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The Way of the Explorer
as a wave. However, since the later Greek thinkers, it was believed to be
corpuscular or particle-like, and from Galileo to Newton onward for three
centuries, the argument persisted. One side or the other would prevail,
but only for a time, as new discoveries were made, lending credence to the
opposing camp. Then by 1880, James Clerk Maxwell and his electromagnetic
theory seemed to definitively settle the issue. His theory claimed that
light was most certainly wavelike. Of course, this too passed.
With the discovery of the photo-electric effect by Philipp von Lenard
in 1902, and the solution to quantized heat radiation by Max Planck, the
pendulous answer again began to swing toward Newton and those who
believed light was a particle. It was Einstein, still an unknown in 1905,
who put the wave and particle ideas together, with the mathematics to
show that light came in little packets of energy, subsequently called photons,
each carrying a quantum of energy proportional to the frequency of
the light. Light, and all radiation, clearly had both wave and particle characteristics.
Einstein had cobbled together concepts previously considered
separate.
A few years later, Louis de Broglie asserted that not only light, but all
matter possessed both wave and particle properties at the subatomic level.
That is to say, he brought into question the fundamental way matter was
believed to exist. Atoms were not like little ping-pong balls after all. This
brought us to the strange new world of quantum physics, an eerie world so
baffling and mysterious that both Einstein and Planck had difficulty accepting
it until the very end of their lives.
The dual nature of matter as both particle and wave is the foundation
of quantum physics; we now call it the wave/particle duality. 1 Since the
days of Newton, waves and particles have been given precisely definable
and measurable attributes, though the definiteness of the attributes of each
are quite different. Particles may be said to have a definite position, mass,
velocity, and spin. Their momentum and energy are attributes that can be
computed. However, waves have no mass, no definite position, nor spin.
Waves can also overlap constructively or destructively (in other words,
coexist at the same location)—matter cannot. But waves do have polarization,
energy proportional to frequency, and a constant velocity (the speed
of light in free space). These different attributes and their measures were
and are a source of consternation to many physicists. How can such different
concepts be brought together
Einstein resolved one critical issue even before the ascension of quantum
theory by postulating that the energy equivalent of matter at rest was
the product of its mass and the velocity of light squared, expressed in his
famous equation, E=MC 2 . This equation helped relate the energy of waves
to that of particles: Energy (waves) equals mass (particles) multiplied by