This forum gives conflicting info on the HUP

[Ken G]

Have you seen Lee Smolin's latest book Time Reborn? Our choice, according to Smolin, is epistemic/statistical QM or Aristotle was right!

I find Smolin to be very thought-provoking, but I wish people would stop portraying science as a kind of "guessing game" about the "truth" such that you could either be "wrong" or "right." That's just not what science has ever been. The fact is Aristotle was right, Galileo was right, and Newton was right-- they were right in the only things they were ever saying, which was "here is a constructive way of looking at the situation that advances the goals of science." And they were right, it was. None of them ever said "here's the absolute truth that will stand for all ages", because no one who ever says that is going to be right-- if that is our standard of rightness, then none of them are it.

 

[DevilsAvocado]

I can't say I am following that logic, but I'm pretty confident that Bohmians are not such fools that they can't see their interpretation can be refuted by well known EPR-type observations!

I can only pass on the well known fact that local hidden variables are as dead as the Norwegian Blue Parrot – you just can't "take all the outcomes of the measurements you need to agree with" in advance, since this is proven impossible beyond all reasonable doubt and mathematical possibilities.

 

[DevilsAvocado]

I find Smolin to be very thought-provoking, but I wish people would stop portraying science as a kind of "guessing game" about the "truth" such that you could either be "wrong" or "right." That's just not what science has ever been. The fact is Aristotle was right, Galileo was right, and Newton was right-- they were right in the only things they were ever saying, which was "here is a constructive way of looking at the situation that advances the goals of science." And they were right, it was. None of them ever said "here's the absolute truth that will stand for all ages", because no one who ever says that is going to be right-- if that is our standard of rightness, then none of them are it.

Well, we all have our different preferences. Personally, I find it provoking to reduce the work of a faculty member at the Perimeter Institute for Theoretical Physics, an adjunct professor of physics at the University of Waterloo and a member of the graduate faculty of the philosophy department at the University of Toronto, awarded the Majorana Prize (2007) and the Klopsteg Memorial Award (2009) – as a "guessing game".

Maybe you read too much into the phrases right/wrong. Lee Smolin is of course intelligent enough to know the real premises of science, and the same thing naturally goes for Einstein:

"Newton, forgive me, you found the only way which, in your age, was just about possible for a man of highest thought and creative power." -- Albert Einstein​

 

[Ken G]

I can only pass on the well known fact that local hidden variables are as dead as the Norwegian Blue Parrot – you just can't "take all the outcomes of the measurements you need to agree with" in advance, since this is proven impossible beyond all reasonable doubt and mathematical possibilities.

Do you realize that by slipping in the word "local" in your sentence, you have disqualified your remarks from the perspective of Bohmian mechanics, which by their pilot-wave approach, reflect inherently non-local hidden variables?

 

[Ken G]

Well, we all have our different preferences. Personally, I find it provoking to reduce the work of a faculty member at the Perimeter Institute for Theoretical Physics, an adjunct professor of physics at the University of Waterloo and a member of the graduate faculty of the philosophy department at the University of Toronto, awarded the Majorana Prize (2007) and the Klopsteg Memorial Award (2009) – as a "guessing game".

You misunderstand me. I was not saying Smolin was playing a guessing game, I'm saying that Smolin, by saying "either Aristotle was right and Galileo/Newton/Einstein were wrong, or the other way around", is in effect framing what those great minds were doing as playing a guessing game, a kind of intellectual musical chairs: who will be in the chair of "rightness" when the music stops and all truth is revealed? But science never works like that, and framing it that way feeds misconceptions about what science really is. Whatever you think about his intellect, and his understanding of what science is, describing the situation as "who was right, who was wrong" is a faulty way to frame scientific progress. It seems a harmless flaw in his exposition, but actually, I think it is one of the few aspects of what he is saying that people can really understand, and glom onto. So it is important to get that part right, maybe even more important than a relativistic treatment of the Bohmian interpretation.

 

[DevilsAvocado]

Do you realize that by slipping in the word "local" in your sentence, you have disqualified your remarks from the perspective of Bohmian mechanics, which by their pilot-wave approach, reflect inherently non-local hidden variables?

