Dark Matter: WIMPs, MACHOs or Sacred Cows?

The term dunkle materie or dark matter was first used in 1933 by the Swiss astronomer Fritz Zwicky. It appeared in a Swiss scientific journal in which Zwicky detailed the curious results he had obtained when he measured the individual velocities within a large group of galaxies known as the Coma cluster. He found that all of the galaxies that he measured within the cluster were moving so rapidly relative to one another that the cluster should have dissipated long ago. The visible mass of the galaxies making up the cluster was far too little to produce enough gravitation to hold the cluster together. For the Coma cluster to have its observed dynamics, it would be necessary to assume that its true mass was two to four times larger than its mass visible from earth. Zwicky proposed that large quantities of dark matter existed within the galaxies, but outside of the stars, and it was this mass that supplied the extra gravitation needed to hold the cluster together. At first Zwicky and his single cluster of galaxies were ignored. Then as the velocities of greater numbers of galaxies were measured, it became apparent that all clusters of galaxies moved much faster than could be accounted for by their visible mass. According to cosmologies based on General Relativity or Newtonian Gravitation, the vast majority of a galaxy’s mass must reside the dark area surrounding the galaxy, invisible to detection. Measurements of the rotational motion of many galaxies force the observer to the improbable conclusion that the light “visible” portion of a galaxy contains only a small percentage of its total mass, while most of the mass resides in vast unseen halos in regions far outside the disk of visible stars.
About the same time that Zwicky was examining the Coma cluster, the Dutch astronomer Jan Oort began to systematically measure the relative velocities of the local group of stars that surround our solar system. After measuring several of these velocities, an unexpected pattern began to develop. All of these stars were moving so fast that the group should have flown apart long ago. For the group to be held together by gravity in its present configuration it would have to contain at least three times as much mass as could be accounted for by the group’s visible stars and detectable clouds of gas. To account for this, Oort proposed that, in the case of our solar system, a vast accumulation of dust, asteroids, comets, and small planets orbited the sun in the outer regions far beyond Pluto. This “Oort Cloud,” as it has come to be known, has been actively sought, but very little direct evidence for its existence has ever been uncovered. Although Oort brought the dark matter problem much closer to home, most cosmologists continued to ignore the phenomenon for many years.
Then, during the 1960s, the American astronomer, Vera Rubin, began to measure the rotation rates of spiral galaxies and found that they were all spinning much too fast to stay together, unless they contained vast amounts of unseen mass that could not be accounted for by their visible stars. Around 1970, she began to study the Andromeda galaxy, which is our closest neighbor, and quite similar to the Milky Way. Like most spiral galaxies, Andromeda has a large luminous bulge of densely packed stars at its center that is surrounded by a very thin disk of stars situated quite close together near the bulge, but gradually becoming very sparse at the outer edges. Until Rubin’s investigations, it was assumed that the majority of a galaxy’s mass was located in its central bulge and that only a small portion of it resided in the outer disk. However when Andromeda’s mass distribution was calculated, using the dynamics of its motion rather than the distribution of its stars, a totally unexpected result was obtained. Not only did Andromeda contain only about 10 percent of the stars necessary to generate enough gravity to hold it together, but because of the dynamics of its motion, the extra 90 percent of its hidden mass had to be situated in an invisible halo at the outer edges of the disk.
These results prompted other researchers to begin looking for new examples of this perplexing mass deficit. Almost everywhere they pointed their telescopes, similar results were found. The “existence” of dark matter seemed ubiquitous, even if its identity remained an enigma. As more examples were found, the magnitude of the mass deficit problem continued to grow. In 1993, NASA’s ROSAT X-ray satellite discovered a huge cloud of hot gas encompassing a small cluster of galaxies known as NGC 2300. In order for this cloud to maintain its structure, it would need to contain 30 times as much mass as could be accounted for by the gas making up the cloud. Additional observations even led some theorists to conclude that as much as 99 percent of the mass of the universe could not be accounted for.
