2,324 reputation
1122
bio website staff.science.uu.nl/~hooft101
location Utrecht, Netherlands
age
visits member for 1 year, 11 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.


Mar
1
comment How does Bell's theorem rule out the possibility of local hidden variables?
@Gugg: I just don't agree with the Zeilinger quote. Determinism indeed implies that the experimenter's decisions, and questions, are generated by physical forces themselves, so his attitude would dismiss determinism categorically, and I am not ready to go that far. And my bottom line remains to be a simple one: I now have models telling me what might happen, and what they say does not disturb me. Important: I still keep causality intact.
Mar
1
comment How does Bell's theorem rule out the possibility of local hidden variables?
@user7348 : Non-locality would generate serious trouble with special relativity and causality. And I don't need it. That's why I don't introduce it. Non-local correlations is not the same as non-locality in the equations of motion. In QFT, the equations of motion are local but the vacuum-correlations are not. This is because the vacuum is a special solution of the e.o.m.
Feb
27
comment What are the 't Hooft papers about classical models underlying QM?
except that it raises the suspicion that what's really happening in this world might be just these ontological states, and the rest is due to our limited understanding, somewhat contaminated with some sort of religious feeling that God likes to superimpose. So, the answer to @Motl's objection is that it's our equations used to describe observed reality that allow for superpositions, not reality itself. I thought that this statement would be trivial and unimportant, but if not understanding it causes someone to reject the models first-hand, apparently the statement is important after all.
Feb
27
comment What are the 't Hooft papers about classical models underlying QM?
Our theory is now that physicists describing the real world have no way of knowing whether they are describing an ontological event, or just any other solution of their equations (except when it's about cats, where we think we DO know!). The simple reason for this is that Schroedinger's equation is linear. We keep that property throughout. But now I add something new: a true, ontological state should, some way or other, evolve to become again a true, ontological state. That's just a constraint on the set of Schroedinger's equations that we impose. What's wrong with that? Nothing of course,
Feb
27
comment What are the 't Hooft papers about classical models underlying QM?
There's this little point that @Motl failed to grasp about these models: It's the "ontological, true" events described here that are such that any superposition of such events is NOT an ontological event. That's just like cats: the dead cat is ontological, the live one is, but any superposition of the two isn't, or at least, that's the case in our models. Now the superposition of the two cats DOES obey Schroedinger's equation. What I have done is take all "ontological" states of a system and look at the equations they obey. Now superpositions of ontological states also obey the equations.
Nov
8
comment Will Determinism be ever possible?
sigoldberg1 and Seamus's remarks about Laplace apply if the world is described by real numbers. The problem with real numbers is that they each require infinite sets of digits. If you can't control the millionth digit you will have indeterminism. This problem would not arise if we would have theories based only on integers, or even better, bounded integers.
Nov
7
comment Will Determinism be ever possible?
Indeed, I should have stated more clearly that I mean local reality, and that this should be interpreted in a completely classical sense. But, as you say, this "reality" is not about particles with position, momentum, etc. My minority view is that there is a loophole in the arguments usually employed against local reality.
Nov
1
comment Is flying really easier on smaller scales?
Apologies to AlanSE, my comments and questions were to be directed to @miceterminator.
Oct
30
comment Is flying really easier on smaller scales?
But this is what I read on my screen, signed by your name. If you didn't mean $\sqrt{\text{diameter}}$, then what are you trying to say?
Oct
28
comment Is flying really easier on smaller scales?
@AlanSE Please explain why you write $\sqrt{\text{diameter}}$ where I would have expected $\text{diameter}^2$, assuming that strength of muscle tissue is more or less size independent. Of course, the energy produced by a muscle scales with its volume, times frequency.
Sep
12
comment Why do people categorically dismiss some simple quantum models?
In principle, yes, one should be able to construct a Bohmian field theory, but I think it would be inelegant. To my taste, Bohmian mechanics adds far too many "unobservable observables" in the form of pilot waves. This would be awful for field theories, where the pilot wave would be a field functional, or a function of infinitely many particle positions.
