Talk:Complementarity (physics)/Archive 1

Duality
The section on Englert-Greenberger duality is due to User:Drezet; thought I'd mention that here, since the edit history does not make clear that this was copied here from Afshar experiment. Thanks Drezet! linas 01:56, 7 February 2006 (UTC)
 * I have hived it off into its own page since complementarity is Bohr's creation and the later Englert-Greenberger duality is a much more focussed application of this. --Michael C. Price talk 14:53, 13 July 2006 (UTC)

"simultaneously"?
Is the word "simultaneously" correct, in view of the Ashaf experiment? In that experiment an attempt is made to measure such properties of a single photon one after the other, which thus would not test a simultaneous measurement claim - but I wonder if that word belongs here. An exact citation of Bohr would be most beneficial. Harald88 10:40, 29 April 2006 (UTC)
 * The Heisenberg uncertainty relationship applies to the simulatneous measurement of position and momentum (or more generally of any two conjugate variables). Most physicists interpret complementarity as being enshrined in the HUP, but a more exact quote would be helpful.  --Michael C. Price talk 18:43, 28 October 2006 (UTC)

Quote from Bohr's assistant?

 * "There is no quantum world. There is only an abstract physical description. It is wrong to think that the task of physics is to find out how nature is. Physics concerns what we can say about nature."


 * I recall this quote being from Bohr's assistant rather than from Bohr himself. Not that it really matters I suppose. --Carl A Looper 00:38, 22 December 2006 (UTC)


 * The assistant is quoting Bohr.--Michael C. Price talk 08:08, 22 December 2006 (UTC)

Is this principle now under debate?
Having just read this: Physicists Modify Double-Slit Experiment to Confirm Einstein's Belief I'm wondering whether the principle of complementarity should be noted as being under debate? Not being an expert I'm open to correction and enlightenment. --210.175.46.205 04:05, 13 March 2007 (UTC)


 * The "article" you cited is actually a press release by the researcher's university publicity office. In fact, Foundations of Physics, regardless of who's on its editorial board, is well known for publishing loads of crackpot articles (in addition to some reasonable, thought-provoking ones). If every theory that was challenged in this journal had to be flagged as being under debate, then that would include pretty much everything in physics, ever (every aspect of special relativity, general relativity, quantum mechanics, astronomy, etc.). As of now, this is very, very far from being under debate. Steve 20:06, 31 July 2007 (UTC)


 * It isn't more under debate than the Copenhagen interpretation, and is pretty much related to that. Gah4 (talk) 13:32, 12 March 2019 (UTC)

Impossibility of superpositions ?!
I provide obviously wrong statement from the article:

"This means that there is a limitation on the precision with which an electron can possess (i.e., manifest) position, since an infinitely precise position would dictate that its manifested momentum would be infinitely imprecise, or undefined (i.e., non-manifest or not possessed), which is not possible."

This is completely wrong. What Heisenberg inequality show is that -- if the position is localized in space, then the momentum is superposed! Inversely, if the momentum is well defined, the particle is superposed at many locations in space. So the "uncertainty" is NOT criterion for impossibility, but shows that there is some minimal requirement for quantum superpositions! If one of two non-commuting observables is well measured, then its complementary observable will be superposed. Danko Georgiev MD (talk) 09:18, 20 February 2008 (UTC)

But wait a minute. Both of you are wrong. Both of you forgot that the uncertainty is in both quantities. It is the product that is constrained, so a large uncertainty in the one yields a small uncertainty in the other, but that both uncertainties are non-zero has not changed.

Now this way of stating it does not tell us anything about 'superposing' etc., but at least it is accurate. Georgiev's mention of only one as "superposed" cannot be accurate. 99.130.73.126 (talk) 03:08, 17 February 2009 (UTC)

Either/Or presentation of complementarity
Following from the above, the current article relentlessly takes the view that complementatirity takes a binary form --- you obeserve a particle and not a wave, or a wave and not a particle. As dicssuseed above, the uncertainty principle actually means that greater precision in position measurements means less in wavelength/momentum measurements, and vice versa, so that mixtures are possible.

I think this is an important issue in undestanding the Afshar experiment.

1Z (talk) 09:22, 30 April 2009 (UTC)

An evaluated wave function (a waveform) can be understood as representing four things, two of which have no foundation in math or science.


 * 1 The waveform represents (by virtue of the function) the experimental setup. ie. the waveform is a function of the experimental setup.
 * 2 The waveform (squared) represents the distribution of all (past and future) particle detections in the same experimental setup.
 * 3 The waveform, without any empirical foundation, represents the particle. It is unempirical since particles (as distinct from particle detections) are un-observables.
 * 4 The waveform (squared) without any rational foundation represents the particle detection. It is irrational since there is no functional relationship between the waveform and any particle detection.

There is only one wave function, namely, Schrodingers. The function evaluates an experimental setup (the argument) in terms of the distribution of particle detections to be expected from that setup (the result). One must, of course, square the waveform. Given the same setup the wave function will always evaluate to the same distribution. This is why there is no functional relationship between a waveform (for a given experiment) and the location (in space and time) of any particle detections in that experiment. The experiment is always the same but each particle detection is different, ie. no relationship whatsoever.

There is, however, an expectation, manufactured by the pionneers of quantum mechanics (for a classical audience), that there would be a functional relationship if it wasn't for the fundamental limits of the proposed system. The result of such a null expectation is the fanciful concept of "wave function collapse" (or to be more accurate: "waveform collapse"), as if there could be a functional relationship between a waveform and a particle detection.

