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But that's what I said; that only one detector will click. So how can my answer be wrong? At worst it may be incomplete, but not wrong.Careful said:Wrong answer ! ... Anyway, in practice only one detector will click
But that's what I said; that only one detector will click. So how can my answer be wrong? At worst it may be incomplete, but not wrong.Careful said:Wrong answer ! ... Anyway, in practice only one detector will click
You don't get it, I shoud have phrased it in the following way: if you believe one particle to be present and you ignore this subtle issue, then you might conclude that only one particle will be measured. Now, you should not ignore this issue and think why it could lead to the conclusion that (dependent upon the circumstances) both detectors click !Demystifier said:But that's what I said; that only one detector will click. So how can my answer be wrong? At worst it may be incomplete, but not wrong.
Demystifier said:But that's what I said; that only one detector will click.
Again, ''wrong'' answer ... it depends upon how you construct the detector and what you are going to measure. There is no single reality in a single creation operator! There are good reasons though why in scattering experiments we may ignore these subtleties in practice but because this is a fundamental issue about *reality* we cannot be that blunt. Just make the excercise where you construct two local nondiagonal projection operators, take their product and see what happens in case you let both points approach one and another.arkajad said:Indeed, that is what happens, and that is what can be easily modeled with an appropriate extension of QT. And there is certainly more than one such extension.
Careful said:Just make the excercise where you construct two local nondiagonal projection operators, take their product and see what happens in case you let both points approach one and another.
Phew, that's a bit on the defensive side no? It was actually Demystifier who asked me to give my reasons why I think a Bohm-de Broglie type of reality fails (I simply said that his paper did not convince me to change my mind). He has to understand that if he does that, he declares lots of theoretically possible experiments in QFT as impossible, so he should take this from the good side and go and study precisely those experiments where disagreement in the interpretation may arise.arkajad said:I've made my exercise. Now it is time for you to make yours - and publish it, so that other people can see and take it apart.
arkajad said:You do not observe time, even outside quantum theory
Careful said:He has to understand that if he does that, he declares lots of theoretically possible experiments in QFT as impossible...
rpt said:DevilsAvocado,
My understanding is that "time" is not real.
(Therefore unphysical - sorry about this comment)
Sure, you are entirely correct here, but the point is that demystifier does not seem to have grasped this issue. That is also why I told you many posts ago that I appreciated what you tried to do: by constructing measurement devices, you try to get a grip on this question. However, I do feel that more questions can be asked about nature than just position observations (such as the Bohmians do) and this issue complicates severy once one goes over to QFT. I have never seen actually a realistic construction of ''localized'' position observables within QFT made by ardent proponents of this approach. What Demystifier tells in the abstract is yeh, ''not adressing this core issue'' to put it mildly. Once you turn on gravity, this issue gets even exponentially more complicated than it is in flat spacetime, so I definately feel this is not the right way to go, although I certainly do not have a proof against it.arkajad said:I have studied some of QFT, certainly not all, but somehow I have forgotten which part of QFT tells you unquestionably which experiments are theoretically possible and which are not. Can you be so kind and remind how this can be unquestionably deduced from QFT and from which particular version of it?
Perhaps wrongly but I had an impression that that this a debatable subject that does not belong strictly to QFT but to its rather fuzzy meta-structure that differs from one author to another and that is being constantly checked by experiments.
I agree with what you say except that I would not associate these creation operators to particles per se as I stressed before. They correspond to pure particles for some observables, but for others, they don't.arkajad said:I tend to agree that creations of particles are "events", perhaps the only real and fundamental events that we can have at this point of our knowledge about functioning of the Nature. Yet they are classical events in the sense that either a particle has been created or not. They are 0-1 Boolean beables. As particles can be created at any place at any time - there should be a mechanism of coupling such a 0-1 field (well, there are different kinds of particles, but let us leave it alone for a while) to the field states. I may have one idea about how it can be done in detail. I would like to see how it can be done in a different way than by a non-Hamiltonian, Lindblad-type coupling.
Sure, the state of the universe exists and the creation operators do too. But if you would ask me whether ''particles'' (ie. detector clicks, let's call the hypothetical elementary particles ''atoms'') exist and whether we know the number of them, my answer would be a resounding no. Hypothetically, we have a number operator for the ''atoms'', but that does not translate directly (under all circumstances, in practice it works rather well if the ''atoms'' are sufficiently far away from one and another) into a number of ''particles''. That is my objection against the Bohmian approach (where ''atoms'' and ''particles'' are one and the same thing). I hope demystifier shows up from the vacuum and joins the party :-)DevilsAvocado said:Careful & arkajad, I’m just curios – what’s your opinion: Does anything in QM exist before measurement, "creation", or tracks in a bubble chamber, etc?
