Talk:Classical physics

Cake
Where is the cake?--209.80.246.13 (talk) 15:35, 24 November 2009 (UTC)

Old discussions (this section title added later)
There is a contradiction on this page. It is said on this page that classical physics is strictly deterministic. It is also said that it includes the general theory of relativity (which makes the distinction between classical physics and einstieinian physics pretty blurry!) But the general theory of relativity implies nonlinear (not information conservative; irreversible) transformations, and is thus not deterministic.

There is an indisputable (at least by the laws of mathematics) logical contradiction in this page as it stands, which should be corrected, as it is, at best, confusing, and in the average case, misleading.

-- Kevin Baas 21:32, 15 Feb 2004 (UTC)


 * There is no contradiction. General relativity and nonlinear dynamics are deterministic. You are confusing the principle of determinism with the ability to find an analytic solution to nonlinear differential equations from a set of initial conditions. The latter is a practical difficulty, but is in complete accordance with determinism. Nonlinearity and determinism have nothing to do with each other. In fact, most quantum systems are linear. The page was a mess, however, and you are right to have been confused. I've now rewritten the page to be more in line what the accepted theory. -- Decumanus 22:39, 19 Feb 2004 (UTC)

No. I was not confused. I did not blur the concepts together that you are suggesting. I am speaking of, not "deterministic systems" in the mathematical sense, which chaos is included in. I am speaking of scientific determinism, which is defined in terms of capacity to predict. Although chaos is mathematically deterministic, it is not scientifically deterministic. A scientific determinstic system is also reversible.

This is the form of "deterministic" that we are discussing. General Relativity systems are not reversible (with probability one), and mutually, are not scientifically deterministic.

Nonlinear theories do not fit the category of classical physics, which assumes linearity/reversibility/scientific determinism. There is no confusion in this. It is very straightforward and historically irrefutable.

You, on the other hand, seem to be confusing mathematical determinism with scientific determinism. -- Kevin Baas 21:25, 20 Feb 2004 (UTC)


 * I'm very aware of the distinction between the two types of determinism. I have done quite a bit of work in that field. Nonlinear theores such as general relativity is considered part of classical physics by the community of physicists. Perhaps it shoudln't be, but it is. The definition of classical physics that is the one prevailing used is physics that is not quantum physics.


 * Your point is well taken between the difference between the two types of determinism. This is an enormous open question. But the time being, the underlying assumption is that nature is deterministic even if by practical standards it is not. I worked with Ilya Prigogine on this question a lot. Prigogine thought that perhaps that practical limitations on determinism led to a philosophical one. But there is no established mathematical way of expressing this yet. On the quantum level, the introduction of complex eigenvalues in Hilbert space is perhaps one way of achieving this. But it is simply too radical of yet to say that nonlinear systems are not deterministic. Perhaps one day we can achieve a better understanding of this for chaotic systems. It is a very interesting question. The opinion I expressed here are, in my opinion, the conservative and established viewpoint, which is what I feel belongs in Wikipedia. Your curiosity is well-founded, however. I see that you a professional background in computation.


 * I should add that my approach in writing this article is to edit it such that the vast majority of physicists would read it and say, yes, that's what classical physics is. I do not always agree with such established viewpoint (regarding determinism) myself, but I feel it is the one to be expressed in an encyclopedia. :) -- Decumanus 23:34, 20 Feb 2004 (UTC)


 * By the way, I apologize for not having read your user page and seen that you would obviously understand more than the average layman about numerical solutions as well as about chaos. The last couple days have been grueling with the physics on Wikipedia. There has been an on-going war about Big Bang and Black holes, and I have been sitting back watching the fur fly. I think it sort of put me in a huffy mode, and so my original comment to you was definitely in the wrong tone :) -- Decumanus 00:54, 21 Feb 2004 (UTC)


 * That's alright. I have been in a "huffy mode" before, myself.  Yet your tone was not so derogatory as you suggest.  I agree with your logic regarding the content of this page, and apparently your (contrasting) sentiments, as well.  In light of your argument, I am satisfied with the page as it stands.


 * As a side note, you mentioned that there is, to a significant degree, an open question involved... Do you think that, then, justifies some sort of note regarding this at the bottom of the page? And included in this note, perhaps, a link to a page that goes into more detail.  This would be in keeping with the NPOV philosophy of Wikipedia and the inter-linking imperative of the medium.  I wouldn't know how to write such a note, for you seem far more familiar with this open question(/debate?) than I am.  But I would suggest, at least, that, if included, it be stated in such a manner so as to seem, not antagonistic of the normative definition, but rather with motivation to clarify any "confusions" that a critical reader might have.