To complicate matters further (and introduce not only false expectations but also errors) Neils Bohr extends the concept of a what-if functional relationship into the concept of "complementarity". The fundamentals of the principle are sound. For example, one can not construct an experimental set-up in which (say) one aperture is open (the other closed) AND in the same place at the same time, have (for example) both apertures open. But while experimental setups posses this limit, there is nothing to stop one evaluating the waveform of such an impossible experiment and, more importantly, constructing experiments which actually possess such waveforms. The principle of complementarity does not work in the way Bohr might have imagined.

to be continued —Preceding unsigned comment added by 202.6.86.1 (talk) 22:53, 5 April 2010 (UTC)

Gravity and Particles
The claim that "gravitation only affect particles, and not waves" is surely wrong as gravity is known to affect photons in gravitational lensing.

1Z (talk) 09:22, 30 April 2009 (UTC)

Bohr: Causality and Complementarity
I do not have the time myself, but if anyone would like to work on this article, this 4th volume of Bohr's "philosophical writings" will be helpful. Published in 1998/1999, this collection of his papers is edited by Jan Faye and Henry J. Volse. I bought a copy last year and read some of it, planning to work on this article, but have too much other material I am responsible for so it probably won't be happening. The book is not expensive. DinDraithou (talk) 21:59, 1 May 2011 (UTC)
 * Also I am not a physicist, although I briefly aspired to be before getting into linguistics and so on. DinDraithou (talk) 22:04, 1 May 2011 (UTC)

Paragraph removed
I removed the following text, which appeared in two places:

"The complementarity principle states that some objects have multiple properties that appear to be contradictory. Sometimes it is possible to switch back and forth between different views of an object to observe these properties, but in principle, it is impossible to view both at the same time, despite their simultaneous coexistence in reality. For example, we can think of an electron as either a particle or a wave, depending on the situation. An object that's both a particle and a wave would seem to be impossible because, normally, such things are mutually exclusive. Nonetheless, an electron is truly both at once."

The principle says nothing about the properties appearing to be contradictory. It instead states that they are complementary. Also, the principle says nothing about "simultaneous coexistence in reality" of complementary properties. It merely states that how they are perceived depends upon how they are looked at.J-Wiki (talk) 01:22, 9 April 2012 (UTC)

Moved incomplete section to talk page
I found this incomplete section in the article, but I don't know how to finish it; I am therefore moving it here for clarity.

Additional considerations
In his original lecture on the topic, Bohr pointed out that just as the finitude of the speed of light implies the impossibility of a sharp separation between space and

Best regards.85.51.23.190 (talk) 22:01, 10 September 2012 (UTC)


 * This paragraph was apparently vandalized on 8/31. I restored the full paragraph as it existed then.J-Wiki (talk) 00:13, 8 October 2012 (UTC)

This article is complete screwed up, to say it mildly. Suggest to delete it. I tried to clear up the misunderstanding that complementary is the same as non-commuting operators, but it is really far from perfect yet and it is kind of silly to start with.

Burningbrand (talk) 15:05, 11 January 2016 (UTC)

Completely unnecessary editorializing
"Today nobody presumably believes that the mind is anything other than an emergent property of a physical brain's complexity..."

Of course, many, many people believe that it is other than that, and many believe that it can be philosophically demonstrated that it is other than that. But ultimately the question is what the heck is this person's assertion of their personal metaphysical belief doing in this encyclopedia article? GeneCallahan (talk) 15:12, 21 January 2016 (UTC)

Anyway, I will remove that sentence unless someone offers a good argument for why it belongs here. GeneCallahan (talk) 23:58, 21 January 2016 (UTC)

Generalized principle of complementarity
Principle of Bohr's complementarity can be given a more general form and stated as follows: the rational side of reality and conjugate irrational side of reality are complementary to each other. For example, an additional pair of "Particle - Wave" rational side of the pair is a particle. Irrational side - this is the de Broglie wave, which does not bear the energy and distributed in a multidimensional configuration space. Einstein called this wave "wave - the ghost". Niels Bohr established the following additional pairs - "Physicochemical causality - Biological purposefulness"; "Thoughts and Feelings"; "Determinism and Free will"; "Logic and Intuition," etc. German physicist and Nobel Prize winner, Max Born believed that complementarity - this is an important concept, because it clarifies many other areas of reality. This applies to such pairs of concepts as: "Matter, and the Life", "Body and Soul", "Necessity and Freedom", etc. It is easy to see that all these couples satisfy the generalized principle of complementarity.

According to the generalization of the principle of complementarity, Life should be in all corners of the Universe. Also "Evolutionism" and "Creationism" are complementary to each other. Alexander Klimets (talk) 12:04, 1 August 2016 (UTC)


 * You already have 3 warnings on your user talk page for article talk page disruption. Do you have a concrete proposal to make a change to the article? - DVdm (talk) 20:30, 23 September 2016 (UTC)
 * In the "Wikipedia" in Russia (in the "Talk") more freedom of speech. Alexander Klimets (talk) 08:18, 24 September 2016 (UTC)
 * Good for you in Russia, but here we have WP:NOTFREESPEECH. - DVdm (talk) 09:42, 24 September 2016 (UTC)

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conscious observer
Why does the example of a two-slit experiment require a conscious observer to decide which slit a particle passes though? As far as I know, it works in the absence of consciousness or observers. Gah4 (talk) 07:45, 3 June 2018 (UTC)
 * You are correct. Very few physicists regard consciousness as a necessary precursor to prevent the wave-like behaviour from manifesting.Flaviusvulso (talk) 05:24, 8 March 2019 (UTC)