In article ,
(John Baez) writes:


Lee Smolin told me some neat stuff about MOND - that's "Modified
Newtonian Dynamics", which is Mordehai Milgrom's way of trying to explain
the strange behavior of galaxies without invoking dark matter. The basic
problem with galaxies is that the outer parts rotate faster than they
should given how much mass we actually see.

For the non-experts, I should point out that "dark matter" has been used
in several contexts. First, the mass-to-light ratio of the universe is
less than 1 in solar units. No big deal; that just means that on
average stars aren't as bright as the sun and doesn't necessarily imply
some form of "mysterious" dark matter (although it could). Second,
there is a lot of non-baryonic matter, which can't consist of any known
particles. No-one debates this, but we don't know what it is---except
perhaps if MOND is correct. Third, when some folks used to believe
(some still do) that Omega_matter=1, then one needs a lot of additional
dark matter to make up the difference between 1 and the 0.3 which is
more or less directly inferred.

Dark matter, non-baryonic matter etc is often presented as something
mysterious, but a priori why should most of the universe be composed of
something we are familiar with, being made of baryons dependent on the
light of a star? Thus, I don't agree with some MOND enthusiasts that
dark matter is a priori a bad idea, a deus ex machina to save
appearances etc.

Also, it is possible that there is dark matter AND some form of MOND
is correct. Most people will cry "ugly!", "it has to be one or the
other!" etc. Just a few years ago, such armchair-cosmology arguments
were used to "prove" that a universe with a cosmological constant is so
unnatural it can't be correct.

Another interesting point, noted in McGaugh's pages, is that MOND has
actually made a lot of predictions, which years later were verified by
observation, often by folks who didn't even know about MOND or
predictions. Many of the more mainstream cosmological ideas don't even
make testable predictions, much less have had them verified. In this
respect, MOND has been a good guy.

Instead, it's just a blatant attempt to fit the experimental data.
And it's not even elegant. In fact, it's downright ugly.

Initially, perhaps, but since predictions were made, it is NOT just a
posteriori curve fitting, and CAN be falsified.

Here are two reviews that Smolin especially recommended:

13) Robert H. Sanders and Stacy S. McGaugh, Modified Newtonian Dynamics
as an Alternative to Dark Matter, available as astro-ph/0204521.

Sanders is also a MOND proponent and has written several papers on it.

14) Anthony Aguirre, Alternatives to dark matter (?), available as
astro-ph/0310572.

Here's McGaugh's website with links to many papers on MOND, including
Milgrom's original papers:

15) The MOND pages, http://www.astro.umd.edu/~ssm/mond/litsub.html

McGaugh is a strong proponent of MOND - though he didn't start out that
way - so the selection may be biased.

True to some extent, perhaps...but less biased than a lot of anti-MOND
propaganda! :-)

Does anyone know an intelligent
detailed critique of MOND? If so, I want to see it!

Indeed!