Archive for October, 2019

(106) What is meant by an ‘observer’ in QM? Do you have to directly observe the electron in order to collapse the wave? – Quora

Sunday, October 13th, 2019

In almost any imaginable theory an experiment involves the preparation of a system in what we call a “state” and the subsequent observation of various quantities which we call “observables”.

The measurement process has several stages, and a lot of confusion about what is meant by an “observer” in QM arises from not keeping them separate.
Two of these stages are often identified with the notion of “collapse”.
One is where a small part of the world appearing to be in a pure state (which is a linear superposition of the eigenstates of any particular observable) interacts with some part of the external world which is not in a pure state in such a way that the small part ends up appearing to be in a classical statistical mixture of eigenstates. After this interaction is complete the observer still may not know which eigenvalue applies (ie what the observed value of the measurement will be) but the situation is no more (nor less!) mysterious than that of a coin toss which has not yet been observed. For this kind of collapse (which has been understood in principle since von Neumann but for which in the last few decades specific more detailed examples have come to be touted as “decoherence”) the part of the world “causing” the collapse could be anything from surrounding thermal radiation, to an actual measurement instrument, or a cat, or another human observer (cf “Wigner’s friend”) who learns the truth before you do.

But if you are the observer we are interested in, then the system remains in a mixed state until you become aware of the result, and collapse of the classical probability distribution happens only in your mind.

So tl;dr there is no collapse of the wave. What there is are first decoherence of the wave (which can be caused by interaction with almost anything that is even slightly complicated), and then later collapse of the resulting probability distribution which is where you and your “consciousness” come in.

Source: (106) What is meant by an ‘observer’ in QM? Do you have to directly observe the electron in order to collapse the wave? – Quora

Speculative Science is not necessarily “Post-empirical” Pseudo-Science

Tuesday, October 8th, 2019

In the promo for his piece: Post-empirical science is an oxymoron, and it is dangerous | Aeon EssaysJim Baggott is identified just as a “popular-science author”, but in fact he’s also a real scientist with research awards and applied experience. And this shows in the quality of his essay which objects to much of the sensationalist mumbo-jumbo that passes for popular science writing these days. But there are other real scientists among those he objects to and I think there is plenty of room for people to work on (and write about) speculative ideas that do not yet have testable consequences.

In his article, Baggott refers to an earlier article by Massimo Pigliucci entitled Must Science be Testable? which carried the subhead “String wars among physicists have highlighted just how much science needs philosophy – and not just the amateur version” (to which I responded with a comment at the time).

For me, YES, science must be testable, and No science does not “need” philosophy – especially the “professional” version.

That’s not a statement about how the world “is”, but about how I choose to define the word “science”, and I suspect that most of my scientific colleagues feel similarly (in general terms though not perhaps in all the details).

More completely, I think of science as the game (a word I shall not try to define!) of making the most complete and accurate predictions from the most compact set of assumptions. It differs from some games in that the “scoring” system is not precisely defined and is largely a matter of personal taste (kind of like judged aesthetic events like gymnastics and diving in the Olympics).

String Theory is a part of that game because it is an attempt (still in progress) to interpolate between General Relativity and Quantum Field Theory in a way that reduces the number of bits needed in order to describe the assumptions while not failing to at least match the accuracy of any of the separate theories’ predictions. One can argue as to whether it is likely to succeed, but any claim to have properly constructed it will be testable in several ways – not all experimental. One is just whether it is logically and mathematically consistent. Another is whether it has limiting cases which match GR & QFT. But then it will almost surely make predictions in situations where the other two break down, and so it will also probably be possible to design experiments which detect whether or not those predictions are correct.

A “theory” which I would not consider real science is the “many worlds” interpretation of quantum mechanics. It is designed to exactly mimic the predictions of standard QM and requires exactly the same mathematical tools but just dignifies some of them with the label “real” which sadly does not seem to have any real meaning; however I can see how the interpretation might earn some points if we added a criterion of aesthetic appeal or conceptual accessibility to the scoring table.

There are also some similar-sounding “multiverse” theories that go beyond the many worlds idea and may possibly one day make predictions re observable effects from “nearby” “branes” and such; and the “mirrorverse” idea that Leah Broussard is proposing to explain some observed anomalies in neutron decay time measurements seems to be one of these. As yet it may be even further from being properly constructed than string theory, but I think Baggott is overstating the case against it.

Baggot and others like Sabine Hossenfelder can argue that certain lines of investigation are a poor allocation of scientific resources, but that is very far from making it appropriate to identify them as “pseudo-science”.