# Talk:Uncertainty principle

WikiProject Physics (Rated B-class, Top-importance)
This article is within the scope of WikiProject Physics, a collaborative effort to improve the coverage of Physics on Wikipedia. If you would like to participate, please visit the project page, where you can join the discussion and see a list of open tasks.
B  This article has been rated as B-Class on the project's quality scale.
Top  This article has been rated as Top-importance on the project's importance scale.
WikiProject Philosophy (Rated B-class, Mid-importance)
This article is within the scope of WikiProject Philosophy, a collaborative effort to improve the coverage of content related to philosophy on Wikipedia. If you would like to support the project, please visit the project page, where you can get more details on how you can help, and where you can join the general discussion about philosophy content on Wikipedia.
B  This article has been rated as B-Class on the project's quality scale.
Mid  This article has been rated as Mid-importance on the project's importance scale.

_____

## Observer Effect

Is the quoted statement correct? Didn't the modern double-slit experiment, conducted sometime after the sited reference, reveal that it was not simply detecting the particle that collapsed the wave function but rather the observation of the result? Please help!

"It must be emphasized that measurement does not mean only a process in which a physicist-observer takes part, but rather any interaction between classical and quantum objects regardless of any observer."

## The principle of uncertainty at the Planck scale.

The article should be mentioned on the ratio of uncertainties ${\displaystyle \sigma _{r_{s}}\sigma _{r}\geq \ell _{P}^{2}}$, where ${\displaystyle r_{s}}$ - the gravitational radius, ${\displaystyle r}$ - radial coordinate, ${\displaystyle \ell _{P}}$ - Planck length. This is another form of Heisenberg's uncertainty principle between the momentum and the coordinate at the Planck scale. Indeed, this relation can be written as follows: ${\displaystyle \sigma _{(2GM/c^{2})}\sigma _{r}\geq G\hbar /c^{3}}$, where ${\displaystyle G}$ - gravitational constant, ${\displaystyle M}$ - body mass, ${\displaystyle c}$ - speed of light, the ${\displaystyle \hbar }$ - Dirac's constant. Cutting left and right of the same constants, we arrive at the relation of the Heisenberg uncertainty ${\displaystyle \sigma _{(Mc)}\sigma _{r}\geq \hbar /2}$. Installed uncertainty relation predicts the emergence of virtual black holes (quantum foam) at the Planck scale.

178.120.122.41 (talk) 10:52, 4 March 2017 (UTC)

I agree it should be mentioned. Try to find published sources that discuss this. El_C 10:58, 4 March 2017 (UTC)
With a a strong emphasis on reputable sources. The discussion is normally a warren of fringe science. Cuzkatzimhut (talk) 11:59, 4 March 2017 (UTC)
I've seen it here and here and here. 178.120.122.41 (talk) 14:02, 4 March 2017 (UTC)

I am relieved to notice that @User:‎Isambard Kingdom reverted this borderline COI contri. The OP's strategic self-reversion with Minsk IP succor is something I have not encountered yet, but it smacks of creativity in mooting the 3R rule. Personally, I am not as keen as I should be to fuss about the marginal Virtual black holes here, but showcasing this stuff on a high traffic and high quality article such as this is too much. A quick review of this here (UP) article's history is a reminder of incessant, unrelenting, attempts to showcase marginal projects. Cuzkatzimhut (talk) 17:49, 11 March 2017 (UTC) As evidenced by today's unsocked activity, the campaign to self-promote the content of the virtual black hole article has not abated. The educated reader would immediately appreciate there are literally dozens of such rough-and-ready trivial applications of the UP to the Planck scale context, and choosing this one as an illustration of such applications is not exactly an informative act. Cuzkatzimhut (talk) 14:36, 17 March 2017 (UTC)

Stephen Hawking put forward the concept of virtual black holes (1995). Do you think that Hawking is a marginal? 178.120.93.51 (talk) 05:28, 20 March 2017 (UTC)
Tendentious. Hawking is not arguing in support of this marginal addition .Cuzkatzimhut (talk) 10:17, 20 March 2017 (UTC) In particular, capturing the eyeballs of this article's readers for self promotion is highly inappropriate. I tried to stay out of the flagrant misuse of the virtual black holes article, but evidently this was misconstrued. Please heed the not a forum spec at the top of this very page. Cuzkatzimhut (talk) 13:59, 20 March 2017 (UTC)

In accordance with the uncertainty relation ${\displaystyle \sigma _{r_{s}}\sigma _{r}\geq \ell _{P}^{2}}$ or ${\displaystyle r_{s}\sim \ell _{P}^{2}/r}$, the metric tensor in the Schwarzschild solution (on the Planck scale) has the form ${\displaystyle g_{00}=1-r_{s}/r\approx 1-\ell _{P}^{2}/r^{2}\approx 1-\sigma _{g}}$, where ${\displaystyle \sigma _{g}\sim \ell _{P}^{2}/r^{2}}$ are the fluctuations of the metric tensor.

