"Of all the communities available to us there
is not one I would want to devote myself to, except for the society of the true searchers, which
has very few living members at any time."
In 1916 Einstein devised an improved fundamental statistical theory of heat,
embracing the quantum of energy. His theory predicted that as light passed through
a substance it could stimulate the emission of more light. This effect is at
the heart of the modern laser (Light Amplification by Stimulated
Emission of Radiation).
This theory was further developed by the Indian physicist S.N. Bose. He sent a draft paper
to Einstein, who was inspired to develop a still more general approach. The terms stimulation and
cooperative phenomena, used in laser physics, could describe the discovery process as well.
By the 1920s most physicists had realized that their familiar mechanics, developed
over centuries by Newton and many others, could not fully describe the world
of atoms. Physics had to be rebuilt to take into account the fundamental discreteness
of energy that was first pointed out by Planck and Einstein. Einstein himself
contributed a number of key ideas to the developing quantum theory. But through
the early 1920s much in quantum theory remained obscure.
Beginning in 1925 a bold new quantum theory emerged, the creation of a whole
generation of theoretical physicists from many nations. Soon scientists were
vigorously debating how to interpret the new quantum mechanics. Einstein took
an active part in these discussions. Heisenberg, Bohr, and other creators of
the theory insisted that it left no meaningful way open to discuss certain details
of an atom's behavior. For example, one could never predict the precise moment
when an atom would emit a quantum of light. Einstein could not accept this lack
of certainty and he raised one objection after another. At the Solvay Conferences
of 1927 and 1930 the debate between Bohr and Einstein went on day and night,
neither man conceding defeat.
"Quantum mechanics is certainly imposing. But an inner voice tells me that it is not yet the
real thing. The theory says a lot, but does not really bring us closer to the secret of the 'Old One.'
I, at any rate, am convinced that He is not playing at dice."
By the mid 1930s, Einstein had accepted quantum mechanics as a consistent theory
for the statistics of the behavior of atoms. He recognized that it was "the
most successful physical theory of our time." This theory, which he had helped
to create, could explain nearly all the physical phenomena of the everyday world.
Eventually the applications would include transistors, lasers, a new chemistry,
and more. Yet Einstein could not accept quantum mechanics as a completed theory,
for its mathematics did not describe individual events. Einstein felt that a
more basic theory, one that could completely describe how each individual atom
behaved, might yet be found. By following the approach of his own general theory
of relativity, he hoped to dig deeper than quantum mechanics. The search for
a deeper theory was to occupy much of rest of his life.