Transcript Polar bear fiber optics, twenty years later:

And now for something completely different
The hairs of the polar bear are transparent light pipes that
direct ultraviolet light to its skin -- which is guess what
color? Black! So what’s white and black and warm all
over? A polar bear under the arctic sun.
Paul G. Hewitt, Conceptual Physics, 6th Edition, 1989,
p. 501
Polar bear fiber optics,
twenty years later:
Fuzzy Wuzzy wasn’t photonic,
was he?
Daniel W. Koon
Department of Physics
St. Lawrence University
Special thanks to:
Reid Hutchins, SLU ‘98
Michael Owen, SLU Geology
Catherine Jahncke, SLU Physics
Karen Johnson, SLU Physics
John Scott Foster, Seneca Park Zoo, Rochester, NY
Craig Bohren, Penn State
David Lavigne, Guelph, Ontario
Wherever Nils goes, his
bear is sure to follow. Nils
Are Øritsland found this
three-month old cub in
early spring, tamed it, and
named it Douglas before
discovering it was a
female. Polar bear cubs
are born hairless, blind,
and weighing about half a
pound. Alaskan Eskimos
call them ah tik tok,
meaning “those that go
down to the sea”.
“Polar Bear: Lonely Nomad of the North”, National
Geographic 139:4, 574 (April 1971).
“Dr. Langley invented the bolometer
A curious sort of thermometer
It can measure the heat
From a polar bear’s seat
At a distance of half a kilometer.”
Unknown, Applied Optics 19 (3), 403 (1980).
Lavigne, D. M. and
Øritsland, N. A., "Black
Polar Bears", Nature
251, 218-9 (1974).
Lavigne, D. M. and
Øritsland, N. A.,
"Black Polar Bears",
Nature 251, 218-9
(1974).
Factoid #1
Seals, polar bears, NATO Arctic
camouflage paint all appear highly
reflecting (“white”) in the visible, but poorly
reflecting (“black”) in the ultraviolet.
For more of the history of this factoid, see, for example, D.
W. Koon, “The power of the polar myth”, New Scientist,
April 25, 1998, p. 50.
The fiber-optic myth. I:
The engineers
Who?
R. E. Grojean, J. A. Sousa, M. C.
Henry
What? Measured reflectivity, studied
individual polar bear hairs
When? Mid 1970’s
Where? Northeastern University and the US
Army Research and Development
Lab, Natick, MA
Why?
To understand how the polar bear pelt
changes reflectivity so dramatically in
going from the visible to the UV
Reflectance of polar bear and seal pelts
Grojean, R. E.; Sousa, J. A.; and Henry, M. C.,
“Utilization of solar radiation by polar animals: an optical
model for pelts”, Appl. Opt. 19, 339 (1980).
Structure of a polar bear hair
Grojean, R. E.; Sousa, J. A.; and Henry, M. C.,
“Utilization of solar radiation by polar animals:
an optical model for pelts”, Appl. Opt. 19, 339
(1980).
Hairs of polar bear (top), pig (bottom)
Tributsch, H., Glosowsky, H., Küppers, U., and
Wetzel, H., “Light collection and sensing through the
polar bear pelt”, Sol. Energy Mater. 21, 219 (1990).
Factoid #2
Polar bear hairs are not white, but
transparent: light can be transmitted across
the width of a single hair.
“The efficiency of transmission of solar
radiation to the skin must be particularly high
for the UV, since the pelts appear black
when viewed in the UV while the hairs
themselves appear quite transparent.”
Conclusion: The hairs guide UV to the skin.
The relevant scientific literature:
Grojean, R. E., Sousa, J. A., and Henry, M. C., “Utilization of solar
radiation by polar animals: an optical model for pelts”, Appl. Opt.
19, 339 (1980).
Bohren, Craig F. and Sardie, Joseph M., “Utilization of solar
radiation by polar animals: an optical model for pelts; an
alternative explanation”, Appl. Opt. 20, 1894 (1981).
Grojean, R. E., Sousa, J. A., and Henry, M. C., “Utilization of solar
radiation by polar animals: an optical model for pelts; authors’
reply to an alternative explanation”, Appl. Opt. 20, 1896 (1981).
Tributsch, H., Glosowsky, H., Küppers, U., and Wetzel, H., “Light
collection and sensing through the polar bear pelt”, Sol. Energy
Mater. 21, 219 (1990).
Koon, Daniel W., "Is polar bear hair fiber optic?", Applied Optics
37, 3198 (1998).
Objections to the fiber optic theory:
The Arctic is poor in UV, and when the bears most need it,
even less is available.
How does light entering the fibers from random directions get
launched down the hair?
How does the light “know” to travel toward the skin rather
than away from it?
Why is UV guided fiber-optically down the hair, but visible
light is not?
