# Repudiating the Uncertainty Principle **URL:** \ **Category:** Factual Questions\ **Created:** [September 10, 2011, 3:56pm UTC](https://boards.straightdope.com/t/repudiating-the-uncertainty-principle/595831 "2011-09-10T15:56:33Z")\ **Posts on this page:** 19\ **Page:** 1
**Author:** ![panache45](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/panache45/32/64_2.png) [@panache45](https://boards.straightdope.com/u/panache45)\ **Post date:** [September 10, 2011, 3:56pm UTC](https://boards.straightdope.com/t/repudiating-the-uncertainty-principle/595831/1 "2011-09-10T15:56:33Z")
Is the Uncertainty Principle universally subscribed to by all reputable physicists, or are there dissenters? ---
**Author:** ![Half\_Man\_Half\_Wit](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/half_man_half_wit/32/21766_2.png) [@Half\_Man\_Half\_Wit](https://boards.straightdope.com/u/Half_Man_Half_Wit)\ **Post date:** [September 10, 2011, 4:14pm UTC](https://boards.straightdope.com/t/repudiating-the-uncertainty-principle/595831/2 "2011-09-10T16:14:00Z")
The only one I can think of criticising the uncertainty principle was Karl Popper, who of course was not a physicist, but a philosopher – and even he did not disagree with the principle totally, but rather considered it to apply only to the statistical ensemble formed by a large number of measurements, rather than to any individual measurement. Otherwise, the UP follows pretty immediately from the mathematics we use to formulate quantum theories, which has a pretty impressive phenomenological track record; I’m not even sure how one would disagree with it without advocating throwing the last 90 years of physics out of the window… ---
**Author:** ![WarmNPrickly](https://avatars.discourse-cdn.com/v4/letter/w/d78d45/32.png) [@WarmNPrickly](https://boards.straightdope.com/u/WarmNPrickly)\ **Post date:** [September 10, 2011, 4:16pm UTC](https://boards.straightdope.com/t/repudiating-the-uncertainty-principle/595831/3 "2011-09-10T16:16:36Z")
The uncertainty principle is a mathematical property of waves. There may be differing opinions on what it means about the nature of matter, but as far as I know, there is no descent among rational scientists. Some things are, at the very least, unknowable. I would argue beyond unknowable, and say they aren’t definable, by which I mean, the precise momentum and location of a particle doesn’t even exist. ---
**Author:** ![Asympotically\_fat](https://avatars.discourse-cdn.com/v4/letter/a/e47c2d/32.png) [@Asympotically\_fat](https://boards.straightdope.com/u/Asympotically_fat)\ **Post date:** [September 10, 2011, 4:41pm UTC](https://boards.straightdope.com/t/repudiating-the-uncertainty-principle/595831/4 "2011-09-10T16:41:40Z")
You’d have to reject quantum physics at a basic level. As **Half Man Half Wit** says it’s a relatively simple result of the mathematics of quantum mechanics. Of course how exactly to interpret the uncertainity principle ontologically is still a matter of great debate. ---
**Author:** ![colonial](https://avatars.discourse-cdn.com/v4/letter/c/34f0e0/32.png) [@colonial](https://boards.straightdope.com/u/colonial)\ **Post date:** [September 10, 2011, 5:11pm UTC](https://boards.straightdope.com/t/repudiating-the-uncertainty-principle/595831/5 "2011-09-10T17:11:58Z")
Subject to correction by an expert here, but I think there are at least two interpretations of Quantum Mecahnics providing dissent in principle from the Uncertainly Principle: (1) the Bohm/DeBroglie “Pilot Wave” school, and (2) the Everett/DeWitt “Many Worlds” According to (1) every event in the universe is intantaneously connected with the rest of the universe by an event-generated “Pilot Wave”. Conjugate properties such as position and momentum could be exactly described by examination of these Pilot Waves. Unfortunately there is, again in principle, no way to examine them, so they really do not do much good except as sort of emotional support for those who wish to bring back the causality banished by Prof. W. Heisenberg. Uncertainty arises from apparent inability to select one definite location out of many possbile locations for something called the “wave function collapse”, which takes place whenever anything happens in the universe. According to (2) there _is_ no wave function collapse. What about the location then? Well, says the theory, there is an event for _all_ possible locations. Why doesn’t everything split into differently located clones of itself then? They _do_ split, says the theory flamboyantly, and each new event goes sashaying off into a new, separate _parallel universe_, and that takes care of the matter. From what little I know I gather that (1) is supported by a tiny minority of modern physicists, while (2) is considered mainstream, although not majority opinion. ---
