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mathew3
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Can someone list some of the phenomena only explicable via QM?
mathew3 said:Can someone list some of the phenomena only explicable via QM?
berkeman said:What is the context of the question? Is this for schoolwork?
mathew3 said:No. Not at all. I just want to see if I can come up with a classical counterpart or where the classical counterpart fails.
berkeman said:How about tunneling? I'm not aware of any classical explanation for that.
akhmeteli said:I am not sure about "classical explanation", but there seems to be at least a "classical counterpart" of tunneling. As I wrote earlier, "I suspect theoretically you can jump over a classical barrier having lesser kinetic energy than the potential energy your mass would have at the top of the barrier. In fact, in the course of a high jump you can bend over the barrier in such a way that your center of gravity will be outside of your body and pass under the barrier." According to Wikipedia (http://en.wikipedia.org/wiki/Fosbury_Flop ), high jumpers do achieve this, but I did not check the Wikipedia source.
berkeman said:That's not what QM tunneling is.
1) The universeCan someone list some of the phenomena only explicable via QM?
akhmeteli said:If you don't think this is a counterpart of quantum tunneling, what are your arguments?
akhmeteli said:I am not sure about "classical explanation", but there seems to be at least a "classical counterpart" of tunneling. As I wrote earlier, "I suspect theoretically you can jump over a classical barrier having lesser kinetic energy than the potential energy your mass would have at the top of the barrier. In fact, in the course of a high jump you can bend over the barrier in such a way that your center of gravity will be outside of your body and pass under the barrier." According to Wikipedia (http://en.wikipedia.org/wiki/Fosbury_Flop ), high jumpers do achieve this, but I did not check the Wikipedia source.
Drakkith said:The "barrier" referred to in quantum tunneling isn't a physical barrier like a wall you can jump over. It refers to the amount of energy needed to overcome the strength of a repulsive or attractive force. For example, fusion in the sun could not occur in classical physics because the energy of the particles in the core is not sufficient to bring them together in range of the strong force to fuse. Quantum tunneling describes the mechanism that allows protons to overcome the repulsion and fuse if they have "almost" enough energy. Similarly this allows alpha particles to overcome the strong force in heavy elements like uranium or plutonium and is the mechanism behind fission.
The trouble, as explained before, is that, just because you describe something that is plausible does not make it possible. Classical phyiscs does not predict tunneling.akhmeteli said:I think this is still a "counterpart" of quantum tunneling. Indeed, what is "tunneling", in the first place? This is a way to pass through a high hill, and this is what is done (or theoretically can be done) in high jump without any "tunnel" under the bar. I agree that the analogy is not complete, as quantum tunneling can occur in one dimension, whereas high jump needs at least two dimensions. This does not seem very important though, as you can "rewrite" my example for one dimension for some elastic forces instead of gravity. The main point still stands: an extended object can pass through a high potential energy area, having kinetic energy below that required for the entire object to be at the top of the potential energy hill. The only problem is "esthetic": such an example would not be as graphic and natural as that of high jump, but the principle is the same.
DaveC426913 said:The trouble, as explained before, is that, just because you describe something that is plausible does not make it possible. Classical phyiscs does not predict tunneling.
In our classical description of particles they simply do not have the properties you ascribe to them. And you can't just patch it up by tacking on an extra variable to an equation here or there.
DaveC426913 said:akhmeteli, having a classical explanation for something does not simply mean you can come up with an analogy that might form the start of a plausible description, and then leave the details of the math to the eggheads.
DaveC426913 said:With a classical description of subatomic particles, there is no known way a particle can jump from one side of an energy barrier to another. The particles are essentially little balls - there is no "bending in the middle".
To posit that particles can "bend in the middle" is to toss out classical mechanics and start proposing quantum mechanical explanations.
DaveC426913 said:The trouble, as explained before, is that, just because you describe something that is plausible does not make it possible.
As my analogy shows, in some sense it does.DaveC426913 said:Classical phyiscs does not predict tunneling.
Did I mention any particles, let alone ascribe anything to them?DaveC426913 said:In our classical description of particles they simply do not have the properties you ascribe to them.
