A reading of this article:
I have received several requests for layman’s interpretation of this topic and I shall, in this article, attempt to illuminate what is going on. In order to do that, I will first have to try and describe in layman’s terms just what the standard theory says occurs when magnetic reconnection takes place. The scientific press has been rather mute in portraying the problems with this theory.
For those of you who are totally unfamiliar with the topic, magnetic reconnection is claimed to account for sudden releases of kinetic energy within a field of plasma. Scientists presume these sudden releases of energy are caused by “reconnecting” magnetic field lines. This topic is vitally important in modern cosmology because “reconnection” plays a role in explanations of practically everything we observe in space. Magnetic reconnection is observed to occur on the Sun, in the auroras, in neutron stars, in comets, and practically every other place that matter in a plasma state exists.
The standard theory of magnetic reconnection is incredibly obtuse and difficult to understand. Make no mistake, the scientists don’t have any idea what is really going on, which is why there are so many competing theories of “reconnection”. What they are attempting to do is model what is going on without providing an explanation of why it is actually occurring. Their position is similar to the one Newton took when he proposed his law of gravity. Newton never actually proposed a theory as to what caused gravity, he simply proposed an equation that could mathematically describe it. A quick look at the magnetic reconnection page on wiki gives us a list of several different models to chose from. So unlike Newton’s law of gravity, there is no singular model that can actually explain mathematically what is occurring either.
Before I can begin describing magnetic reconnection, first I have to describe what a plasma is. Magnetic reconnection is something that ONLY takes place within plasma physics. A plasma can basically be considered to be an electrically conductive gas. The following description applies to current carrying plasmas that have magnetic fields.
A neon sign is a form of plasma. The neon sign is an electrified glass tube containing a “rarefied” gas (the gas pressure in the tube is well below atmospheric pressure). When a voltage is applied to electrodes inserted through the glass, an electrical glow discharge results.
The following is a diagram of a Crookes tube, which operates in a similar manner to a neon sign.
The molecules inside the low pressure Crookes tube become excited and the potential difference and subsequent electric field pulls the bound electrons toward the anode (positive electrode) while the cathode (negative electrode) pulls the nucleus. So the molecules of the gas are basically pulled apart into positive and negative charges. This separation of the gas into charged particles is called ionization.
Of the many ways that plasma is created in the lab and in space, they all have one thing in common. There must be a steady source of electrical input in order to sustain the plasma. Without a constant electrical input, the gas will neutralize itself and return to a stable non-ionized state. We can see this in neon signs and novelty plasma globes. When the electrical current is shut off, the glowing plasma dissipates back into a neutral gas.
Because plasma is composed directly of negative electrons and positive ions, the gas is nearly super conductive. It is one of the best known conductors of electricity in the universe. Plasma also has a few other properties that we need to describe; in particular, plasma is very cellular in nature. That is to say, differing regions of plasma will wall themselves off from each other and form a boundary between themselves called a double layer.
The inside region of each plasma cell can basically be considered to have a net neutral charge balance. That is to say, the number of positive and negative charges in a given region of plasma will equal each other, thereby cancelling out most, but not all, electrical currents within the plasma. This near net balance of positive and negative charges on the whole is called quasineutrality. The quasineutrality of a plasma requires that plasma currents close on themselves in electric circuits. Such circuits follow Kirchhoff’s circuit laws and possess a resistance and inductance.
So we can say with total certainty that ALL plasmas have at least some minuscule amount of electrical current flowing through them at any given moment. If they didn’t, they would revert back to being neutral gases. Further we can say that because there is electrical current flowing through the plasma, there will be magnetic fields created in and around the plasma itself. Magnetic fields are the result of moving charged particles. When an electron moves, it creates a magnetic field in its wake. If all the charged particles in a plasma were to stop moving completely, there would be no magnetic field. Maxwell’s electrical laws make this abundantly clear – all magnetic fields require an electrical current. Even the magnetic field in a bar magnet is caused by flowing electrons.
