Knowledge derived from
physics informs us that the
world from which we obtain
sensory information is very
different from the world as we
experience it. We know that the
universe consists of
electromagnetic fields, atomic
particles, and the empty spaces
that separate atomic nuclei
from the charged particles that
spin around them. The picture
the brain creates is limited by
the range of stimuli to which
our senses are attuned, a range
that renders us incapable of
perceiving large segments of
the electromagnetic spectrum
and matter at the atomic scale.

    If we had the sensory
apparatus of some other of the
earth's organisms, "reality"
would seem quite different.
Honeybees and snakes respond
to frequencies of light to which
we do not. Bats can navigate
around thin obstructions by
means of echolocation. Fish
respond to sound frequencies
and odors that have no
perceptual reality for us, while
the sensory world of the
amoeba is so primitive and so
foreign to our own that it defies
characterization.