E Is for Energy
An SBCC professor emeritus and former UCSB lecturer in physics,
Professor Elwood Schapansky retired several years ago to be reborn
as a glacier-hopping pilot, ferrying climbers and tourists to Mt.
McKinley. But he is still a good and patient teacher.
Last Wednesday afternoon, by the heat of a wood-burning stove
and the refracted light of numerous prisms, he sat and talked with
Martha Sadler for almost two hours about Einstein, electrons, and
why the sky is blue. And eventually, after some initial resistance,
he gave up the secret of E=MC².
What follows is an edited transcript of that discussion.
If energy is neither created nor destroyed, where does it
come from?
I cannot answer that question. Either God created it, if you are
a religious person, or — all I know is that it’s existed from time
immemorial. If you want to talk about just on earth, the sun is
bombarding earth with millions of joules of electromagnetic energy
every moment. We cannot create it, we can only find a way to use
what is there.
I’ve heard it said that the universe is winding down.
What does that mean?
That’s the idea of entropy, which has to do with the conversion
of energy from an ordered state into a disordered state. What that
means to most scientists is that the usable energy is decreasing.
It’s easier just to concentrate on what’s happening here on earth.
Every time we go out and burn a gallon of gas, that gallon of gas
was in a nice container and it was localized and readily usable,
and once we’ve used it, where is it? It still exists. It’s in the
molecules of carbon dioxide and other gases that are floating
around our universe — and somebody can still use those, but they’re
less usable to us. The gas is converted into kinetic energy which
makes your engine hot, you spew out heat as you go down the road,
and when you apply the brakes to stop the car the car all of its
remaining kinetic energy is converted into heat.
I suppose that’s why brake pads are fire
resistant.
Yes, you have to have something that can get very hot and can
dissipate the energy without burning up.
What is energy? Does E=MC² mean energy equals mass times
the speed of light squared?
No, you’re just taking one isolated little Einsteinian equation
and making it significant, and that’s way, way, way, way beyond
where we are. We can define energy very simply: It is the ability
to do work.
Is it measured in Joules? Yes, Joules or
ergs.
Does each thing have an intrinsic amount of energy? Like
that pillow on that couch, does it have a specific amount of
energy?
Sure, I could throw that into the fire and the chemical energy
of the bonds that keep that together will be converted into heat.
Most of it will go up the chimney but some of it will
make you warm and so, yeah, there’s an intrinsic amount of energy
there. Every atom in our universe has energy, some very difficult
to get to and some easier to get to. In fact, there’s such an
immense amount of energy that’s inaccessible because everything at
the nuclear level — if we could somehow get the energy that’s
stored in the nucleus out of there, then we’d have —
A nuclear bomb!
Well, a bomb or a nuclear reactor. But it’s not that easy, there
are only certain atoms that have nuclei that we can easily get that
energy out of there. It’s there by the barrels full, but we just
can’t get it. You can’t get the carbon atoms that most of that
pillow is made of to engage in a nuclear reaction. You can get that
kind of energy from thing like uranium and plutonium. Those atoms
are unstable enough that they will split and give up their
energy.
Do two things that weigh the same have the same amount
of energy, I mean, if they’re in the same position? No,
they have the same amount of gravitational potential energy. They
don’t have the same amount of chemical or nuclear energy, just
gravitational energy.
Oh. That’s probably an important
distinction.
There’s no relationship. It’s a completely different form of
energy.
One hears talk about electrons changing energy levels.
What does that mean?
That has to do with photons. A little bit earlier, my wife’s
crystals created a lot of colors in here, each of those colors that
you saw has to do with electrons changing energy levels. Let me ask
you something: What is your concept of an electron?
That model of an atom that used to sit in classrooms
that looks kind of like a solar system.
Okay, yes, the classical concept is that electrons whiz around a
stationary nucleus. The reality is that you cannot isolate an
individual electron, you can only talk about where it is quantum
mechanically. What that means is that you can’t say where it is —
you can say what the probability is of finding it in a certain
place. Also, classically, an electron could have any degree of
energy, and it could even fall into the nucleus like a satellite
falling to earth. Well, they don’t behave like that.
Is there another visual model that you could suggest?
Like a rainbow, or storm, or something?
No, it becomes very abstract. So for practical purposes the
planetary model is useful in visualizing, even though we realize
it’s not correct. It’s what we have to rely upon due to our human
frailty.
Is an electron a particle of matter?
Yes, it’s has mass, so it’s a particle of matter.
Okay, is it true that the space between atomic particles
is much, much, much, much, much, much larger than the particles
themselves?
Right, just as the space between the earth and sun is larger
than the objects themselves. The same is true at the atomic
level.
And do the electrons orbit the nucleus?
It’s still okay to think of a nucleus with electrons in orbit at
certain distances. The electrons have different energies, and we
can represent those energies as a hierarchy of orbits. In this
scheme, an electron can be in this energy, or that energy, but it
can’t ever be in between. I’m kind of using a hybrid idea—I’m
trying to simplify it—but let us imagine that there are certain
allowed orbits, corresponding to certain energy levels. And that’s
very important, because let’s say we have an electron that’s up
here in a high orbit because it has a lot of energy. It can only
switch from this high energy orbit to a specific lower energy
orbit. How does it get rid of that extra energy?
