can't possibly be a physical thing. Under a strict interpretation of QM, I don't think there can be a physical thing going on. It's like asking what physical thing is going on to give a particle mass.
steevey Posted February 26, 2011 Posted February 26, 2011 (edited) That's still not a virtual particle. Yeah, I got that The point of quantum mechanics is that the electron, for most of the time, has no defined location. It is merely somewhere, with the probability of finding it at a given point given by the square of the wavefunction. It's not that it's a small particle that pops from one place to the next -- it has no single location. Well that, when its just in an undetermined wave state I already know. But, when the electron is determined, its position or location seems to be going to different places without appearing the intervening space. How else could an electron have a chance of appearing on the other side of the universe if it couldn't just "appear" in different locations without traveling the distance to get there? It's like asking what physical thing is going on to give a particle mass. Matter gives things mass doesn't it? It's how much matter, which should be physical. If there's a physical phenomena, shouldn't there be a physical cause? A physical cause for the interference pattern is that physically, the electron isn't just a particle, its also a wave. Edited February 26, 2011 by steevey
swansont Posted February 26, 2011 Posted February 26, 2011 Well thats the way I've heard it from multiple sources, and if thats not whats happening, what is? Why else would scientists say "the electrons appears at another location without traveling through the intervening space"? Well that, when its just in an undetermined wave state I already know. But, when the electron is determined, its position or location seems to be going to different places without appearing the intervening space. How else could an electron have a chance of appearing on the other side of the universe if it couldn't just "appear" in different locations without traveling the distance to get there? It isn't literally true. That's the key — once again, there's a classical framework being used to describe something quantum mechanical. You aren't detecting the electron, so its position is undetermined. One says it can tunnel through a barrier but again, that's a classical description; the QM shows that a wave function penetrates barriers if they are finite height. The answer to "what is actually happening" is still "I can't explain it to you, and what I can explain, I can't explain in terms you can understand without a few years of physics" If you didn't recognize what ajb said about spin being tied up with Lie algebra and group theory (i.e. the rotation subgroup of Lorentz group), then you don't have enough of a background for a more complete explanation. Lacking that, you have to be satisfied with flawed analogies. Picking at the flaws in the analogies is unproductive.
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