Again, it seems to me that you are pushing a disproportionate expansion of the topic of this thread. Are you sure you really want that? Let me just say that once I started a thread dealing with these issues (https://www.physicsforums.com/showpost.php?p=2530114&postcount=1 ), and there are almost 750 posts there:-)DaveC426913 said:And you can't just patch it up by tacking on an extra variable to an equation here or there.
Drakkith said:The OP wanted things which do NOT have classical counterparts.
Drakkith said:Quantum tunneling is one of them.
Drakkith said:Your analogy, while certainly applicable under other circumstances, is not correct here. If there was a classical counterpart we wouldn't have to use analogies in the first place!
Drakkith said:Sorry, your example is just plain incorrect. A person jumping over a barrier and shifting their weight is using energy to move their body.
Drakkith said:ALSO, a person must have enough energy on the jump to get enough of their body over the pole in the first place, otherwise shifting their weight will not work. The key is that a particle does NOT have to have enough energy to move past the barrier while the person does."
Drakkith said:And no, your analogy does not fit those two definitions, as it is not remarkably similar nor does it have the same function or characteristics.
Except that classical particles do not behave that way.akhmeteli said:I believe my analogy is legitimate.
Does your analogy map onto to actual behavior of classical particles? No.akhmeteli said:What plausibility/possibility are you talking about and how is it relevant?
I don't doubt the high jumper. I only refute its relevance.akhmeteli said:If you think that in real life a high jumper cannot always have his/her center of gravity below the bar, maybe you're right, but, first, what are your arguments, and, second, is it really important for physics?
That is the entire purpose of this thread.akhmeteli said:If you are saying that quantum theory cannot be emulated by a classical theory, are you sure you want to open this can of worms in this thread?
We are talking about the quantum tunneling of particles through a barrier. Have you forgotten?akhmeteli said:Did I mention any particles, let alone ascribe anything to them?
Please re-read the subject line and most of the OP's posts after that.akhmeteli said:Again, it seems to me that you are pushing a disproportionate expansion of the topic of this thread.
No, the OP does.akhmeteli said:Are you sure you really want that?
DaveC426913 said:Except that classical particles do not behave that way.
DaveC426913 said:Does your analogy map onto to actual behavior of classical particles? No.
DaveC426913 said:The mathematical description of a classical particle does not include any properties that could cause it to bend around a barrier. For one, classical particles are points.
DaveC426913 said:I don't doubt the high jumper. I only refute its relevance.
DaveC426913 said:That is the entire purpose of this thread.
Are there phenomena that can only be described by QM, and not by classical physics?
mathew3 said:Akhmeteli and Davec426913
Let me thank the both of you very much. As usual in the forum both of you are correct. Dave you are correct in saying I initially asked for phenomena classical physics couldn't couldn't explain. But in #3 I explained that I wanted this to explore classical counterparts, if any and where they would fail.
DaveC426913 said:Indeed there are.
DaveC426913 said:Electron tunneling is one.
DaveC426913 said:We are talking about the quantum tunneling of particles through a barrier. Have you forgotten?
DaveC426913 said:Please re-read the subject line and most of the OP's posts after that.
DaveC426913 said:No, the OP does.
akhmeteli, please, before posting again, please review the thread from the beginning. You seem to have missed the entire point of the thread.
Drakkith said:but in the end quantum tunneling cannot be explained by mainstream classical physics, which is exactly the point.
mathew3 said:I don't think this is carved in stone. For instance take F=iV/c where i is current V is voltage and c is the speed of light. Current and voltage are indirectly proportional. As i decreases due to the imposition of the energy barrier it's accompanying voltage V increases boosting it over the barrier. In a closed system, which an electrical circuit may be considered as, power in must equal power out. Now that is a perfectly reasonable classical explanation. Is it true? Has it been experimentally verified? Who knows if its true but one could make the argument that tunneling is its experimental verification. The point is there is a classical explanation. Whether or not it is accepted as THE explanation is quite another matter.
I'll call you on that. Please describe, using classical physics, how tunneling works.akhmeteli said:I don’t want to open this discussion without necessity, but what’s important is that classical objects do behave this way.
