how is observer defined in context to quantum physics?does it have

nouveau_riche

how is observer defined in context to quantum physics?
does it have to b a concious observer?

Polyrhythmic

It doesn't have to be a conscious observer. Contrary to what many popular myths suggest, consciousness is not part of quantum mechanics. What we mean by observation is anything that is mathematically equivalent to applying an operator on a quantum mechanical state. For example, applying the position operator and getting its eigenvalue is equal to measuring a particle's position. An observation might be a collision between two electrons, or a specific measurement conducted in a laboratory.

nouveau_riche

what makes something(event) as mathematically equivalent to applying an operator?

I like Serena

The example that I like is the experiment where electrons are shot through a double-slit, impacting on a photographic plate behind it.

In the dark, you'll get an interference pattern.
In the light (with a short wavelength), you'll get a particle impact pattern.

In light with a long wavelength (in which an observer would not be able to distinguish through which slit the electron goes), you'll get an interference pattern again.

This is without anyone actually watching!
It's enough that someone might be able to see through which slit the electron goes. Weird huh!

Polyrhythmic

That's one of the axioms of quantum mechanics, measurements correspond to eigenvalues of hermitian operators. I guess you should read an introductory text to the subject in order to understand what is going on.

nouveau_riche

not much...
if an observer is not interested in measuring the position of photon then even the short wavelength will cause an interference...weird?

nouveau_riche

i have read some introductory but wasn't sattisfied with the conclusion

I like Serena

There!




Dr. Quantum thinks it's weird!

(Just found this on facebook! )

nouveau_riche

suppose the intereference experiment is set up again,the light used is of very high frequency(so that it's wavelength could match with that of slits) ,now the distance at which interefence pattern is seen is at max distant from slit(max in sense that pattern can b seen nicely).,now one of the observer set up apparatus to see the intereference pattern while the other one set up an apparutus to measure position of photon(to see from which slit it passes through)
question is-will the interference pattern b lost or both will see their portion of reality ?

I like Serena

Hmm, afaik the measurement making it observable which slit the electron passes through, collapses the electron's wave function, so regardless of the other observer, the interference pattern would be lost.

Do you have information that this is otherwise?

nouveau_riche

out of many answers that i have recieved for the above experiment many say that it's impossible to set up an apparatus like that ,one observer have to eliminate the other
like refer

http://www.physicsforums.com/showthr...=434366&page=2

nouveau_riche

the important point to b highlighted here is that both observer aren't aware of the act of measurement made by the other one,so if the pattern get lost ,the other observer get's to know the history of interaction of that particle

danR

As a layperson, I have trouble enough following mainstream theorizing, without the potential added confusion of 'Dr.' Quantum's entanglement with new age 'physics'.

Experts may be able to parse out the material in those videos that's valid, but then they might rather direct me to videos by established theorists and expositors of QM.

I like Serena

I've read the thread you mentioned and I have to say I have trouble understanding what is said exactly. As yet I see no reason to change my previous statement.
Here's a section of the wikipedia article that supports my statement:

http://en.wikipedia.org/wiki/Double-...interpretation

nouveau_riche

i would prefer the paragraph in that wiki link that could justify ur point.

alxm

"Awareness" has nothing to do with it. Either you perform a measurement or you don't. And by 'measurement' I mean it in the QM sense, which means any interaction with the environment-at-large which could, even if only in principle, be used to determine which path the particle took.

It does not matter if anything or anybody is "aware" of the results of the measurement.

Please use the search function. This question about what constitutes an observer or measurement in QM has been asked and answered here literally hundreds of times already.

DrChinese

Just to be clear: It is NOT the effect of the apparatus in and of itself that causes the collapse. It is the overall context of the setup, as to whether knowledge is gained or not.

Take a double slit setup using light. Place one polarizer over the left slit at angle L, another over the right slit at angle R. When L-R=0, there IS interference. When L-R=90 degrees, there is NO interference. Obviously, the presence or absence of a polarizer does not change anything unless which slit information is gained. That becomes progressively more feasible as L-R goes from 0 to 90 degrees.