Keratin, a protein that makes up all hair, is known to be
strongly absorbing in the UV, but relatively transparent in
the visible.
Absorption in various amino acids
“Biophysical Chemistry: Principles, Techniques &
Applications”, Alan G. Marshall (John Wiley & Sons, NY:
1978), p. 399
Some of the popular literature:
Time Magazine, Dec. 4, 1978.
Natural History, Oct. 1981.
Science News, March 8, 1986.
“Arctic Dreams”, Barry Lopez, 1986.
Christian Science Monitor, Dec. 1, 1987.
Scientific American, March 1988.
National Public Radio’s “All Things Considered”, March
5, 1995.
Polar bear exhibit, New England Science Center,
Worcester, MA.
For the bibliography to end all bibliographies, go to
http://it.stlawu.edu/~koon/mar_ref.html.
Examples from the popular literature
Time Magazine, Dec. 4, 1978. See http://it.stlawu.edu/
~koon/polar.html for more references.
More popular literature,
closer to home
"Polar bears ... have a thick coat of hollow hair
that traps any solar heat, allowing absorption of
the heat into their black skin."
The Alaska Zoo (Anchorage),
http://www.alaskazoo.com/polar_bears.htm
The fiber-optic myth. II:
The 95% solution
"[Grojean, Gregory Kowalski and Charles DiMarzio] have discovered that
the shaggy fur of polar bears is 95 percent efficient in converting the sun's
ultraviolet rays into usable heat."
Grow, Glenn S., "Warming up to polar bears' solar secrets", The
Christian Science Monitor, Dec. 1, 1987, p. 19.
"Through thermal balance equations, Grojean calculated that the bears
trap 90 percent of ultraviolet light and 17 percent from the entire solar
spectrum. The figures were confirmed by an Irish Arctic research team in
the early '80s."
Croke, Vicki, "Solar Polar Bears? Two Boston Scientists Think So.",
Boston Globe, June 4, 1990, p. 41.
"[T]he hair...collects heat...[H ]airs change 95% of the sun's rays to heat."
Brown, Gary, "The Great Bear Almanac" (Lyons & Burford: New York,
1993), p. 68.
The fiber-optic myth. II:
The 95% solution
This 95% figure is never directly claimed in the technical
literature
Unless you count this....
“A rudimentary calculation of the amount of solar energy
available (i.e., not reflected) for heating, based on the
measured reflection coefficient of the pelt, indicates a avalue
of 0.324 cal/cm2-min compared with 0.307 cal/cm2-min
measured at the skin by Oritsland.” (Grojean et al., Appl. Opt.
19, 339 (1980).)
The fiber-optic myth. III:
Saved by fluorescence?
Tributsch, H., Glosowsky, H., Küppers, U., and Wetzel,
H., “Light collection and sensing through the polar bear
pelt”, Sol. Energy Mater. 21, 219 (1990).
The fiber-optic myth. IV:
Medical applications
"Polar-bear fur: good for more than rugs", Chronicle
of Higher Education, March 17, 1995.
“Aristotle maintained that
women have fewer teeth than
men; although he was twice
married, it never occurred to
him to verify this statement by
examining his wives’ mouths.”
Bertrand Russell
“Mrs. Aristotle’s mouth”:
The tabletop version
Length of hair
Output light
15mm
Dim, red
10mm
Brighter, golden
7mm
Brighter still, yellow
Hair courtesy of John Scott Foster, Seneca Park Zoo,
Rochester, NY
Attenuation spectrum, polar bear
FOUL(UP):
A Fiber-Optic Ursine Link (Universal Prototype)
for telecommunications
D. W. Koon and C. L. Jahncke, Physics Dept., St. Lawrence Univers
ABSTRACT:
We have constructed what we believe is the first prototype
of a fiber-optic link to use the hair of an Arctic mammal.
The potential advantages of ursine fiber technology over
conventional technology are discussed.
http:// it.stlawu.edu/~physics/clj/foulup.html
FOUL(UP): experimental setup
Laser
Microscope objective
Ursine fiber-optic link
Silicon-diode sensor
Laser power supply
http://it.stlawu.edu/~physics/clj/foulup.html
FOUL(UP): output signal
Filtered output of the
sensor for a laser signal
modulated at 102kHz.
Specs:
4mm length of hair
3mW, 650nm laser input
3% output at 102kHz
http://it.stlawu.edu/~physics/clj/foulup.html
Conclusions:
Polar bear hair is a lousy optical fiber in the visible and
even worse in the UV: if “fiber optics” explained the
black appearance of polar bears in the UV, then it
would “explain” the bears into being black in the
visible as well.
Publishing in the popular media is a dangerous
business. You are as likely to spread ignorance as
wisdom.
Not even peer review can stop bad science.
Public outreach needs to include teaching the public to
be skeptical of what we say.