Let us be clear, a constant source of electrical input is required in order to sustain a plasma for any length of time. Any termination of the input will cause the plasma to recombine back into a neutral gas and any “walling off” of a plasma from its power source will cause it to recombine back into a neutral gas.
The following are indisputable facts about plasma:
-All plasmas require a constant source of electrical input to sustain them.
-All plasmas have electrical currents flowing through them at all times.
-All magnetic fields in a plasma are caused by the electrical currents that are flowing through them.
-All plasmas must obey Kirchoff’s circuit laws and any interruption of the circuit for any length of time will result in the plasma recombining back into a neutral gas, since particles of opposite charges are attracted to each other and naturally want to neutralize each other.
Now that you know what a plasma is, I shall attempt to describe what the standard theories of magnetic reconnection say is occurring. As I stated earlier, none of the current theories actually have a reason as to WHY magnetic reconnection occurs. The theorists are limited by the models they employ to describe the plasma itself.
Plasma is a messy thing to model. It is like trying to model how food coloring spreads in a bowl of water. Because plasma is so incredibly messy to model, physicists employ some “tricks” to make the process easier to deal with. In order to make the process of modeling plasma manageable, scientists treat the plasma as a perfectly conductive fluid with zero resistance. That is to say, they treat the plasma as if the magnetic fields created by the electrical currents in the plasma are simply frozen into the plasma itself and remove any mention of the electrical currents necessary to create and maintain them.
Obviously this violates Maxwell’s equations which state that in order to have a magnetic field in a plasma, one must have an electrical current flowing through it to produce the magnetic field in the first place. If all the electrons in a plasma were actually frozen into the plasma, there would be no magnetic fields because there would be no moving electrons.
This treatment of the plasma as a perfectly conductive fluid with “frozen-in” magnetic fields is called magnetohydrodynamic theory (MHD). In reality, plasma itself is never perfectly conductive. Because it must obey circuit laws, there is always some resistance, which therefore means there is always some current flowing with any given plasma.
The elimination of the electrical currents allows physicists to model the plasma’s magnetic fields in a much simpler fashion. It is from these models of plasma that magnetic reconnection theory was born. In MHD models, plasma really is treated like a magnetized fluid, hence the term “hydrodynamic.” This also gives rise to all the “shock” terminology that one hears in plasma physics because the physicists are treating movements of plasma as they would treat movements of water droplets. By eliminating the electrical currents in their models they can then set about modeling the behavior of plasma without having to deal with the circuit laws that any real plasma must obey.
This elimination of electrical currents in space plasma models and treating the plasma as a perfectly conductive fluid works very well and is a great approximation for how a single cell of plasma behaves. However, one must remember that this treatment is itself an approximation and it breaks down horribly when trying to define how two entirely separate cells of plasma behave when they interact with each other.
Now I want to get back to this double layer business. I mentioned earlier that differing regions of plasma naturally want to wall themselves off from each other. Basically what happens is two plasma regions that have differing characteristics will form a “potential drop” between them creating a double layer. A region of plasma that has relatively hot (diffuse) electrons moving into a region of plasma with relatively cool (dense) electrons will create a charge imbalance between the two regions.
The plasma always tries to maintain quasineutrality, so two differing regions must act upon one an other in order to make sure this condition of quasineutrality is not violated. The plasma accomplishes this by only violating quasineutrality within a very narrow area called a double layer. This allows both regions of plasma to maintain quasineutrality while being close to one another.
A double layer is a structure in a plasma and consists of two parallel layers with opposite electrical charge. The sheets of charge cause a strong electric field and a correspondingly sharp change in voltage (electrical potential) across the double layer. As the two pieces of plasma attempt to neutralize the charge imbalance between them, electrons are accelerated into the plasma region with a net positive charge and ions are accelerated into the plasma region with a negative charge.
