Decoherence and localization

[durant35]

Can anybody explain this quote from stanford encyclopedia:

Indeed, while it is well-known that localised states of macroscopic objects spread very slowly with time under the free Schrödinger evolution (i.e., if there are no interactions), the situation turns out to be different if they are in interaction with the environment. Although the different components that couple to the environment will be individually incredibly localised, collectively they can have a spread that is many orders of magnitude larger. That is, the state of the object and the environment could be a superposition of zillions of very well localised terms, each with slightly different positions, and that are collectively spread over amacroscopic distance, even in the case of everyday objects

 

[bhobba]

That is, the state of the object and the environment could be a superposition of zillions of very well localised terms, each with slightly different positions, and that are collectively spread over amacroscopic distance, even in the case of everyday objects

Out there in the macro world when we speak of superposition's we mean superposition's of position. Every state is a superposition of many other states and in an infinite number of ways. However in the macro world, due to the general radial nature of interactions objects are in an effective eigenstate of position so are not in superposition.

What prevents the well known spreading issue of localised quantum objects and effectively keeps them in an eigenstate of position is they constantly interact with the environment.

Thanks
Bill

 

[rkastner]

The quoted section is actually an argument against the adequacy of the unitary-only decoherence approach for accounting for the macroscopic world of experience. It is clarified in this footnote: "As a numerical example, take a macroscopic particle of radius 1cm (mass 10g) interacting with air under normal conditions. After an hour the overall spread of its state is of the order of 1m. (This estimate uses equations [3.107] and [3.73] in Joos and Zeh (1985).)"

This and other weaknesses in the decoherence/unitary-only account give us reason to consider alternative interpretations. An example is including non-unitary collapse as a real physical process. Most 'mainstream' physicists and philosophers of physics are leery of taking non-unitary collapse seriously because the more known models (GRW collapse) are so ad hoc in character. A more natural alternative is provided in the Transactional Interpretation, which has been generally overlooked because of hesitancy over its use of advanced field solutions. However, there is nothing inconsistent about it, and as Bohr once said, it might be 'crazy enough to be true.' An overview is provided here: https://arxiv.org/abs/1608.00660