Layman's Question on Quantum Mechanics

[vanesch]

It isn't for me mainly because I am not convinced that a toy model that I manipulated by hand that happened to mimick large-scale phenomena is accurate.

That was not the point of course. The point was that toy models can show emergent phenomena such as phase transitions to occur in toy universes (where they are supposed to be "fundamental").
As such, the argument that emergent phenomena *prove* that the reductionist approach is bound to fail in principle is shown to be false as a general argument, because we have a counter example (in a toy universe).

This leaves you with the hope that the same can in principle be done in the real universe: that it is CONCEIVABLE that phase transitions and other fancy emergent stuff MIGHT BE derivable from the microphysics, if only we had enough brains.

I haven't seen one that is able to, for example, mimick every aspect of an antiferromagnetic phase, for example, all the way up to producing a spin-density wave. All you get is a resemblance to one part of the picture. To get the resemblance to another part, you construct ANOTHER toy model, because the previous one just can't do it.
So what we have here are examples where (i) you claim you can show a toy model system resembling a phase transition seen in a larger system and (ii) me showing you other examples where such toy models don't work - in fact, I claim that there are many more examples in this category than there are in the first. If this is true, then it is just a matter of taste on if this is a convincing evidence one way or the other. My taste runs on it being not convincing.

Well, I find it convincing, from the moment that there is ONE example in the bin (i), because that shows that there is no fundamental reason why all the things in bin (ii) could not eventually be moved to bin (i). Bin (i) is not empty. That leaves us with some hope. The hope that the universe is running on a mathematical model. A single one.

it means that even when one obtains complete knowledge of all of our current fundamental interactions, one can STILL end up with nothing more a set of emergent phenomena. We would have known more, but we certainly do not know everything.

Sure. The issue is if this "turtling down" is infinite, or will stop. If we take it that the universe is running on a certain mathematical model, then it should stop, the day we find that mathematical model, no ?
And if it is NOT running on a mathematical model, then anything goes, right ?

That said, we will of course never KNOW if we have it or not (because we cannot do every conceivable experiment). Maybe that's your point.

 

[nrqed]

Oh no, you may have read it wrong. I wasn't the least bit offended at all. I was just a bit amused that it is being resurrected all over again.
Zz.

Ah ok. Thanks a lot for posting this, I genuinely felt bad. I did not mean to sound rude but in rereading my post I realized that I did come out rude and without tact. I am sincerely glad you were not offended because you would have had good reasons to be.

Thanks again!

Pat

 

[quantumcarl]

I was wondering, (as a layperson to the study of quantum physics), if the phenomenon of non-location (and all those related events) is a result of the observer, or the instruments of the observer, being unable to discern what actually takes place at a microscopic level.

Perhaps whatever is non-local moves so fast it appears to us as though its in two different places at the same time. Could it be occilating between two locations at a rate which is undetectable to an instrument or observer in our scale and position in the classical environment?

For instance, we are at a scale of x times that of the quantum. The mechanisms that support us as observers, and our instruments, are far removed from the mechanisms and the scale and the speed at which events unfold... microscopically.

Can the physicist be sure his or her perception and the readings their instruments dictate are "up to speed" with the microscopic scale of a quantum field?

 

[ZapperZ]

I was wondering, (as a layperson to the study of quantum physics), if the phenomenon of non-location (and all those related events) is a result of the observer, or the instruments of the observer, being unable to discern what actually takes place at a microscopic level.

Perhaps whatever is non-local moves so fast it appears to us as though its in two different places at the same time. Could it be occilating between two locations at a rate which is undetectable to an instrument or observer in our scale and position in the classical environment?

For instance, we are at a scale of x times that of the quantum. The mechanisms that support us as observers, and our instruments, are far removed from the mechanisms and the scale and the speed at which events unfold... microscopically.

Can the physicist be sure his or her perception and the readings their instruments dictate are "up to speed" with the microscopic scale of a quantum field?

See, the problem here has more to do with your understanding of a more general principle of superposition. Being in "two locations" is an example of such principle. Now couple that with what QM defines as non-commutative operators as observables, we have a situation where one really cannot learn QM only in bits and pieces.

The principle of superposition is well-verified. This is because, while one cannot see a superposition of locations, for example, one can detect the CONSEQUENCES of it by doing an indirect measurement. One can measure an observable that doesn't commute with the position operator. Such act does not cause a complete collapse of the position superposition. Thus the value that one obtains would reflect such superposition.

