Seasons

Well, Psimagus, in my reality, The Greek letter Psi is just the letter that is used for the wave function in equations, and anyone who has read anything about QM other than popularizations knows that.

It is used ONLY for the probability wavefunction. Not a coulomb wavefunction, not an electromagnetic wavefunction, not a water, wind, sound, shock, or any other sort of wavefunction. And it does not propagate as part of the quantum.

Of course you won't find the three-letter English word, "Psi", in technical papers.

Oh really?

{QUOTE GOOGLE}
Results 1 - 100 of about 1,220,000 for Psi wave. (0.19 seconds)
Results 1 - 100 of about 206,000 for Psi wavefunction. (0.31 seconds)
{/QUOTE GOOGLE}

Dear Bev: (continued):

The wave function is also called the "probability amplitude wave" and sometimes the "probability wave," but these expressions are a bit imprecise.

The wave function (a.k.a. Psi) has to satisfy the Schoedinger equation, which is a form of the wave equation; hence it represents a wave, hence the term "wave function." The term "wave function" has a much more general meaning in Physics than it does in everyday language, however. It refers not only to nice regular, periodic phenomena like ocean waves, but to the result of adding together an infinite number of such waves. You can get isolated sharp spikes, for example.

Dear Bev:

when I think of the slits experiments, I keep thinking photons, and then it seems to jump to psi (probably because I am not really studying everything you both told me to look at).
Well, this is what is called "wave-particle duality." Light is in some ways like a particle, in some ways like a wave. So in a complete explanation, one will sometimes be using language suggestive of waves, and at other times, language suggestive of particles. This can be confusing, since we are accustomed to thinking of these as very different sorts of things.

But before I drone on any further, let me check in with you: has what I have said so far made sense to you? What question would you ask now?

Dear Bev (continued):

probably because I am not really studying everything you both told me to look at

As a matter of fact, Bev, I think many of the sites I have mentioned are well worth looking at. For one thing, many of them have neat graphics, like this one:

http://www.colorado.edu/physics/2000/schroedinger/two-slit2.html

A picture is indeed often worth many, many words in this sort of thing, and this site has very good moving pictures. I am here limited to verbal descriptions, which can get quite tedious.

I also recommend the Wikipedia article on the two-slit experiment.

http://en.wikipedia.org/wiki/Double-slit_experiment

Actually, I don't know how much math and physics you have, so I'm not sure just what to say or to recommend. I don't wish to patronize you, but I don't wish to talk over your head, either.

Irina,

anyone who has read anything about QM other than popularizations knows that.

Now I'm sure that that wasn't aimed at anyone in particular, but you might want to have a quick look at the reviews of Penrose's book: http://www.amazon.com/Road-Reality-Complete-Guide-Universe/dp/0679454438

And perhaps read a little about him, just in case you're tempted to write him off as a mere popularizer, whose opinions are not worthy of serious consideration.

http://en.wikipedia.org/wiki/Roger_Penrose

I'm no unquestioning admirer - there are things he says that I take issue with, particularly in the field of AI. But I wouldn't consider my own meagre understanding of quantum mechanics to be so far in excess of one of most acclaimed and awarded quantum physicists of his generation, that I would simply ignore his views. Especially if I couldn't find any relevant references to refute him in a matter like the propagation of Ψ.

Of course, there is one way to test the matter - take this discussion to the sci.physics newsgroup, or one of the quantum physics forums out on the net, and see what the professionals think. What do you think?

Psimagus: In my universe, Penrose is a brilliant mathematician worthy of the greatest respect. In your universe, he is no doubt the same, but he apparently says completely different things from what he says in my universe. I'm sure those things are true in your universe, but many of them are false in mine; at least, in the way you seem to interpret them, they are.

I don't know how much math and physics you have, so I'm not sure just what to say or to recommend. I don't wish to patronize you, but I don't wish to talk over your head, either.
Hey, I have no physics, and I set the world record for taking algebra 1...but I do find this fascinating. I love the thought, that a branch of science has things that are as bizarre as myths and dragons.

