[extropy-chat] FWD [Skeptic] Re: Looking for examples of naturally evolved X-ray vision?

[Terry W. Colvin]

Includes comments on Superman's vision and the Museum of Jurassic 
Technology...

>>> fortean1 at mindspring.com 01/18/06 10:09 PM >>>
On 1/18/06, Terry W. Colvin <fortean1 at mindspring.com> fnarded:

> I was helping my daughter come up with some ideas for a school science
> project and I stumbled onto a couple unknowns.
>
> Animals have evolved a wide variety of abilities to seek food and avoid
> predators. Echo-location, color vision, and compound eyes are just a
> few. All provide important information regarding the immediate
> surroundings. My daughter asked me why the visible light spectrum IS the
> visible light spectrum. After all, animals hear at a wide range of
> frequencies that humans cannot, so why not have the same thing occurring
> in vision? Are there animals with X-ray vision?


Several reasons why not:
1. Animals don't generate the light they see by, by and large, they detect
light generated by the sun or by other animals.
2. Therefore the light that is used to see by must be something that is
reflected by the things you want to see.
3. X-rays mostly go right through things you might want to see.  Infrared is
mostly absorbed by them.
4 Given that early life evolved in water, the visible spectrum is the about
the only bit *not* blocked by atmosphere plus water. IR, X-rays, Radio, and
UV are all blocked by water. Not much point seeing a frequency which is
blocked.
5. X-rays are extremely energetic, and actually break down biological
tissue; hard to make a biological detector.
 6. X-rays are extremely energetic, and would be hard or impossible for
living systems to generate.

(deleted)

>>>>>>>>>>>>>>>>>>>>

This discussion reminds me of the old Superman comic books I used to
read, with Superman having x-ray vision.  As it was depicted, there were
cones emerging from his eyes (as if they were emitting x-rays, rather
than receiving radiation, which is what eyes do).  The radiation then
apparently penetrates the thing he wants to look through (like a wall),
but then somehow stops at the object he wants to observe, and is
reflected back to him (again through the wall) so he can see it.  The
physics seems rather implausible.

Tom Wheeler

--------------------------------


> 3. X-rays mostly go right through things you might want to see.


Yeah, when you look at an x-ray picture, basically what you see is a 
differential.  That is, less x-rays penetrate the bone and dense tissue, 
so they appear as shades of grey.  Looking at an x-ray picture of a bone 
is really a little like looking at something made of glass.  You "see" 
all the way through it.  The detail you see is due to differences in 
density.  This is what makes CT so awesome--since the images are 
captured by electronic sensors rather than conventional film and stored 
as a block of data that can be manipulated, you can display images where 
minute differences in density can be emphasized.  For example, you can 
tell the difference between white matter and grey matter in a brain, or 
between pancreatic tissue and stomach tissue.   You can't really do that 
with conventional film...though in theory the difference in density is 
there (because either in CT or regular radiography the same proportion 
of photons are going through and being attenuated by the tissues), the 
human eye can't see the subtle shades of grey that a computer could.

> 5. X-rays are extremely energetic, and
> actually break down biological
> tissue; hard to make a biological detector.


Yeah, like someone else pointed out here, the damage tends to be done in 
one of two general ways.  Either the photon strikes the DNA molecule 
itself, or it ionizes a water molecule in a cell and causes the creation 
of a free radical that can damage the DNA or other chemical processes 
inside a cell. Either way, bad things tend to happen to the cell.

> This discussion reminds me of the old Superman
> comic books I used to read, with Superman
> having x-ray vision.  As it was depicted, there
> were cones emerging from his eyes (as if they
> were emitting x-rays, rather than receiving radiation,
>  which is what eyes do).  The radiation then
> apparently penetrates the thing he wants to look
> through (like a wall), but then somehow stops at
> the object he wants to observe, and is reflected
> back to him (again through the wall) so he can
> see it.  The physics seems rather implausible.


Speaking of improbable physics, remember what Superman used to do when 
criminals shot at him?  He'd just stand there and let them shoot their 
bullets into his chest, but then he'd duck when they threw the empty 
guns at him.  :-)

------------------------------

You have to visit the site.  The Museum of Jurassic Technology is sort 
of a simultaneous tribute to and parody of museums.  Its exhibits are 
dead on in capturing the style of old natural history museums, even 
when describing a bat that uses x-ray sonar and can fly through solid 
objects.  The one on display at the museum (I?ve been there) is 
supposedly trapped inside a solid lead block, but can be viewed using 
special x-ray goggles.  I stongly suspect the bat is one of the parody 
exhibits...

----------------------------

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.  [1]  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.

The earth's sun _does_ produce X-Rays and they do reach the earth.
There are several reasons why we did not evolve the ability to detect
them.

The ionizing radiation factor has already been mentioned.

X-Rays have a tendency not to interact with low density objects; this
is problematic for two reasons. First this would make it difficult to
see things like predators or pools of water since they would not be
reflecting significant amounts of the sun's X-rays. Second in order to
see your retina must interact with whatever type of photon you "see"
with. This means that in order to pick up the X-Rays in any
significant number you would need to have either a much more dense or
much thicker retina.

Possibly more importantly the sun produces X-Rays in relatively small
quantities compared to other types of photons. The sun can be thought
of as a Black Body at a temp of about 6000K. At this temperature we
get the following curve:
http://hyperphysics.phy-astr.gsu.edu/hbase/vision/solirrad.html
Examining the curve shows us that natural selection loves us and wants
us to be happy. We evolved to see photons right at the sun's peak
power density.

YT,
Dan Noland



-- 
"Only a zit on the wart on the heinie of progress." Copyright 1992, Frank Rice


Terry W. Colvin, Sierra Vista, Arizona (USA) < fortean1 at mindspring.com >
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