May 04, 2006
Seeing Electricity in Space
We tend to
perceive only what’s familiar. So when new discoveries open up
unfamiliar worlds, they present us with a dilemma. To see new worlds
accurately may require a radical step—the suspension of prior beliefs.
Let’s start with what’s familiar.
Prior ideas, experiences and memories form the foundation of our
thinking. They make up the “what’s familiar”. “What’s familiar” is
things we bump into and think of as solid, other things we splash in
and think of as liquid, a few things we feel blowing past us and
think of as gas. “What’s familiar” is thinking of these things as
made up of atoms, atoms that have mass, atoms that have positively
charged particles on the inside and negatively charged particles on
the outside, atoms that can gain and lose these particles but that
have few electrical effects. “What’s familiar” is the accumulation
of our thinking and acting and remembering as creatures who live on
the surface of a wet, rocky body called Earth.
But there are things and events above the surface and below the
surface—even on the surface—that we have not thought about or
remembered. Not long ago our ancestors thought differently about
things and remembered events differently. What was familiar for them
was not thinking in terms of solids, liquids and gases but thinking
in terms of earth, water, air and fire. And if what’s familiar has
changed before, it can change again.
For some time now we’ve been accumulating
above the surface. Early in the twentieth century we began to
discover atoms that are unfamiliar because they are missing one or
more negatively charged particles. The remaining portions of these
atoms are positively charged. The presence of these negatively and
positively charged particles is the distinguishing characteristic of
what we now call plasma. In the second half of the twentieth
century we discovered that plasma
fills the space between
planets and stars.
Plasma behaves in unfamiliar ways. But our habits of perception can
make it difficult to see plasma as something completely different
from a gas. Its similarities to a gas are overshadowed by the
dissimilarities. And if we can break free from prior ideas about
gases, we make the unfamiliar ways of plasma familiar. And we can
see a new universe.
A charged particle that moves is an electric current. This is a
familiar thought when we’re doing electrical things, but we’ve not
thought about it when we’re doing things in space. An electrical
current is accompanied by a magnetic field that wraps around the
current and gets weaker with distance from the current. With more
charged particles moving in the same direction, and with moving
faster, the magnetic field gets stronger. Again, this is a familiar
thought when we’re doing electrical things. But when astronomers
discovered magnetic fields in space, they were surprised and
mystified about how to explain them. They tried to conjure magnetism
out of gravity and mass.
Because the charged particles are moving through this magnetic field
that gets stronger toward the axis of movement, particles that are
not moving exactly along that axis are squeezed toward the axis.
Plasma scientists call this the “pinch effect”. Outlying charged
particles, together with the neutral atoms they bump into, are
pulled into the current channel. Outlying areas are depleted and the
channel gets denser. It self-constricts until the gas pressure on
the inside balances the magnetic pressure on the outside. This
balance of pressures along the axis produces long, thin filaments of
matter that are sharply separated from their rarified environments.
We remember that this is what happens in a lightning stroke (or at
least this is how we think about what happens in a lightning
stroke), and it seems familiar: We understand. But we had not
thought about this happening in space.
Kristian Birkeland thought this might be what happens in the aurora.
He trekked to the Arctic Circle to measure the magnetic fields from
the constricted channels that made up the auroral currents. (These
“Birkeland currents” were later named after him.) He speculated that
this might be what happens in the filaments that make up solar
prominences and the solar
corona. He thought the filaments
might carry electric currents from the Sun to Earth.
Such ideas were too unfamiliar for astronomers conditioned to think
in terms of gravity and mass. They clung to their familiar ideas of
mass particles until artificial satellites orbited through and
measured the electrical filaments that were the auroral currents.
Even then, the idea was too unfamiliar for them to recognize that
the moving charged particles from the Sun were also currents.
Because gravity-oriented astronomers are familiar with moving
masses, they seldom think about charges. What’s not familiar, what
has no conceptual framework for understanding, is often not even
perceived. So they think of moving charged particles from the Sun as
a “wind” instead of an electric current. They think of charged
particles falling on a planet or on a moon as a “rain” instead of an
electrical discharge. They think of charged particles moving along a
magnetic field as a “jet” instead of a field-aligned power cable.
They think of abrupt changes in the density and speed of charged
particles as a “shock front” instead of a double layer that can
dissipate electrical energy and even explode.
They can’t see the electrical-particle forest for the mass-particle
trees. They are lost in a plasma universe, seeing charged particles
in motion but thinking in terms of gas kinetics and gravity.
Plasma cosmologists think differently. They remember their
experience with currents in a laboratory. They are familiar with the
“right-hand rule”: When they point the thumb of their right hand in
the direction of the current, their fingers will curl in the
direction of the magnetic field. In the space between two parallel
currents, the two magnetic fields will have opposite directions.
Because north and south poles attract each other, the two currents
will move toward each other. But as they get closer, the electrical
repulsion between them will become stronger than the magnetic
attraction. The two currents will begin to twist around each other.
Thunderbolts of the Gods, Chapter One, page 24.)
Plasma cosmologists recognize these twisting filaments in the