Seasons

Dear Bev:

What exactly is "psi" again? How does it relate to a probability amplitude wave? Sorry to make you go backwards, but 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). So right now, I'm the kid in the back of the class who sat through a whole hour before raising her hand to say, "I have a question....what are you talking about?"

Actually, Bev, I am really glad you wrote. You are not slowing anything down.

This is the way it is in my universe:

There is a Greek letter, which is sort of like a trident or a sai; since it is not in our alphabet, and since I don't know how to get Greek letters on Forge chat, I write "psi" instead. I am sorry if this has been confusing. You can see a "Psi" in the Schroedinger equation, the central equation of Quantum Mechanics, here:

http://scienceworld.wolfram.com/physics/SchroedingerEquation.html

In the first equation, just to the left of the equals sign, you see something that looks like a fraction, and at the right of the 'numerator' you see a letter that looks sort of like a pitchfork with the handle broken off, with a serif on the middle tine. That is an upper-case psi. But the important thing is not the letter, but what it stands for. In QM, the letter psi is the standard way to represent what is often called the "wave function' (a.k.a. wavefunction, wave vector, state vector, probability amplitude wave, etc.). I often wrote "psi" instead of "the wave function" for the sake of brevity. It's just a shorthand, like "t" for time.

Results 1 - 100 of about 13,500,000 for Ψ. (0.19 seconds)

Whooah!

ΨΨΨΨΨΨΨΨΨΨΨΨΨΨΨΨΨΨΨΨΨΨΨΨΨΨΨΨΨΨ<0>

Well, that's an object lesson in making assumptions as to the limitations of the Forge's character set without testing it first, and no mistake!

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?"