Sir Isaac Newton gave us the original notion that gravity is the organizing principle in all of astronomy.1
By the late 1800s, scientists had developed the ideal gas laws, and qualified Newton in saying that gravity definitely pulls in, but hydrostatic pressure (as a function of heat) also pushes back out. So the balance of these forces determines whether or not a dusty plasma will undergo gravitational collapse. If the gravity is strong and/or the gas pressure is weak, collapse will occur.2,3,4
The first indication that this was not a complete theory came from evidence that a dusty plasma is more likely to collapse if there has been a supernova nearby. If gravity and gas pressure are the only two factors, then either the supernova added mass to the dusty plasma, and/or removed heat. It is certainly true that the ejecta from a supernova will add mass. But the thermalization of the momentum of the relativistic particles will add a lot more heat. Explosions actually disperse matter; they don't cause condensation.
Then, in the mid-1980s, high-precision, space-based instrumentation enabled accurate estimates of the actual amount of matter in dusty plasmas. Gravity was found to be somewhere between 1/5 and 1/20 of the force necessary to cause the collapses.
To absorb the anomaly without having to redo 350 years of work, scientists invented cold dark matter (CDM) as a new source of gravity.5
Cleverly designed to not be detectable any other way, the quantity of CDM in any given region of the Universe can be set equal to the gravitational anomaly. But CDM is turning into a false economy, because it simply does not behave as "missing mass".
CDM is credited with exerting gravitational force on dusty plasmas, causing their collapse. It also supplies 4/5 of the centripetal force that keeps spiral galaxies organized. But CDM does not itself collapse, nor does it accumulate around the aggregates that it creates (i.e., the "cuspy halo
" problem). In other words, there is no concentration of CDM around planets, stars, black holes, or at the centers of galaxies. This constitutes a violation of Newton's 3rd
law of motion, which states that when a body exerts a force on another body, that other body exerts the same force on the first body (just in the opposite direction). If CDM exerts force on other bodies, why don't they exert force on it? We could solve the problem if we could say that one of the properties of CDM is that it likes to be diffuse. But then we'd expect it to be thoroughly distributed throughout the Universe. As such, its gravitational force, coming from all directions, would cancel itself out, and it would be completely
undetectable. Since the missing force cannot come from a diffuse source, this problem is intractable, by definition.
CDM also lacks inertial forces, since objects moving through it experience no friction, which would surely be detectable if it was 4/5 of the matter in the Universe.
So CDM really only displays 1/2 of one of the properties of mass: it exerts gravitational force on other objects, but it does not respond in turn to their gravity, nor does it have inertia. Calling it "matter" is actually just bad semantics. In reality, all that we really have is a major gravitational anomaly, coming from an unidentified force. The proper search for the source of this force should start simply with an enumeration of its properties.
1. Newton, I. (1687): Philosophiæ Naturalis Principia Mathematica. New York: Daniel Adee ⇧
2. Lane, J. H. (1870): On the Theoretical Temperature of the Sun under the Hypothesis of a Gaseous Mass Maintaining its Volume by its Internal Heat and Depending on the Laws of Gases Known to Terrestrial Experiment. The American Journal of Science and Arts, 2 (50): 57-74 ⇧
3. Jeans, J. (1902): The Stability of a Spherical Nebula. Philosophical Transactions of the Royal Society of London, Series A, 199: 1-53 ⇧
4. Eddington, A. S. (1927): Stars and Atoms. Oxford: The Clarendon Press ⇧
5. Blumenthal, G. R.; Faber, S. M.; Primack, J. R.; Rees, M. J. (1984): Formation of galaxies and large-scale structure with cold dark matter. Nature, 311: 517-525 ⇧