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Talk:Brownian motion

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by University of Arkansas - phys.org — Preceding unsigned comment added by 2a02:587:410b:c290:5918:f010:9a03:72e9 (talk) 23:10, 3 October 2020 (UTC)[reply]

Einstein's theory[edit]

In the subsection Brownian_motion#Einstein's_theory, at the first line of the Taylor Series expansion, we have the following equality:

${\displaystyle \rho (x,t)+\tau {\frac {\partial \rho ($x)}{\partial t}}+\cdots =\rho (x,t+\tau )=\int _{-\infty }^{\infty }\rho (x-\Delta ,t)\cdot \varphi (\Delta )\,\mathrm {d} \Delta =\mathbb {E} _{\Delta }[\rho (x-\Delta ,t)]}

On the right hand side, why do we have ${\displaystyle \rho (x-\Delta ,t)}$ insted of ${\displaystyle \rho (x+\Delta ,t)}$?, since Einstein himself derived the Diffusion Equation from^[1] ${\displaystyle f(x,t+\tau )=\int _{-\infty }^{\infty }f(x+\Delta ,t)\cdot \varphi (\Delta )\mathrm {d} \Delta }$.

Zaphodxvii (talk) 04:31, 31 December 2020 (UTC)[reply]

To editor UiawsbdNicoDude: Wikipedia takes a dim view of self-proclaimed experts because we only regurgitate sources. If you have a disagreement with content, please explain if you think a cited source is not reliable, if you think the content does not accurately summarize what the source says, or if you have better sources. I ask all new editors to temper their enthusiasm with humility, as we have a system here that has worked for twenty years and we do not need your lack of collaboration. (I am not watching this page, so please ping me if you want my attention.) Chris Troutman (talk) 04:36, 2 December 2022 (UTC)[reply]

Greetings. The article has been tagged since 2012 with "citation needed". The B-class criteria (#1) states, The article is suitably referenced, with inline citations. It has reliable sources, and any important or controversial material which is likely to be challenged is cited.

There is also a "needing clarification" tag since April 2010 and "too technical" since June 2011. Criteria #4 states, The article is reasonably well-written and #6 states, The article presents its content in an appropriately understandable way.

There are many unsourced paragraphs and the article fails the B-class assessment. -- Otr500 (talk) 08:07, 27 February 2023 (UTC)[reply]

The last paragraph of the history section claims that Einsteins 1905 paper and Smoluchowskis 1906 paper present Brownian motion as proof that molecules exist. I have now, for another reason read those papers, and at no point is the existence of molecules questioned, or considered necessary to be proven. Both papers already work within the assumption that molecules exist. -- 141.76.69.115 (talk) 09:55, 21 June 2024 (UTC)[reply]

This is why Wikipedia relies on secondary sources. The papers indeed "assume" molecules. Based on this assumption, the physical model of Brownian motion makes certain predictions which match critical experimental evidence which otherwise is not explained. Retrospectively, historians trace the acceptance of molecules to the realization that these papers provide a good model, and hence molecules became broadly accepted. That is how physics proceeds. Primary sources should not be the basis of claims in Wikipedia. Johnjbarton (talk) 14:46, 21 June 2024 (UTC)[reply]

I think then a secondary source should be cited there. 141.76.69.115 (talk) 08:14, 2 July 2024 (UTC)[reply]