B Does this theorem “theoretically” falsify macrorealism?

[Daria K]

Hello!

Recently I found this article: http://quantum-journal.org/papers/q-2017-07-14-13/pdf/

Being familiar with some basis of quantum formalism, I, nevertheless, experienced several difficulties with understanding of the theorem described in this paper. I would really appreciate if someone could tell me does this theorem really disprove some types of macrorealism or it only provides the conditions for empirical tests of macrorealism (like Leggett inequality)? I could metaphorically rephrase my question: "Does this no-go theorem prove, that the moon is not there when nobody looks?"

I understand, that this question is based on my layman concepts, and everything is much more deep and complex, but I really need your help.

Thank you in advance!

 

[bhobba]

I had a scan.

I am a realist agnostic myself believing in the ensemble interpretation which doesn't specify an exact position regarding that one way or the other, but the paper says it all even in layman terms. It clearly states its impossible to prove one way or other. All that has happened is some people have come up with some theorems that suggest to them (ie via a certain point of view they have) that non-realism is more likely.

That's fine if you are into that sort of thing - but its an advanced area not really suitable for a beginner.

As a beginner you are better off learning real QM and making up your own mind. I suggest, if you actually want the real deal, not pop-sci accounts, Susskind's books:
https://www.amazon.com/dp/0465075681/?tag=pfamazon01-20
https://www.amazon.com/dp/0465062903/?tag=pfamazon01-20

If you need to brush up on calculus:
https://www.amazon.com/dp/0471827223/?tag=pfamazon01-20

Regardless of if you are a realist or not rest assured the moon is there if you look or not because its always in contact with its environment eg the Cosmic Background Radiation. Via the process of decoherence it basically means that macro objects like the moon behave classically, part of which is being there if you look or not - intuitively its being looked at and is entangled with the environment all the time. So you run into the issue of exactly what is a macro object since those around us are entangled with the environment - that's the issue for approaches like the paper you posted. Now if you want to find out if a macro object totally isolated from an environment has classical properties how would you do it? Why you would have to interact with it in some way so it no longer isolated is it? So in a certain sense its a bit, well I won't say pointless, but rather academic. Still it's a legit area of investigation. Micro objects like say an electron is another matter. The borderline between the two is a very interesting thing as well leading to some very strange effects eg look up buckyballs.

Thanks
Bill

 

[Daria K]

Dear Bill,

Thank you very much for your answer. Maybe my confusion appeared because I interpreted the macro objects with "macro properties" in this paper as not isolated from their environment. Also I thought that we can rule out macrorealism only empirically, for example, by violating Leggett-Garg inequalities, but in this theorem there is nothing to "violate".

The best decision, I think, is to continue studying QM in order not to fall into such misunderstandings again. That is why I am grateful for the resources you mentioned.

Daria.

 

[Demystifier]

As they say in the paper, their theorem does not rule out all types of macro-realism, such as that provided by Bohmian mechanics.