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Slit Diffraction

Slit Diffraction

There have been many claims of successful demonstrations of anomalous

perturbation of stochastic processes correlated with human intention (Radin &

Nelson, 1989), although the mechanism underlying such anomalies is not

known. The experiment reported in this paper was originally conceived as a

means of testing whether such statistical anomalies derive from an ability

of the human operator to observe and collapse the quantum-mechanical

wavefunction by extra-sensory means, rather than from an ability to select

from allowed outcomes. First results from York University have already been

reported elsewhere, couched in these terms (Jeffers, 1996). Briefly, human

operators were invited to ª visualizeº (observe, by extra-sensory means)

monochromatic light passing through a double slit,




to its registration as

an interference pattern by an optical detector. It was predicted that such

extra-sensory observation would manifest as a measurable departure of the

interference pattern from theory due to premature wavefunction collapse. 



As sketched in Figure 1, a double-slit interference pattern is generated

by a low power He-Ne laser illuminating a commercially available stainless

steel disc in which two slits are cut 10



m m wide and 10 m

m apart. The

resulting interference fringes are detected by a linear diode array (Princeton

Applied Research Model #1453 with 1024 diodes). Figure 2 shows an ideal

(scalar Fraunhofer theory) interference pattern to which the measured

interference pattern has been shown to conform very closely after subtraction

of background counts and correction for gain variation of the detector array



et al.,1992). A stepper motor is used to chop the beam close to

the laser aperture, effectively blocking the beam for two out of every three

seconds. The diode array responses during the blocked and un-blocked phases

are digitized and passed to a PC for analysis. The response during the interval

with the beam blocked serves as the background to be subtracted from the

response during the subsequent interval with the beam un-blocked.


The chosen target of the analysis is the contrast of the interference pattern

defined as

where I



max is the intensity at the central antinode and Imin

is the average of the

(two) intensities at the first node on each side of the maximum. To counteract

the effects of jitter in the interference pattern, the locations of the extrema are

determined afresh for each exposure. The values of the intensity extrema are

deduced from the stationary points of a quadratic fit to the intensities (




diode responses) at the three detector positions spanning each extremum.

End of  Slit Diffraction