Did the Canadians Nuke the Uncertainty Principle?

[studiot]

http://prl.aps.org/abstract/PRL/v109/i10/e100404

[ajb]

No, their work tells us that Heisenberg's original argument is wrong. I have posted a little about this on my BLOG.

 

The uncertainty principle is really rooted in the fact that the operators associated with classical observables do not (necessarily) commute.

 

Heisenberg argued that the uncertainty principles is due to the act of observing which "upsets" the system. This may not be a correct way of understanding the principle, which is what they showed.

[Phi for All]

http://prl.aps.org/a...109/i10/e100404

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Moderator Note

In the future, please give more direction for discussion than a title and a link. Since we're here to hear your perspective, just a few words on that would be appreciated greatly. Thanks!

[Diffeomorphism]

Negative. In Heisenberg's time, there was no technology to more accurately measure things in the quantum world. There will still always be an uncertainty with any measurement macro or micro in scale. For example, electrons have a 90% probability of being located in a certain energy level around the atom. There will still be a level of uncertainty after disturbing or exciting the electron with a photon beam. Another example on a macro scale, I can put a penny on a scale an each time the scale will read differently for many reasons. There are no exact measurements. There will always be a deviation even though today we may be able to measure it more accurately.

[studiot]

There are no exact measurements.

 

 

 

If I measure the charge on an electron in 'electron' or (proton) charge units surely I can measure with absolute certainty?

 

 

Furthermore I have always understood the Uncertainty Principle to apply to ideal thought experiments as well as real ones.

Edited September 9, 2012 by studiot

[swansont]

Negative. In Heisenberg's time, there was no technology to more accurately measure things in the quantum world. There will still always be an uncertainty with any measurement macro or micro in scale. For example, electrons have a 90% probability of being located in a certain energy level around the atom. There will still be a level of uncertainty after disturbing or exciting the electron with a photon beam. Another example on a macro scale, I can put a penny on a scale an each time the scale will read differently for many reasons. There are no exact measurements. There will always be a deviation even though today we may be able to measure it more accurately.

The HUP is not about measurement uncertainty or accuracy, it's about the inherent uncertainty in the system.

 

If I measure the charge on an electron in 'electron' or (proton) charge units surely I can measure with absolute certainty?

 

 

Furthermore I have always understood the Uncertainty Principle to apply to ideal thought experiments as well as real ones.

The value of the fundamental charge has uncertainty. Since it's quantized, you can distinguish the number of charges.

[studiot]

The value of the fundamental charge has uncertainty

 

 

Can you explain exactly what you mean?

 

 

I thought the value of the charge on one electron = the value of charge on one electron exactly, (if I measure charge in electron charges, not coulombs)

Edited September 9, 2012 by studiot

[swansont]

Can you explain exactly what you mean?

 

 

I thought the value of the charge on one electron = the value of charge on one electron exactly, (if I measure charge in electron charges, not coulombs)

Measuring in fundamental charges is a tautology and ducks the issue. That's similar to defining a value and have it be exact (e.g. speed of light), but there would always be some other measurement that depends on it.

[studiot]

Measuring in fundamental charges is a tautology and ducks the issue. That's similar to defining a value and have it be exact (e.g. speed of light), but there would always be some other measurement that depends on it.

 

Surely you can see that charge is the odd man out?

 

It is the one physical quantity that we can only measure integral units. So far as we can tell (and that includes Plank units) there is no theoretical barrier to indefinite subdivision of the others and so can be measured in real valued units.

 

We can also see this at the macroscopic scale, for instance the number of pennies in my pocket. I can achieve an exact measurement of this quantity, any time I like.

 

Please bear in mind this was in response to an all embracing statement (not yours) that there are no exact measurements - a statement which I hold to be too strong to be accurate.

[swansont]

Angular momentum is quantized as well. But that doesn't mean you can determine Planck's constant to arbitrary accuracy. Knowing the number of pennies in your pocket doesn't mean you know how much copper and zinc you have. You've replaced measuring with counting and that merely masks the issue.

[studiot]

and ducks the issue.

 

You've replaced measuring with counting and that merely masks the issue.

 

With respect, you are the one ducking the issue not I.

 

Radioactivity measuring decices used to be called counters for good reason.

 

Counts and counts per second or counts per area or volume have long been established as perfectly respectable units to measure in many areas of science, besides radioactivity.

 

However there is the possibility of uncertainty in some forms of counting.

 

For example yesterday I looked in the field and said to my friend, the statistician, "I see four horses"

 

She replied "How many? I see two foals, a stallion and one pregnant mare"

 

go well

Edited September 10, 2012 by studiot

[swansont]

I'm pointing out that there is a fundamental difference between counting and measurement, the way measurement was used. However, even your use of radioactivity counters doesn't work. You won't get the same thing if you run the experiment again; the statistical uncertainty in such a measurement varies as the square root of N. You get an exact number, but it's not an exact measurement.