The production of a double layer requires plasma regions with a significant excess of positive or negative charge, that is, where quasineutrality is violated. We can think of the double layer as the plasma creating an electromagnetic barrier between two regions of differing plasma. As I mentioned earlier, charged particles naturally want to neutralize each other and particles of differing charge are attracted to each other. So if you have a plasma region with a comparatively net negative charge and a plasma region with a comparatively net positive charge, when they come together they naturally want to neutralize the charge imbalance between them. However, this charge neutralization does not take place across the entire plasma region instantaneously since a double layer forms and accelerates the charged particles to maintain a quasineutral state in both fields of differing plasma. The acceleration of particles across the double layer allows the plasma to balance the charge difference between the two sheets.
The voltage drop across a current-carrying double layer is proportional to the total current, and it might be thought of as a resistive element (or load) which absorbs energy in an electric circuit. Since the double layer acts as a load, there has to be an external power source maintaining the potential difference and driving the current.
A double layer can also become unstable, in which case an explosive release of energy will occur.
Alfven gives us an explanation for such an explosion:
A simple mechanism of explosion is the following. The double layer can be considered as a double diode (a diode is a two-terminal electronic component that conducts electric current in only one direction), limited by a slab of plasma on the cathode (negative) side and another slab on the anode (positive) side. Electrons (negatively charged particles) starting from the cathode (negative side) get accelerated in the diode and impinge upon the anode (positively charged) slab with a considerable momentum which they transfer to the plasma. Similarly, accelerated ions (positively charged particles) transfer momentum to the cathode (negatively charged) slab. The result is that the anode and cathode plasma columns are pushed away from each other. When the distance between the electrodes in the diodes becomes larger the drop in voltage increases. This run-away phenomenon leads to an explosion…
The reason why plasma forms double layers can only be described by circuit theory using a resistive plasma that has an electrical current flowing through it. To be clear, MHD theory is incapable of accounting for WHY a double layer should form in a plasma. It, at best, can only describe it as a geometrical construct.
I want to highlight my “Newton” analogy again. When scientists use MHD theory to describe how two parcels of plasma interact with each other, they are only describing a mathematical construct that describes what the interaction looks like on a computer screen. There is no explanation of WHY this interaction is occurring, there is only a description of what the interaction looks like. Newton did not propose a theory of what gravity is, he only proposed a theory that describes how it acts. The same is true of all MHD models of “magnetic reconnection.” In MHD theory, there is no explanation of why two parcels of plasma should suddenly decide to create a resistive barrier between themselves and experience an explosive release of energy.
So now we can see the difference between what electrical engineers say is occurring and what astrophysicists say is occurring in space with regards to magnetic reconnection. The electrical engineers are treating the plasma as they would treat any other electrical circuit. They are saying that the explosive release of energy that takes place between two plasma parcels is strictly due to a voltage difference between two regions of plasma. It is a property of the circuit and has nothing to do with “reconnecting field lines.” This explanation gives us the WHY and it is based entirely on laboratory proven facts of plasma behavior.
All models of MHD reconnection can be considered classic reification of theory. That is to say, they all treat the models as if they are representative of what is actually occurring in physical reality. In reality, FIRST one must have an electric current BEFORE one can have a magnetic field. This relationship is entirely reversed in MHD theory. The idea of MHD is that magnetic fields can induce currents in a moving conductive fluid, which create forces on the fluid, and also change the magnetic field itself.
In the Sweet-Parker model of magnetic reconnection, the plasma is still basically treated as a perfectly conductive fluid. However, in order to describe the incredible speed at which “reconnection” (which is really nothing more than an exploding double layer) takes place, they must add back in ad hoc resistivity along the boundary of the two plasma parcels in order to create a mechanism that accelerates the electrons to observed rates. There is no mention of a double layer condition between two differing plasma parcels in MHD reconnection, something we know must exist from laboratory observations of plasma. There is no mention of a double layer because MHD theory is completely incapable of modeling such behavior. Only circuit theory can account for the mechanics of a double layer.