Careful said:... I hope demystifier shows up from the vacuum and joins the party :-)
Then we are in the same timezone, I work better at night so I will stay up still for a while.DevilsAvocado said:The position of the vacuum is normally Croatia and the time over there is 01:20 AM, so I guess it’s going to take awhile...
I’m basically at the same longitude and I’m having severe troubles with my eyelids right now... neeed tooo... :zzz:
Thanks for your answers! I get back to you tomorrow, promise!
Only now I understand what were you talking about. Of course within QFT there are detectors that will act like that. But there are also other that will react differently.Careful said:So instead of say, 3 clicks, you will just get one.
It isn't philosophy anymore when you take the Bohmian idea seriously! That's my point (and objection at the same time). Cute picture btw :-)arkajad said:Only now I understand what were you talking about. Of course within QFT there are detectors that will act like that. But there are also other that will react differently.
As to "what exists before" - this question belongs, in my opinion, to the Philosophy section, not to Quantum Physics. But, roughly, I think John Archibald Wheeler may have been right when he speculated that Nature somehow "observes (or 'measures') itself all the time" - this is http://en.wikipedia.org/wiki/Ouroboros" .
Oh, now I see your point. And I completely agree with you. In general, the number of "clicks" does not need to be equal to the number of Bohmian trajectories. But the first paper I mentionedCareful said:... the conclusion that (dependent upon the circumstances) both detectors click !
Hint: construct two local observables which are not diagonal in the particle basis.
But I don't see how you solve it (btw I think the Unruh effect is plain wrong *physically*, so don't talk to me about that ). I mean you cannot really claim -in my opinion- that you have a single real point like particle which gives two detector clicks at spacelike separated points. That kind of reality is even more perverse than saying there is no particle reality at all: so the sane thing to do in my opinion, would be to limit the class of observables and make predictions which distinguish your theory from ordinary QFT.Demystifier said:Oh, now I see your point. And I completely agree with you. In general, the number of "clicks" does not need to be equal to the number of Bohmian trajectories. But the first paper I mentioned
http://xxx.lanl.gov/abs/0904.2287 [Int. J. Mod. Phys. A25:1477-1505, 2010]
discusses that issue as well. Even a short discussion of the Unruh effect is presented. See the discussion around Eqs. (11)-(14) and page 22.
But if the theory is nonlocal (as the Bell theorem shows that ANY hidden variable theory MUST be), then it should not be surprising at all. In any case, your argument against it (that this kind of reality is "too perverse") seems rather subjective to me.Careful said:I mean you cannot really claim -in my opinion- that you have a single real point like particle which gives two detector clicks at spacelike separated points. That kind of reality is even more perverse than saying there is no particle reality at all
Demystifier said:But if the theory is nonlocal (as the Bell theorem shows that ANY hidden variable theory MUST be), then it should not be surprising at all. In any case, your argument against it (that this kind of reality is "too perverse") seems rather subjective to me.
Yes but I was talking about very tiny detectors of a micron size or so- that should be feasible even with current technology I believe. The point however is that it is more a principled debate and I guess it is time for people in your sector of ideas to put their money on the table and see if you win or lose.Demystifier said:One additional comment. As you seem to be aware, it is very difficult to make such an experiment (with two spacelike separated clicks caused by a 1-particle state in a superposition of two spacelike separated wave packets) in practice. In fact, to do this in practice, one would need to prepare an entangled state of two DETECTORS. Since detectors are macroscopic objects, it is practically impossible to really do that in practice. Nevertheless, if one would still do that, it would be a demonstration of quantum nonlocality at the MACROSCOPIC level. (The existing experiments demonstrate quantum nonlocality at the microscopic level only.)
You are right. But as I said, such an experiment requires also an entangled state of two DETECTORS. Therefore, we really must deal with Bell-type nonlocality, i.e., nonlocality of interaction in hidden-variable theories.Careful said:No, it really isn't. You mix up two things here: nonlocality of interaction in hidden variable theories with nolocality of being of point particle events. The very POINT of hidden variable theories is to dispose of the latter (as the Bohmian approach does), so there is a huge difference between unmeasurable nonlocal signalling and *measurable* nonlocality. I would hope you understand that this distinction is the very core of the idea of Bohm-de Broglie.
I don't see how could I win or lose. Both standard theory and Bohmian mechanics make the same measurable predictions, even in this case. So if the experiment would show that Bohmian mechanics is wrong, then it would also show that standard QM (including QFT) is wrong as well. It would be very interesting, but Bohmian and standard theory would lose together.Careful said:Yes but I was talking about very tiny detectors of a micron size or so- that should be feasible even with current technology I believe. The point however is that it is more a principled debate and I guess it is time for people in your sector of ideas to put their money on the table and see if you win or lose.