"For the space-time region with size ${\displaystyle r}$, the uncertainty of the metric tensor is of the order of ${\displaystyle \sigma _{g}\sim \ell _{P}^{2}/r^{2}}$", (see Regge T., Gravitational fields and Quantum mechanics, Nuovo Gimento, 7, 215 1958).
The equation for the fluctuations of the metric tensor ${\displaystyle \sigma _{g}}$ agrees with the Bohr-Rosenfeld uncertainty relations ${\displaystyle \sigma _{g}(\sigma _{r})^{2}\geq 2\ell _{P}^{2}}$ or ${\displaystyle \sigma _{g}\sim 2\ell _{P}^{2}/r^{2}}$, (see Hans-Jürgen Treder, Ansprachen und Vorträge auf den Festveranstaltungen des Einstein-Komiees bei Akademie der Wissenschaften, vom 28.2. bis 2.3, 1979 in Berlin) 178.120.141.104 (talk) 08:31, 21 March 2017 (UTC)

You appear confused. My point is not that the obvious relation does not hold. It is that it is one of hundreds of evident applications of the uncertainty principle--God knows there is a plethora in atomic and condensed matter, nuclear , particle, physics, etc... They need not be listed in this article. This is absolutely the wrong venue for this. The reader has no need for it, and has to be protected from it. This is not a promotional soapbox for endless specialized side-discussions. Cuzkatzimhut (talk) 16:13, 21 March 2017 (UTC)

## What's a "timelimited signal"?

This article mentions that "a function cannot be both time limited and band limited", but "time limited" is currently referencing an article about the concept of deadline, which makes no sense. — Preceding unsigned comment added by 187.39.123.82 (talk) 20:18, 16 June 2017 (UTC)

Band limited means that a signal only has frequencies over a given, finite width, band. The spectral intensity is zero outside. On the other hand, time limited means it is only non-zero over a finite time interval. There is a not so obvious exception for periodic signals, which have similar properties to time limited signals. Note that the (time vs. frequency) Fourier transform has an integral from t=-infinity to t=+infinity. This question comes up more often in terms of sampling theory and Nyquist sampling, but it also applies here. Gah4 (talk) 16:30, 24 June 2017 (UTC)

## Observer effect vs Heisenberg uncertainty principle

I came to this page to remind myself of the precise articulation of the HUP, and was quite intrigued to read on the page that it is distinct from, and often confused with, the observer effect in physics. However, in checking the first reference provided for that statement (the Sci Am article), I read: "Yet the uncertainty principle comes in two superficially similar formulations that even many practicing physicists tend to confuse. Werner Heisenberg's own version is that in observing the world, we inevitably disturb it. And that is wrong, as a research team at the Vienna University of Technology has now vividly demonstrated." This would seem to indicate that Heisenberg's "own version" was the observer effect. Can someone knowledgeable in the field clarify (not just for my edification, but in the article since it seems secondary sources might talk about different "versions" of HUP where this article takes a POV that there is one HUP)? And I'd also recommend adding a back-link to HUP in the observer effect article if relevant. Martinp (talk) 13:02, 23 June 2017 (UTC)

