Seasons

[re: 4003]

Irina,

The comment of yours that I replied to was:

As for the electromagnetic wave according to Classical Physics, Quantum Mechanics says (again, speaking precisely) that there is no such thing.
As I said, Quantum Mechanics claims to supercede Classical Physics; it says that Classical Physics is wrong.

to which I responded:

Not wrong, just incomplete. It doesn't seek to replace Classical physics, just attempts to put some foundations under it (since we find the whole edifice, being built from the top down, disconcertingly doesn't seem to quite meet the ground.) Classical physics works superbly well at a macroscopic scale - it just completely fails to work at a tiny scale.

and you said:

No, wrong. Max Planck invented his eponymous constant because Classical Electromagnetic Theory gave the wrong predictions for blackbody radiation.

Yes. Classical physics gave the wrong predictions - that is perfectly true. It did not do so because classical physics itself is "wrong"; but because it's incomplete. It lacks adequate capability to model quantum-scale behaviour. Quantum mechanics does not seek to overthrow and replace classical physics - I have never heard anyone claim that at a macroscopic level classical physics should be purged, and replaced with another model.

The results it predicted were wrong, that is all. That does not mean we should throw the baby out with the bathwater, and write classical physics off completely.

Well, Psimagus, I think you have just proved the theory of multiple realities. Clearly, QM (or at least, the terminology employed) is a very different thing in your universe than it is in mine. I have once again arived at the point of considering the'debate' to be hopeless. Perhaps if I drank absinthe...

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.


Ah yes, the Einstein-Podolsky-Rosen paradox. They rather shot themselves in the foot there - it was originally devised to disprove "spooky" quantum non-locality, but then it was actually performed.

Yes, it is perfectly true. But it would be erroneous to assume that there is any faster-than-light communication involved in this - it is spooky, but it does not break any fundamental laws. There must be causal contact to entangle them (in plain terms, they have to be put together.) Then we let them fly off in opposite directions, for a few light minutes/hours/days/years, before measuring one (I guess we'd have to have sent an observer on a slow boar to Pluto to be there ahead of time.) He measures his electron and immediately knows the value of the other. But he has no control over what the value will be, and so no prior knowledge of it. And he only gets to measure it once, and then it's gone. The information has spent all that time diverging at light speed (not faster,) and any message sent from the observer to another observer on the other side of the solar system to tip him off will only travel at light-speed (and not faster). At no point does any material or information travel faster than light.


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!

But it doesn't change. If it's measured, it's the same that's all. It was never any different, but there's no way of sending a message predicting its state to a second observer that can possibly catch up with it.

It violates only classical prejudices about how stuff "ought" to work, not any laws.

There's quite a good description @ http://en.wikipedia.org/wiki/EPR_paradox#Description_of_the_paradox

a slow boar to Pluto

Yegods! I must dilute this drink a little more - naturally I meant a "slow boat"! Though a tusked celestial messenger rooting through the heavens has a certain pagan appeal to it

Well, Psimagus, I think you have just proved the theory of multiple realities. Clearly, QM (or at least, the terminology employed) is a very different thing in your universe than it is in mine.

Just one reference to Psi propagating - that's all I ask

But I am inclined to agree - the Irinaverse is a wondrous thing, and I look forward to experiencing it at the end of days when all models are realized in the Omega Point. But until then, I fear I'm stuck in this more mathematical (but probably a good deal less magical,) strand of the multiverse.

I have once again arived at the point of considering the'debate' to be hopeless.
Perhaps if I drank absinthe...

Well, I would always recommend that!

Just one reference to Psi propagating - that's all I ask


OK, googling on "wave function propagation" (in quotes, so as to require the exact phrase to be found) produces about 576 hits. Choose any one you like.

Yes. But there are an awful lot of wave functions in existence other than Psi. And when I go to the first match (a 122 page pdf) and search for both "psi" and the greek letter /psi/, there is no match.

Oh well - try the second. Uhh, no match.

Try the third... fourth... no match.

fifth... subscriber only site, no access.

sixth... seventh... eighth... ninth... tenth... no match.

psi may apparently be the only wave-function in the Irinaverse, but in the universe that my instantiation of google describes, it is not. These links (and I'm not going to work through all 576 of them!) refer to "electromagnetic wave functions", and "semiclassical initial value representation (IVR) methods for wave function propagation", and "Coulomb wave functions", and even some more x-ray crystallography diffraction techniques by the look of it.

They are not Psi. They make no reference to Psi anywhere in their hundreds of pages. I'm actually surprised that there is not one single reference to psi tucked away in a single footnote or appendix, but this is the case. I have double checked. Not only is psi not described as propagating - it's not even mentioned.
I wonder if perhaps I have been sidelined into a universe where psi has been abolished, and noone's told me. Perhaps it never existed here. But if so, google's trapped here too.

These are not references to psi propagating. They are references to other wave-functions propagating, ie: wave-functions that can propagate (in this universe.)

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

Sorry - on closer inspection (note to self: next time at least try to read more than only every other word!) I shouldn't have agreed with this. It's not that if you change one state (because you can't,) it's if you detect one state...

You don't have any control over, or prior knowledge of what the state will be when it's detected - all you know is that one will instantly predict the other.

Some interpretations of QM say the state is hidden until it's detected. Others (seems to be the current consensus,) say there is no state until it's detected.

Sorry - on closer inspection (note to self: next time at least try to read more than only every other word!) I shouldn't have agreed with this. It's not that if you change one state (because you can't,) it's if you detect one state...