Sep
7
comment Why do people categorically dismiss some simple quantum models?
Think of qft as a large set of quantum harmonic oscillators, each oscillating at isolated points in space. Then assume that each oscillator shows interactions only with its direct neighbors. In qft, these are quantum interactions. To most theorists, this looks sufficiently local, no spooky signals.
Sep
7
comment Why do people categorically dismiss some simple quantum models?
@user7348: No, quantum field theory as it stands has causality built in; for that, it is sufficient to demand that all commutators vanish outside the light cone. This guarantees that no signal ever will go faster than light. So qft obeys relativity and has ordinary qm particles in its non-relativistic limit. Everything is fine, no problem with relativity, until you try to understand what the ontology is. You have to remember that spacelike correlations are fine if you can explain them in terms of intial states in the past.
Sep
6
comment Why do people categorically dismiss some simple quantum models?
If you repeat an experiment, or do it many times, you therefore can't modify one observable without affecting an other one, somewhere, somehow. It is difficult to understand how this happens, you have to remember that the vacuum surrounding us is a very complicated entangled state. All this is the real reason why Bell may be violated in the CA. So I ignore Bell, and in that case qm (rather: qft) is local.
Sep
6
comment Why do people categorically dismiss some simple quantum models?
@ user7348: I do not accept Bell's theorem that easily. It is difficult to see exactly what happens, but it is crucial that all CA observables at all times commute. After my unitary mapping, therefore, only observables that are orthogonal to each other are uniquely defined in terms of CA variables. Now, since the mapping is complicated, these observables are different every time you do an experiment. Therefore we can have counterfactual observables that do not commute.
Sep
6
comment Why do people categorically dismiss some simple quantum models?
@ drake: I don't know what theories you talk about. In my theory, obtained from a local mapping from a local CA, the only non-locality is over a small number of lattice sites. Further away, all commutators outside the light cone do vanish.
Sep
6
comment Does any particle ever reach any singularity inside the black hole?
Your theory about leaving the black hole alive is not going to hold up at all, it's wild guesses that would create totally unnecessary conflicts with everything we do know about black holes. Simple thermodynamical arguments tell us that, in the real world, the only thing that can get out of a black hole is Hawking radiation. Astronauts would be suppressed by gigantic Boltzmann exponentials. The classical story would have you come out in some other universe; that's against any thermodynamical law so with hbar, it won't happen, even there.
Sep
6
comment Does any particle ever reach any singularity inside the black hole?
Mass is defined asymptotically, yes, but the mass term always comes in the combination $Mr$, so when $r\rightarrow-\infty$, where the angular part of the metric goes as $r^2$, you have to replace $r$ by $|r|$ to see what happens. So $M$ goes to $-M$. Look up the Penrose diagrams in Hawking and Ellis for example. And look up the Kerr metric (too long for these "comments"). If you do AdS/CFT you are doing quantum, and you won't avoid thermalization. Only the classical theory would seem to allow you to get out, God knows in which universe.
Sep
6
comment Does any particle ever reach any singularity inside the black hole?
You were talking of rotating black holes. If they don't rotate the negative $r$ region is closed off by a singularity. But if the holes rotates, you can get at $r<0$ because the singularity is only at the equator - you need to take a northern or southern route, also to avoid the region with closed timelike curves (at small negative $r$ and large $\sin^2\theta$. I'm talking of the Kerr and Kerr-Newmann metric (necessary for rotation).
Sep
5
comment Does any particle ever reach any singularity inside the black hole?
And then, sorry, but the location of a horizon is a function of the $r$ variable, not $t$, so after passing that second horizon you will enter into the negative $r$ regime. The coordinates $r$ and $t$ do interchange, in the sense that, between the two horizons, $t$ becomes spacelike and $r$ timelike. But does the BH get opposite spin? Please think: how did you define the spin direction, in which coordinates? The statement is empty.