This classroom
experiment is one of the best ways I know to demonstrate to students
the power of suggestion and the necessity for blind and double-blind
experimentation, even when the experimenter thinks that he can
maintain an unbiased attitude. Of course, it also serves an a
good introduction to polarization of light.
Extensive analytical work was performed on
the Shroud of Turin, claimed by some to be the burial shroud of
Christ. Scientists were allowed to extensively study the relic,
including the removal of samples for carbon-14 dating, which provided
an origination date between 1260 and 1390 A.D. Techniques used
prior to the carbon-14 dating included x-ray and ultraviolet fluorescence,
mass spectrometry, and visible and electron microscopy, and the
work, in general, was of good quality, although some incorrect
conclusions were drawn because of inappropriate sampling methods.
An interesting sidelight to the main investigation was a study
of the claim that button-like images in the eye areas of the Shroud
were lepton coins of Pontius Pilate, placed over the eyelids.
This claim was made by Chicago theology professor Francis Filas,
who noted that under high-magnification, the image on the right
eye appeared to show the letters UCAI and a shepherd's crook,
which were characteristics of a coin in existence at the time
of the crucifixion. This inspired Alan and Mary Whanger (Whanger,
A. D., and Whanger, M. (1985). Polarized image overlay technique:
a new image comparison method and its applications. Applied Optics,
24, 766-772) to invent a technique called "Polarized Image
Overlay", in which two projectors were fitted with oppositely
polarized filters. One projected the image from the eye of the
Shroud, and the other the image of a lepton coin. A third polarizer
was used by the observer to switch from one image to the other
so as to note congruencies between the coin the the image of the
Shroud eye. Was this really any more than a complex Rorschach
test that misinterpreted scorch marks on the cloth? The Whangers
attempted to alleviate that concern by doing the image analysis
of other coins and with other observers, although there is no
evidence that the tests were done blind. In any event, the question
of Shroud authenticity was settled by the carbon-14 dating results,
so you can be the judge of the reality of the coins in the eyes
of the Shroud image.
The classroom experiment can be done with
two overhead projectors rather than with the 35-mm slide projectors
used in the original studies. Large polarizers, available from
various educational supply companies, can be used to cover the
projection lenses of the overhead projectors, and small polarizers
are then distributed to the class for use as analyzers. Images
of various ancient coins and the image of the Shroud eye are scanned
into a computer and digitally-modified to account for angular
differences upon display. The experiment has been done two ways.
First, the Polarized Image Overlay experiment is performed in
a manner similar to the original work, except that the students
are not informed which coin is the lepton of Pontius Pilate. Results
from this experimental design have resulted in a chance distribution,
with approximately 20% of students choosing the lepton on Pontius
Pilate from a selection of 5 coins. A more interesting way to
perform the experiment is to attempt to bias the student selection
by providing them with false information regarding the coin that
"should" be selected. Not surprisingly, the distribution
of coin choice in this experiment tends to be biased towards the
coin that "should be" but "really isn't".
The experiment can also be done using a computer
graphics program that allows one image to be superimposed over
another image and the transparency of each image to be modified.
No matter how the experiment is done, it is definitely a wakeup
call for the students.
Figure 1. The coin in the eye
of the Shroud of Turin
(A) Images of the lepton coin of Pontius Pilate and an enhanced
image of the cloth in the area of the Shroud eye. Numbers are
for screen alignment.
(B) An image of the face on the Shroud of Turin
Page prepared by: Mike Epstein
Last Modified: 30 April 1999
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