Yeh so what, that was never a dispute, was it?Demystifier said:You are right. But as I said, such an experiment requires also an entangled state of two DETECTORS. Therefore, we really must deal with Bell-type nonlocality, i.e., nonlocality of interaction in hidden-variable theories.
But it is not a paradox, you see, it just shows that the ontology is wrong. I have no doubt that you can try to be clever and talk your way out of it, but where lies the point that you have to admit that you are becoming *unreasonable*? To use your own words: perhaps you should not think like an intellectual here and try to get out of the sh*t, but more act like a genius and avoid the brown liquid all together (my translation ).Demystifier said:By the way, your interesting example (suggesting that the Bohmian theory is "too perverse") is quite similar to an example which is already known: the "surreal" particle trajectories. In the case of "surreal" trajectories, the Bohmian trajectory is completely different from the measured trace which is supposed to represent the "actual" particle trajectory. Yet, Bohmian mechanics easily resolves this "paradox" through quantum nonlocality.
You see, that is where I disagree, because what you call a paradox, I call an ontological inconsistency ! And it seems to me that such experiments as alluded to above should be forbidden in your theory.Demystifier said:I don't see how could I win or lose. Both standard theory and Bohmian mechanics make the same measurable predictions, even in this case. So if the experiment would show that Bohmian mechanics is wrong, then it would also show that standard QM (including QFT) is wrong as well. It would be very interesting, but Bohmian and standard theory would lose together.
I don't think that this makes the ontology wrong. Counterintuitive yes, but not necessarily wrong.Careful said:But it is not a paradox, you see, it just shows that the ontology is wrong. I have no doubt that you can try to be clever and talk your way out of it, but where lies the point that you have to admit that you are becoming *unreasonable*? To use your own words: perhaps you should not think like an intellectual here and try to get out of the sh*t, but more act like a genius and avoid the brown liquid all together (my translation ).
Ok, I am not going to discuss about whether drinking pure alcohol is bad for ones health (sorry I could not resist) . But you know, we have already such theory with a realist ontology, and that's the one I explained to you: QFT. You may dislike the ''reality'' of creation operators, but it is not leading to such ''paradoxes'' as you face. That's what I mean, perhaps you are trying to solve the right problem (measurement) in the wrong way. Actually, in my view, you did not solve the issue of awareness yet in the Bohmian approach: suppose all we have are position measurements, how can one speak then about something like music, painting, love and all that. That may sound philosophical to you, but it really isn't.Demystifier said:I don't think that this makes the ontology wrong. Counterintuitive yes, but not necessarily wrong.
A better negative characterization of such an ontology could be "unreasonable", as you suggested.
I disagree. You cannot say that standard QFT predicts two clicks unless you specify HOW EXACTLY you could measure them. And if you try to specify it, you will find out that you need to know something about detectors on the QUANTUM level. Try it, it could be very illuminating!Careful said:I mean, you may try to be clever now and look for a different reason why the second detector clicks or so, but the point is that this is a well defined prediction even within FREE QFT and I don't need to consider QUANTUM detectors here. So, I don't have to even talk about entanglement between detectors. All I need are just two different local particle bases corresponding to commuting operators whose product is nonvanishing (which is common stuff in free QFT).
Are you sure that you really HAVE such a realist ontology? Let me test you: Do creation operators exist before you perform a measurement? If not, then what DOES exist before you perform a measurement?Careful said:But you know, we have already such theory with a realist ontology, and that's the one I explained to you: QFT. You may dislike the ''reality'' of creation operators, but it is not leading to such ''paradoxes'' as you face.
I agree with that (if you followed my discussion with arkadiusz) but I just wanted to point out that QFT does not *require* such view.Demystifier said:I disagree. You cannot say that standard QFT predicts two clicks unless you specify HOW EXACTLY you could measure them. And if you try to specify it, you will find out that you need to know something about detectors on the QUANTUM level. Try it, it could be very illuminating!
Sure creation operators do exist but in a timeless and space-less way. Point is, that there is no ontology in space-time prior to measurement.Demystifier said:Are you sure that you really HAVE such a realist ontology? Let me test you: Do creation operators exist before you perform a measurement? If not, then what DOES exist before you perform a measurement?
Fine. And then what exactly happens during the measurement? And what exactly IS a measurement? And can there be a measurement without a conscious observer?Careful said:Point is, that there is no ontology in space-time prior to measurement.
No, a theory of consciousness is a mandatory extension of the theory also in your line of thought actually.Demystifier said:Fine. And then what exactly happens during the measurement? And what exactly IS a measurement? And can there be a measurement without a conscious observer?