Talk:Quantum mechanics

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Former featured article Quantum mechanics is a former featured article. Please see the links under Article Milestones below for its original nomination page (for older articles, check the nomination archive) and why it was removed.
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The citation is in: Miranda Devine. "Being sure is never a certain thing", Sydney Morning Herald, June 16, 2005.

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Contents

[edit] Simple Introduction

Some other science articles are starting to produce introductory versions of themselves to make them more accessible to the average encyclopedia reader. You can see what has been done so far at special relativity, general relativity and evolution, all of which now have special introduction articles. These are intermediate between the very simple articles on Simple Wikipedia and the regular encyclopedia articles. They serve a valuable function in producing something that is useful for getting someone up to speed so that they can then tackle the real article. Those who want even simpler explanations can drop down to Simple Wikipedia. I propose that this article as well consider an introductory version. What do you think?--Filll 22:40, 12 December 2006 (UTC)

there already is an introduction to quantum mechanics article. --Blckavnger 22:51, 12 December 2006 (UTC)

Then it needs to be linked in a way that is parallel to the other science articles.--Filll 23:04, 12 December 2006 (UTC)

It used to be that way. --Ancheta Wis 10:10, 14 December 2006 (UTC)

It is good now. There are 7 such articles at the moment.--Filll 15:07, 14 December 2006 (UTC)

[edit] Walter Ernhart Planck

This bit in the article troubles me, but I'm just short of bold enough to remove it myself:

Dr. Walter Ernhart Planck's "proton collapse" experiment cast doubt upon the distribution of protons in an atom and temporarily cast doubt upon the Rutherford model (1924)

Can anyone verify this or remove it if needed? Thanks, Figma 05:48, 12 January 2007 (UTC)

Removed in lieu of a citation. --Ancheta Wis 06:26, 13 January 2007 (UTC)
Thanks for getting rid of that. I have searched for any information on a "Walter Ernhart Planck", and have turned up nothing but outright copies of this Wikipedia article on various paranormal, occult and New Age websites. --Swwright 07:17, 13 January 2007 (UTC)

Someone seems to have edited a paragraph or two with a "snoop dogg" filter. I'm not all that wiki-literate, or I would fix it myself.

[edit] Fundamental

Quantum mechanics is a more fundamental theory than Newtonian mechanics and classical electromagnetism, in the sense that it provides accurate and precise descriptions for many phenomena that these "classical" theories simply cannot explain on the atomic and subatomic level.

Surely the thing that makes it more fundemental (rather than simply correct when these other theroies are wrong) is that these other theories can be derived from QM as emergent results. —The preceding unsigned comment was added by Paul Murray (talk • contribs) 03:51, 16 January 2007 (UTC).

[edit] C.S. Lewis, once again

There was a long discussion (see archive 7) about whether it was appropriate to include C.S. Lewis' opinion here.

I'm a great fan of Lewis, but I will say that it struck me as odd to see his opinion in this article. At the same time, I think the question he raised--the difference between the epistemic and ontological views of the Heisenberg Uncertainty Principle--is something many of us are puzzled by. (I can remember asking the question in High School, although not with such big words :-).)

So here's a suggestion: rephrase the paragraph to something like this:

At first glance, it is unclear whether the Heisenberg uncertainty principle is actually a matter of ontological indeterminacy, or if it is merely an epistemic limitation. Many writers outside of physics have raised this question, such as C.S. Lewis, who was a professor of English. [Add correct ref here--see below re current ref] This viewpoint is closely related to hidden variables theories of quantum physics. The Bohr-Einstein debates provide a vibrant critique of the Copenhagen Interpretation from an epistemological point of view.

I would do that edit, but I know I'm out of my depth here. And in any case, the "at first glance" would have to be countered by the opposite view (since clearly most physicists seem to believe that the H.P. is an actual indeterminacy, i.e. there are no hidden variables). So something would need to be added to the above paragraph beyond what I've written. It might start out

However, most physicists believe that the Heisenberg uncertainty principle really does reflect a true indeterminacy in the world, not just a limitation on what an observer can learn.

Also, the footnote on the C.S. Lewis quote is wrong, as was also pointed out in archive 7. Unfortunately, I don't know how to fix that. —The preceding unsigned comment was added by Mcswell (talk • contribs) 23:38, 17 January 2007 (UTC).

