We have a theory, which is called quantum
electrodynamics.
The physicists has got a history, at least
a theoretical history, of synthesis perpetually.
Of course, experiment is always finding new
phenomena, problem is to work them together.
And sometimes we see that they're different
aspects of the same phenomenon.
An example, is of course, the simplest and
earliest one, is that the laws of motion explain
the properties of heat.
Because heat was motion.
And if you knew how motion worked you could
understand thermal properties.
It also explained properties of sound, which
is otherwise a mystery, as the motion of the
atoms and waves in the gas.
Newton, who worked out the laws of motion,
also gave us another theory about the forces
between large masses and distances from one
another called the theory of gravity.
As the time went on, phenomena associated
with electricity, rubbing combs in your hair
and things like that, and magnetism became
interesting to the experimental physicists
and they discovered relations between them
experimentally until they saw, ultimately,
that they are not two different phenomena
but different aspects of the same thing.
Another phenomenon that Newton had studied
was light.
So without time, it looked at first, like
there were many things.
Motion and gravity, electricity and magnetism,
later, and light, but when Maxwell put together
the laws of electricity and magnetism he found
out, that the equations that he had, produced
expectation that would be behavior of waves
that would propagate at a speed, which was
figured out from electrical measurement, which
came out the same as the speed that light
actually propagated, and so there was a new
theory of light, which is that it was an electromagnetic
wave.
And Maxwell's great synthesis in 1873 was
to connect electricity, magnetism, and light.
Light is just one aspect of the electromagnetic
wave which can have different kinds of wavelengths
from that point of view.
And if you have different wavelengths ...
If the wavelength is very short between about
400 millions of a centimeter and 700 millions
of a centimeter then you see it directly with
the eye, but if it gets longer the wave is
...
Well it's the long end that's red and then
the other end it's blue, and if it gets more
longer than the red we call it infrared.
The rays are there, but the eye doesn't seem
...
The pit viper has an eye that sees the infrared.
And if you go in the other direction, beyond
the violet, then we can't see it again, but
the bee has an eye that sees the ultraviolet.
And if we go still further, to the far other
violet, no animal has it that can see it,
but we can make instruments that will detected
it or photographic plates and so on up into
x-rays and so forth.
And down in the other direction far infrared
you get into radio waves and we can build
instruments that detect them and we can use
them to advertise soap.
In it ... in addition ...
So that there is an enormous range of one
property, the wavelength, a range of phenomena
that's a complete enormous spectrum.
The spectrum we see with the eye is very narrow
range.
And this entire spectrum is all put together
with a one theory of electromagnetic wave.
I'm going to talk about that part of it except
I'm going to call it light instead of saying
electromagnetic radiation.
Light is what we see, it's only one little
part, but from the physicists point of view,
the accident that the human eye happens to
be sensitive to waves from here to here is
not essential.
The phenomena are the same over the whole
range and I'm going to call them all light,
but it could be radio waves or x-rays or what
have you.
