WARNING: I am not a physicist, and I don't even play one on TV. Treat all comments with
extreme scepticism!Tim wrote:
Because of this limitation on the theoretical knowledge of, say, a particle, you don't know where it is is going to be until you measure it. At that point you fix its value; until then, it could have been in either of two positions (in a simple situation). This is where the whole famous Schrodinger's Cat gedanken experiment comes into consideration...you don't know if the cat is alive or dead until you open up the box, in which case it could even be said that the act of opening up the box kills or doesn't kill the cat.
About the measurement with position and momentum, suppose I know I can only measure the position of a thing in time t. Suppose you can only measure the momentum of that same particle on the exact same time t. Does that mean that I can never tell you my answer?
No, it's nastier than that. It's not just that you can't measure position and momentum simultaneously. It's that a particle
cannot have both an exactly defined position and an exactly defined momentum at any given time, regardless of how you measure it!
I am reading the Schrödinger's cat experiment on Wiki, but that only says that personal observation leads to a fixed state. Now I want you to do this (thought) experiment: Same box, same you. But this time, I open the box, but you can't see or smell what's inside. Is the cat dead or not? It's been observed, so the cat can only have one of the states. But since you haven't saw it, it has both states?
"
Measurement"
in quantum mechanics isn't the same thing as "
measurement"
in real life. We don't actually
know what causes a measurement! The most popular definition within the most popular model (the Copenhagen Interpretation) is basically 'any interaction with a macroscopic object'. So, in other words, the cat is never actually in a superposition to start with - the superposition collapses when the particle hits or does not hit the detector, and covering your eyes and nose would make no difference.
Some supporters of the Copenhagen Interpretation believe that definition is wrong, and that the observer must be conscious. In that case, if you couldn't see or smell the contents of the box, the superposition would be maintained. Of course, in real life you'd need to be behind a glass shield or the presence/absence of claws raking into you would be a bit of a giveaway - cats don't like being shut in boxes!
Some famous scientist (probably Feynman) once said that anyone who says that they fully understand quantum mechanics is either lying or insane, so don't feel bad if you don't really get it just yet. 
Let's say that I'm lying in my bed right now, so I must be able to fully understand it But I think I am capable to understand most of it, but I just need some (web) pointers, as I don't know where to look for good information. Any pointers would be nice.
-- Tim
From everything I've found on the Internet, I've come to the conclusion that if you rely on the Internet you're doomed. There are too many interpretations out there, every site endorses a different one, and half of them don't mention what interpretation their explanation is coming from (or they take bits from more than one interpretation). This is because they are trying to make it simple.
If you have a good mathematical background, my advice would be to try to find a good, university-level textbook on the subject on eBay or through a second-hand bookshop. Otherwise, I don't think there is one...
____________________________
Stupidity kills.
Absolute stupidity
Kills absolutely.