It is not a constraint*. I have provided an example. The OP asked for examples. Examples are not exclusive or constraining and do not constitute an exhaustive list.akhmeteli said:I reject your “particle” constraint. The OP did not introduce such a constraint, and quantum tunneling is not necessarily “quantum tunneling of particles”, see, e.g., http://prc.aps.org/abstract/PRC/v82/i6/e064607. In principle, quantum tunneling is possible for anything: particles, objects, and what not.
You said nothing above, so you still have not made your point.akhmeteli said:See above.
If the OP were the best judge of what answers he'd get, he would not need to ask the question. The nature of a question is that it solicits input about things one does not already know about.akhmeteli said:With all due respect, the OP is a better judge than we are of what is relevant
The fact that the OP welcome you input does not make your input right. I am bot trying to shut you down; I am simply ensuring that any assertions you do make are within he bounds of accepted science.akhmeteli said:... he seems to welcome my input (see post 23 in this thread).
What is the difference between these two statements?mathew3 said:I initially asked for phenomena classical physics couldn't couldn't explain. But in #3 I explained that I wanted this to explore classical counterparts, if any and where they would fail.
I agree that mainstream classical physics has yet to explain the effect of quantum tunneling. It does not necessarily follow that "mainstream" classical physics cannot explain or calculate the effect of quantum tunneling.Drakkith said:No, the point is that nowhere (that I know of) in mainstream classical physics can you ever explain or calculate the effect of quantum tunneling.
For a scientist, particularly a research scientist, only B, i.e., that it is true- should be of concern.Drakkith said:Just because one person claims he can by using a modified version of classical physics doesn't mean that A: it is accepted, B: that it is true, and C: that it would be considered "Mainstream Classical Physics" in the first place.
Not quite. The biggest reason that QM is successful is that it predicts and agrees with different effects that are NOT reproducible using some of the available classical physics rules.Drakkith said:The biggest reason that QM is successful is that it predicts and agrees with different effects that are NOT reproducible using classical physics rules.
Drakkith said:Unfortunately I don't believe your article counts as "Classical Physics".
Drakkith said:Nowhere at any point in time before QM was developed was there a method of explaining tunneling.
Drakkith said:Your example is exactly correct for something that is not explainable in classical physics.
Drakkith said:Note that there are specific rules on PF about what is and isn't considered "mainstream" and I doubt your modification of Klein-Gordon-Maxwell electrodynamics would be. But if I'm wrong then please correct me.
Drakkith said:Edit: Also, realize that your example primarily fails because it simply isn't even talking about the same concepts. A "counterpart" to tunneling would be to say that Classical Physics shows how a proton or electron or whatever gets through a barrier without the required energy. Replacing a proton with a whole person is like comparing the orbit of the Sun around the galaxy with a child on a merry-go-round.
Drakkith said:The two are similar only in a few basic ways and neither are a counterpart of each other. We can argue all day long on how relevant it is to compare the two, because they are comparable in certain ways, but in the end quantum tunneling cannot be explained by mainstream classical physics, which is exactly the point.
mathew3 said:I agree that mainstream classical physics has yet to explain the effect of quantum tunneling. It does not necessarily follow that "mainstream" classical physics cannot explain or calculate the effect of quantum tunneling.
For a scientist, particularly a research scientist, only B, i.e., that it is true- should be of concern.
Not quite. The biggest reason that QM is successful is that it predicts and agrees with different effects that are NOT reproducible using some of the available classical physics rules.
I don't know of anybody who rejects QM- at least QM formalism. Nobody doubts or rejects its predictive power based upon the calculation of probabilities. However there are a few respected scientists who have posed arguments as to a classically based QM. See New Foundations for Classical Mechanics' by David Hestenes.DaveC426913 said:Are you aware of any respected physicists who are making advances in classical physics while rejecting QM?
From where most of our discoveries spring from- inquiring minds building upon the knowledge of our predecessors. If you mean from what theoretical fount, again, there is Hestenes.DaveC426913;3547596 Since classical physics does not [I said:currently[/I] have any explanation, where will it spring forth from?
But it does mean they are not for discussion in this forum, which is dedicated to accepted mainstream physics.mathew3 said:Just because they haven't been accepted by or presented within "mainstream" physics doesn't mean they are not possible or untrue.