Evidence for Electromagnetic Waves
You claim that light, microwaves, and X-rays are all the same kind
of stuff, but they seem very different to me. How do we know that these
are all just electromagnetic waves with different wavelengths?
One thing that all the forms of electromagnetic radiation have in common is that they
can travel through empty space. This is not true of other kinds of waves;
sound waves, for example, need some kind of material, like air or
water, in which to move.
So how do we know that all the different kinds of electromagnetic waves can travel through
Well, it's obvious that visible light can do this; that's why we can see light
from the sun and stars, which are separated from us by enormous stretches of emptiness.
Astronomers have been making observations of this visible light for centuries. Modern
astronomy, though, has other ways of observing the cosmos; instruments have been developed
that can detect types of radiation other than light, so that we can now take "pictures"
of the sky in infrared, radio, or x-ray
So all those kinds of waves must be able to travel through
outer space, just the way light can.|
Exactly! The fact that this information can
reach us, across millions of miles of space, points to a fundamental
similarity between light and these other forms of radiation. They all must have some
method of moving through empty space, boldly going where no other
waves have gone before.
(We'll discuss the way that electromagnetic waves move later in
section.) And not only can they all travel through the void,
they all do it at the same speed: the speed of light. If they
moved at different speeds, the planets, stars, and galaxies
would appear to be in different places depending on which
wavelength we used to view them--but they don't. So
you see, it
isn't so incredible to say that light, x-rays, and microwaves are all different forms
of the same thing.|
To see some pictures taken using different kinds of
electromagnetic waves, check out this
collection of astronomy links.
(There is also a text-only version
of these links, which loads more quickly.)