From Wikipedia, the free encyclopedia.
The neutrality of this article is disputed. The factual accuracy of this article is disputed
Plasma cosmology is a non-standard cosmological view which relies on the electromagnetic effects of plasma for explaining the large-scale structure of the universe, energy storage, and energy flow between seperate areas of the universe, among other things. In the mid-1990's, interest in plasma cosmologies arose among the standard (Big Bang) cosmological community, mostly as a "fallback" theory, in case COBE failed to discover variations in the cosmic microwave background or in case primordial helium abundances turned out to be unexplainable by standard cosmologies. This interest rapidly waned as more precise measurements, such as those from COBE, appeared to support standard cosmologies in the late 1990's. However, both Peratt and Lerner have shown how the CMB can also support plasma cosmology. In particular, Lerner has shown how the COBE results themselves can support plasma cosmology. Regardless of this, as of 2003, plasma cosmology is still not accepted by most cosmologists.
Within astrophysics, plasma physics and electromagnetic fields are active areas of research. Many astrophysical bodies are believed to be made of plasma, and even within the conventional Big Bang cosmology, the entire early universe consisted of plasma before recombination (eg. the process inwhich electrons become confined to protons to make neutral atoms) occurred. Though, in contrast to the Big Bang's poor performance, plasma cosmology's predictions of nucleosynthesis have performed well.
Despite the general importance of plasma in astrophysics, and the assertions of the standard model that electromagnetic forces may be important for describing local phenonmenon, the standard model continues to delineate that these forces are not important at large cosmological distances. The reason for this is generally believed that unlike the other three forces which are attractive only, electromagnetism is both attractive and repulsive and over large cosmological distances, electromagnetic forces are believed to cancel each other. This is not always the case however. It can be shown that the electromagnetic forces are several orders of magnitude greater than the gravitational forces in a plasma and that the electromagnetic forces can have a longer range than gravitational forces.
One of the most well developed models of plasma cosmology which challenges the standard Big Bang cosmology was first developed in 1965 by Hannes Alfven. In this model, the universe exists as a mixture of matter and antimater which Alfven called ambiplasma. The cellular regions of matter and anti-matter can mutually annhilate, leaving protons and electrons. This may cause a rapid expansion of the region local to the annihilation. The Alfven model deals with the problem of cancellation explained above by postulating that the regions of matter and anti-matter are larger than the presently observable universe, and are seperated by double-layers in the plasma. Alfven heavily stressed the importance of the cellular and filamentary nature of plasmas at any scale, from the laboratory to the galactic.
Alfven's model possesses a number of highly appealing properties. Firstly, it addresses the question of what happened before expansion, which is not addressed by standard Big Bang cosmology. Alfven postulated that the universe has always existed, and that the expansion we might now be seeing is merely a local phase of a much larger history. Secondly, the model does not invoke any exotic physics (other than anti-matter, which has been verified on Earth in high-energy colliders), instead modelling the universe using the well-understood electromagnetic forces along with gravity.
Unfortunately, there are a number of problems with Alfven's model. From a theoretical point of view, Alfven was unable to formalize his model to the point where it is possible to perform numerical simulations similar to those now routinely performed to model the behavior of early galaxies in the standard cosmology and which are used to predict the correlation function of the universe.
Although 3-D formation simulations of single galaxies have been performed using the plasma model (see articles by Anthony Peratt) wherein electromagnetic forces are taken into account along with gravitation, there have been no published papers which attempt to calculate correlation functions and therefore allow detailed comparison with observations.
Another problem is, ironically, that plasma cosmologies depend on physics which is, while not completely well-understood, quite well-documented from laboratory experimentation. Because the standard Big Bang model involves physics that is poorly understood, one can adjust Big Bang models to fit observations by invoking exotic physics, such as the existence of as-yet unobserved particles. Due to its empirical foundations (Alfven was a laboratory physicist at heart, developing power-transmission systems and the like), it is much harder to modify Alfven's model to fit cosmological observations.
From an observational point of view, the gamma rays emitted by even small amounts of matter/antimatter annihilation should be easily visible using gamma ray telescopes. However, such gamma rays have not been observed. One could rescue this model by proposing, as Alfven does, that the bubble of matter we are in is larger than the observable universe. This then brings up the question of how one would go about testing the model if the structures that it predicts cannot be observed. In order to test the model, one would have to find some signature of the model in current observations, and this requires that the model be formalized to the point where detailed quantitative predictions can be made. That opens the theoretical problem mentioned in the last paragraph.
It must be remembered that Alfven's model of the universe is not the only model within the field of plasma cosmology. Alfven did play a very large role in founding the fields of plasma physics and plasma cosmology, however many physicists have expounded on his model and there are in fact versions today which greatly account for much of the observable phenomena in the universe, including the CMB, the distribution of galaxies, the formation of galaxies, redshift, large-scale energy flow and storage, etc..
Although there are many local redshifting mechanisms observed in laboratory experimentation with plasmas, one problem in using a majority of them to explain cosmological redshifts is that it is difficult to account for a change in the energy of a photon going through plasma without photon scattering (changing the photons direction of propagation.) Thus if cosmological redshifts were due to interaction with plasma, one would expect some scattering that would cause distant objects to appear somewhat blurry, or to disappear completely. This is not observed. However, in some non-linear optical phenomena there are forms of scattering in which the direction of propagation of the photons is not changed. Specifically, one promising candidate for astrophysical application is Forward Brillouin Scattering, found locally in Laser Fusion devices, as an example. This form of forward scattering causes a redshift and a broadening of spectral lines without changing the direction of propagation of the incident light.
Almost all astrophysicists believe that the standard Big Bang cosmology makes more detailed and observable predictions than any plasma cosmology model that has been proposed, and almost all papers published on cosmology implicitly assume the correctness of the big bang model. Examples of these detailed predictions include the distribution of nuclear elements and the clumpiness of the galaxies. While both are claimed to be accounted for in some manner within plasma cosmology, there have been no published papers which make predictions on the primordial helium abundance (although this subject is addressed in Lerner's book,) or which calculate correlation functions. Hence, as of 2003, there is relatively little interest in the Alfven model or in any other plasma cosmology by the cosmological community. However, outside of this standard community, interest in plasma cosmology continues.
The following physicists and astronomers helped, either directly or indirectly, to develop this field:
Overview
Criticisms of Alfven's model
Other work
Major figures in plasma cosmology
See also
Links and resources
Publications
Related Books
