There's an episode of Family
Guy where they go to the science museum, and under a banner
reading 'The Miracle Of Electricity' is an old man turning
an ordinary household lamp on and off. When he sees the crowd
staring at him, he says, "What? You don't think this
is a miracle? When I saw this at the aught-six World's Fair,
I almost crapped my pants!" I completely agree. Honestly,
all I want to know is how the TV works. Or how light bulbs
work. Or how the computer I'm typing this on works. Or how
the subway train I'm riding works. I feel uncomfortable about
the yawning gap between my dependency on electricity and my
knowledge of it.
I've had opportunities my whole life to learn. I did the
thing as a kid where you wire a christmas tree bulb to a nine-volt
battery. I went to very good schools, where I learned the
Maxwell
equations and the basics of quantum
electrodynamics. I continue to read books, talk to my
friends in the science world, play with interactive
web pages, and generally scour the memosphere for information
on the subject. After all this effort, I don't feel like I'm
getting any closer. What I'm starting to suspect is that nobody
really understands electricity at the gut level. People have
discovered a very useful and accurate set of mathematical
descriptions of it, and the mastery of those descriptions
has enabled us to make cell phones and iPods and what have
you. But almost no one seems to be able to verbalize or even
visualize the meaning of the equations. What follows is my
attempt to summarize the subject for myself. If anyone reading
this is a scientist who can clarify further, I'd appreciate
it.
So first of all, when I say electricity, I mean the electromagnetic
force as described by the standard model of particle physics.
More specifically, I mean the interactions between photons
and electrons that underlie electricity (and most of the other
physical phenomena we encounter in our daily lives on Earth
as well.) Where I run into trouble is when I ask what electrons
and photons are, and why they are the way they are. The central
difficulty is that electrons and photons aren't 'things' at
all, in the sense of the macroscopic objects that we're used
to. Some physicists describe electrons and photons as bumps
or knots in fields, the electron and electromagnetic fields
respectively. So what is an electron field, or an electromagnetic
field? This is where the texts all get very evasive, and who
can blame them? Fields are even less 'thing-like' than particles
are - they're invisible and intangible. The concept of fields
resists us when we try to encode it with body imagery. The
best way to get a grip on fields so far is with computer visualization.
Here are some quotes from Roger
Penrose's book The Road To Reality. (Lest I come across
as math-ier than I am, I bought this weighty tome purely for
the illustrations, all
beautiful ink drawings by the author.) Roger Penrose is
a greybearded eminence among mathematicians and physicists,
not a crazy person. And yet here's how he describes a single
electron:
We form a picture in which there are two 'particles', each
of which is massless, and where each one is continually
converting itself into the other one... Being massless,
each should be traveling with the speed of light, but we
can think of them, rather, as 'jiggling' backwards and forwards...
Penrose nicknames these two components of the resonating
electron as the zig and zag particles. The zig particle constantly
and rapidly spins clockwise (left-handed), at the same rate
as the zag particle spins counterclockwise (right-handed).
Taken together, you can think of the zig and zag as a single
particle bouncing back and forth, whose velocity is constantly
reversing itself, and whose spin direction is constant overall.
This picture is fine when we view the electron from afar,
but if we want to really consider it up close, the electron
takes on greater and greater complexity:
The actual motion is composed of a vast number of such
individual processes (in fact infinitely many of them) all
superposed, and we may think of the electron's perceived
motion as being some sort of 'average'...
Even this describes merely the free electron. An actual
electron will be continually undergoing interactions with
other particles (such as photons, the quanta of the electromagnetic
field.) All interaction processes should also be included
in the overall superposition.
This shimmering, twinkling entity sounds more like a form
of energy than a thing, and physicists since Einstein
have considered matter and energy to be fundamentally interchangeable
at the subatomic level. Protons, neutrons and their
constituent up and down quarks all have this vibrating,
flickering quality, and all have the zig and zag components.
