What did Heisenberg know about the measurement problem?

[MichPod]

TL;DR Summary

An interesting passage from "Physics and Philosophy" book of Heisenberg

While reading a book "Physics and Philosophy: The Revolution in Modern Science." by Werner Heisenberg, 1958, I was much surprised by the following passage near the end of Chapter 3:

"The measuring device deserves this name only if it is in close
contact with the rest of the world, if there is an interaction between
the device and the observer. Therefore, the uncertainty
with respect to the microscopic behavior of the world will enter
into the quantum-theoretical system here just as well as in the
first interpretation. If the measuring device would be isolated
from the rest of the world, it would be neither a measuring
device nor could it be described in the terms of classical physics
at all."

(bold selection is mine)

It looked to me as if Heisenberg knew something about decoherence theory. Or else, how could he know by that time that the "measuring device" cannot be isolated from the rest of the world? What was known by that time for him or for the scientific community to make such claims which look to me to go way beyond original "Copenhagen" interpretation of 20th-30th?

 

[Demystifier]

The reason why measuring device cannot be isolated from the rest of the world is not decoherence. The reason is interaction. Decoherence is just an effect of this interaction. Hence, Heisenberg didn't need to know anything about decoherence to make that conclusion. He just needed to know that there are interactions, which he certainly did.

 

[MichPod]

He just needed to know that there are interactions, which he certainly did.

Yet IMO the Copenhagen interpretation talks about the interaction between a quantum system and a measuring device, not about interaction of measuring device with the rest of the world. Heisenberg clearly claims that the measurement device cannot be isolated from the rest of the world, otherwise it would not work. But how could he know that? Based on what?

 

[Demystifier]

Yet IMO the Copenhagen interpretation talks about the interaction between a quantum system and a measuring device, not about interaction of measuring device with the rest of the world. Heisenberg clearly claims that the measurement device cannot be isolated from the rest of the world, otherwise it would not work. But how could he know that? Based on what?

Read more carefully his first sentence, especially its second part. By the rest of the world, it seems that he really means the observer. With that interpretation, now his statement sounds much different, doesn't it?

 

[EPR]

Contextuality

 

[MichPod]

Read more carefully his first sentence, especially its second part. By the rest of the world, it seems that he really means the observer. With that interpretation, now his statement sounds much different, doesn't it?

Yes, he starts to talk about the observer. But in the end he makes a bold declaration which really shocked me "cannot be isolated from the rest of the world, otherwise it would not work". So I am really not sure if he still meant the observer (human) or "rest of the world" (environment). Now, if we just have a camera which makes photos which are analyzed by the human much later, then we (probably, depends on how strict we want to be) have isolated the measurement device from the observer. So technically, we do not need a "contact" between device and observer to make a measurement (again, subject of interpretation and stricktness).

Moreover, a little bit before this passage, Heisenberg writes:

"It applies to the physical, not the psychical act of observation, and we may say
that the transition from the "possible" to the "actual" takes
place as soon as the interaction of the object with the measuring
device, and thereby with the rest of the world, has come into
play; it is not connected with the act of registration of the result
by the mind of the observer."

So for me in this context it sounds like he is not really interested in the observer, but he IS interested in the interaction with environment.

 

[EPR]

Yes, he starts to talk about the observer. But in the end he makes a bold declaration which really shocked me "cannot be isolated from the rest of the world, otherwise it would not work". So I am really not sure if he still meant the observer (human) or "rest of the world" (environment). Now, if we just have a camera which makes photos which are analyzed by the human much later, then we (probably, depends on how strict we want to be) have isolated the measurement device from the observer. So technically, we do not need a "contact" between device and observer to make a measurement (again, subject of interpretation and stricktness).

Moreover, a little bit before this passage, Heisenberg writes:

"It applies to the physical, not the psychical act of observation, and we may say
that the transition from the "possible" to the "actual" takes
place as soon as the interaction of the object with the measuring
device, and thereby with the rest of the world, has come into
play; it is not connected with the act of registration of the result
by the mind of the observer."

So for me in this context it sounds like he is not really interested in the observer.

He doesn't know what the context really is in and of itself but he knows quantum contextuality is a very basic feature of the theory. In theory, it could be the observer or something else entirely. Few physicists will venture that far to claim it's the role of the observer though.

 

[MichPod]

He doesn't know what the context really is in and of itself but he knows quantum contextuality is a very basic feature of the theory. In theory, it could be the observer or something else entirely. Few physicists will venture that far to claim it's the role of the observer though.

I am not sure if I understand well enough what quantum contextuality is. But it looks to me that it is well defined by the particular sort of the measurement performed. And the type of measurement may be thought as well defined by the measuring device. So in the respect to contextuality, there was no need for Heisenberg to claim that the measurement device would not work if isolated from the rest of the world.

 

[EPR]

'Particles' have definite properties within a certain context. If you changed the context(e.g. changed the FOR of an accelerated particle), its properties would be different. In nonrelativistic qm, it's usually assumed that the environment and the measurement apparatus are the context in which definite particle properties arise. Without this context, measurements/observations would never take place. Taken to the extreme, this view means the measurement apparatus would probably not exist either.

 

[EPR]

This is a philosophical conclusion that cannot be tested. You should probably take it with a grain of salt.

 

[julcab12]

They can't somehow get away of the observer effect in QM. It has shown that even observing the results after the photon is produced leads to collapsing the wave function and loading a back-history as shown by delayed choice quantum eraser.

Furthermore, Here is recent update on Updated Tracking the Dynamics of an Ideal Quantum Measurement from the old March 2019 version. Even the linearity of time is broken or blurry according to them.

https://journals.aps.org/prl/pdf/10.1103/PhysRevLett.124.080401

https://thenextweb.com/insights/202...uantum-measurement-but-the-moment-was-blurry/

https://www.su.se/english/research/research-news/scientists-film-a-quantum-measurement-1.487234

During the measurement some of the superpositions are lost – and this loss happens gradually – while others are preserved as they should be for an ideal quantum measurement.

 

[MichPod]

I am practically interested here in understanding what did Heisenberg know exactly in that time to write the sentences and claims he wrote.

 

[A. Neumaier]

Summary:: An interesting passage from "Physics and Philosophy" book of Heisenberg

how could he know by that time that the "measuring device" cannot be isolated from the rest of the world?

In 1927, Heisenberg had invented what is today called the Heisenberg cut. von Neumann already showed in 1932 that the Heisenberg cut is needed but can be placed anywhere. This says it all.

if we just have a camera which makes photos which are analyzed by the human much later, then we (probably, depends on how strict we want to be) have isolated the measurement device from the observer.

No, now the camera is the observer, and must have access to the measurement device, hence the latter cannot be isolated.