Modified Newtonian Dynamics (MOND) was proposed in 1981/1983/1989 (depends who you ask) by Mordehai Milgrom:
http://ca.geocities.com/mercy@rogers.com/
Experiments"Is it possible to design an experiment that would confirm MOND predictions, or rule it out? Unfortunately, conditions for conducting this experiment can be found only outside the Solar system. However, the Pioneer and Voyager probes are currently traveling beyond Pluto and perhaps they have already reached this zone. To check that, let's calculate the radius of the gravitational sphere of influence of the Sun, inside which a probe undergoes an acceleration greater than a0.
We have seen above that the equation relating the acceleration a to the distance r from the Sun is
(GM)/r2=µ(a/a0)a
So, for a=a0, assuming µ(a/a0)=µ(1)=1, with G=6.67 10-8 and M (the mass of the Sun)=2 1033 g, we get r=3.5 1017 m. This is roughly a tenth of a parsec, four times the distance between Pioneer 10, the most remote probe, and the Sun. It is therefore doubtful that an experiment could be accurate enough to test the departure from Newton's second law. Perhaps µ(1) is less than 1, but it's very likely greater than 0.2. Consequently, experiments on MOND will have to wait for the next age of space exploration."
Observations"In search for observations that would validate his theory, Milgrom noticed that a special class of objects, the low surface brightness galaxies (LSB) are of particular interest: the radius of a LSB is large compared to its mass, and thus almost all stars are within the flat part of the rotation curve. Also, other theories predict that the velocity at the edge depends on the average surface brightness in addition to the LSB mass. Finally, no data on the rotation curve of these galaxies was available at the time. Milgrom thus could make the prediction that LSBs would have a rotation curve essentially flat, and with a relation between the flat velocity and the mass of the LSB identical to that of brighter galaxies.
Since then, many such LSBs have been observed, and while some astronomers have claimed their data invalidated MOND, others said it confirmed the prediction. At the time of this writing, the debate is still hot, and scientists are waiting for more accurate observations."
Criticisms http://en.wikipedia.org/wiki/Modified_Newtonian_dynamics"An empirical criticism of MOND, released in August 2006, involves the Bullet cluster (Milgrom's comments[1]) , a system of two colliding galaxy clusters. In most instances where phenomena associated with either MOND or dark matter are present, they appear to flow from physical locations with similar centers of gravity. But, the dark matter-like effects in this colliding galactic cluster system appears to emanate from different points in space than the center of mass of the visible matter in the system, which is unusually easy to discern due to the high energy collisions of the gas in the vicinity of the colliding galactic clusters.[2]. MOND proponents admit that a purely baryonic MOND is not able to explain this observation. Therefore a "marriage" of MOND with ordinary hot neutrinos of 2eV has been proposed to save the hypothesis [3].
One more recent empirical finding which would be hard to reconcile with MOND (even the relativistic TeVeS version) is the possibility of large scale mapping of dark matter using gravitational lensing (Massey et al. 2007). It is not yet clear whether the effect - especially gravitational lensing by areas with no visible galaxy clusters - can be explained by any version of MOND, unless dark matter is included (which would go against the very reason MOND was proposed).
Another criticism of MOND is that it violates Occam's Razor, which states that the simplest explanation is usually correct."
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But that's not the end of the story -
http://arxiv.org/abs/astro-ph/0701848"MOND...in its original form it could not address gravitational lensing or cosmology. After reviewing some of the evidence in favor of MOND, I recollect the development of relativistic formulations for it to cope with the last deficiency" - Jacob D. Bekenstein
