2,299 reputation
1122
bio website staff.science.uu.nl/~hooft101
location Utrecht, Netherlands
age
visits member for 1 year, 8 months
seen Feb 4 at 15:15

Theoretical physicist, Utrecht University.

University Professor. Elementary particle physics, quantum gravity, black holes, quantum mechanics.

Won some prizes (such as the nobel prize 1999), but please don't hold that against me.


Aug
20
answered Does any particle ever reach any singularity inside the black hole?
Aug
20
comment Can superdeterminism resolve contextuality, entanglement and Shor's algorithm in quantum mechanics?
"Superdeterminism" becomes a lot less ridiculous if you simply state the following: In a Bell-like experiment, neither Alice nor Bob can "change their minds" as to what to measure, without having one or more changes of the settings of the experiment in the distant past. If you do change any of these settings, not only the number of mouse droppings might or might not change, but the entire experiment is reset. This already removes Bell's contradiction. No non-local physical law is needed.
Aug
20
comment In 't Hooft beable models, do measurements keep states classical?
And well, before anybody else makes a nasty remark about it: discussing vacuum fluctuations this way requires second quantization. I have not yet been able to do second quantization of my formalism for (super) string theory; other little math obstacles will have to be put out of the way first. Will the second quantized string still act as a CA? I expect yes, but I don't know. I was hoping more experienced string guys would jump in.
Aug
20
comment In 't Hooft beable models, do measurements keep states classical?
Finally: in the CA models of QM, there's something else: the physical vacuum, $|\,\emptyset\,\rangle$, must be a superposition of all (or nearly all?) CA states $|n\rangle$. We can still choose the phase angles there and it is tempting to define these as being 0 (all inner products positive). That will uniquely define most other phases in the QM picture. May come out handy.
Aug
20
comment In 't Hooft beable models, do measurements keep states classical?
Rotations over arbitrary angles and Lorentz transformations are symmetry operators of such a kind. This may be the reason why we, humans, have become blind to the distinction between beables and changeables: we are mistaken in thinking that our ontological world has all these continuous symmetries!
Aug
20
comment In 't Hooft beable models, do measurements keep states classical?
Nothing stops me from using genuine QM amplitudes when defining how the Earth-Mars exchange operator works; it's just semantics, not physics. Same in a CA. All operators that are not diagonal on the CA basis are "physically useless", but they may be mathematically useful when turning to another basis. If you look at the math in my papers, you see an astonishing fact: the evolution operator works the same way on all beables, as it works on interchange operators (changeables)! This makes symmetry transformations between them possible!
Aug
20
comment Is it possible to reproduce the energy spectrum of quantum chaos using classical cellular automata?
Some say it's trivial, some say it's impossible, some say it's hardly impressive, some say it's wrong wrong wrong. For me, it's as if I hear Moslem extremists argue with Jehovah's witnesses. Isn't is about time that we consider the mathematical equations? The simpler the systems we are discussing, the more transparent things become. What we could try to agree about is that there's nothing mystical about QM. If a "universe" is very small, "ontology" doesn't mean so much anymore, but just consider such systems, and ask yourself what they could become when you replace them by more complex worlds.
Aug
20
comment Discreteness and Determinism in Superstrings?
@Ron: No, according to my rules, which are exactly as in QM, perturbations don't have to be small, not $\delta\rho$ but $\psi$ is the wave function. Its sign can be positive or negative, and its absolute square is the probability. Earth-Mars interchange acts on $\psi$, not $\rho$.
Aug
20
comment Why do people categorically dismiss some simple quantum models?
@Scary Monster: The claim is that any CA can be cast in the language of QM, although in most cases the QM models you get will be uninteresting; there will be states, and they will obey Schroedinger equations. Now many CA models are computationally universal, so certainly not integrable, and therefore the asociated QM theory is also expected to be non-trivial. But of course the math is much harder; it's much more instructive to search for cases where you can do (perturbative) calculations.
Aug
20
comment Why do people categorically dismiss some simple quantum models?
@ Motl: In ordinary applications of QM you can ignore this, since the templates are good enough, but not in questions of the interpretation of QM.
Aug
20
comment Why do people categorically dismiss some simple quantum models?
@ Motl: Apparently you axiomatize QM by basing it on "postulates". Clearly you won't understand my theory if you are not prepared to make any amendments, since your postulates are imprecise. You said that "experiment has shown that one can superimpose quantum states". Not true, you can only do this with the templates you are using, but not in the real world. When you consider superposition of two states, you ignore the environment of these two states, which are never the same, hence always orthogonal.
Aug
20
revised Why do people categorically dismiss some simple quantum models?
changes: details of my views on some of these questions, in particular where to put the emphasis, continuously change
Aug
20
awarded  Nice Answer
Aug
19
comment Discreteness and Determinism in Superstrings?
@Ron: But you might consider staying on. Once you agree that the beable basis exists (or might exist), just continue doing QM there. Observe however, that you can do the same with any totally classical system such as the planets obeying Newton's laws. Their evolution law (at integer time steps) is also a permutator. You may pause at the question how the "Earth-Mars exchange operator" evolves with time, and conclude that you can understand the physics of the system without solving the problem, but you might also add that operator to your set of observables. It's the same planets you talk about.
Aug
19
comment Discreteness and Determinism in Superstrings?
@Ron, OK, maybe this is again just a question of semantics. I would say that Feynman diagrams represent a causal QFT (if done correctly), no matter which gauge choice or coordinate choice you use. Same for string theory.
Aug
19
revised Discreteness and Determinism in Superstrings?
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Aug
19
revised Why do people categorically dismiss some simple quantum models?
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Aug
19
revised Why do people categorically dismiss some simple quantum models?
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Aug
19
comment In 't Hooft beable models, do measurements keep states classical?
@Ron: Then let me clarify the statement. Call the states in the CA basis $|n\rangle$, where $n=1, ... N$. Whatever wave function $\psi$ I start with, I can call the "probability" that $n$ is realized $\rho_n=|\langle n|\psi\rangle|^2$. Because the evolution is a permutation, this $\rho$ evolves classically. The phase factors in $\langle n|\psi\rangle$ never play any role; they're unobservable. This is because the evolution operator won't let you generate superimposed states from CA states.
Aug
18
revised Why do people categorically dismiss some simple quantum models?
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