I recently watched a program called 'Atom' on bbc4 that said something along the lines of: "If you want to strike fear into the eyes a physicist; mention the measurement problem" - What is the measurement problem and why is it such a problem?
But why fear? I would say "fascination and excitement". Many students of quantum mechanics (including me) get "hooked" precisely by the contraintuitive nature of QM and the sense that it never completely fits into your mind.There are two kinds of physicists: practical ones and those who want to understand nature on the deepest possible level.
The measurement problem "strikes fear into the eyes" only for the latter.
Ah, but you're missing another option here. There could be physicists who are "practical ones" but also interested in understanding nature "on the deepest possible level". The difference being that until there's truly something that can distinguish and answer those questions, everything that is being argued is simply a matter of tastes and would not lead to any kind of agreement.There are two kinds of physicists: practical ones and those who want to understand nature on the deepest possible level.
The measurement problem "strikes fear into the eyes" only for the latter.
Also, my sense is that it would be hard to really develop a theory of quantum cosmology (where the entire universe is treated using quantum rules, with no observer outside to measure it) without at least partially addressing the measurement problem, so it's not purely philosophical in this sense.It depends. The problem and solutions proposed in the literature are mostly philosophical. However, if a particular mechanism of solution, like Legett's [mentioned above] or Penrose's leads, to experimentally verifiable predictions in the areas not yet tested, then it is a matter of physics.
If you want to strike fear into the eyes a physicist; mention the measurement problem
Please, define what the quantum mechanical measurement is (the definition that you use).if you don't know what the quantum mechanical measurement is, you can pretend that you don't have any problems with it, and nothing will force you to admit that you have no idea what it is.
You have no idea what the measurement problem is. It is clearly defined during last 80 years. You confuse OP and violate PF guidelines:What that problem actually is? Perhaps not everyone will agree, but I would summarize the problem by the following questions:
Do physical observables have some values even when we do not measure them?
If no, then how exactly measurement makes them?
If yes, then how exactly measurement changes them?
Regards, Dany.Specifically, we aren't here to defend mainstream science, we are here to explain it.
I will therefore ask people … to please refrain from posting statements of their opinions unless they can quote a peer reviewed published paper, textbook, or other source which supports this as a current subject of scientific debate in accordance with our guidelines.
I was talking about the process, that is mathematically described as the state being projected onto some eigenstates. This is what quantum mechanical measurement usually means.Please, define what the quantum mechanical measurement is (the definition that you use).
We are violating only the philosophy "shut up and calculate", but that yet is not a big crime.You have no idea what the measurement problem is. It is clearly defined during last 80 years. You confuse OP and violate PF guidelines:
No. It is not a measurement. You are talking about the universally valid phenomenon called the collapse of the wave packet.I was talking about the process, that is mathematically described as the state being projected onto some eigenstates. This is what quantum mechanical measurement usually means.
Let us talk physics. Your definitions still not clear to me. What is the physics the measurement apparatus obey? Is it the classical physics only (macroscopic)? If so (CI), then why you call it the quantum mechanical measurement? If your physical system under test is macroscopic (obey laws of the classical physics), you will find that every dynamical variable is measurable (observable); if your physical system under test is microscopic (obey laws of the quantum physics), then only the dynamical variables that form the mutually commuting set of self-adjoint operators will be observable. But the measurement set-ups are the same. Clearly for me that you perform the same measurements, only the results are different. Therefore, it is the demonstration that the quantum world is not the classical world. In addition, the above type of measurements is accompanied by the collapse of the wave packet.It is mathematically clear, but what is it physically?
At the same instant when you perform the measurement. It is the transition from the Quantum World to the Classical World. Symbolically we call it the E. Schrödinger Cat.When does the projection occur?
Interaction with the measurement apparatus.What initiates the projection?
If a Gaussian wave packet, that is badly delocalized, hits a wall, and collapses into a smaller area, when does the collapse occur? This is a measurement of the position. When does the measurement occur?At the same instant when you perform the measurement.
Be careful before such statements. I have published several papers on this issue in peer reviewed physics journals. For one of these journals the editor is the Nobel-prize winner G. 't Hooft (who, by the way, also explores the measurement problem in QM). How about you?You have no idea what the measurement problem is. It is clearly defined during last 80 years. You confuse OP and violate PF guidelines:
Brilliant!If you don't know how to drive a car, you cannot go behind a steering wheel and pretend that you know how to drive a car, because everybody can see that you cannot drive a car.
But if you don't know what the quantum mechanical measurement is, you can pretend that you don't have any problems with it, and nothing will force you to admit that you have no idea what it is.
hmhm.. yeah it's mine. I used to think this way in programming, one older programmer emphasized this to me. In social life you can always accuse others when things don't work, and nothing forces you to see your own mistake, but in programming your own program, that doesn't work, forces you to see your mistake mercilessly. And watch how the justice works here: If you refuse to find your own mistake in the code, you cannot get the program working anymore!Brilliant!
Is that written by you? Do I have a permission to cite it somewhere?
I remember hearing this too. It sounds like misunderstanding of quantum mechanics. Perhaps measurements can change past events in some very exotic interpretation, but its not part of the popular Copenhagenian interpretation at least.but I also heard that some wackos actually think that measurement and discovery can change past events???
I'm not sure what you are saying here, but the Shrodinger's cat paradox is a real paradox. You'll have to understand QM before it. What is paradoxical is how macroscopic and living beings could be in superposition of very different states.Also I don't understand how Schrödinger's cat can be anything other than pure philosophy as it doesn't change anything physically it's just our understanding of the events.
The OP question is: What is the measurement problem and why is it such a problem? There are several sessions here at PF related to that question but at least during last year nobody suggest the discussion of the roots and the present status of the problem which is now under intensive development.Be careful before such statements.
I have no idea what you are talking about.For people like you who think that all conceptual problems of QM are already solved a long time ago.