# Tag Info

29

You're right; the Schrödinger's equation induces a unitary time evolution, and it is deterministic. Indeterminism in Quantum Mechanics is given by another "evolution" that the wavefunction may experience: wavefunction collapse. This is the source of indeterminism in Quantum Mechanics, and is a mechanism that is still not well understood at a fundamental ...

26

First of all, "loopholes" is no disrespect. It's standard nomenclature. Given a law, a "loophole" is a way to circumvent it. Bell's inequalities, in their mathematical formulation, are laws that prevent superdeterminism, so if we believe it should exist, we have to find loopholes in the assumptions. It might be that the loophole is so big that the whole law ...

20

The idea of my latest paper is simple. I experienced in other blogs that most people refuse to go with me all the way. I'll give my argument step by step and you may choose where you want to step out. Consider superstring theory, in its original, completely quantized version. Many people believe it might have something to do with the world we live in. It ...

20

No. Shor's algorithm isn't demonstration of MWI. MWI is a way to think about Shor's algorithm, just like other interpretations of QM. Deutsch advocates MWI as a way to think about quantum algorithms because it is an easy way. where else did all the exponentially many combinations happen? Why do you need many worlds for exponentially many combinations ...

16

Nobody has explained to me how Shor's quantum factorization algorithm works under the transactional interpretation, and I expect this is because the transactional interpretation cannot actually explain this algorithm. If it can't, then chances are the transactional interpretation doesn't actually work. (I have looked at some of the papers that purport to ...

14

I realize I'm late to this discussion. For whatever it's worth, I disagree in the strongest terms with Ron Maimon and Dmytry, when they criticize Yudkowsky for being "too conceptual." As I see it, that's exactly what you should and must do if your goal is to explain QM to an audience of non-physicists! Indeed, most popularizations of QM go off the rails ...

14

Every working interpretation of quantum mechanics, and the Copenhagen interpretation and Consistent Histories in particular, correctly predicts that Shor's algorithm works much like the other algorithms. The question As he often asked, where else did all the exponentially many combinations happen? is loaded because the computational power of a quantum ...

14

The idea of superdeterminism is not really about free will. Free will is a concept that is very hard to define in a logical-positivistic way. If you don't believe me, try to define it! If you can't say exactly what you mean by a notion, in terms of "If I do this and that, what happens?" then it is not clear that the notion is well-defined. There are many ...

13

You say "ridiculous sounding ideas often end up becoming standards science" - but take into account that "ridiculous sounding ideas" much more often, by a large factor, end up becoming no science at all. I agree that "that form of idealogical bullying should never exist" - except that it's not ideological, but just a practical matter of deciding which ...

12

I agree with Luboš that this question has a lot to do with psychology. I think the tic-tac-toe analogy is relevant. There are an infinite number of games that are precisely equivalent to tic-tac-toe, but humans are probably terrible at playing most of these games. Chess is even worse. You can teach a child the rules of chess in a few minutes, but imagine ...

12

Dear Jack, there is no physical phenomenon that could be called the collapse. The collapse of the wave function, as first emphasized by Werner Heisenberg and then many others, is just the event when we learn something about a physical property of a physical system. When we learn that Osama bin Laden is located in a building in Pakistan, his wave function - ...

12

There are observables corresponding to the light going through both slits. You can write down a basis: "it went through slit A + slit B", and "it went through slit A - slit B". Although maybe you can't detect these observables easily with an experiment, they're perfectly good observables, they're orthogonal, and a clever enough experiment should be able to ...

12

Bell's theorems indeed rule out simple theories where hidden variables obey local equations. However, no matter how you reason, it's always at some point where you need another assumption. In its simplest form, it is the assumption that two observers, Bob an Alice, have the "free will" to choose along which axis they will measure the spin of a particle ...

11

The paper does not go into details about what interpretations would be disproved by their results. There's a good reason for this: There are no interpretations that would be disproved by their results. They are disproving a straw-man. Here is the central result proved by the paper, phrased in a less obscure way: "If a system is in the state $|+_Z\rangle$ ...

