I haven't been reading a lot lately. I think that when I'm feeling stressed -- and I know, I know: my levels of stress seem to start at a very low level (My socks! I can't find the other SOCK! Dammit!) -- I don't like to learn, don't like to read things that make me think. I want comfort. A big bowl of tomato soup, please, and a nice chocolate brownie. Oh, wait -- I can't chew yet. Dammit!
I've been feeling that way of late, but there are hopeful signs. One of them is that I was happy when I came across this, here:
The measurement problem in quantum mechanics is the unresolved problem of how (or if) wavefunction collapse occurs. The inability to observe this process directly has given rise to different interpretations of quantum mechanics, and poses a key set of questions that each interpretation must answer. The wavefunction in quantum mechanics evolves according to the Schrödinger equation into a linear superposition of different states, but actual measurements always find the physical system in a definite state. Any future evolution is based on the state the system was discovered to be in when the measurement was made, meaning that the measurement “did something” to the process under examination. Whatever that “something” may be does not appear to be explained by the basic theory.
This isn't a scholarly web page -- I'd not understand that -- but the concept is a fascinating one: quantum entanglement, also known to a certain sproing-haired gentleman (no, not Larry of The Three Stooges, and did you hear that they're going to make a T3S movie?) as 'spooky action at a distance'. But here's the thing. When I read ' the measurement did something to the process under examination', I think: No, it didn't . It was what it was. You just didn't know about it until you looked, so you guessed, and one (or more) of the guesses was wrong.
I know that deep physicists (and likely college physics freshmen) have a much better view of this, and understand that this isn't the way it is, at all. But thats the way I think: It is....or it isn't. Superpositional states? Piffle.
Reading it was fun, though.
4 comments:
Hi Bill,
I do have a physics and math Bachelor’s degree and I understand your confusion because I have experienced it myself. You write:
“When I read 'the measurement did something to the process under examination', I think: No, it didn't . It was what it was. You just didn't know about it until you looked, so you guessed, and one (or more) of the guesses was wrong.”
Before I had studied quantum physics in depth I thought the same way but let me cut through the jargon and confusion. The most important part of physics is the experiment because without it physicists become religious mathematical philosophers. The experimental verification of the collapse of the wavefunction comes from measurements over many identically prepared particles. When you perform an experiment on identically prepared systems you should get the same result every time. This is not the case in quantum physics, the system randomly collapses into one of the many possible values which we call “eigenvalues”.
Suppose we measure one system and find an eigenvalue. If we keep measuring the system we find the same eigenvalue with absolute certainty. However, if we stop the measurement the wavefunction starts to spread out according to the time-dependent Schrodinger equation. This means if we make another measurement there is a probability that we find it in a new eigenvalue! This was experimentally shown in 1977 by Misra and Sudarshan.
Quantum mechanics is experimentally verified to a high degree of precision but we are predicting the exact probabilities. For instance if you predicted 6 eigenvalues each with a 1 in 6 chance of being observed and found only 2 eigenvalues with a 1 in 2 chance then the theory would be wrong.
The interpretation that a measurement did something to the system is called decoherence and I personally favor this interpretation because it is testable and similar to our understanding of entropy.
Another interpretation is that the wavefucntion never collapses but instead there are multiple universes and each universe has one of the eigenvalues. This is usually the type of physics that laymen love, but it is not experimentally testable and can be sliced to pieces with Occam’s razor.
Then there is the religious interpretation that “consciousness” causes collapse [See: What the bleep do we know? or “The Secret”] and that the wavefunction does not collapse until observed by a conscious entity. This interpretation has made millions of dollars from laymen but again it is not testable and has done nothing to move the theory forward.
For now avoid entanglement unless you are willing to learn about mixed and pure quantum states as well as the Stern-Gerlach experiement.
Best of luck,
Brian
Thank you for the explanation. I liked it. I didn't necessarily understand it... but I liked it. It was fun.
Wow~
This was SUPER interesting .. . understandable ... and quite revelatory. One of the things it revealed to me is that I know very very little about physics. lol
And this is why I like smart people.
Post a Comment