The Lewis reference is still wrong, and I'd love to know what the real sources are, but I agree it doesn't belong here. 70.94.45.243 21:52, 5 February 2007 (UTC)

[edit] Roll back recent vandalism

I see changes made by http://en.wikipedia.org/wiki/Special:Contributions/75.66.122.180 on 24 January 2007 are article vandalism. I'm not sure how changes can directly be rolled back, but that should probably be done. 128.111.53.203 00:43, 24 January 2007 (UTC)

Is done. --Van helsing 10:35, 24 January 2007 (UTC)

[edit] Nonlocality proven?

This comment is addressed to whoever made a recent edit in the article on Quantum Mechanics, in the "Philosophical consequences" section, working from cacheng.unige.ch at L'Université de Genève.

The matter of nonlocality is not quite settled, contrary to the assertion made in the recent edit. I happen to agree with the "nonlocality" view, but there are still highly-reputed physicists who are working to construct a viable hidden-variable theory (cf. Scarani and Gisin, at http://arxiv.org/abs/quant-ph/0110074 -- unless I am totally mis-understanding that paper). The assertion about the proven status of nonlocality, has no citation to back it up, and appears therefore to be personal opinion. Please undo this change.

If you disagree or have more recent knowledge, please reply; I would dearly love to have citations to back up the nonlocality view. Thank you. — SWWrightTalk 00:06, 21 February 2007 (UTC)

Here are a few comments. Honestly I haven't read the whole paper, but here's my understanding of what i've read: firstly, they admit that Bell's theorem excludes any sort of hidden-variable theory; instead, they propose something they call "hidden communication". <quote>the correlations are not entirely pre-established at the source; but they admit the existence of some form of communication between the particles [...]</quote>
Furthermore, Scarani and Gisin also admit that their theory violates special relativity: <quote>Therefore the model must single out the frame in which the hidden communication occurs</quote>.
IMHO, nonlocality is not seriously disputed anymore. - Saibod 11:32, 19 March 2007 (UTC)

The reason to desire locality is that according to special relativity, nothing can travel faster than the speed of light. The EPR paradox is an illustration of how quantum mechanics is incompatible with this idea. The paper you refer to invokes the EPR paradox to motivate a search for alternative theories to quantum mechanics but at the same time is willing to accept 'superluminal' signaling, i.e. faster than light communication. So it still does not have locality in the conventional sense of the word. Since non locality is generally accepted, lets leave it in for now. --V. 02:16, 1 March 2007 (UTC)

No, actually the EPR paradox is *not* incompatible with special relativity. See EPR_Paradox#Locality_in_the_EPR_experiment. The "spooky action at a distance" is instantaneous, but it is impossible to transfer information, thus there is no violation of causality. There are severe misconceptions about this in the section on relativity and QM about this, and especially in the main article on relativity and QM itself. I'm going to try and correct these. - Saibod 11:32, 19 March 2007 (UTC)

[edit] "Quantum theory"

I propose that quantum theory, currently a disambiguation page, be merged here. Comments? --Smack (talk) 06:59, 26 February 2007 (UTC)

[edit] Conan O'Brien and Jim Carrey Discuss Quantum Mechanics

Anyone care to comment on this? Does any of it make sense, or is it just babble? Jouster 17:45, 27 February 2007 (UTC)

They are babbling, in that neither of them has any idea what he is saying ... but to my semi-educated ear they appear to have talked to a genuine physicist while scripting their lines, because some of it actually makes sense. — SWWrightTalk 06:46, 28 February 2007 (UTC)

[edit] Awkward phrasing?

I cannot help but feel that

Some fundamental aspects of the theory are still actively studied. A common misconception is that Einstein was a part of it. However this is not true. Physicists begged him to join them in the quest but he did not accept these offerings because he said, "God does not roll dice".

sounds like a middle-school book report. Anyone else agree? Jouster 14:29, 3 March 2007 (UTC)

also inaccurate, Einstein certainly made some notable contributions to the field of QM (like spontaneous emission), he just did not subscribe to the Copenhagen interpretation. this is what the "god does not throw dice" referred to.--V. 19:28, 3 March 2007 (UTC)
Would anyone care to make the appropriate changes, then? I don't have any substantive expertise in the subject. Jouster 20:04, 3 March 2007 (UTC)

[edit] Glitch

Question. Can by some quantum glitch, fluctuation, matter appear from nothing for a long amount of time? Ozone 19:28, 19 March 2007 (UTC)

I'm not sure, but I'd say that it can, with exceedingly low probability. --Smack (talk) 05:28, 20 March 2007 (UTC)
Define "from nothing". Conservation dictates that you can't create matter or energy from, strictly speaking, "nothing", so if that's what you mean, the answer would seem to be, "No." On the other hand, entangled quantum states, blah blah blah, energy at a distant point coalescing into matter somewhere else would seem quite possible, if, again, stupendously-improbable. Jouster  (whisper) 19:30, 20 March 2007 (UTC)