11

Can someone explain the quantum physics-consciousness connection? There is none. There's a whole lot that can be said about this, but at a basic level, the explanation is that an observation in quantum mechanics is best thought of as an interaction with another particle (technically: a classical system). It doesn't have to involve a conscious observer. ...

11

Generally, when you make a quantum calculation, you have to make some sort of measurement of the qubits at the end of the algorithm where the result you're looking for is a very probable (but not necessarily certain) result. In any interpretation that actually agrees with the basic results of quantum mechanics, these probabilities will still hold and the ...

11

I believe this theorem, although it is simple, is somewhat useful, because it does rule out a certain class of interpretations of quantum mechanics, although none of these are the standard ones you see listed in books. For people who believe the Copenhagen interpretation (or many worlds/many-minds/CCC or even Bohm), the wavefunction is the physical state of ...

11

Except in very elementary examples (single particles), the QM wave function has nothing to do with a wave (apart from the historical origin). For a system consisting of $N>1$ particles, the wave function is a function in configuration space (with 3N variables), not one in 3-space (whose coordinates are positions $x$ with 3 components). This can be read ...

11

Why is the Copenhagen interpretation the most accepted one? I would say the answer is this: it's the oldest more or less "complete" interpretation hence you'll find it in many (all?) early text books, which is basically from where people writing modern text books copy from. the overwhelming majority of physicists doesn't really care about the ...

10

"More generally, can the potential term in the Schrödinger equation be dependent on the wavefunction itself?" The answer is negative: The resulting Schroedinger-like equation would turn out to be non-linear. It would not be associated with a unitary time evolutor (the self-adjoint generator, the Hamiltonian operator, would not be defined) against some ...

10

Newtonian physics is generally a good approximation in a problem as long as any significant differences in the action involved in the problem are much larger than Planck's constant (if not, quantum mechanics will be needed), the speeds involved in the problem are much less than the speed of light (if not, special relativity will be needed), and as long as ...

10

This is essentially a philosophical rather than a physical question. (I don't mean that as a pejorative statement, by the way, just a descriptive one.) There are different philosophical approaches regarding the meaning of probability. Broadly speaking, some people think of probability in a frequentist sense, meaning that probabilities refer to the frequency ...

10

Laplace's determinism is not physically correct over long periods of time. That is, it neglects chaos/"sensitive dependence on initial conditions"/exponential growth of microscopic perturbations already in Newtonian dynamics, which was seriously thought about only in the 20th century. Being true, this also will not be overcome. Stochasticity enters ...

9

I skimmed a majority of the articles, and there are no glaring errors that I could find, but there is an unnecessary verbosity which is best eliminated by reading a terser introduction to the Everett interpretation. The amount of text that is presented is not commensurate with the amount of insight. The philosophical issues are discussed at great length, ...

9

I think at least some readers should have noted by now that many of these arguments, particularly the more pathetic ones, are questions of wording rather than physics. Once you made your model simple enough, you can map anything onto anything. Now this was my starting point: if a system is sufficiently trivial, you can do anything you like. Now how can we ...

9

I'm not sure its more complicated than the fact that the Copenhagen Interpretation is the oldest and most widely taught. Couple this with the fact that many physicists don't spend too much time worrying about things like Quantum Interpretation, and you're left with a population that, when pressed, say they follow the Copenhagen one. This is not to say this ...

8

Yes, the density matrix reconciles all quantum aspects of the probabilities with the classical aspect of the probabilities so that these two "parts" can no longer be separated in any invariant way. As the OP states in the discussion, the same density matrix may be prepared in numerous ways. One of them may look more "classical" – e.g. the method following ...

8

You are right, it is wrong to think that in gauge theory "gauge transformations are just a redundancy". This becomes true only if one abandons locality, ignores all boundary effects, all instanton effects, hence most of what is interesting about gauge theory. Of course forming gauge equivalence classes (say of observables) is something one wants to do every ...

8

The statistical interpretation of quantum mechanics is alive, healthy, and very robust against attacks. The statistical interpretation is precisely that part of the foundations of quantum mechanics where all physicists agree. In the foundations, everything beyond that is controversial. In particular, the Copenhagen interpretation implies the statistical ...

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