Heat?
No, in this particular case it’s light. It gives off a burst of
light called a photon, so every color that you see in a rainbow is
really coming from electrons going from a high energy state to a
lower energy state.
That is beautiful!
It is beautiful. And this is one of the fabulous things that
Einstein did: One of Einstein’s relationships is the relationship
between the energy of the photon and its wavelength. We can imagine
— and don’t say that Schapansky said this is true, but we can
imagine — that electrons are going to try to stay as close to the
nucleus as possible, though they can’t fall into the nucleus. So
along comes another atom, which bangs into it, and gives it some
energy, and all of a sudden the electron is in another orbit. But
it can’t be just any old orbit: If the amount of energy that came
in isn’t exactly right, it wouldn’t go up to this higher level. Nor
will it stay long in that high orbit. Just like if you let loose of
a ball it’s going to fall to earth, that excited electron is going
drop down to its lowest allowable energy state. And it sheds that
extra energy as a photon or a packet of light.
Speaking of photons, I was looking at the moon the other
night, and I was bothered that I could see the light coming from
the moon but I couldn’t see the light going to the moon. Can you
only see photons when they’re coming straight at you?
In essence, yes.
I didn’t know they were so directional. Yes,
they are, they only go in a straight line. Except that, believe it
or not, in relativity, Einstein was able to show that photons
coming from the sun that don’t hit the earth actually curve around
the earth, because the photon has a mass equivalence, and as such
it is attracted to the earth.
That’s part of its crazy wave-or-particle
riddle?
Exactly. So here’s an even better question for you since you’re
talking about photons. Why is the sky blue?
Because it’s reflecting the ocean?
No!
Okay, okay! Because something’s releasing photons at the
blue wavelength? Because some electrons are descending down from
one energy level to another in blue packets?
That’s kind of right, but where is that energy coming from?
From the sun? But the sun should be giving energy,
driving the energy levels up, not down?
Yes, but the oxygen in the atmosphere has exactly the right
energy structure so that a blue photon coming from the sun will be
absorbed. Then the blue photon will be instantly reradiated. It has
nothing to do with the ocean.
Why is it reradiated?
Well, because—remember, we said earlier that when it absorbs it
the electron goes to a higher energy state—
But it can’t stay there!
Right. It is excited but it wants to come back to its natural
state. So it gives off this blue photon. But which way does it give
it off? It gives it off any way it wants to. It’s completely
random. So if I look over there I see blue, because countless
billions of oxygen atoms are spitting out blue light every which
way so that some of it comes to my eye.
So why is the sunset orange?
Because the yellow light goes straight on through. The long
wavelength, lower energy light is not absorbed. If the electron
could absorb it, it would move the electron up to one of these
forbidden energy bands, and that’s not possible. So only the light
that can move it from an allowable state to another allowable state
is okay. In physic classes, we would call this scattering. The
oxygen is scattering the blue light, and leaving the rest of it
alone.
Do electrons ever die or disappear?
Yes, they can change from mass into pure energy. If an electron
runs into a positron, they will be turned back into a photon.
Can you change pure energy into mass?
Say you have a very, very high-energy photon. It comes into
contact with an atom and lo and behold, magically, two electrons
are created.
And the gamma ray disappears? Yes. It’s the
reverse of the nuclear reaction. In a nuclear reaction mass is
converted into heat and other forms of pure energy—light, potential
energy, kinetic energy, etc. It has to be reversible, though there
are not many examples of this. The best example of converting pure
energy into mass is the creation of an electron and its partner,
called a positron.
You know this? Absolutely. You can
spontaneously have a gamma ray, which is a very very energetic X
ray, moving through space and it vanishes and—poof—an electron and
a positron come out. Now, this is the first time your E=MC² becomes
meaningful. E is equal to MC² is the formula I use to calculate how
much energy this photon needs in order to create the mass of an
electron and a positron. When you first brought that up, that was
so far removed from everyday energy, because that literally has to
do with relativity and the mass-energy equivalent. It means here’s
energy, and there’s mass, and a constant–which is the speed of
light squared–relates them. If I want to create some mass, I’m
going to have to have this much energy—I can calculate how much
energy I have to have. If we’re going to convert radiation energy,
or light energy, into mass, then that’s the formula.
So that’s the energy the formula refers to, not just any
old energy.
Right, it’s not a useful formula unless you’re trying to create
mass. And that happens all the time. You go to any particle
accelerator, and you’re taking neutrons or protons or alpha
particles and you’re banging them into something, so all of this
stuff comes out. And one of the things that comes out is high
energy gamma radiation. You can see it happen. They put all these
photographic films around and all at once, out in space, two
electrons appear, one of them positive, one of them negative, and
this is all in a magnetic field so one of them is circling one way,
one of them is circling the other way, and you say, “My God! There
are two electrons! Where did they come from?” Well, E is equal to
MC squared. There was enough energy in that gamma ray to create
exactly that amount of mass.
Thank you. I’ve wondered about that for a long
time.
Keep up the conversation by leaving your comments below or
emailing Martha Sadler.