Great, Psimagus has just ruined "What the Bleep do We Know" for everyone here. You mean I can't control quantum states? What if I have a really positive attitude about it? What if I send that woman who says she channels spirits from Atlantis my money so I can learn how?

On a more serious note, I have a dumb question that I really need to ask again to try to keep up. Sorry to keep slowing you two down. I know I should read over all the old post again or google something. I am going to ask the stupid question anyway.

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?"

I know I am a PITA, but define it one more time please. I'll try to pay better attention.

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's the Greek letter that looks sort of like a trident or a sai. Apparently, Google does not search for the Greek letter psi when you write "psi", which is perfectly understandable. Because I don't know how to get a real Psi on the Forge chat system, I wrote it out as "Psi". Of course you won't find the three-letter English word, "Psi", in technical papers. They will use the Greek letter itself in equations, and in accompanying text they will call it the wave function, or something like that. To call attention to the absence of the English word "psi" would b (in my universe) a merely linguistic quibble and would have nothing to do with the content of QM. Similarly,
your attempt to get anything from Google for "Psi diffracts" would have been doomed to failure in my universe as well, for the same reason. Google is a very powerful tool, but if someone doesn't have a certain background knowledge in making a search, they will get strange results. In the Wikipedia article on the two-slit experiment (in my universe), it describes the two-slit experiment thus:

"A beam of light perpendicular to the X axis which propagates in the direction z encounters a screen S1 which presents a narrow (with respect to the wavelength of the ray) slit. After having passed through the slit, the wave function diffracts with an angular opening that causes it to encounter a second screen S2 which presents two slits. The successive propagation of the wave results in the formation of the interference figure on the final screen F."

[from http://en.wikipedia.org/wiki/Bohr-Einstein_debates]


Please notice that this passage ascribes both propagation and diffraction to the wave function. In fact, it describes the two-slit experiment in pretty much the same way I have been doing; but then, it is an article from my universe.

Bev,

No, it's a good question (and I wouldn't condemn you to trawl back through... good grief, it really is hundreds of posts with no forum search facility!)

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

I can't speak for the Irinaverse, but in my universe (which I'd like to think I'm not accidentally marooned alone in, Psi-less in Gaza,) psi is a measure of probability plotted across spacetime. It's colloquially called a "probability wave(form)", but it doesn't propagate like a regular wave.
Kee thinking about the photons - they're what's important in the functioning of the experiment, psi is only relevant in explaining the results.
Imagine the universe is a chessboard (it's a small universe.) There is a minimum unit of "stuff" (the quantum - this one's a photon, but there are others,) and a cellular structure to space time, so the quantum can only occupy a square on the chessboard. It can't straddle a line, because the squares are so small - the same size as the quantum in fact. Spacetime is digital. But quanta are tricky to pin down - in fact, until you look for them you can't tell where they are exactly. You might assume it's on B5 (because that's what the classical formulae tell you,) but it could turn out to be on B4, or B6, or C5 if you actually stuck a detector there. You get the idea. There's a lower probability that it might be more than one square away, even a very (VERY) low probability that it might turn up on G8 at the other end of the board - you don't know till you look. Psi can be calculated for every quantum's probability of being on any particular square (using Schroedinger's formula)
In this case, we've only got the one, so you could pencil in the probability values (between 0.0 and 1.0) on each square, the numbers reducing smoothly as the distance from the classically predicted point increases.
The "map" of those probabilities across the board is the "probability wave" (or "waveform", but lose the "amplitude".) It sort of looks wavy, in that the values form something like a ripple, but a) all the values are greater than 0 (so the wave has no troughs,) and b) it doesn't propagate. The values are all across the board, but the speed of light will only allow the quantum to move 1 square per time instant.
I'm going to descrine a 3-d model here - compare the difference with the 2-d model I posted before - if you can ever find it !)
If our quantum, nominally on B5 moves into the board at a diagonal to B6 on another board behind it, representing the next time instant, all the Psi values across that board are adjusted instantly (with no need to wait for anything to travel to them at 1 square per instant.) The quantum is now nominally on B6, so it's less likely to turn up on B4 (now 2 squares away,) and more likely to turn up on B7 ( now only 1 square away from where the classical formulae tell us it must be.) Remember, these "nominal" values are where classical theory tells us they "ought" to be - it's just at a quantum scale they very often aren't. At the angle it's moving, classical physics would suggest a trajectory through a stack of boards, B5-B6-B7-B8, but the probability values on each square of each successive board would fluctuate.
Psi is just the map of these probabilities - a mathematical model. The fact that the value we've pencilled on G8 changes instantly when our quantum move a square at the other end of the board doesn't mean that there's any faster-than-light communication involved - we could only test G8 by going there. We could only communicate any discovery of our quantum there at no greater than lightspeed. But it does demonstrate that Psi can't propagate (unless it does so at greater than lightspeed,) because it's managed to adjust squares at the other end of the board in the time light travels from one square to an adjoining one.

Does that make any sense? Sorry, I haven't slept for quite a long time and my brain's not at its best to explain.

Well, my universe's google doesn't have any problems - 13 and a half million matches for capital Psi:

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

where ? is the Greek letter /psi/, pasted in from the Windoes character map.

There is apparently a shortcut ( U+03A8 ) according to the character map, but it's easier to just copy and paste.

You need to complain to the God of the Irinaverse, or your timeline's google admin or something I think....