The general theory of substorms basically states that magnetic energy from solar plasma is re-directed down the magnetic field lines from the Earth’s magnetotail when a reconnection event occurs.
So in their models of Sweet-Parker reconnection, the physicists start off with two parcels of plasma sitting next to each other and then throw a sheet of electrical current between them. Why this current sheet should exist in a real resistive plasma according to their models is not clearly defined. They claim that the current sheet creates a region of resistive plasma around it which is necessary to account for why magnetic energy should be dissipated across the boundary of two plasma parcels, which themselves are generally assumed to be perfectly conductive. The resistivity is necessary because, in a perfectly conducting medium, a magnetic field passing through another magnetic field would do nothing to the field lines.
Why this plasma should be resistive and why this current sheet should exist within MHD theory is not readily explained. While they have explanations for incorporating them into their models, they would be perfectly happy NOT using them if that is what made their model meet with observation. The existence of the current sheet and a resistive region on the boundary of two plasma parcels is NOT something that the MHD model predicted should be there from the start. They are things that were thrown into the MHD model in an after-the-fact manner in order to get their models to meet with observation. This is in contrast to circuit theory and the double layer treatment of “magnetic reconnection” which predicts and explains the existence of a current sheet in the form of a double layer boundary right from the start. It is impossible to remove the double layer mechanism from the circuit theory of plasmas without violating the known laws of physics and invalidating the theory. Circuit theory MUST have a current sheet in the form of a double layer, while MHD theory can get along just fine without such a current sheet, that should tell you something about the validity of the MHD model.
This resistivity-out-of-nowhere along the boundary of two plasma parcels is called “anomalous resistivity” and is claimed to be a consequence of scattering created by the current sheet that creates drag between the electrons and ions. Of course, this is ridiculous because the space plasma that they claim this “anomalous resistivity” occurs in are basically collisionless. It is necessary for them to concoct such “anomalous resistivity” because without it, their models don’t even come close to accurately matching the observed data.
In response to this collisionless problem, scientists then set about concocting a collisionless model that could more readily meet with observations of the magnetosphere. But this model also suffers from the “anomalous resistivity” problem, only this time there is no convincing theoretical argument for the spontaneous occurrence of reconnection. Scientists simply took the “anomalous resistivity” argument and moved it down to the micro-level of ions and electrons rather than the macro-level as the Sweet-Parker model uses. Again, the “why” is left to languish in the hell of failure. But that aside, scientists have to propose ONE theory that can explain all observations and it must be internally consistent and be able to explain all observations of “reconnection” in all different types of plasma. There is only one theory that can do that, and it involves exploding double layers.
In concocting their theory of reconnecting field lines, they take a snapshot of how the magnetic fields look in the plasma before the “reconnection” event takes place and they take a snapshot of how it looks afterwards. They then integrate the field lines between these two snapshots in space and time and from this then make the claim that “magnetic reconnection” has occurred. Such a model makes it appear as if the magnetic field line that was at location A is now at location B and has “reconnected.” This integration beautifully washes over what is actually occurring with the currents within the plasma and makes it appear as if there has been no violations of physical law.
In reality, such explanations are totally meaningless. It is meaningless to assert that a field line that was at A is now at B, because there is no way to identify or distinguish one magnetic field line from another in a vector continuum. The only way that the integration even comes close to being valid is when the parallel electric field (the electric field component parallel to the magnetic field line) is zero. This condition is not satisfied in standing theories of magnetic reconnection.
Since a magnetic field is an infinite continuum, there can be no splitting and reconnecting of field lines. In order for a field line (which is a mathematical construct used to describe the location of a magnetic field) to “reconnect” it would first have to be spliced in half. This splicing creates what is tantamount to a magnetic monopole, which we know do not exist. It is impossible for a magnetic field line to ever have an end-point. It is no more possible for a field line to have an end point than a contour line on a topographical map to have an end point.