**Author:** ![MikeS](https://avatars.discourse-cdn.com/v4/letter/m/919ad9/32.png) [@MikeS](https://boards.straightdope.com/u/MikeS)\ **Post date:** [September 10, 2011, 5:24pm UTC](https://boards.straightdope.com/t/repudiating-the-uncertainty-principle/595831/6 "2011-09-10T17:24:09Z")
> [@colonial](#): > > From what little I know I gather that (1) is supported by a tiny minority of modern > physicists, while (2) is considered mainstream, although not majority opinion. As a physicist, I agree with your assessment of the acceptance of #1, but I wouldn’t call many-worlds “mainstream”; rather, it’s a minority opinion among the minority of physicists who think deeply about quantum interpretations. The vast, vast majority of physicists, if you were to ask them, would either say something about the Copenhagen interpretation or take an agnostic position along the lines of “we don’t really need to know what’s going on a ‘deep’ level; the calculations allow us to predict things, and that’s what we really care about.” ---
**Author:** ![Wendell\_Wagner](https://avatars.discourse-cdn.com/v4/letter/w/8491ac/32.png) [@Wendell\_Wagner](https://boards.straightdope.com/u/Wendell_Wagner)\ **Post date:** [September 10, 2011, 5:36pm UTC](https://boards.straightdope.com/t/repudiating-the-uncertainty-principle/595831/7 "2011-09-10T17:36:29Z")
This article lists fourteen different interpretations of quantum mechanics, although it’s probably possible to argue about just what a different interpretation is: > **[Interpretations of quantum mechanics](https://en.wikipedia.org/wiki/Interpretations_of_quantum_mechanics)** > > An interpretation of quantum mechanics is an attempt to explain how the mathematical theory of quantum mechanics might correspond to experienced reality. Although quantum mechanics has held up to rigorous and extremely precise tests in an extraordinarily broad range of experiments, there exist a number of contending schools of thought over their interpretation. These views on interpretation differ on such fundamental questions as whether quantum mechanics is deterministic or stochastic, local or... ---
**Author:** ![Asympotically\_fat](https://avatars.discourse-cdn.com/v4/letter/a/e47c2d/32.png) [@Asympotically\_fat](https://boards.straightdope.com/u/Asympotically_fat)\ **Post date:** [September 10, 2011, 5:45pm UTC](https://boards.straightdope.com/t/repudiating-the-uncertainty-principle/595831/8 "2011-09-10T17:45:56Z")
I would say as the uncertainty principle is a very simple result of the mathematics of QM and in order to be regarded as an “interpretation” of QM an ontology/formalism cannot disagree with the quantitive predictions of QM (and neither the de Broglie-Bohm or many worlds intepretations disgaree with the quanititve predictions of QM), then all interpretations of QM agree with uncertainity principle. What they disgaree on is the interpretation of the principle. ---
**Author:** ![Half\_Man\_Half\_Wit](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/half_man_half_wit/32/21766_2.png) [@Half\_Man\_Half\_Wit](https://boards.straightdope.com/u/Half_Man_Half_Wit)\ **Post date:** [September 10, 2011, 5:49pm UTC](https://boards.straightdope.com/t/repudiating-the-uncertainty-principle/595831/9 "2011-09-10T17:49:41Z")
One should take care to note, however, that in all proper _interpretations_ of quantum mechanics, including De Broglie-Bohm theory and many worlds, the uncertainty principle is equally valid (otherwise, they would not be interpretations of QM, but bona fide distinct theories), though, as noted by **These Are My Own Pants** above, they may differ in an ontological sense – in Bohmian mechanics, for instance, while a definite momentum and position of a particle simultaneously exists, they are nevertheless not exactly knowable. EDIT: Above, I meant **Pants** ’ post above his post above this one, which I didn’t see until I posted. ---
