The Two Faces of Light
For
God, who said, "Let light shine out of darkness," has shone in our
hearts to give the light of the knowledge of the glory of God in the
face of Jesus Christ. (2 Cor. 4:6 ESV)
The
nature of light is fascinating. It has a dual personality, sometimes
acting as tiny particles of energy called photons, and at other times
as a continuous wave like a wave in the ocean.
One way to demonstrate both natures is to shine light through two very
close, tiny pinholes in a sheet of aluminum foil. When the
light, which emerges from the two holes, falls on a screen on the other
side, it forms an intricate pattern of darkness and
brightness. If one of the holes is covered over, the pattern
disappears.
These results can be explained by considering light to be like water
waves with alternating peaks and valleys. When two such waves
come together, there will be regions where the peaks and valleys
combine to double the heights and depths, and other regions where they
cancel each other, leaving the water surface calm. Hence the
pattern of the light on the screen is explained by saying light acts
like a wave.
However, if the light intensity in this demonstration is dimmed so that
only sensitive light detectors in an optics laboratory can detect it,
then the light photons can be counted one by one, thus showing them to
be individual tiny bundles of energy, each one traveling through one
hole or the other. And yet the light lands on the screen only
in the formerly bright regions, not the dark regions, thus preserving
the intricate pattern.
Furthermore, if one hole is covered, this pattern disappears just as
before. So the mystery is: how does the particle
“know” that another hole even exists when it passes
through one of the holes? The distance between the holes is
very large on the scale of the size of the light particles.
And yet just the availability of a second path somehow makes the
particles either reinforce each other or cancel each other out.
These results seem contradictory and have fascinated me for
years. The mathematics that physicists use can explain the
effect, but it does nothing for helping our intuition about
it. There is more. Can you believe, that a similar
experiment with beams of electrons, which are tiny charged particles,
show the same pattern of reinforcement and cancellation on a
phosphorous screen in a darkened laboratory? It turns out
that all subatomic particles, as well as atoms and molecules, have the
same dual nature, acting as waves as well as particles. Until
next time…
…