The Modified Newtonian Dynamics/Talk

The Modified Newtonian Dynamics 11:18 am [Added copyright notices] . . . . . 80.11.172.xxx And nobody's reacting ? --Taw

Well, we should expect a reaction tomorow, but I don't think anything is actually wrong with the text of the copyright notice. Everything on the wikipedia is copyrighted, we just license it on the terms of the GNU FDL, as long as the author is not specifically revoking those rights, it is perfectly acceptable that he mentions on the page that the text is copyrighted. But that's just my opinion. MRC

Adding a copyright notice seems right to me. How could I take such a picture of M51 myself? BTW, any reason all quotes are question marks now? dlebansais

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Yes, because you copied the text from a Microsoft Windows document with "curly quotes", which are not valid ISO-8859-1 characters. Please see Wiki special characters for how to do these correctly. --LDC

Hopefully, everything is fixed now. dlebansais

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I added the reason why most astrophysicists are unlikely to take MOND as the first explanation for odd galaxy rotation curves.

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As far as I can see, the maths (as presented here) do not make sense. Surely there is no way a paper could have been published with this glaring weakness, so I am guessing the problem is in the Wikipedia article.

"In the every day world, a is greater than a₀ for all physical effects, therefore µ(a/a₀)=1 and F=ma as usual."

Now µ is defined as equalling either 1 (when x > 1) or x (when x < 1). Now these equations imply that on Earth x < 1 (and hence µ < 1). (a/a₀ must be large, as a is greater than a₀, so µ must be small to get it to equal 1). In this case x*a (and hence µ * a) must actually be pretty close to the value of a₀ so as to cancel out and produce F=ma.

Why??? What determines the value of x (and hence µ) in this case, so that it cancels out so conveniently for the "on earth" situation? I can create any number of formulae which can do anything I want if I don't have to obey any rules determining the values of the variables.

Basically it is saying "Well on Earth, x (arbitrarily chosen) times a is equal to a₀ (an undefined constant) so everything works out just fine!" That's not particularly rigorous.

Obviously the theory MUST conform to the net f=ma result on Earth, lest it be laughed off. But this conformity seems VERY contrived at the moment, and that really weakens the rest of the argument. I'm not criticising the theory, but as a person who knows nothing of this particular subject, yet is able to follow the maths, I have a problem with this as a Wikipedia article. - MMGB