**Author:** ![colonial](https://avatars.discourse-cdn.com/v4/letter/c/34f0e0/32.png) [@colonial](https://boards.straightdope.com/u/colonial)\ **Post date:** [September 10, 2011, 6:12pm UTC](https://boards.straightdope.com/t/repudiating-the-uncertainty-principle/595831/10 "2011-09-10T18:12:30Z")
> [@These are my own pants](#): > > I would say as the uncertainty principle is a very simple result of the mathematics of QM and in order to be regarded as an “interpretation” of QM an ontology/formalism cannot disagree with the quantitive predictions of QM (and neither the de Broglie-Bohm or many worlds intepretations disgaree with the quanititve predictions of QM), then all interpretations of QM agree with uncertainity principle. What they disgaree on is the interpretation of the principle. My understanding has been that the all science has always been most fundamentally the result of physical as opposed to mathematical considerations. Pi is a property of circles, but circles are not a property of pi. ---
**Author:** ![Lumpy](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/lumpy/32/446_2.png) [@Lumpy](https://boards.straightdope.com/u/Lumpy)\ **Post date:** [September 10, 2011, 7:55pm UTC](https://boards.straightdope.com/t/repudiating-the-uncertainty-principle/595831/11 "2011-09-10T19:55:23Z")
Here’s an article from Scientific American about how in principle, using an interferometer-like setup, it is possible to image an object without actually shining any photons on it! This would seem on the face of it to contradict the Uncertainty Principle by obtaining information about an object without directly interacting with it. [http://www.fortunecity.com/emachines/e11/86/seedark.html](http://www.fortunecity.com/emachines/e11/86/seedark.html) ---
**Author:** ![Asympotically\_fat](https://avatars.discourse-cdn.com/v4/letter/a/e47c2d/32.png) [@Asympotically\_fat](https://boards.straightdope.com/u/Asympotically_fat)\ **Post date:** [September 10, 2011, 8:27pm UTC](https://boards.straightdope.com/t/repudiating-the-uncertainty-principle/595831/12 "2011-09-10T20:27:18Z")
> [@colonial](#): > > My understanding has been that the all science has always been most fundamentally the result of physical > as opposed to mathematical considerations. Pi is a property of circles, but circles are not a property of pi. QM creates a formalism and that formalism is mathematical. The unceratinity principle arises out of this mathematical formalism. What the formalism does is tell you how to predict the results of experiments (and the uncertianity principle is in fact a limitation on that abilty to predict the results of experiments). The direct physical interpretation of the uncertainity principle is that it represents the uncertainity seen in repeated sets of measurements made on the same experimnetal set-up. Anything more than this and your in to the relams of ontology. Ontology is the philosophy dealing with ‘existance’ and ‘non-existance’ i.e. what is ‘_really_’ there. The fomralism of QM doesn’t automatically suggest an ontology in the way that many classical theories do (which are so often inside our normal everyday experince to such an extent that the question of ontology rarely even arises). You cannot ignore the mathematical nature of the uncertainity principle, which when stated generally is: σ[sub]Y[/sub][sup]2[/sup]σ[sub]Z[/sub][sup]2[/sup] ≥ ( [sup]1[/sup]/[sub]2i[/sub] 〈[Ŷ,Ẑ]〉) It only truly makes sense in the context of the mathematical formalism of QM ---
**Author:** ![Half\_Man\_Half\_Wit](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/half_man_half_wit/32/21766_2.png) [@Half\_Man\_Half\_Wit](https://boards.straightdope.com/u/Half_Man_Half_Wit)\ **Post date:** [September 11, 2011, 10:49am UTC](https://boards.straightdope.com/t/repudiating-the-uncertainty-principle/595831/13 "2011-09-11T10:49:01Z")
> [@Lumpy](#): > > Here’s an article from Scientific American about how in principle, using an interferometer-like setup, it is possible to image an object without actually shining any photons on it! This would seem on the face of it to contradict the Uncertainty Principle by obtaining information about an object without directly interacting with it. > [http://www.fortunecity.com/emachines/e11/86/seedark.html](http://www.fortunecity.com/emachines/e11/86/seedark.html) While it’s often heuristically derived that way (see [Heisenberg’s microscope](http://en.wikipedia.org/wiki/Heisenberg%27s_microscope)), the appearance of uncertainty in quantum theory is actually _not_ due to interaction with the measured object; even interaction-free measurements don’t yield a way to circumvent it. ---
