MALON said:
... I will push everything else out of my brain.
Heh, good luck with that. Better to compartmentalize it and file it as "suspect".
If you describe it in detail sufficiently, I will be super happy man.
If you don't find yourself capable of explaining it properly (or don't feel like it), could you at least link me to a credible site?
Thanks, really man.
-MALON
First of all, the disclaimer: I'm not a quantum physicist. I'm trying to understand this stuff at the conceptual level, so I won't be any help with the math. All I can do is try to convey my understanding, which you should also file under "suspect", for good measure. I'm sure somebody here will jump in where I screw up.
First, the definition of a "Truth" as used below: "as far as I can tell" :-)
The first big Truth of QM is that really small things appear to behave as mathematical entities. My current favorite way to think about it is as if photons, electrons, etc. are really just objects in a computer simulation. I think this idea was pioneered by Edward Fredkin. The idea of the Universe as cellular automata is often taken as a Truth by its proponents, but I think they're getting ahead of themselves. Nevertheless, if you switch your view of quantum thingies from little balls zapping around, to little data entites getting processed, I find it's easier to get past preconceptions from our macro existence.
A corollary of the above is that quantum entities get to do whatever the hell they want, and it doesn't have to make sense 'cause it works in the laboratory, and in your computer chips. This isn't directly related to the observer problem, but it will be handy when you start trying to conceptualize all the weirdness presented to you by the experiments where the "Observer Effect" supposedly lurks.
I don't even understand why probability is in wave form at all.
I'm not entirely sure about this, but I think it must be a convention, since the "wave" nature of quantum entities was first discovered by seeing the interference patterns, which are classically created by waves in a medium, i.e. water.
Quantum wave probability functions (now *my* terminology is probably breaking down) are different in that the crests and troughs in the function's definitions represent the likelihood that the entity will be in that place at that time. I think of them as analogous waves, since the math used for them resembles that for classical waves.
The Truth about the "Observer Effect" is that it just doesn't exist, at least in the way commonly tauted. The deal is that in every experiment there is some guy fiddling around with his apparatus. He is considered the "observer" since he decides the positions of stuff. However, he is no more special with regard to affecting wave functions than the wall of his lab if he mis-aligns his equipment. The wall is just as good at deciding quantum states as he is. Think of the term, anthropocentric, and you'll understand why the human is so commonly given a special status.
could you at least link me to a credible site?
Actually, I don't think I've come across one. My understanding of things only came when I started reading exactly how the experiments were done, and what the results were. I then began to be able to distinguish what were facts versus the interpretations of the experiments. It's like that old whisper game where there are a bunch of people in a circle, and one person whispers a story into the ear of the person to the right, who passes on the story by whispering, and so on around the circle. The last person must recite the story out loud, and it usually is hilariously warped beyond recognition.
One thing that helped me was to get a firm grasp of the Young's double slit experiment. It's the root of all quantum evils. Feynman said it better, but I forget. There have been several versions, but my favorite is Mandel's which demonstrates the effect without even "observing" the primary photon (meaning the one that finally shows itself).
Here is a page with some cool stuff (I haven't vetted the opinions, but the experiment's description seemed OK):
http://www.fortunecity.com/emachines/e11/86/seedark.html#Converter"
which should be the same as http://www.fortunecity.com/emachines/e11/86/qphil.html"
For me, this put the role of the observer, measurement, etc. in a pretty solid perspective. The nutshell is that you split a photon twice (partial mirror, then 2 down-converters) down four paths, and then recombine them so you get the interference pattern. Now all you have to do is affect/measure/block *one* of the four child photons (virtual, wave, or whatever they are), and the path is chosen, and the whole four branch tree wave function maddness collapses down to a single path indicated by the photon blocked/measured (i.e. its closest sibling in the sub-branch). Hopefully, the diagrams will be clear.
