[extropy-chat] Looking for examples of naturally evolved X-ray vision?
robert.bradbury at gmail.com
Tue Jan 17 21:35:31 UTC 2006
You can sense IR photons (as heat) if there are sufficient numbers of them.
But one problem with photons in the UV-thru-X-ray range is that the photons
are energetic enough to break atomic bonds. This is particularly true for
UV-B and UV-C.  So the sensing systems for these wavelengths *are*
going to decay over time and would require expensive repair or replacement.
X-rays in fact are so energetic that they break the bonds in the water
molecules and produce multiple free radicals which cause extensive DNA
damage. This is why X-ray exposure must be limited.
There is a problem of producing large numbers of photons with these
energies. Other than the stars, supernovas, neutron star collisions, etc.
there *aren't* a lot of natural processes that can generate the high energy
photons. UV-lamps typically require high temperatures or high voltages and
X-rays require very high voltages. One might be able to have biological
systems construct "capacitors" to store charges (an electric eel comes to
mind) but the voltages one usually finds in biological systems are measured
in millivolts (neuron voltages are usually < 100 mv) while one is talking
significantly higher voltages to start playing with significant numbers of
UV & X-ray photons. This is particularly a problem in biological systems
based on salt water. Salt water is a good conductor -- so its probably
difficult to build up very large voltages in biological systems. (Neurons
use lipid membranes to maintain charge separation but high voltages would
punch through those.)
Since there aren't any biological systems producing photons at those
wavelengths it doesn't make much sense to evolve sensors for them. The
exception might be reflected UV light from the sun. I believe that bees are
capable of sensing UV light.
The only systems I can think of where one may moving towards generating
higher amounts of energy is deep sea fish that can produce their own light
(presumably to attract or recognize prey).
As an aside, CCD arrays are quite good at reading UV & X-rays at certain
frequencies and are used in various UV & X-ray astronomy cameras as well as
CAT scanners I believe. There are also CCD array like detectors that can
detect IR but they are usually based on structures with elements like
Hg+Te+Cd or Pb+Se which aren't exactly abundant in biological systems.
1. See UV photon energy in Nanosystems Table 6.2 (pg 151) and the Bond
Dissociation energies om Table 3.8 (pg 52).
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