**Author:** ![KarlGauss](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/karlgauss/32/3713_2.png) [@KarlGauss](https://boards.straightdope.com/u/KarlGauss)\ **Post date:** [September 11, 2011, 11:24am UTC](https://boards.straightdope.com/t/repudiating-the-uncertainty-principle/595831/14 "2011-09-11T11:24:56Z")
> [@MikeS](#): > > As a physicist, I agree with your assessment of the acceptance of #1, but I wouldn’t call many-worlds “mainstream”; rather, it’s a minority opinion among the minority of physicists who think deeply about quantum interpretations. Maybe, but according to [the Wiki article on ‘Interpretation of Quantum Mechanics’](http://en.wikipedia.org/wiki/Interpretation_of_quantum_mechanics) mentioned above, it actually _is_ a majority - 58 percent. ---
**Author:** ![colonial](https://avatars.discourse-cdn.com/v4/letter/c/34f0e0/32.png) [@colonial](https://boards.straightdope.com/u/colonial)\ **Post date:** [September 11, 2011, 12:26pm UTC](https://boards.straightdope.com/t/repudiating-the-uncertainty-principle/595831/15 "2011-09-11T12:26:32Z")
After reading and rereading posts by Half Man Half Wit and These Are My Own Pants, and various googling, it appears I was wrong: No QM interpretation, including the two I suggested, provides grounds for dissent from the Uncertainty Principle. What the Pilot Wave and Many Worlds interpretations do is restore _determinism_, which had been questioned or banished by their competitors. I erred by assuming that the Uncertainty Principle was incompatible with determinism. ---
**Author:** ![BigT](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/bigt/32/12044_2.png) [@BigT](https://boards.straightdope.com/u/BigT)\ **Post date:** [September 11, 2011, 2:10pm UTC](https://boards.straightdope.com/t/repudiating-the-uncertainty-principle/595831/16 "2011-09-11T14:10:37Z")
**These are my own pants** , I’m not quite sure why, but the formula you gave is messed up. The angle brackets don’t appear correctly for me, anyways. Below is a version that works for me. If the doesn’t appear correctly to you guys, here’s a link to a [graphical version](http://upload.wikimedia.org/math/8/d/3/8d3fd1291b19e4cb295cd3f731caa96d.png) from wiki (although it uses A and B for Y and Z and a nicer looking fraction). σ[sub]Y[/sub][sup]2[/sup]σ[sub]Z[/sub][sup]2[/sup] ≥ ( [sup]1[/sup]/[sub]2i[/sub] ⟨[Ŷ,Ẑ]⟩) I’d also like more clarification from **Half Man Half Wit**. If neither measurement disturbs the particle, why can you not set up two different devices that simultaneously make both location and momentum measurements? What happens if you try? ---
**Author:** ![Asympotically\_fat](https://avatars.discourse-cdn.com/v4/letter/a/e47c2d/32.png) [@Asympotically\_fat](https://boards.straightdope.com/u/Asympotically_fat)\ **Post date:** [September 11, 2011, 3:02pm UTC](https://boards.straightdope.com/t/repudiating-the-uncertainty-principle/595831/17 "2011-09-11T15:02:19Z")
> [@BigT](#): > > **These are my own pants** , I’m not quite sure why, but the formula you gave is messed up. The angle brackets don’t appear correctly for me, anyways. Below is a version that works for me. If the doesn’t appear correctly to you guys, here’s a link to a [graphical version](http://upload.wikimedia.org/math/8/d/3/8d3fd1291b19e4cb295cd3f731caa96d.png) from wiki (although it uses A and B for Y and Z and a nicer looking fraction). > > σ[sub]Y[/sub][sup]2[/sup]σ[sub]Z[/sub][sup]2[/sup] ≥ ( [sup]1[/sup]/[sub]2i[/sub] ⟨[Ŷ,Ẑ]⟩) The problems of using html characters. > [@](#): > > I’d also like more clarification from **Half Man Half Wit**. If neither measurement disturbs the particle, why can you not set up two different devices that simultaneously make both location and momentum measurements? What happens if you try? This is where understanding the mathematical formalism of QM is handy. The postulates of QM say that the state of a system immediately after a measurement is the eigenfunction corresponding to that measurement. Imcompatible observables do not have shared eigenfunctions (or at least do not have a complete set of shared eigenfunctions). In English this means that: 1. quantum measurement theory does not allow for truly simlulataneous measurements of incompatible observables, though it does allow for measurement of such observables instantaneously in sequence. 2. measuring 1 incompatible observable then the other is possible, but the 2nd measurement necessarily changes the quantum state of the system, so lets say if you were to perform 3 measurements instaneously in sequence of postion, momentum and postion, QM predicts that the 1st and the 3rd measurement will not necessarily yield the same result. I.e. it’s impossible to measure postion then momentum without having the second measurement change the quantum state of the system. ---