 * And regard to the "open question"... There are two questions here: (1)the relationship of mathematical to sceintific determinism, formally and philosophicly. (2)Whether or not the dichomoty classical-quantum is more useful than a more articulated classification.  You refer, if I understand you correctly, primarily to the first.  To me, this does not seem like a difficult question.  Perhaps the difficulty is cultural and paradigmatic.  Something I would like to know more about, in any case.  I do not imagine myself alone in this respect.  But are there canonized words/phrases that wikipedia pages can be made about, discussing this issue?  Perhaps on the determinism pages themselves? (although that neglects the very significant aspect that it is an integral part of a larger debate (I feel this, at least.  Is it, to your knowledge?)), and fails to inform one of this larger debate.)


 * I am delighted to hear that you worked with Ilya. I have read some of her works and found them quite interesting. (I assume you've already infered this from my mention of irreversibility.)  And now I have examined your user page.  Nice.  Good luck in the debates!  -- Kevin Baas 20:02, 21 Feb 2004 (UTC)


 * Oh, and isn't a principle o classical physics the conservation of energy? (Thales of Miletus) And aren't nonlinear systems non-conservative? Yet another, very fundamental contradiction. Is this discussed at all? -- Kevin Baas 21:58, 21 Feb 2004 (UTC)

Old Discussion revisited
My personal bias is that classical physics is pre-twentieth century physics. In other words, before the advent of the special and general theories of relativity (1905 and 1914) and the advent of Quantum Mechanics (a combination of discoveries in the first 25 years of the 20th century). Chaos theory does not really belong here, according to this viewpoint; chaos theory and the theory of dynamical systems was a viewpoint pursued by Smale (and others) from the early 1970s. This can hardly be called "classical"; this physics is contemporary! Physics which is classical in my opinion is Newtonian Mechanics, Boltzmann's Thermodynamics, and Maxwell's equations of Electromagnetism. If one is going to include everything else, except for quantum mechanics, then perhaps instead of referring to this article as "Classical Physics" it should be relabelled as "Physics in the Classical Limit" (ie letting Planck's constant go to zero) or "Physics in the Large". --Gremlin 13:32, 8 Feb 2007 (UTC)

Relativistic Claims
Claims that relativity has never been "superseded" or "depricated [sic]" are 1) simplistic and 2) appropriate to a relativity page, not here. It is also unnecessary to state that relativity is incorporated into relativistic QFT, since the adjective already specifiies this. I shall remove them. --Michael C. Price talk 15:22, 10 July 2006 (UTC)

Relativity part of classical physics?
The article currently contradicts itself over whether GR counts as part of classical physics. (My understanding is that it doesn't, i.e. the list of topics in the Scope section is wrong.)

The article also says (consistently!) that SR is part of classical physics. I've always understood "classical physics" as being essentially "physics before 1905". (I realise that for in relativity, the old physics is usually called "Galilean" rather than "classical".) Are there actually different views on what the term "classical physics" means? Djr32 (talk) 23:02, 30 November 2008 (UTC)


 * According to Stephen Hawking, GR is a classical theory: "Einstein's general theory of relativity... is what is called a classical theory; that is, it does not take account of the uncertainty principle of quantum mechanics" (Brief History of Time, last para of chapter 4). On the other hand, the classical mechanics article suggests that it's a matter of opinion whether any relativistic effects are included in classical mechanics. Djr32 (talk) 20:31, 28 December 2008 (UTC)
 * Hawking is  wrong  about  this  and  many other things.  Classical  Physics  is  actually  before 1900,  and  Modern Physics  is after  1900,  by  common  established  usage.   So  this  Wikipedia  article  is a  disgrace  and  all  wrong.  47.201.178.44 (talk) 03:39, 29 December 2017 (UTC)
 * In the literature, I have seen the term classical physics refer to either pre-1900 (thus excluding relativity) or pre-quantum physics (including relativity). I agree with your edits to the article. What I would like to see revised the most is the leading paragraph, which at the moment is plain wrong. Rentier (talk) 14:36, 30 December 2017 (UTC)

Definition
With regards to the sentence: If a currently accepted theory is considered to be "modern," and its introduction represented a major paradigm shift, then the previous theories, or new theories based on the older paradigm, will often be referred to as belonging to the realm of "classical" physics. Are there any sources corroborating this? As it stands, the entire leading paragraph constitutes original research. I have never seen anything else than pre-quantum (very often) and pre-relativity (rarely) physics called classical, which hardly justifies the phrase will often be referred to. As a counter-example, I do not think anyone would ever call the old quantum theory classical. Furthermore, there exists the term "pre-classical physics" (e.g. ), so probably the article should include a lower bound on time.

I feel the whole lead may need to go, although I do not like to remove content. Any suggestions? Rentier (talk) 12:16, 24 March 2016 (UTC)

Assessment comment
Substituted at 11:51, 29 April 2016 (UTC)

Difference between modern physics and past physics
?? 2402:8100:396D:2F39:9A9:5A36:3169:8706 (talk) 00:58, 30 March 2022 (UTC)