Gradually the idea of dark matter gained wider and wider acceptance until today its search has become the primary pursuit of not only most astronomers but also many particle physicists as well. Yet after several years of intensely probing both the macrocosm and the microcosm not even the slightest trace of this missing mass has ever been identified.
Each new and unexpected discovery in astronomy was eagerly scrutinized by the theorists as a possible clue to the identity of dark matter. In 1991, the Compton Gamma Ray Observatory (GRO) spacecraft discovered the sky to be sprinkled very uniformly with bursts of gamma photons for which no visible sources could be located. Dark matter enthusiasts quickly pointed out that these bursts could be coming from deposits of some kind of exotic weakly interacting matter that existed, otherwise unseen, in the halo surrounding the visible disk of the Milky Way. They proposed that these bursts might be caused by chunks of “dark matter” colliding with, and annihilating, chunks of “anti-dark matter.” However by 1994, when over 700 of these bursts had been carefully analyzed, it became apparent that the majority of them came from the universe at large, and not from within the Milky Way halo. It was found that the duration of the dimmest flashes was about twice as long as the brightest flashes. Also the photons from the dim flashes were red-shifted compared to the photons from the bright flashes. This would seem to indicate that the bursts originated at sources spread far and wide throughout the universe.
If the assumption is made that the majority of these bursts were similar in duration and magnitude when produced at their source, then this data can be used to support the idea that the dim red-shifted bursts originated farther away than the bright bursts, and that their large red shifts are cosmological in nature. If these dim bursts had originated within the galactic halo, then their red shifts would indicate that their sources were moving rapidly away from the observer. If this were true, we would also expect to find blue-shifted bursts from sources moving toward us, which seem to be completely absent. While the identity of the phenomenon that creates these gamma photon bursts is still open for speculation, it is doubtful that they originate in the vastly massive yet invisible halo that General Relativity demands must surround ours and other galaxies.
The scientists working on the dark matter problem can basically be divided into two groups: MACHOs and WIMPs. The MACHO group, (Massive Compact Halo Objects), is attempting to conceive of and then identify configurations of ordinary matter that could account for the missing mass. The WIMP group, (Weakly Interacting Massive Particles) is theorizing the existence of new and exotic fundamental particles that can’t be detected, and then attempting to devise ways to detect them.
The main obstacle encountered by the MACHO scientists is that ordinary matter, whether in the form of gas clouds, dust clouds, or compact bodies, is easily detected by astronomers’ instruments. Gas clouds, which consist of individual atoms and molecules, are easily detected by the characteristic radiation that they absorb and emit. Dust clouds, which contain particles of many atoms and molecules stuck together, tend to scatter light of many wavelengths. If the universe contained enough dust to make up the dark matter deficit, the light from the stars would be so scattered that we would be lucky if we could even see Andromeda let alone the blue galaxies at the edge of the universe. Additionally, dust is easily visible because it covers such a large area of space. For example, a one cubic meter block of gold would only obscure the view of approximately one square meter of space, whereas, the same block of gold hammered into gold leaf would cover an area nearly 12,000,000 times larger: 11.7 square kilometers.
Jupiter = 1
Brown Dwarf = 10
Red Dwarf = 100
Sun = 1,000
Supergiant Star = 10,000
Quasar = 100,000
Yet another problem with dust as dark matter concerns the identity of the elements making up the dust particles. Hydrogen and helium make up 99 percent of the visible matter in the universe but cannot form particles of dust because they are gaseous elements and do not form solids except at temperatures very close to absolute zero. This would mean that dark matter dust would have to be composed of the heavier elements. If the universe contained these vast amounts of heavy elements, then it would seem that these abundances could be easily verified independently by studying the composition of the cosmic ray flux. However, the High Energy Astronomical Observatory HEAO-3 satellite found that the relative abundances of elements making up the cosmic rays were very similar to the elemental abundances of the universe at large. It was found that the 79 stable elements heavier than hydrogen and helium accounted for only about 1 percent of cosmic ray events. As difficult as it is to envision the cosmological process that can accelerate atomic nuclei to the enormous energies of some cosmic rays, it is virtually impossible to imagine how the heavy elements could have been excluded from this acceleration process if they really did make up the majority of mass in the universe. How could it be that hydrogen and helium make up 99 percent of the nuclei found in cosmic rays as well as in the solar system but only account for a very small percentage of the total atoms in the universe? The answer to this is very simple. There is no way that significant quantities of heavy elements could hide in the universe.