OH and the posts start at about 3715, I have been re-reading them in an attempt to understand

Thanks Psimagus and Irina. Irina I promise to do more reading and check the sites. It's not that they aren't good sites, it's just that I don't always stop to follow up on them, and then the discussion moves on.

I did know what Ψ was in terms of it being a Greek letter*, but it's good that you explained it because there are probably others reading who don't ask as many questions as I do. My background is Psychology (BS), law (JD but in another sense, also BS) and a Masters in Teaching (MAT but also BS in the same way as the JD**). As you can see, I'm rather well versed in BS without much in the way of "hard science" and only the required math (which tends to be statistics). It doesn't matter though, because we have all ranges of people who read these posts, so if you explain some basics that I happen to know, I am sure someone will be happy you did.

I found Psimagus' checkerboard analogy to be helpful. I also think in understand the dual slit experiment. If I understand the central issue here we are trying to determine the best way to predict the movement of quanta over spacetime. We are talking about a model which works for large number of quanta in a "best fit" sort of way, but which does not necessarily apply to one specific quantum. Your man Schroedinger wrote an equation about this while I was out looking for chocolate bunnies.

It may be there is some level of equivocation going on in the debate, so I am glad I asked you to define the terms. It seems that Irina and Psimagus disagree as to how Ψ should be used as it applies to Schreodinger's equation and quantum physics. Also, Irina says that predicting quantum movement can be done based on standard wave function (propagation). Is that it?

* I was once in an honorary fraternity called ΨX but we never discussed quantum physics. Also, to me Δ means defendant more often than it means change and π stands for plaintiff, not 3.14.

** When you think of my background, think of Mel Brooks' History of the World, specifically the scene withe the Roman unemployment office. "Oh, you area BS artist. Have you BSed today? Did you try to BS today?"

Dear Prob123:
Re yur message 4013:
Sorry to take so long getting back to you. You wrote:
Ok, another QM question..found this..is it true?

Now, if two quantum states are "entangled" then if you change one of those states, then by definition, you must also change the state in the other system it is entangled with. For example, atomic particles like electrons have a mysterious property called "spin" (it doesn't literally mean they are spinning). It is possible to entangle the spin of one electron with the spin of a different electron. In an electron, spin has only two possible states that we call "up" and "down" (again don't take that literally). So when two electrons are entangled like this we know that when one has "spin up", the other will always have "spin down" and vice versa.

This is interesting in itself. But it becomes even more interesting when we realise that the wavefunction doesn't imply any limitation of distance or velocity. So in theory, if one of our electrons is here, and the other entangled one is on the opposite side of the universe, then if we change the spin of the one here, the spin of the one there should also change instantaneously!
I think it is not quite right to say that "if you change one of those states, then by definition, you must also change the state in the other system it is entangled with." I think I see why the author said that, however.
The simple, archetypal entanglement scenario is something like this: two particles (let's say they are photons) are simultaneously created, with opposite spins (you don't have to know what spin is, just that it has two values, traditionally called "spin up" and "spin down."). They fly off in opposite directions. Then each one comes to a diffraction grating, which is a device sensitive to spin. They arrive at precisely the same time. It either allows the particle to pass, or allows the particle to go through. The gratings are, in fact, set so that each particle will have 1/2 a chance of going through. And, when the experiment is repeated, this is exactly what happens: in the long run, each grating permits about half the particles that come to it to go through. But QM cannot predict, in any specific case, whether they will go through or not; it only says that the probability is 1/2.
What is odd is this: in each simultaneously created pair, the one goes through if and only if the other goes through. It never happens that the one goes through and the other does not.
Imagine that two people each take a coin from a common source, go off at some distance to each other, and flip their coins simultaneously. The coins are presumably fair, so each one has 1/2 a chance of getting heads. And, sure enough, they do, but it also happens that whenever one gets 'heads', the other does as well. That would suggest that the two coins were connected in some way (hence the term 'entanglement'). There are two ways that this might occur: (1) somehow, one coin's coming up heads (or not) would cause the other coin to come up heads (or not), and (2) each pair of coins might have been set to go through (or not) in advance. Analogously, there are two ways one might explain the coincidence in the case of the two particles: (1) somehow, one particle's going through the grating (or not) would cause the other particle to go through the grating (or not), and (2) each pair of coins might have been set to go through (or not) in advance.
Einstein had, however, convinced everyone that no causal influence could travel faster than light. Since the two events at the gratings occur simultaneously, and some distance apart, neither one could cause the other. So (1) is not an option. That leaves (2), which is plausible since the two particles have a common origin (you can't just take any two particles and do this).
Einstein thought that this showed that Quantum Mechanics was incomplete. To abbreviate his reasoning somewhat: there must have been something about the two particles that determined in advance whether they would go through or not. Otherwise, why would they always do the same? But QM cannot predict whether a specific particle would go through or not. It only says that there is a chance of 1/2 that they will. Therefore, Einstein (and others) concluded, there is something about the particles that QM is unable to account for, and QM is, therefore, incomplete.
From the conclusion that the particles always do the same thing, I think someone leapt to the conclusion that if you somehow forced the one particle to go through, then the other particle would also. At least, that is what the statement, "Now, if two quantum states are 'entangled' then if you change one of those states, then by definition, you must also change the state in the other system it is entangled with." But I don't think the two particles are that intimately connected, according to QM. If they were, they would genuinely break Einstein's prohibition on faster-than-light communication. You could send a message to me instantaneously by forcing the particle at your end to go through (or not), thus forcing the other one to do the same. I would observe the other one, thus receiving the message.
Does this make sense? Does it answer your question? Do you have more questions?