Do you realize that the only logical interpretation of "take all the outcomes of the measurements you need" is local?

If you meant something else, why not explain it, instead of current unfruitful dispute?

 

[DevilsAvocado]

You misunderstand me. I was not saying Smolin was playing a guessing game, I'm saying that Smolin, by saying "either Aristotle was right and Galileo/Newton/Einstein were wrong, or the other way around", is in effect framing what those great minds were doing as playing a guessing game, a kind of intellectual musical chairs: who will be in the chair of "rightness" when the music stops and all truth is revealed?

This is your interpretation. I interpret Smolin as just basically saying that we have to choose between – based on empirical evidence and current knowledge – a world where a preferred notion of rest is possible, or there is no deeper level of description than statistical quantum mechanics.

Note that this is Smolin's 'hypothesis' on current knowledge. He is of course smart enough to realize that this could be changed, tomorrow, in case of some bright genius presenting a new idea.

I don't think Smolin would ever talk about 'metaphysical eternal truths'... everything in his book points towards the opposite direction...

Read it before judgment!

 

[Ken G]

Do you realize that the only logical interpretation of "take all the outcomes of the measurements you need" is local?

The measurements are local of course, but the hidden variables that Bohmian mechanics uses to account for them, and maintain classical properties, are nonlocal.

 

[Ken G]

This is your interpretation. I interpret Smolin as just basically saying that we have to choose between – based on empirical evidence and current knowledge – a world where a preferred notion of rest is possible, or there is no deeper level of description than statistical quantum mechanics.

Well you can choose to interpret those words he said that way, but others might not. The point is, had he said what you said, I'd have no objection, but he said what he said, and I voiced my objection. Clearly you have noticed the difference, as you needed to change his words when you inserted your interpretations. The issue here is the difference between us making "choices," which of course we must do to do science, versus scientists being "right" or "wrong." The "rightness" of science is advancing the progress of science, period, and they all did that. Was Ptolemy right or wrong? Some of both, of course, and the partition will always be a moving target. Was Copernicus right or wrong? Some of both, of course, and again that partition will always be a moving target. There's not a scorecard, there's the progress of science.

Note that this is Smolin's 'hypothesis' on current knowledge. He is of course smart enough to realize that this could be changed, tomorrow, in case of some bright genius presenting a new idea.

I am well aware that he probably knows that, the issue is what he said, and how people who do not know that can hear what he said. Ergo my point.

I don't think Smolin would ever talk about 'metaphysical eternal truths'... everything in his book points towards the opposite direction...

That doesn't surprise me, he is a deep thinker. All the same, his words were unfortunately chosen, and nothing you are saying speaks to that, indeed what you are saying here essentially support that.

Read it before judgment!

Who said I was judging Smolin? I spoke about a particular set of his words, and judged them. I did read them first, and then I pointed out the unfortunate aspect of them. What Smolin says somewhere else is of zero relevance to my point.

 

[DevilsAvocado]

Seriously Ken, this is on the brink to become hilarious...

You could at least have checked the provided Wikipedia link, before going baloney over something that obviously is completely wrong:

[my bolding]

Smolin argues for what he calls a revolutionary view that time is real, in contrast to existing scientific orthodoxy which holds that time is merely a "stubbornly persistent illusion" (Einstein's words).[1] Smolin reasons that physicists have improperly rejected the reality of time because they confuse their mathematical models—which are timeless but deal in abstractions that do not exist—with reality.[1] Smolin hypothesizes instead that the very laws of physics are not fixed, but that they actually evolve over time.

Satisfied?

 

[atyy]

Ah, now I think I see the source of confusion. One should distinguish two things:
1) SINGLE measurement, from which no information about probability distribution can be extracted (except that the obtained value has probability larger than one).
2) Statistical ENSEMBLE of similar measurements, from which the probability distribution can be extraced.

I was talking about the former, while it seems that you are talking about the latter. If I simultaneously measure position and momentum ONLY ONCE, I cannot extract any information about the joint probability distribution.