Thus, it would seem that the dark matter must be in the form of a solid body, and it must be largely composed of hydrogen and helium. The physical properties of these two elements set strict parameters as to the possible size of such dark matter bodies. A hydrogen/helium gas cloud will only compress to form a compact or solid body if it is massive and dense enough to have an escape velocity that is greater than the thermal velocity of the individual gas molecules. A Jupiter-size body is near the lower limit for a compact body that can compress from a hydrogen/helium cloud. In a much larger body, such as a star, hydrogen and helium will fuse and release energy that will eventually be converted into light at the star’s surface. Red dwarf stars, which are about 100 times as massive as Jupiter, are near the lower-limit for compact bodies that have the gravitational compression great enough to ignite the fires of hydrogen fusion and thus to shine. Therefore, if bodies smaller than Jupiter couldn’t compress from hydrogen/helium clouds, then they would remain as easily detectable gas clouds. And if bodies larger that Jupiter shine too brightly to hide, then all of this “missing” or dark matter must be contained in bodies between the size of Jupiter and a red dwarf star. These long sought bodies have been called brown dwarfs because, while not as bright as red dwarfs, some of them should emit enough infrared radiation to make their detection possible.
One problem with brown dwarfs as dark matter is that they represent only a small band on a very large spectrum of different sized astronomical bodies. The sheer numbers of brown dwarfs needed to make up the mass deficit makes their prolific existence seem highly unlikely. How could it be that the universe organized itself into brown dwarfs to the near exclusion of all other sized bodies? If the Andromeda galaxy contains 200 billion stars with an average mass of the sun, then it would also have to contain approximately 20 trillion brown dwarfs, mostly located in the nether regions around the outside of the galaxy’s disk.
Another question is how these bodies manage to keep an almost perfect separation from one another. While each body may be invisible by itself, the joining of two or more would create a visible star. In a crowded halo containing trillions of brown dwarfs, it would seem that at least some if not many should join together to form visible stars.
Besides brown dwarfs, it has been proposed that dark matter was ordinary matter that fell into black holes. The biggest problem with this idea (even if you believe in black holes) is that black holes are thought to exist in the matter-rich centers of galaxies. It is difficult to conceive of great numbers of black holes being created in the visibly empty environment of a galactic halo. If black holes formed, why didn’t stars also form out of the same material? Also, black holes are only thought to form after a long life as a visible star. Where are all of the pre-black hole stars? If these black holes were created during the Big Bang, or even if they existed before, how did they become separated from the other matter in the universe? Why didn’t the galaxies form around the black holes instead of the other way around?
On the other hand, the WIMP astronomers believe that the missing mass of the universe may be contained in one or many kinds of stable, massive, exotic, particles, that don’t respond to either the electromagnetic or the strong nuclear interactions. These particles are thought to be all-pervasive yet elusive even to the extent that vast quantities of them constantly zip through our bodies undetected. Many types of WIMPs have been postulated and given names such as axions and quark nuggets but none have ever been discovered. The search for the top quark, and its attendant construction of the superconducting super collider, is motivated by the hope that when the top quark is created, it will be able to combine with other quarks to form a very massive and hitherto unknown stable particle. Thus suggesting that such particles could have been created in great numbers during the Big Bang and be responsible for the missing mass of the universe that we detect today.
