The heisenburg uncertainty principle

[tom.stoer]

@ThomasT:

I would like to empasize what I said above, namely that QM makes NEGATIVE statements about reality in the sense that QM tells us something about the ABSENCE of certain QUALITIES (I call it qualities just to indicate that it's not just an attribute with a value) or in the sense that QM tells us that something will NOT work / will NOT happen / will NOT be observed IN PRINCIPLE.

This "in principle" is due to certain "limitations or absence qualities of nature", not because of limitation in the measuring process which is not addressed at all, neither in terms of the description of the devices, not in terms of using a theory of measurement in the QM principles.

In that sense these statements are not speculations "about a deeper reality beyond that"; they are theorems about this deeper reality - unfortunately NEGATIVE or NO-GO theorems.

It is a philosophical qestion if you accept a negative statement regarding "X not having quality A". I would say that it's reasonable to assume that the moon is there even if nobody is looking at it. If you accept this statement then you agree to something called realism (even if there is a variety of different "realisms" in philosophy). As soon as you have accepted "reality" it makes sense to ask about qualities of reality. Now quantum mechanics tells you something about these qualia in the negative sense; it says that "local realism" is absent in "reality" (Bell), it says that classical probability theory does not apply to "reality" (Kochen-Specker). Even my very first statement "that the moon is there even if nobody is looking at it" is below or beyond the phenomenological level.

You may call realism speculative, but if you deny it you have to explain where physical laws reside if not in this "reality". If you limit physics to its purely phenomenological domain you have no chance to find a home for your physical laws except for god or solipsism.

 

[tom.stoer]

You think that negative statements are crucial part of QM.
But I don't agree with you. Negative statements have very limited value.
Real test for a theory is verification of it's positive predictions.

Yes, I think that negative statements are crucial. They are crucial if one wants to explain what nature really IS. Unfortunately one has to accept that they are negative in the sense that in most cases they tell you what nature not is - what a pitty - but this is essentially what survives from realism.

But of course I agree with you that positive predictions and their verification have much more value in practice! QM has not been widely accepted because the HUT tells you what can't be achieve in principle, but because thousands of experiments tell you what can be achieved in practice.

But note that Popper rephrased "verification" into something like "failure of falsification". He said that a failed attempts of falsification do support a theory. This is exactly what Bell and the experimentalists did: explain an approach how to falsify QM and gather support for QM from these failed attempt.

And it is not clear for me how negative statements can be regarded as ontological.

I hope this became clear in the meantime.

 

[zonde]

Yes, I think that negative statements are crucial. They are crucial if one wants to explain what nature really IS. Unfortunately one has to accept that they are negative in the sense that in most cases they tell you what nature not is - what a pitty - but this is essentially what survives from realism.

I like the way it is said in wikipedia:
"Like all theorems applied in physics, a no-go theorem is only as good as its assumptions, including hidden implicit assumptions."
But what is our strategy in case of no-go theorems and in case of ordinary theorems making positive statements.
Well if we want to increase our predictive abilities we have to stick to assumptions of ordinary theorem.
However it is the other way around with no-go theorems. If we want to increase our predictive abilities we have to relax some assumptions of no-go theorem and look if it helps. In a sense we have to spread our research.

But note that Popper rephrased "verification" into something like "failure of falsification". He said that a failed attempts of falsification do support a theory. This is exactly what Bell and the experimentalists did: explain an approach how to falsify QM and gather support for QM from these failed attempt.

The problem with experimental verification is that any real experiment invoke number of additional assumptions to those in theory.
This is not a major problem for theory making positive statements. But it can be a real nightmare in case of no-go theorem.

In case of Bell theorem it seems quite clear that it rules out non-contextual hidden variables. This is where I see the promising direction where to go (in context of what I said about relaxing assumptions) - contextual hidden variables.
Therefore I cling to phase measurement as it is contextual and is not covered by Bell theorem.

 

[DrChinese]

And, by the way, I think you should pay attention to, and respect, Zonde's posts. He really is much more knowledgeable than both of us. And yes, I know, you're wondering how I know these things (like, eg., that billschnieder is a working scientist) -- well I just know these things and I'm not going to tell you how I know these things.