That's how the universe started according to quantum cosmology.1Z 19:52, 20 March 2007 (UTC)

Jouster: We have the uncertainty principle for energy and time. --Smack (talk) 05:21, 21 March 2007 (UTC)
I understand the concept, at least on a basic level, of the uncertainty principle. I do not understand, however, how uncertainty allows for violation of conservation. This is almost certainly my own shortcoming, as I know very little about physics beyond Newtonian. Jouster  (whisper) 08:19, 21 March 2007 (UTC)
This isn't vanilla quantum mechanics. See string theory landscape and cosmic inflation. 1Z 11:49, 21 March 2007 (UTC)

Thank you. Damn, all the good ideas have been taken Peterdjones, 1Z. Ozone 20:55, 21 March 2007 (UTC)

[edit] Need for Section on The Philosophy of the Coppenhagen Interpretation of QM

I agree with the user (just below) saying that there ought to be a Wikipedia entry about the Coppenhagen Interpretation of QM -- or a section in this entry on the Coppenhagen philosopy of QM.

http://en.wikipedia.org/w/index.php?title=User:Michael_D._Wolok&action=edit

The Coppenhagen interpretation of QM says that nothing EXISTS in the world such as position and mometum -- NOT UNTIL A SENTIENT BEING MAKES A MEASUREMENT. It is not that there is uncertainty, it is that such a thing does not exist. The sentient creature capable of measurement does a GOD-LIKE act of CREATION when s/he/it performs the measurement and COLLAPSES the wavefunction. Prior to the measurement, yes, the wavefunction was "in a superposition of states" but what EXISTED was indeed that wavefunction. The wavefunction (by multiplying itself by its complex conjugate) becomes a probability distribution, but the WAVEFUNCTION ITSELF IS WHAT EXISTS in the world. The wavefunction exists in the world whether or not a mind ever existed, whether or not a measurement is ever made, whether or not the wavefunction ever gets collapsed by a creature wishing to do his/her God-like act of creating a magnitude into the world. So, Einstein, you focused only on what did NOT exist in the world without a mind -- which is what so riled you up about those Coppenhagen folks. But Einstein, you forgot that the Coppenhagen folks were just as vehement about the wavefunction EXISTING independent of any mind (like you greatly prefer) as they were about the magnitudes NOT existing until a mind collapsed the wavefunction. In short, Einstein saw the glass as half empty and then totally forgot that he was focused on only half of the glass. Another summary: as idealist (non-existence without mind) as the Coppenhagen folks were about magnitudes (position, momentum etc), those same Coppenhagen folks were total realists about the wavefunction's ontological status.

A BONUS ON UNDERSTANDING BAYESIAN STATISTICS

To the Sampling Theory statistician, the truth is a pure number. The unknown parameter, if given an audience with God, could be stated as e.g. 3.452. The data, however, are random variables. To the Bayesian, just the opposite is true. The Bayesian says, "waddaya mean my data are random variables? I got 2.17. What's random about that?" To the Bayesian, the parameter, the truth, is a probability density function. There are many implications for statistics, terminology, and computation procedure, but here the philosophy part of the Sampling Theory - Bayesian dichotomy is aided by a one-to-one correspondence of the Bayesian with the Coppenhagen interpretation of QM. When the Bayesian says "I got 2.17! What's random about that?", that is isomorphic to the Coppenhagen QM'er saying "That was the measurement result. I collapsed the wavefunction." When a Bayesian talks about the parameter, the truth being a probability density function, that is isomorphic to the Coppenhagen QM'er saying that "what really exists in the world is the wavefunction". When the Coppenhagen QM'er talks of this wavefunction being in a superposition of states, that is isomorphic to the Bayesian talking about the prior distribution on the parameter. Bayesian statistics may seem weird (in some ways: truth is a probability density function) but in other ways not (which I can't go into). But clearly the Bayesian Statistician's isomorphic ontology with the Coppenhagen QM'er makes Bayesian Statistics in a sense, well, sensible. Sampling Theory statistics is Newtonian; Bayesian Statistics is specifically Coppenhagen QM.199.196.144.11 19:24, 21 March 2007 (UTC)

There is an article on the Copenhagen interpretation, although I don't knwo whether it is philosophical enough for you.1Z 20:04, 21 March 2007 (UTC)

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