**Author:** ![Half\_Man\_Half\_Wit](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/half_man_half_wit/32/21766_2.png) [@Half\_Man\_Half\_Wit](https://boards.straightdope.com/u/Half_Man_Half_Wit)\ **Post date:** [September 11, 2011, 3:39pm UTC](https://boards.straightdope.com/t/repudiating-the-uncertainty-principle/595831/18 "2011-09-11T15:39:04Z")
> [@BigT](#): > > I’d also like more clarification from **Half Man Half Wit**. If neither measurement disturbs the particle, why can you not set up two different devices that simultaneously make both location and momentum measurements? What happens if you try? Well, at least qualitatively, even non-interaction can lead to a change in the wave function of the particle. If you have a particle prepared in the superposed state of |here\> + |there\>, you make a measurement here, and detect the particle, then afterwards the particle will be in the state |here\>, with a highly localized wave function in position-representation, and consequently a broad momentum distribution\*. But, if you make a measurement here, and don’t detect the particle, then, assuming 100% detector efficiency for the moment, the same analysis applies – the particle afterwards will be in the highly localized state |there\>, again with a broad distribution of momentum. So the disturbance of the particle is not what makes it obey the uncertainty relation. This is basically how those ‘interaction-free’ measurements work: the particle enters into a superposition of traversing either the upper or lower arm of the interferometer; the lower arm may be blocked by something, such that it would be absorbed if it traversed this arm and the block is present; then, both paths are recombined again, in such a way that interference of the particle with itself guarantees that the particle must exit the interferometer at exit 1, if both arms are unblocked. But if the lower arm is blocked, the interference is impossible, so the particle may also exit at exit 2 – though obviously, it can’t actually have traversed the lower arm, since if it had, it would have been absorbed! This is why these things are sometimes called ‘counterfactual measurements’: you get an answer to what would happen if the particle took a certain path – which it however doesn’t actually take. \*If these are unfamiliar terms, think about it the following way: a physical system can be represented as a point in what’s called phase space. For one single particle undergoing linear motion, this phase space is two-dimensional, with, say, the particle’s position indicated on the x-axis, and the particle’s momentum indicated on the y-axis. So a particle having a definite momentum p and position x will be represented in the phase space by a point at coordinates (x, p). Now, a _quantum_ system has the peculiar property that it can’t be perfectly localized in phase space, so there’s no single point which you can associate it with. But, you can constrain it in some small area – so instead of some definite value for momentum and position, you now have a range of values associated with the particle, corresponding to the projection of the area the particle occupies to the x- and y-axes. For this area, there exists a minimum value – equal to Planck’s constant. Nothing you do will localize the particle in an area smaller than that. So, when you increase your accuracy in one value, the accuracy in the other must decrease – if the particle starts out in a circular area, and you increase the accuracy of your position measurement, the area gets ‘squeezed’ to an ellipse, the projection onto the x-axis gets smaller, and the projection on the p-axis gets bigger. So, if the position is known very well, consequently, the momentum can’t be – that’s all there is to the uncertainty principle. I’m not sure I explained that too well, so here’s a picture: ```auto Classical particle: | | p |- * | | | | ______|________ x Quantum particle: |_ ___ | | h | Δp|_ |___| | | ΔpΔx = h | | _____|___ | _____ Δx After p-measurement accuracy increase: |_ ______ Δp|_ | h | | | | ΔpΔx = h | | _____|______ | _____ Δx ``` ---
**Author:** ![AskNott](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/asknott/32/5790_2.png) [@AskNott](https://boards.straightdope.com/u/AskNott)\ **Post date:** [September 11, 2011, 9:56pm UTC](https://boards.straightdope.com/t/repudiating-the-uncertainty-principle/595831/19 "2011-09-11T21:56:01Z")
I’m uncertain how to answer that.