Rather weirdly, only the left-handed
zig components experience the weak nuclear force, the one
that transforms one flavor of subatomic particle into another.
Is this the most meshuggenah thing you've ever heard?
The electricity in the wires comes from the rotation of giant
electric dynamos at your local power plant. For some reason
unknown to me, rotating a magnet around a wire creates an
electric current. To make the magnet rotate, the usual method
is to burn something (coal, oil, natural gas or what have
you) to heat water into steam, which then turns the big turbines.
If you're lucky enough to have some other form of mechanical
energy around, like a waterfall or a geothermal vent, hooray,
free electricity. Nuclear power plants heat the water with
energy released from the radioactive decay of uranium or some
other lively unstable element. Maybe someday we'll find a
better way to get the turbines to turn, though I wouldn't
hold my breath for room-temperature fusion.
What makes magnets magnetic? It turns out to be the magnetism
of their component atoms' electrons. Each electron, as it
spins, acts as its own little magnetic dynamo. In most stable
materials, the outermost orbitals of each atom are filled
with their quota of electrons, and all the electrons cancel
each others' magnetism out. Metals are unusual in that their
outermost electron orbitals are unfilled. The outer electrons
are free to flip their spin axes this way and that. This freedom
to change orientation is what makes metals such good electrical
conductor. If you put a whole bunch of freely-wiggling electrons
in a magnetic field, their spin spin axes tend to line up.
In iron and its chemical cousins, the electrons can stay lined
up even after you take the external field away. Taken together,
all these tiny spins generate a magnetic field big enough
to be felt on the macroscopic scale, thus making your pictures
stick to the fridge.
Physicists use the word 'potential' to describe the energy
stored in a given thing at a given instant. Gravitational
potential is very easy to see. If something is higher off
the ground, it has greater gravitational potential. As it
falls, it releases its gravitational potential, converting
it into kinetic energy. Electromagnetic potential is invisible,
and much harder to conceptualize. The third rail looks exactly
like the first and second rails. You'd never guess just by
looking at it that an electrically charged object could kill
you instantly if you so much as brushed a fingertip against
it. No wonder cows are terrified of electric fences.
What's particularly strange and counterintuitive about electrical
potential is that if you raise it across all points in a circuit
by the same amount, the circuit will still operate identically.
Think of a bird perched on a high-voltage power line. The
air insulates the bird from the ground, so there's no difference
between the bird's electrical potential and the wire's. The
absolute value of the potential for both bird and wire is
large, but it's also irrelevant. What matters to electromagnetism
are differences of potential across a circuit's various
components. You'd think that a wire at a higher potential
would glow, or hum, or have lightning shooting off of it,
but again, electric potential is invisible. We can only see
the photons that go shooting off when the potential gets released.
Our direct sensory experience of electromagnetism is severely
limited, and other animals detect it in ways we're only beginning
to understand. People
at the Theoretical and Computational Biophysics Group think
that birds can see the Earth's magnetic field. Literally
see it, the way we see patterns in wood grain. This could
explain how birds are able to fly thousands of miles in a
straight line without getting lost. The bill on a duckbilled
platypus is a sensitive electrical detector that enables it
to 'see' the muscle contractions of its prey in muddy riverbottoms
where visibility is zero. Imagine how much easier electromagnetism
would be to understand if we could just see the damn field
lines.
Photons are the minutest constituents of the electromagnetic
force, and they're just so weird you can't believe it. According
to Einstein, photons don't travel
through time at all. Also, photons are both particles and
waves. It's sort of like how smooth-seeming water waves are
made of vast numbers of individual water molecules. Unlike
water molecules, though, lone photons retain their wave aspect
in isolation. Experiments have shown that photons always 'know'
they're part of a wave and spookily correlate their behavior
with other distant photons. Don't even get me started on lasers
and holograms, or higher dimensions, or the other many strange
rabbit holes that dot the electromagnetic landscape.
© ethan hein 2007 | back
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