This has been done and observed many times, and are often known as the Schrodinger Cat-type states. The existence of the bonding-antibonding bonds in H2 molecule is a prime example. The energy gap measure in the SQUID experiments of Delft and Stony Brook is another. Rather than just repeat everything that has been said many times on here, I'll just copy off an entry in my Journal.

These are the papers that clearly show the Schrodinger Cat-type states (alive+dead, and not alive or dead). All the relevant details are there and anyone interested should read them. Also included is the reference to a couple of review articles which are easier to read, and the reference to two Leggett's papers, who was responsible in suggesting this type of experiments using SQUIDs in the first place. Again, the papers have a wealth of citations and references.

The two experiments from Delft and Stony Brook using SQUIDs are:

C.H. van der Wal et al., Science v.290, p.773 (2000).
J.R. Friedman et al., Nature v.406, p.43 (2000).

Don't miss out the two review articles on these:

G. Blatter, Nature v.406, p.25 (2000).
J. Clarke, Science v.299, p.1850 (2003).

However, what I think is more relevant is the paper by Leggett (who, by the way, started it all by proposing the SQUIDs experiment in the first place):

A.J. Leggett "Testing the limits of quantum mechanics: motivation, state of play, prospects", J. Phys. Condens. Matt., v.14, p.415 (2002).

A.J. Leggett "The Quantum Measurement Problem", Science v.307, p.871 (2005).

This paper clearly outlines the so-called "measurement problem" with regards to the Schrodinger Cat-type measurements.

Zz.

 

[quantumcarl]

we have a situation where one really cannot learn QM only in bits and pieces.

Yeah, you're right to point that out. I can't ask a coherent question about qm because I haven't studied it from the bottom up... I don't imagine "suffering fools" is part of the qm curriculum. Do I still get some mouse ears for effort?

 

[ZapperZ]

Yeah, you're right to point that out. I can't ask a coherent question about qm because I haven't studied it from the bottom up... I don't imagine "suffering fools" is part of the qm curriculum. Do I still get some mouse ears for effort?

In many cases, the problem here isn't with you. It's more with ME. I see a lot of these questions, and I wish I have more of a patience to write a many-page answer on why there's a huge part of QM that one is missing. This is especially true on questions of quantum entanglement. I see people asking about this and that, and I notice that they haven't actually understood the physics that is the central issue in this phenomenon. You will never realize why it is so "strange" if you don't understand (i) quantum superposition and (ii) the commutation relations of observables. Undergraduate physics majors could spend a whole semester doing nothing but the understanding and applications of these two principles. In fact, the commutation relations of observables is sometime called the First Quantization. It is THAT important.

Physics is a difficult subject because one has to have a mastery of many different, sometime apparently unrelated, areas. And one certainly cannot fully comprehend a particular area by just focusing on one single aspect of it, because that's like looking at the hoof of the animal and trying to deduce what the animal looks like. Realizing the interconnectedness of a particular area is one of the first steps of learning it.

Zz.

 

[quantumcarl]

In many cases, the problem here isn't with you. It's more with ME. I see a lot of these questions, and I wish I have more of a patience to write a many-page answer on why there's a huge part of QM that one is missing. This is especially true on questions of quantum entanglement. I see people asking about this and that, and I notice that they haven't actually understood the physics that is the central issue in this phenomenon. You will never realize why it is so "strange" if you don't understand (i) quantum superposition and (ii) the commutation relations of observables. Undergraduate physics majors could spend a whole semester doing nothing but the understanding and applications of these two principles. In fact, the commutation relations of observables is sometime called the First Quantization. It is THAT important.

Physics is a difficult subject because one has to have a mastery of many different, sometime apparently unrelated, areas. And one certainly cannot fully comprehend a particular area by just focusing on one single aspect of it, because that's like looking at the hoof of the animal and trying to deduce what the animal looks like. Realizing the interconnectedness of a particular area is one of the first steps of learning it.

Thank you Zapper z.

To begin with I have learned more about QM physics from you and the other contributors to this thread than from anywhere else.

What I have learned has helped me understand that applying QM to philosophy will never be as easy as the people who compiled "What the Bleep..." make it look. In fact... they have only made themselves look rather foolish where they try to analogize QM properities with what you have taught me to regard as "emergent properties".

There is definitely a potential for a unification of classical and quantum physics and the laws governing them... but... there is also a potential for the sculpture of George Washington at Mt. Rushmore to start talking. (That would be an earfull!)

When I am able to figure out what SQUID and/or KALAMARI have to do with QM, I'll constitute a position of being a better contributor to this section of the illustrious PhysicsForum!

If this means I have to change my name, I'm not doing it. I tried that already and its a big mess. Greg or his adminstrators send out the automated swat team w/dogs when you do.