[studiot]

You won't get the same thing if you run the experiment again; the statistical uncertainty in such a measurement varies as the square root of N. You get an exact number, but it's not an exact measurement.

 

This is just plain wrong.

 

There is no other way to describe it.

 

The count is an exact measurement. Period.

 

It is, however true that you are very unlikely to achieve the same count in a repeat of the experiment.

 

This is not due to the inability of the observer to measure correctly and with absolute accuracy.

It is due to the inherently variable nature of the process involved.

 

As to the ridiculous comment about how much copper (how many grams or whatever) was in my pocket?

 

If asked in an examination how many pennies I had in my pocket and I replied I have 35 grams how many marks would I be awarded.

 

Answer : an exact number - zero. Because I didn't answer the question asked.

 

All this, is however, getting further off topic.

 

If the BBC report claiming that the uncertainty principle had been disproved, which I investigated and posted the best information I could find, is true then it is at least as important as the recent claim of FTL neutrinos.

 

Since I do not have much access to North American data I had hoped that there would be those here who do and have sufficient interest.

 

However so far all that has happened is that I have been attacked by two moderators.

[ajb]

If the BBC report claiming that the uncertainty principle had been disproved, which I investigated and posted the best information I could find, is true then it is at least as important as the recent claim of FTL neutrinos.

 

 

The claim is not that the uncertainty principle is incorrect, rather the claim is that Heisenberg's original argument based on the idea that the very act of measurement "induces" the uncertainty principle is not correct; see the "Heisenberg Microscope". Heisenberg's argument is rather heuristic from the start and used ideas from classical optics.

 

The uncertainty principle itself still remains.

[studiot]

Thank you for this and your earlier comment, ajb.

 

You did indeed read what I thought was my very clear question and provided your answer.

 

I will have to investigate Heisenberg's original work because I had the impression that the principle arose in another manner.

 

So if I find your history correct I will have learned something new.

Edited September 10, 2012 by studiot

[swansont]

There is no "attack", I simply disagree; there is a difference between an exact number and an exact measurement. Focusing on the number ignores the physical phenomena that underlies it. One wants to measure e.g. a decay rate, but since it's a stochastic process, one measurement is insufficient, since it is almost certainly going to be wrong. So even though the number is exact, as it will be an integer, the measurement is not. The fact that it is not repeatable tells you that the measurement was not exact. An exact measurement would have both infinite precision and infinite accuracy.

 

IOW, I think Diffeomorphism's characterization is, in general, pretty accurate, given the context of it.

[Phi for All]

However so far all that has happened is that I have been attacked by two moderators.

!

Moderator Note

In the future, please give more direction for discussion than a title and a link. Since we're here to hear your perspective, just a few words on that would be appreciated greatly. Thanks!

Oh GOD, how HORRIBLE of me to attack you in such a senseless and brutal fashion! Can you ever forgive me? I can assure you that any future attacks will have a great many more smileys and perhaps a few hundred more "thanks".

 

 

 

Or perhaps I'm overreacting a bit....

[studiot]

I call it an attack because each time you reply you run away from or duck most of my previous post and pick on one point to well -- attack.

 

This, coupled with the comment of the other moderator who obviously did not read my question as he or she made no effort to answer or discuss it, has driven away genuine discussion.

 

Cap Refsmat has recently been deploring the low membership / activity here.

 

Do you think this will help?

 

In this case you are promoting a far to narrow view of the word measurement. The output of a measurement is clearly going to be set in appropriate units. Some units are numbers some are not.

Of those that are numbers some are confined to the integers, some are not.

 

Each and every occurrence of a given phenomenon is entitled to its own measurement, with its own accuracy. Precision is not necessarily applicable to an individual measurement, despite what you claim.

 

It may be that as a result of a series or set of measurements (in the plural) further conclusions may be drawn.

This does not alter the output of each individual measurement.

 

But I'm sure you know all this so why the argument?

Edited September 10, 2012 by studiot

[imatfaal]

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Moderator Note

Back on topic please.

