What does it take to solve the measurement problem?Okay, this is mostly conventional wisdom of the last 90 years. Quantum mechanics depends on measurements, without precisely defining it.We summarise different aspects of the measurement problem in quantum mechanics. We argue that it is a real problem which requires a solution, and identify the properties a theory needs to solve the problem. We show that no current interpretation of quantum mechanics solves the problem, and that, being interpretations rather than extensions of quantum mechanics, they cannot solve it. Finally, we speculate what a solution of the measurement problem might be good for.
Does that make the theory inadequate?
If quantum theory is not a valid scientific theory, then maybe we need to redefine theory. We have a trillion dollar semiconductor economy based on the theory. It is the most commercially successful scientific theory of the XX century.
She has also announced a new book, and promises a whole chapter on free will.
EXISTENTIAL PHYSICSI am glad to see her address these issues, but she believes in superdeterminism, which is as wacky as the simulation hypothesis that she mocks.A Scientist's Guide To Life's Biggest Questions
A contrarian scientist wrestles with the big questions that modern physics raises, and what physics says about the human condition
Not only can we not currently explain the origin of the universe, it is questionable we will ever be able to explain it. The notion that there are universes within particles, or that particles are conscious, is ascientific, as is the hypothesis that our universe is a computer simulation. On the other hand, the idea that the universe itself is conscious is difficult to rule out entirely.
According to Sabine Hossenfelder, it is not a coincidence that quantum entanglement and vacuum energy have become the go-to explanations of alternative healers, or that people believe their deceased grandmother is still alive because of quantum mechanics. Science and religion have the same roots, and they still tackle some of the same questions: Where do we come from? Where do we go to? How much can we know? The area of science that is closest to answering these questions is physics. Over the last century, physicists have learned a lot about which spiritual ideas are still compatible with the laws of nature. Not always, though, have they stayed on the scientific side of the debate.
In physics, the concept of a multiverse is a key element of a leading area of study based on the theory of everything. It’s called string theory, which is the focus of my research.There are many different notions of the multiverse, and I cannot even tell which he is referring to.
Update: Dr. Bee writes in defense of superdeterminism:
In a superdeterministic model, these quantities de- scribe an ensemble [9] rather than an ontic state (hence rendering the measurement update of the wavefunction purely epistemic), but that doesn’t make superdetermin- istic models classical. This should not be surprising, given the purpose of superdeterminism is not to return to classical mechanics, but merely to return to locality.This makes no sense to me. Quantum mechanics already has locality. Interest in superdeterminism arose as a loophole in Bell's theorem. If you want a classical theory to replace quantum mechanics, then it must be nonlocal or superdeterministic.
Update: In the current Physics Today, N. David Mermin denies that there is a measurement problem:
Many physicists dismiss this view with the remark that quantum states were collaps- ing in the early universe, long before there were any physicists. I wonder if they also believe that probabilities were updating in the early universe, long before there were any statisticians.This view is becoming a minority, but it should be regarded as the textbook view.Niels Bohr never mentions a quantum measurement problem. I conclude with a state- ment of his that concisely expresses the above view that there is no such problem, provided both occurrences of “our” are read not as all of us collectively but as each of us individ- ually. “In our description of nature the purpose is not to disclose the real essence of the phenomena but only to track down, so far as it is possible, relations between the manifold aspects of our experience.” I believe that this unacknowledged ambiguity of the first per- son plural lies behind much of the misunderstanding that still afflicts the interpretation of quantum mechanics.
Dear Roger,
ReplyDelete> "If quantum theory is not a valid scientific theory, then maybe we need to redefine theory."
Rather than putting it in terms of valid vs. invalid, I would say that the mainstream QM theory is (i) incomplete and (ii) partly inconsistent.
While both these issues require a proper solution to the measurement problem, the emphases are a bit different.
The theory is incomplete in that it's linear, and hence, the irreversible nature of measurements cannot be predicted from it, but must be brought in via a completely external, ad-hoc, postulate. von Neumann famously summarized the problem via the distinction between his Process 1 (the collapse of the wavefunction) vs. Process 2 (the Schroedinger evolution). The Process 2 is governed by *all* the *other* postulates; the Process 1 by the extra collapse postulate. For a succinct summary, see https://www.informationphilosopher.com/problems/measurement/
The theory, IMO, also is partly inconsistent because of two different issues:
(i) IMO, the fundamental physics here is nonlinear, whereas what the mainstream QM's postulates posit is a linear theory. You may think of it as being only partly inconsistent, because you can always get away by saying: "Look, this is just a linearized version that *is* valid over the range of experiments, OK?" There is some merit to it. (I *like* the theory of elasticity.)
(ii) The theory is *badly* inconsistent because it says that during measurements, the wavefunction gets updated to a single eigenfunction out of the entire spectrum. People accept this part of the collapse postulate, without a thought, simply because von Neumann said so. But it is wrong. Yet, since it involves only the Process 1, it's perhaps OK also in this case to be a bit generous and call the overall theory as being only *partly* inconsistent.
So, yes, the theory needs to be completed and the inconsistencies in it removed. My submitted paper carries a proposal for it which, to me at least, seems correct --- even cool!
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> "We have a trillion dollar semiconductor economy based on the theory. It is the most commercially successful scientific theory of the XX century."
When I was a UG student of Metallurgy at COEP, they used to say in the college seminars and all: "We already have a theory which, if it's deployed right, can save billions of dollars in loss per year." This, even if the theory they had in mind was LEFM (Linear Elastic Fracture Mechanics). Fracture is an irrerversible process. Linear elasticity cannot model anything irreversible --- not even the permanent set of an overstretched spring, let alone fracture. So, saying that "we already have a theory" was stretching things a bit too far, really speaking. And yet, if you ask me, there also was a lot of sense to it. When you can save huge amounts of money, even lives, you don't get into theoretical nitty-gritties like reversibility and singularities. You conduct experiments whose scope exceeds that of the theory and use their findings, but then, you put these data in the context of the theoretical *scheme* suggested by LEFM, together with some practical rules/parameters to merge the two. A typical engineering thing. And, BTW, engineers have, over the 3--4 decades since then, succeeded in saving a great range of failures too, even if theoretical development still goes on. (There was a research study about it, too!)
Something similar here, regarding QM too.
You have the Independence Day in your country today. Greetings for the same.
Best,
--Ajit