Walk in Beauty, Irina

Dear Bev:
Thanks for your note!
You wrote:
Thanks Psimagus and Irina. Irina I promise to do more reading and check the sites. It's not that they aren't good sites, it's just that I don't always stop to follow up on them, and then the discussion moves on.

I did know what Ø was in terms of it being a Greek letter*, but it's good that you explained it because there are probably others reading who don't ask as many questions as I do. My background is Psychology (BS), law (JD but in another sense, also BS) and a Masters in Teaching (MAT but also BS in the same way as the JD**). As you can see, I'm rather well versed in BS without much in the way of "hard science" and only the required math (which tends to be statistics). It doesn't matter though, because we have all ranges of people who read these posts, so if you explain some basics that I happen to know, I am sure someone will be happy you did.

I found Psimagus' checkerboard analogy to be helpful. I also think in understand the dual slit experiment. If I understand the central issue here we are trying to determine the best way to predict the movement of quanta over spacetime. We are talking about a model which works for large number of quanta in a "best fit" sort of way, but which does not necessarily apply to one specific quantum. Your man Schroedinger wrote an equation about this while I was out looking for chocolate bunnies.

It may be there is some level of equivocation going on in the debate, so I am glad I asked you to define the terms.


I agree about the equivocation. Psimagus seems to use several words in quite a different sense from mine. This makes it difficult to see when there is really disagreement. As my attempts to forge a common vocabulary with Psimagus have failed, I have decided to simply describe everything in my own language, and express my own opinions, and leave Psimagus to do the same for himself. I believe that my language is the same as physicists normally use, but as you know he disagrees. Feel free to ask me for definitions at any time.


It seems that Irina and Psimagus disagree as to how Ø should be used as it applies to Schreodinger's equation and quantum physics. Also, Irina says that predicting quantum movement can be done based on standard wave function (propagation). Is that it?


Roughly, yes. I'm afraid that I believe that many things that Psimagus has said are false, or expressed in non-standard terminology, or both. I don't think there is any point in my arguing with him about it, however, for this has led nowhere in the past. I leave it to each of you to decide for him/herself who (if either) is right.

* I was once in an honorary fraternity called ØX but we never discussed quantum physics. Also, to me Ä means defendant more often than it means change and ð stands for plaintiff, not 3.14.

** When you think of my background, think of Mel Brooks' History of the World, specifically the scene withe the Roman unemployment office. "Oh, you area BS artist. Have you BSed today? Did you try to BS today?"