But then again, even in classical mechanics I can repeat many times the simultaneous measurement of position and momentum. From such a measurement I CAN extract the joint distribution. Moreover, by using the theory called classical STATISTICAL mechanics I can even predict or explain the joint distribution I measured. So your claim that "classical definitions for joint distribution don't exist" is certainly wrong.

My claim is correct, because it was for quantum mechanics.

What I don't understand is: what do mean by an "accurate" measurement? To define an accurate measurement in some sense, one needs a "correct" answer. In classical mechanics, one way to define a "correct" answer is that one correctly infers the value of the property that the particle had at a certain time. However, for joint measurements this definition of "correct" can't carry over to quantum mechanics, because the joint distribution of position and momentum doesn't exist in general.

 

[Ken G]

Satisfied?

I'm sorry, I don't see why you think that quote has the slightest relevance to anything that was said in our exchange. I know quite a bit about Smolin's ideas, you have not told me anything I didn't already know. I was pointing out a problem in his rhetorical device of saying that modern physics can determine whether it was Aristotle or Einstein that was right or wrong in regard to the relativity of space. Again, I can only tell you, that's just not how science works, and it is harmful to science to frame it that way. What actually happens is, scientists find insights that advance science, no one is ever right or wrong in any absolute sense. Truth in science is highly provisional, that is perhaps the main beauty of science-- it is constantly questioning and seeking knowledge. Science is not about what you know, it is about what you don't know. It seems my perspective is lost on you, but it doesn't matter, I was wrong to bring it up at all because it's not relevant to the thread and should be dropped anyway.

 

[atyy]

Bumping this just in case Demystifier did not see my response in #101.

 

[Ken G]

If Demystifier doesn't take up that cause, I would offer that measurements in science are always axiomatic. There is nothing more basic than a measurement in empirical science, nothing that we use to check that we are doing measurements "accurately"-- other than a body of other measurements we already regard as accurate by experience. We do check precision, and if ten people get ten badly different answers, we label that measurement "imprecise" and drop it from our set of approved techniques. But it is problematic to define a measurement as accurate by saying it agrees with some theory (other than the most basic theories that we already regard as axiomatic).

If quantum mechanics were ever regarded as axiomatic, then the definition of an accurate measurement as one that mimics a projection would be appropriate. I believe that Demystifier's core stance is that all axiomatic approaches to measurement must be classical, so you will always need a better definition of a measurement than that the result agrees with quantum mechanics theory. After all, if you are looking for chinks in the armor of QM as it is currently postulated, you certainly can't have someone scratching their head and saying "what did I do wrong in my measurement, my answer did not come out like QM."

But there is a case where the Ozawa definition could be appropriate, which is when we are not regarding measurements as a test of QM, but rather, as a proxy for understanding what QM is predicting, a lens on the theory if you will. In the form of a gedankenexperiment, which is used to describe a theory not reality, it is fine to use Ozawa's approach, to see in effect what QM thinks a measurement is, rather than what we have axiomatized it to be.

 

[Demystifier]

What I don't understand is: what do mean by an "accurate" measurement?

To help me answer that question, can you quote where exactly did I say that a measurement is "accurate"?

 

[atyy]

To help me answer that question, can you quote where exactly did I say that a measurement is "accurate"?

It's implicit in the OP. If it's not there, then one can trivially measure all values simultaneously.

 

[Demystifier]

My claim that one can simultaneously measure both position and momentum is also compatible with a modern view of quantum measurements based on POVM's (positive operator valued measures). The POVM measurements generalize the more traditional projective measurements.

There is no simultaneous eigenstate of both position and momentum, implying that there is no projector operator to a definite value of both position and momentum. Yet, coherent states can be used to construct a POVM corresponding to a generalized simultaneous measurement of both position and momentum.

For a recent brief pedagogic introduction to modern theory of quantum measurements see also
http://lanl.arxiv.org/abs/1406.5535
The author is the same guy who lead the team which first performed a weak measurement of Bohmian trajectories:
https://www.physicsforums.com/blog.php?b=3077

For an authoritative theoretical treatment see the book
A. Peres, Quantum Theory: Concepts and Methods,
especially Secs. 12-9 and 9-5.