You ARE funni. That's exactly what I was thinking, and I am waiting in suspense for the answers...

 

[arkajad]

The mathematical formalism of quantum mechanics does not tell us that we can not measure precisely and simultaneously position and momentum. Quantum mechanics is simply not able to tell what will happen in such a case. Its mathematical formalism is inadequate for this. There are however extensions of the standard formalism that are more powerful and can describe processes that the standard textbook QM can not describe.

 

[ThomasT]

You ARE funni. That's exactly what I was thinking, and I am waiting in suspense for the answers...

Pretend I didn't say it. In fact, I'm going to delete the post.

 

[DevilsAvocado]

Hidden variable theories which try to explain the apparent randomness of quantum mechanics as a deterministic theory – is not dead, it just https://www.physicsforums.com/showpost.php?p=2860862&postcount=1493"...

 

[arkajad]

What's wrong with some randomness? I do not understand why some people can't admit that they do not have the same computing and descriptive power as the Universe. Is it because they are so proud of themselves? Who they think they are?

 

[DevilsAvocado]

What's wrong with some randomness?

Agree.

 

[DevilsAvocado]

And, by the way, I think you should pay attention to, and respect, Zonde's posts. He really is much more knowledgeable than both of us. And yes, I know, you're wondering how I know these things (like, eg., that billschnieder is a working scientist) -- well I just know these things and I'm not going to tell you how I know these things.

You ARE funni. That's exactly what I was thinking, and I am waiting in suspense for the answers...

Muhahaha! Yeah, ThomasT is a REAL entertainer!

Pretend I didn't say it. In fact, I'm going to delete the post.

What?? Why!?

I had some very interesting comments on that post...

Well, I know, you're wondering how I know these things, well I just know these things, and I'm not going to tell you how I know these things, but I know these things.

Let’s see now... first you said:

In fact, the quantum theory is ONLY about measurements, no more and no less. On what other basis would you develop a statistical probabilistic theory?

And then you retracted your assertion:

Ok, at this time I think I should retract my assertion that "the quantum theory is ONLY about measurements, no more and no less" (apologies to Heisenberg).

And then you changed your mind AGAIN...??

the quantum theory is about measurements, ie., the behavior of instruments ... this is what the qm matrix mechanics of Heisenberg is based on

I don’t know if I should answer here? Or start a new thread in the Philosophy forum called Gobbledygook...??

Naah, let’s have all the fun here instead!

Of course Heisenberg was only an experimental physicist. Instruments were all he cared about! In fact, some say there’s even physical proof:

– Don’t be sad Werner. We will get all your stolen gear back!​

And then you said something about that it makes more sense if nature is local than nonlocal, and I naturally agree. The only problem with that; is that what we have to choose between is locality or reality – not local or nonlocal.

Finally, Hawking supports MWI, and that’s also a different thing.


P.S. Thanks for the laughs TT! You make PF so much funnier!

Ohh, ahh, of course the great Nobel laureate Werner Heisenberg was a theoretical physicist, anything else is gobbledygook!

 

[tom.stoer]

I don't know if it makes sense to repeat this over and over again, so I hesitate to participate in this discussion ...

... anyway, the whole QM formalism does not care about the measurement process, does not explain this process, is not based on measurement and measurement process and does not reflect any limitations regarding measurement. QM says something regarding observables but does not explain how to do this in practice; it does not explain how to construct a "complete" set of such operators, it does not explain which set one one should use etc.

QM is not very precise about the measurement process itself; the statement that observables have a definite value after measurement which collapses the the state to an eigenstate is questioned today. Both orthodox / Copenhagen and MWI interpretation are interpretations only; they are not used as construction principles, but sit on top of the formalism as interpretations / speculations.

I know that the term "measurement" is used over and over again, but unfortunately it has never been explained. One can savely say that QM is about "accessable information on quantum systems" but one should be aware of the fact that measurement itself is still a mystery in QM.

 

[arkajad]

One can savely say that QM is about "accessable information on quantum systems" but one should be aware of the fact that measurement itself is still a mystery in QM.