One of the main problems associated with using WIMPs to account for dark matter is stability. The only massive particles ever found to be stable are the proton, and the neutron when it is combined with protons in the proper proportions to form the various stable isotopes of the elements. Although hundreds of other particles have been created and identified, none have ever shown even a hint of stability.
WIMPs also share a major drawback with MACHOs in answering the dark matter question. This problem deals with location. The dark matter that orchestrates the motion of spiral galaxies resides largely in a halo outside of the disk containing visible stars. If the WIMPs have existed since the Big Bang then they should have shared the same gravitational organization as the ordinary matter. How could it be that almost all WIMPs ended up orbiting galaxies, and almost none ended up in the centers of stars? If gravity was the primary particle-organizing force after the Big Bang, how did dark matter and visible matter become so completely separated in the process? Why do WIMPs even associate with galaxies, which contain only a negligible amount of mass compared to their own? An even more intractable problem is encountered in any attempt to explain how WIMPs, or even MACHOs, became evenly distributed within the hot, X-ray-emitting cloud located in the NGC 2300 galactic cluster. How could these bodies initially take up residence in the galactic halos and then miraculously show up in vast quantities evenly distributed in a cloud that was formed much later?
The answer to all of the seemingly difficult and paradoxical questions posed by the dark matter dilemma is really quite simple. There is no dark matter, because there is no gravitational mass!
The underlying obstacle preventing the scientific community from solving the dark matter problem has nothing to do with a technological inability, but rather, an almost religious faith in the Equivalence Principle. Equivalence was first proposed by Galileo and then rubber-stamped by Newton. Newton did not have an explanation for equivalence, and does not appear to have spent much time considering it. By contrast, Einstein was totally obsessed with promoting the idea of equivalence as an article of faith, even though he was never able to offer even the tiniest shred of positive experimental evidence that could verify a material difference between weight and inertia. As a very paradoxical way of “proving” Equivalence, Einstein stated that no experiment could be performed that would show a body’s inertial mass to have a different quantity that its gravitational mass. The body of data representing the dark matter problem is in fact the experiment that answers Einstein’s challenge.
Even though he spent the greater part of his life in a completely unsuccessful attempt to combine the Equivalence Principle with quantum mechanics, there seems to be no evidence that he ever allowed himself any doubt concerning the ad hoc and somewhat preposterous assumption of equivalence. Einstein’s reputation has since become so exalted that his dogmatic position on Equivalence has gained virtual universal acceptance. It is this most deep-seated of all scientific prejudices that has made the dark matter problem seem so difficult.
As the dark matter “problem” developed, the initial reaction of the authorities in the scientific community was to sweep the problem under the rug with the other anomalous observations that did not support the current theoretical paradigm. However, as instruments improved, and more and more accurate observations were made deeper and deeper into space, the dark matter problem grew larger until soon it became difficult to find a rug under which one could sweep something that certain observations showed to be 100 times more massive than the visible universe.
To the layperson, all of these observations of “missing” mass would tend to cast doubt on the validity of General Relativity. However, for the scientific faithful this option is not possible because Einstein’s theories are accepted as articles of faith, and are no longer subject to question. It is this very rigid attitude toward General Relativity that is responsible for the whole dark matter enigma.
However, if the Equivalence Principle is removed from General Relativity, we essentially arrive at the theory of Absolute Motion, and within this new theory, the dark matter problem completely disappears because it is no longer assumed that inertial mass must be accompanied by an equal quantity or gravitational mass. When size becomes the cause of gravity and mass becomes only its effect, it is no longer necessary to invent unseen gravitational mass to explain observed gravitational motions, because gravity becomes an “expansion” rather than an “attraction.” The missing mass of the universe that has come to be called “dark matter” is not inertial mass but rather it is gravitational mass. The principle of Gravitational Expansion eliminates the need for the idea of gravitational mass by using only the concept of inertial mass to explain the acceleration of gravity. As an example of the way that Absolute Motion Theory differs from General Relativity and gravitational attraction theories, we will examine a mysterious dark matter problem that occurs right here on Earth: cloud formation.

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