Understanding the Observer in Quantum Mechanics: Debunking Common Misconceptions

[Dr3vil]

TL;DR

What collaspes the wave function ... human eye balls or physical measuring device

Im confused What collaspes the wave function ... is it a human eye ball or physical measuring device. The way QM is described on youtube for layfolks is not very good. They make it sound like the physical observer collaspes the wave function ... however its a physical device interacting with the wave function that's collasping it isn't it?

 

[WernerQH]

The collapse of the wave function is a myth. It arises from a misunderstanding of the role of the wave function in the formalism. (Since there is no universally accepted interpretation of QM, physicists disagree on whether or not observers are necessary.) The quantum processes in the interior of the sun can be successfully described using QM, yet some people insist on a description in terms of "state preparation" and "measurement".

 

[Dr3vil]

The quantum processes in the interior of the sun can be successfully described using QM, yet some people insist on a description in terms of "state preparation" and "measurment"

What is state preperation? Googled it however could not understand lingo

 

[PeterDonis]

What collaspes the wave function

In terms of basic QM, i.e., without adopting any particular interpretation, this question can't be answered, since "collapse of the wave function" is not treated as a "real" process; it's just something you do in the math in order to make accurate predictions after you know the result of a measurement. See this Insights article:

https://www.physicsforums.com/insights/the-7-basic-rules-of-quantum-mechanics/

In that article, what you are calling "collapse" is called the von Neumann projection postulate (Rule 7).

 

[PeterDonis]

What is state preperation?

In terms of the 7 Basic Rules that I linked to in my previous post just now, "state preparation" is any process that produces quantum systems in a known pure state (Rules 1 and 2 describe what a "quantum system" and a "pure state" are).

 

[bhobba]

Summary:: What collaspes the wave function ... human eye balls or physical measuring device

Im confused What collaspes the wave function ... is it a human eye ball or physical measuring device. The way QM is described on youtube for layfolks is not very good. They make it sound like the physical observer collaspes the wave function ... however its a physical device interacting with the wave function that's collasping it isn't it?

You are correct - it is not very good at all. In fact, some like What The Bleep Do We Know Anyway are downright nonsense. Here is the truth. Peter has already pointed to the axioms, but they are not the last word. There is something called Gleason's Theorem:
https://en.wikipedia.org/wiki/Gleason's_theorem

It suggests that the state, or equivalently the wave function is nothing but a calculational device in figuring out probabilities. It is not 'real' in how we think of things as real in physics. It is of no importance if it suddenly changes due to observation any more than it is of no importance than the probability of raining tomorrow changes when tomorrow comes. When it actually rains (or not) - we have a new probability for a new tomorrow. Observation is any interaction. It is a bad choice of wording by suggesting consciousness is involved when it is not. Well, most interpretations do not think so anyway. That's the other thing about QM - the formalism (i.e. axioms mentioned by Peter) is agreed by everyone. What they mean, called interpretations, has many different versions.

Thanks
Bill

 

[vanhees71]

In terms of the 7 Basic Rules that I linked to in my previous post just now, "state preparation" is any process that produces quantum systems in a known pure state (Rules 1 and 2 describe what a "quantum system" and a "pure state" are).

State preparation can also be a preparation in a mixed state. E.g., putting a gas with a fixed number of atoms/molecules in a container at some fixed temperature is a preparation of the gas in the statistical operator of the canonical ensemble: $\hat{\rho}=\exp(-\beta \hat{H})/Z$.

 

[atyy]

Summary:: What collaspes the wave function ... human eye balls or physical measuring device

It is not well defined. The thing that collapses the wave function is typically called an "observer" or "measurement device", but quantum mechanics itself does not say what it is, and you have to supply this by ill-defined common sense. This observer collapses the wave function when a measurement is made, and a measurement result is obtained. Again, one has to rely on ill-defined common sense to know when a measurement result is obtained.