If the best insulating windows would be ones that had nothing in between
the two panes of glass, just a vacuum, think about the Earth and the Sun.
Which are separated from each other by 93 million miles of vacuum.
It's kind of amazing, actually, that the lump
of atoms here that is the Earth, the kinetic energy
of those atoms, has anything to do with the
energy of the atoms in the sun, or anything
else in space. It turns out that the way
energy can be transferred through a vacuum is by means of light.
Light is composed of two properties of space time.
One of them is the electric field and the other is the magnetic field.
The electric field is manifested in that if you take something
that has a positive charge like a proton, an H plus atom like what
changes the acidity of water, that has a positive charge and
then an electron is a particle that has a negative charge and you sort
of set those things close to each other, they will feel each other's presence.
They will want to come together even
though there's nothing in between them but vacuum.
The electric field is what these things are feeling
and that is sort of a property of the vacuum.
A property of space.
Another property is the magnetic field
I've drawn two magnets with north and south
poles and so the south pole of one magnet
will be attracted to the north pole of another.
And there are some differences here.
One is that in the magnetic field there's no such thing as a magnetic monopole.
Something that only has a north or a south charge.
Electrical fields, you do have electric monopoles such as
the electron or the proton. But in the magnetic
field you just sort of have things where
the charges are separated from each other like this.
The other difference is that the magnetic
field can reach farther.
If you have 2 magnets and they're pretty strong you can
hold them pretty far apart and you'll feel them pulling together.
Whereas if you take a car
battery and a jumper cable, do not try this
at home, but if you did put the one part of the jumper cable to the plus and
the other part of the same wire took it
close to the minus, if you actually touch it
it would be an explosion, but before you touch it
you don't feel much attraction cause it doesn't
make it as far in space as the magnetic field does.
The two fields are coupled together by the
fact that if you change the electric field,
if you oscillate it, move it up and down,
dial it up and down, it will induce a magnetic field.
And so this is how, for example, an
electromagnet works or an electric
motor uses this this (phenomenon).
Or if you change the magnetic field that can induce an electric field.
And that's how, for example, a generator works.
So if you have some power from a waterfall or something and
you're twisting some magnets around you can use that to generate electricity.
Light is a coupled oscillation of the electric and the magnetic fields.
It's like the energy bounces back and forth
between the electric to magnetic and back again.
If you were to draw a graph of the electric field as
a function of time or distance, either way since it's sort of a wave,
this is a time where the electric field is changing
and as a result this induces a strong magnetic field.
Now here the magnetic field is collapsing and
changing and so that induces a strong electric field
and so the energy is sort of bouncing back
and forth between the electric and the magnetic fields.
Now this thing sets
up a wave that's very analogous to a water wave on the surface of water.
If this is the flat surface of the
water and you make the water actually do like this, there's gravity
tending to pull this water down and tending to push that water up
and make it sort of go back to a flat surface.
But if you do it just right there can be motion
of the water in the wave in a sort of circular pattern like this that creates
another wave a few seconds later that has the same shape as the first wave.
And the point is the only way this can work is if the speed
of the wave is right so that it can sort of self-reproduce itself like this.
Make something that looks like it did only just moved over a little bit in space.
So if you tried to make a water wave and
make it go 100 miles an hour it would break.
It wouldn't work.
It wouldn't self-replicate and so it wouldn't be a wave.
Well, light is the same way.
It has to reproduce itself.
It has to bounce the energy from the
electric field, the magnetic field, and back again
so that it looks the same way after a split second but just moved in space.
And that's what
sets up the speed of light, is this
requirement that it sort of ring like a bell.
So that it self reproduces itself.