Things are well-explained in the very first paragraph of this article, to a thoughtful reader; it is quite unclear what you believe is missing. That Sci Am article is a bit inflammatory in its discussion of history. Heisenberg utilized the observer effect to reassure us that the HUP cannot be beat; the first reaction of the outsider, and the physics community at the time is/was: "But, why can't I beat the HUP? Surely, I'll just....". Cuzkatzimhut (talk) 13:16, 23 June 2017 (UTC)
Cuzkatzimhut, thanks for the reply. Apologies, I seem to have stepped on some toes in how I formulated my question, not intended. Speaking in layman's terms (since I last studied any physics 25 years ago, I'm afraid I can't do any better...), I'm familiar with a formulation of HUP, in the lead of the article, as the simultaneous unknowability of position and momentum, or more generally/loosely precise present state as well as a precise prediction of future motion. This is stated more precisely via the Kennard inequality, also right at the start of the article. I've also heard HUP stated as "observing the world necessarily disturbs it", a version which nonphysicists are fond of quoting as a philosophical observation of greater applicability, e.g. in social systems. The implication of the 3rd para of this article is that this latter formulation is mislabeled as being HUP, that it is actually something else, namely the observer effect, which merely "has been confused with it". Being intrigued by this, I clicked the first reference, the SciAm article, and it appears to take a broader terminological approach, namely that there are 2 formulations of HUP, namely Kennard's and "Heisenberg's original formulation", which it would seem was the original one.
I'm therefore left trying to reconcile terminology. This article, saying "HUP=A. By the way it's confused with A', which is not really HUP but related at the quantum level." Or SciAm, apparently saying "There are 2 formulations of HUP, HUP1=A and HUP2=A' ". In my field, one of the biggest challenges is that terms have both narrow technical and related broader philosophical meanings, and frankly Wikipedia articles in my field are a mishmash of which of these meanings are described. So it set off my spidey senses that something similar may be going on here. Now you or others can reassure me that common practice in physics has become indeed that HUP=A, not A', and the SciAm article happens to in this specific area take a niche/nonmainstream view. Or you can tell me I'm just misunderstanding things. Or it's possible that this article as currently written is taking a specialized, narrow view, which is not wrong, but might make sense to broaden the aperture at the start and reflect if there is a terminological divergence, that some say HUP=Kennard only, and others that HUP=Kennard or observer effect -- if that is indeed the case. That's where I lack sufficient knowledge. Martinp (talk) 23:58, 23 June 2017 (UTC)
Yes, one did get a little spooked. If you looked at the voluminous Archived past volumes of this page, this has been a contentious issue with increased unsound intrusions swept out periodically. Indeed, A'="observing the world necessarily disturbs it", is the observer effect in QM, as described in that article, and mindlessly confused with A, and far more mysterious than A. I strongly disagree with the sensationalist and self-serving habit of pinning A' to Heisenberg's somehow misunderstanding his own principle, with forensic chapter-and-verse unsound history of science (note the weasel words "...many physicists, probably including Heisenberg himself, have been under the misapprehension...". WH's original paper is quite hard-nosed and transforms Gaussians, for crying out loud! It is A). A is a basic fact of Fourier analysis, and so the wave nature of matter, which Heisenberg tried to argue for and defend using A'... and was thus posthumously smeared with misunderstanding his own principle. I do wish to reassure you that "common practice in physics has been indeed that HUP=A". In fact, WH's gedanken-microscope used classical optics, his sad thesis exam Achilles heel, not wavefunction collapse subtleties. QM is weird, and both A and A' are very counterintuitive in their particulars; but more absurd philosophical battles are waged on A' and the problem of measurement, "collapse of the wave function", and interpretations of QM these days than poor technical, unremarkable A, the subject of this article. Cuzkatzimhut (talk) 03:16, 24 June 2017 (UTC)
Seems to me that it eventually gets back to Interpretations of quantum mechanics. Some interpretations make it easier to answer a certain kind of question, and in some cases the observer effect is important. While I believe that the Copenhagen interpretation is now shown to be false (that is, does not always agree with nature), it still works well enough, often enough, to be useful. (Consider Newtonian mechanics, still useful though proven false by both relativity and QM.) The observer effect works often enough, and is often easier to show, but uncertainty is still there, even without observers. At some point, it gets down to the statement of interaction between quantum and classical systems, but there aren't any classical systems. It is easier for us to analyze, to understand, if we assume that there are classical systems, but that is just an approximation. Within that approximation, some explanations work. But in reality, our measuring devices are also quantum systems. Gah4 (talk) 16:41, 24 June 2017 (UTC)
This is part of my point. Such discussions have no place in this article, as per not a forum warning on top of this page. They might end up in the article wikilinked above. This is an article about a feature of Fourier analysis that surprised physicists 90 years ago. Not all aspects of QM are still up for conceptual grabs.Cuzkatzimhut (talk) 17:25, 24 June 2017 (UTC)

## DFT uncertainty principle

The uncertainty principle for the discrete fourier transform is only stated in the article Discrete Fourier transform. I think it should also be included in this article in the section "Harmonic analysis". Fvultier (talk) 09:57, 11 July 2017 (UTC)

I would disagree strongly. The DFT uncertainty principle is covered well in that article and showcased prominently in the "also see" section of this one. It is an obvious transcription of the continuous UP of this article, after the discrete transcription rules are established, done in that article. There is no good reason to overburden this already stressed and problematic article with extra tangents and footnotes. This article has repeatedly (cf. the archived discussions) been abused as an "eyeball harvesting" vehicle, and should be defended against "this too, me too" infiltrations. At the very most, you might choose to insert a short sentence in the harmonic analysis section linking to that article, if, for some obscure reason, you imagined the motivated reader would nevertheless fail to read on to find the perfectly noticeable wikilink in the "also see" section. Of course, the DFT article's UP section may be improved substantially.Cuzkatzimhut (talk) 13:06, 11 July 2017 (UTC)
I agree that this article contains to much information already. The section about the UP in harmonic analysis however does not state the very simple formula ${\displaystyle N\leq \|x\|_{0}\cdot \|X\|_{0}.}$. Fvultier (talk) 21:02, 11 July 2017 (UTC)
It is not that surprising, either. But, if you insisted, a minimal parenthetical one liner with the suitable wikilink and the evocative formula meant to just make people curious, if they were not familiar with it, might be innocuous... Cuzkatzimhut (talk) 21:16, 11 July 2017 (UTC)