Page 114 - The Creation Of The Universe

112 THE CREATION OF THE UNIVERSE

posure to gamma rays can be fatal.) Light is a form of electromagnetic ra-
diation that lies between these two extremes.
The first thing to be noticed about the electromagnetic spectrum is how
25
broad it is: the longest wavelength is 10 times the size of the shortest one.
Written out in full, 10 25 looks like this:
10,000,000,000,000,000,000,000,000
A number that big is pretty meaningless by itself. Let's make a few com-
parisons.
For example, in 4 billion years (the estimated age of the Earth) there are
25
17
about 10 seconds. If you wanted to count from 1 to 10 and did so at the
rate of one number a second nonstop, day and night, it would take you
100 million times longer than the age of the earth! If we were to build a
25
pile of 10 playing cards, we would end up with a stack stretching halfway
across the observable universe.
This is the vast spectrum over which the different wavelengths of the
universe's electromagnetic energy extend. Now the curious thing about this
is that the electromagnetic energy radiated by our Sun is restricted to a
very, very narrow section of this spectrum. 70% of the Sun's radiation has
wavelengths between 0.3 and 1.50 microns and within that narrow band
there are three types of light: visible light, near-infrared light, and ultravio-
let light.
Three kinds of light might seem quite enough but all three combined
make up an almost insignificant section of the total spectrum. Remember
our 10 25 playing cards extending halfway across the universe? Compared
with the total, the width of the band of light radiated by the Sun corre-
sponds to just one of those cards!
Why should sunlight be limited to such a narrow range?
The answer to that question is crucial because the only radiation that is
capable of supporting life on earth is the kind that has wavelengths falling
within this narrow range.
In Energy and the Atmosphere, the British physicist Ian Campbell ad-
dresses this question and says "That the radiation from the Sun (and
from many sequence stars) should be concentrated into a minuscule