The Plasma Model
The idea of a plasma cosmology model was initially championed by Nobel Laureate Hannes Alfén and influenced by the earlier work of Kristian Birkeland, who suggested that electrical currents from the Sun caused the Aurora Borealis. However, it was not until enormous Birkeland currents were detected by an artificial satellite, in 1974, and by the Voyager satellite between Jupiter and its moon Io, in 1979, that this model gained any significant support. Later, in 1984, Farhad Yusef-Zadah, Don Chance and Mark Morris found the first evidence for Birkeland currents on a cosmological scale.
In many ways, the scope of the plasma model may depend on just how much speculation you are willing to entertain. In its restricted form, plasma astrophysics is an accepted line of research within the mainstream of physics, although some have extended speculation to create a much more expansive plasma model of the universe. It is generally accepted that the majority of ordinary matter in the universe exists in the form of plasma, i.e. the fourth state of matter, and that any plasma is a good conductor of electricity. However, there are aspects of interpretation that remain far more contentious, e.g.
- Double Layers
- Frozen-in magnetic fields
- Birkeland currents
- Open Magnetic Fields
- Magnetic Reconnection
While the Introduction to Terminology will attempt to provide an initial outline of some of these issues, it is highlighted that when speculation is not restricted by the accepted cosmological model, the scope of plasma astrophysics can be expanded to become an alternative model. In this context, the dynamics of ionized plasmas play a far more important role in the physics of the universe at scales much larger than the solar system.
So what is the status of plasma cosmology?
It is probably true that most cosmologists, astrophysicists and astronomers may reject some of the wider speculations associated with the plasma model, such that they remain convinced that gravitation alone, as described by general relativity, provides the major ‘force’ at work in the universe, both now and in the past.
So where did the idea of the plasma model originate?
As indicated, many of the ideas are associated with the work of Hannes Alfvén, who was the 1970 Nobel laureate, whose plasma physics experiments in the laboratory suggested that such processes might be scaled to work within the universe at large. This position is often seen to run into trouble in connection with the definition of the Debye length, which is the scale over which mobile charge carriers, e.g. electrons, will screen out electric fields. As such, the Debye length is seen as a limiting factor to the scaling of plasma physics within the universe. While not really contradicting the Debye length on the very large scale, a plasma double layer is a structure that consists of two parallel layers with opposite electrical charge. Charged ions and electrons which enter the double layer are accelerated, decelerated or reflected by the electric field and can be found in a wide variety of plasmas ranging from small-scale discharge tubes through to the Birkeland currents that support the auroras within the Earth’s magnetic field. As such, double layers are typically very thin with lengths ranging from a few millimetres for laboratory plasmas to thousands of kilometres within astrophysical space plasmas.
Note: However, some have argued that plasma phenomena are possibly far more scalable than the suggestions above, where electrical and physical properties remain the same, independent of the size of the plasma. In a laboratory plasma, things happen much more quickly than on galaxy scales, but the phenomena are essentially identical and obey the same laws of physics. It has apparently been demonstrated that plasma phenomena can be scaled to fourteen orders of magnitude, while Alfven hypothesised that they could be scaled to 28 orders or more.
So why did the controversy arise?
Alfvén research also led him to the view that plasma physics played a far more important role in the universe than the standard cosmological gravitational model suggested. In fact, Alfvén asserted that electromagnetic forces might play a far more important role than gravity when acting on interplanetary and interstellar charged particles. In 1939, Alfvén wrote a paper in support of the theory of Kristian Birkeland, who had suggested, as early as 1913, that solar winds generated currents in space that caused the aurora lights as seen at the Earth’s magnetic poles. This work was initially considered counter-intuitive to accepted theory because it was thought that currents could not cross the vacuum of space and therefore the currents had to be generated by the Earth. However, Birkeland's theory was proved to be correct after a probe was sent into space and these currents are now called ‘Birkeland currents’ in his honour.
OK, but what other evidence supports the wider implications of plasma physics?
In part, this is what this section of discussions wants to try to find out. For at one level plasma astrophysics is now accepted as a mainstream field of research, although it rejects some of the wider speculative ideas supported under the banner of plasma cosmology. For example, plasma effects are now thought to explain why the spin of a star slows while it forms. Although the actual mechanism is not necessarily agreed, one proposal called magnetic braking is thought to remove angular momentum and, in so doing, allows the star to contract. However, controversy again arises when it comes to the accepted structural models of galactic formation, which mainstream thinking describes in terms of the gravitational interaction of mass within the system rather than its electro-dynamic interactions. In this context, the standard model assumes the existence of dark matter accounts for the observed galactic rotation curves, while plasma cosmologists argue that plasma effects can better explain the galactic rotation curves without the need for dark matter. Of course, as previously discussed, it would appear that other models may also make the same claim. Another of Alfvén's hypotheses was that Birkeland currents might be the cause for the filamentary structures seen throughout the universe, while galactic magnetic fields and associated currents might be a cause of the contraction of interstellar clouds required for star formation. However, again, this is in direct opposition to the standard view that magnetic fields can hinder collapse, based on the argument that that large-scale Birkeland currents have not been observed and the length scale for charge neutrality is predicted to be far smaller than the relevant cosmological scales.
Note: In 2011, scientists appear to have discovered the largest electrical current in the known universe, so far. At a distance of some 2 billion light years from Earth, it was estimated to have an electrical current of 1018 amps, which would be equivalent to about 1 trillion lightning bolts. While explanations are still speculative, one team has forwarded the idea that a magnetic field from a colossal black hole at the galaxy's core are generating the current, which is powerful enough to light up the jet and drive it through interstellar gases out to a distance of about 150,000 light years.
What is the scope of the evidence against the plasma model?
In 1993, theoretical cosmologist Jim Peebles criticized the Alfvén's model on the grounds that the model would not be consistent with the isotropy of the cosmic microwave background radiation. Pebble also went on to argue that Alfvén's model did not align with Hubble's law, the abundance of light elements or the existence of the cosmic microwave background.
So why do plasma cosmologists persist in their view?
In the 1950’s, experiments involving vaporising titanium wires using very large currents produced a plasma with a spiral structure, which then led to the suggestion that scaling the experiment to galactic dimensions might explain the rotation being observed. Later, in the 1980’s, computer simulations of colliding plasma clouds produced by Anthony Peratt also appeared to produce the spiral structure seen in galaxies. In addition, these simulations also seem to show the cross-section of two plasma filaments joining in a Z-pinch, but now the filaments were some 300,000 lightyears apart and carrying Birkeland currents of 1018 amps. As such, it was suggested that the simulations might account for the jets of material that were then starting to be observed emerging from quasars and active galactic nuclei (AGN), without the need for super-massive black holes. When the simulations extended the timeframe, they then appeared to show the transition of double radio galaxies into radio-quasars and radio-quiet QSO's plus peculiar and Seyfert galaxies, which finally ended in the formation of spiral galaxies. As such, these simulations may, or may not, account for the flatten galactic rotation curves without the need for dark matter. Of course, it may also be realised why plasma cosmology would be rejected by the standard model without overwhelming empirical proof, even if this criteria is not necessarily, or consistently, applied to the standard model itself.
So who is right?
Well, based on the weight of opinion, probability favours the mainstream model. However, at this stage, the discussions being planned for this section only intend to try to review some of the key arguments, both for and against, with an open mind in order to get an initial assessment of the issues.