What the experimenters showed was that Heisenburg's initial measurement-disturbance relationship was incorrect. But this relationship has been ignored for a while - the mathematical formalism of quantum mechanics has shown than Heisenberg Uncertainty principle is intrinsic and not a product of measurement. This experiment does not touch the HUP - and I think most physicists still think that the HUP is correct and will not be shown to be avoidable through weak measurement. To be clear the measurement-disturbance idea was a bit of an old chestnut - wavelengths of light small enough to determine position are energetic enough to disturb momentum. As AJB said above the HUP follows from the non-commutative nature of certainoperators; this allows quantum physicists to be sure that the HUP is not just bad measurement

What the UofT researchers showed was that weak measurement can be so weak that the measurement would not be disturbing enough to create the uncertainty - but they do not deny that the uncertainty is still there. Lee Rozema the lead author was quoted saying "The quantum world is still full of uncertainty, but at least our attempts to look at it don't have to add as much uncertainty as we used to think!"

[studiot]

Imatfaal,

 

Thank you for explaining more details of the article, which, as I already stated, I was unable to obtain the full text.

 

Yes I agree, (my post#13) that this was wandering off topic.

 

However if you look back through this thread it is clear that

 

I have been castigated (gently) by one moderator for not posting my thoughts

 

And also by a different moderator for posting my thoughts.

 

Ah well sigh!

[hypervalent_iodine]

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Moderator Note

studiot,

1. Swansont is not in this thread as a moderator. If you take issue with his posts, please report it as you would any other member and staff will address your concerns as we deem appropriate.


2. Again, please get back on topic.

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Moderator Note

I apologise if you feel somehow attacked by moderator action in this thread as that was not the intention. However, if you wish to discuss this further, I would ask that you please stop derailing this thread and contact staff privately either by using the report feature or by PMing one of us directly.

[Diffeomorphism]

I'm pointing out that there is a fundamental difference between counting and measurement, the way measurement was used. However, even your use of radioactivity counters doesn't work. You won't get the same thing if you run the experiment again; the statistical uncertainty in such a measurement varies as the square root of N. You get an exact number, but it's not an exact measurement.

 

This is what I basically conveyed, but someone said I was of-topic for whatever reason.

[md65536]

Radioactivity measuring decices used to be called counters for good reason.

 

But what does such a device count? Is it 100% certain to correctly count particles?

If there's a physical, inherently uncertain chance that a given particle emission will hit the detector vs. going somewhere else, then does the precision of the count have any real meaning?

 

 

 

As for the coins examples, how many individual measurements would it take to determine the number of coins in your pocket with 100% certainty. Eg. if you put them on a table and took a picture of them with a digital camera, that showed the count with absolute certainty, then the individual pixel sensors would each count as a measurement, or perhaps each photon detected might be a measurement.

 

What would be the minimal number of measurements, using any method? Would you be able to reach 100% certainty by some method other than by taking enough measurements to achieve statistical certainty?

 

 

 

The uncertainty principle is really rooted in the fact that the operators associated with classical observables do not (necessarily) commute.

 

Heisenberg argued that the uncertainty principles is due to the act of observing which "upsets" the system. This may not be a correct way of understanding the principle, which is what they showed.

Your post is like a lesson in how to describe scientific ideas properly, and how not to, respectively.

 

Not that I understand the first sentence, but it's preferable to know what I don't understand and be able to look it up, than to have it explained in a simple way, and mistakenly think that I get it. Worse is when those simple explanations are passed on by other people who don't know what they're talking about, and you get "science" documentaries about QM that include the words "It doesn't make any sense, but..." It's sad that with a popular understanding of QM, people can believe that they understand it AND that it doesn't make sense.

[swansont]

Not that I understand the first sentence, but it's preferable to know what I don't understand and be able to look it up, than to have it explained in a simple way, and mistakenly think that I get it. Worse is when those simple explanations are passed on by other people who don't know what they're talking about, and you get "science" documentaries about QM that include the words "It doesn't make any sense, but..." It's sad that with a popular understanding of QM, people can believe that they understand it AND that it doesn't make sense.

Saying that operators commute or don't is saying that the order in which you make measurements don't matter or they do, respectively. If the operators commute, then you can measure the attributes in either order and you'll always get the same answer. If they don't commute then the answers will vary. The position and momentum operators, for example, don't commute. Measuring one and then immediately measuring the other will not give the same answer if you flip the order. What this experiment showed is that this is NOT because of the perturbation added by making the measurement, e.g. scattering a photon off the particle. That disturbance is there, but it can be made smaller than the uncertainty you measure. There's an inherent uncertainty owing to the existence of wave functions, that is there separate from the measurement.

[ajb]

... and you get "science" documentaries about QM that include the words "It doesn't make any sense, but..." It's sad that with a popular understanding of QM, people can believe that they understand it AND that it doesn't make sense.

 

The theory of quantum mechanics makes sense: the theory is mathematically well-founded and makes predictions about the Universe that have passed all the tests.

 

The real trouble is trying to interpret what quantum mechanics is telling us in terms of our everyday experiences. This is where most of the philosophical troubles arise.