Kids ask the greatest questions. Recently,
during a presentation to a local
school, an eighth grader asked:
“Do any animals, besides humans, use
I couldn’t think of any, and said so at
the time, but the follow up “why?”
took some more thought. The long
history of life on Earth has exhibited a truly bewildering variety
of shapes, sizes and adaptations, including the ability to use electro-magnetic
energy – infrared, visible, and even ultraviolet – but
those frequencies represent a very narrow sliver of an incredibly
broad electro-magnetic spectrum, from ultra-weak radio waves,
all the way to X-rays and even lead-penetrating Gamma rays.
Technically, we are all radio transmitters – everything above absolute
zero emits radio waves – but it’s not easily detected or
controlled, and gets lost in the ‘radio glow’ of everything around
us. Also, the wavelengths we radiate are so long and weak, receptor
antennas would have to be the size of billboards.
As to the upper end of the spectrum, aside from an occasional
ultraviolet strobe from lightning bolts, the sky is pretty dark in
UV, X- and Gamma-rays. For that matter, our atmosphere is
pretty good at blocking most radiation on either side of what we
call the visible spectrum. That’s why, in order to see stars and
galaxies in infrared, ultraviolet, X- and Gamma-rays, we have to
send our telescopes into space: Hubble, Spitzer, Chandra, and
others to come.
The reason most life on Earth has evolved to use only visible light
is that those are the frequencies that penetrate our atmosphere,
drive photosynthesis, and illuminate our oceans and landscapes.