Well, that depends on which QM you have in mind. There are many of them and they differ one from the other by the way they treat "measurements" and, more generally, "events".

 

[tom.stoer]

Well, that depends on which QM you have in mind. There are many of them and they differ one from the other by the way they treat "measurements" and, more generally, "events".

Can you elaborate on them? I know different interpretations, not formalisms. Can you explain what you by "treat"? Is it more than "interprete"?

I am not talking about interpretation which is still vague but about the formal basis of QM which is rather unique.

 

[arkajad]

Can you elaborate on them? I know different interpretations, not formalisms. Can you explain what you by "treat"? Is it more than "interprete"?

It is. But there is also an interpretation involved.

Quoting from J. A. Wheeler ("Geons, Black Holes & Quantum Foam", p. 343):

"I wanted to emphasize in this talk that the essential feature of act of 'measurement' is amplification from the quantum thing observed to the classical thing doing the observing, which need have nothing to do with human intervention or human consciousness"

Thus part of the interpretation is to accept that there are "quantum things" (e.g. electrons) and there are "classical things" (e.g. tables and chairs). Not everybody is ready to accept it. Are YOU ready. If you are, the next thing is to look for a formalism. If you are not - no formalism will help you.

 

[tom.stoer]

I am definately not ready to accept that nature distinguishes between quantum things and classical things!

Due to new approaches like decoherence it seems likely that the reason why only classical states (= vanishing off-diagonal elements of density matrices w.r.t. a basis defined by the measuring device) are observed becomes clear even quantitatively. That means that the time scale at which decoherence acts seems plausible or at least not incompatible with our observation.

Therefore I doubt that there are classical things and quantum things and that they are fundamentally different. They are fundamentally the same, and decoherence gives us a tool to understand the emergence of A classical world

[It is not a tool to understand why exactly THIS classical world emerges; in case of Schrödinger's cat decoherence explains to some extend why the cat we observe is either dead or alive - not some quantum superposition - but decoherence does not explain why a specific cat is dead instead of alive; it eliminates quantum superposition of macroscopic objetcs, but not randomness].

 

[arkajad]

Due to new approaches like decoherence it seems likely that the reason why only classical states (= vanishing off-diagonal elements of density matrices w.r.t. a basis defined by the measuring device) are observed becomes clear even quantitatively.

You are using the term "our observation". Is it a classical thing or a quantum thing. Can quantum things meaningfully "talk" and "write"? And interpret itself? And create quantum mechanics?

You wrote this comment. Is it a classical thing or a quantum thing? If it is a quantum thing - what kind of a thing? An operator? A state vector? Is Hilbert space a quantum thing or a classical thing? Or, say, "time"?

 

[tom.stoer]

I have problems with these questions. An "observation" is not a thing, neither classical nor quantum. I think this is a category mistake.

As I am consisting of quantum objects on a fundamental level I would say that I am a "huge quantum thing" that is able to talk and write.

I am definately neither an operator nor a state vector. This is the same as with "red" and "750 nm". Light with 750 nm appears as red, but the sentence "red is identical with 750 nm" is meaningless (again a category mistake).

 

[arkajad]

If you are not operator and not a state vector, and because I believe you wrote it only once - how do you describe your act of writing within your beloved "decoherence formalism"?
About decoherence formalism: is the separation between the "system" and "environment" a classical thing or a quantum thing? Who is doing this separation? Who is putting the borders or moving them ad hoc as it pleases the mover?

"I think this is a category mistake. "

We are not trying to use some formal theory. We are discussing reality and its description. These are not "mistakes". These are ncessary questions that need to be asked. Of course you can refuse to accept them. Up to you. You will have to pay for it by not getting answers. You will know less about reality.

 

[tom.stoer]

In the decoherence framework one describes the time evolution of mixed states. The Usually one decomposes the Hilbert space into "quantum object", "pointer of the measurement device" and "environment". Then decoherence explains why the ponter appears classical and where the quantum superpositions go to (namely into the environement).

 

[tom.stoer]

bt.w.: I don't think your questions are unreasonable, but they do not have anything to do with the QM formalism but with interpretation and philosophy. They should not be discussed in a thread "The heisenburg uncertainty principle".