Here is a description of the classic Schrödinger's Cat thought experiment, but it's conclusion, the popular one, seems plain wrong to me:
Here is an example suggested by one of the founders of quantum mechanics, Erwin Schrödinger. You set up an experiment where a particle (small enough that quantum mechanical laws matter) has a 50% chance of decaying after an hour. The particle is in a box, and you don't look. After an hour, what is the state of the system? Classically, you would say that the particle has either decayed, or it hasn't, and you'll know when you look. Quantum mechanically, you say that the particle is in an undetermined state—its Y simply says "maybe decayed, maybe not"—and it won't actually decide until you look. The two sound very much alike, but they are different. To make the difference more vivid, you put a cat in the box, with an apparatus that will kill the cat if the particle decays. Now, is the cat in a state of "maybe dead, maybe not," truly an undecided middle ground, until you look?
It sounds as if this conclusion is ridiculous. Or it may sound like this conclusion is meaningless: saying "the cat is half dead/half alive until we check on it" is just a fancy way of saying "the cat is either dead or alive, but we don't know until we look." But remember the experiments we've discussed, and the conclusions we drew. Quantum mechanics says that these two statements are definitively different, and the intuitive one (the cat is either alive or dead, and we just don't know until we look) is wrong. The photon really, genuinely, and importantly, does not have a specific location until we measure one. The cat really isn't alive or dead.
In reality/practicality the cat *IS* alive or dead, because the decayed particle/photon/whatever hit *something* if only the wall of the box, which is good enough to collapse the wave function. It doesn't take prying eyes to affect the situation.
However, there was some time interval (nanosec?) when the particle state *was* indeterminate, and everybody has an opinion about what's up with the cat then.
Contrast the above with the Wikipedia introduction:
Schrödinger's cat is a seemingly paradoxical thought experiment devised by Erwin Schrödinger that attempts to illustrate the incompleteness of an early interpretation of quantum mechanics when going from subatomic to macroscopic systems. Schrödinger proposed his "cat" after debates with Albert Einstein over the Copenhagen interpretation, which Schrödinger defended, stating in essence that if a scenario existed where a cat could be so isolated from external interference (decoherence), the state of the cat can only be known as a superposition (combination) of possible rest states (eigenstates), because finding out (measuring the state) cannot be done without the observer interfering with the experiment — the measurement system (the observer) is entangled with the experiment.
The thought experiment serves to illustrate the strangeness of quantum mechanics and the mathematics necessary to describe quantum states. The idea of a particle existing in a superposition of possible states, while a fact of quantum mechanics, is a concept that does not scale to large systems (like cats), which are not indeterminably probabilistic in nature. Philosophically, these positions which emphasize either probability or determined outcomes are called (respectively) positivism and determinism.
Now, ask yourself: how did this description, where the cat experiment was proposed to more or less *debunk* the link between the cat and the particle, transformed into the previous quote?
As I read it, it says that even during that small interval where the particle is indeterminate, the cat's macroscopic interaction with the world means that it's state is never indeterminate regardless of how it's fate relies on the particle. The many worlds people will say that the universe splits so that one universe has a live cat and the other a dead cat, but that's a whole other kettle of cats.
So, finally, the Truth about the "Observer Effect" is that *any* event which determines a quantum entity's position (or momentum) collapses the probability function. This event can be any interaction, whether it bumps into a wall, bumps into a photomultiplier, bumps into somebody's retina, etc. These are all equally valid "measurements". There might be others I don't know about, like field interactions, etc.
Our existence consists of quantum entities flitting in and out of indeterministic states all around us, all the time. It's only when we catch them at it with our gadgets do we make a fuss about it. They could care less.
Those who say, "it only happened because I observed it", are patting themselves on the back for a feat of prowess equivalent to getting hit by bird droppings. Yeh, marvelous, now we have evidence of bird droppings because you were looking up at that bird. If it weren't for you, those droppings would never have existed, right?
Well, I hope I've done more help than harm.
Cheers.
