In 2000, Martin Bojowald, then a twenty-seven-year-old post-doc
at Pennsylvania State University, used a relatively new theory
called loop quantum gravity—a cunning combination of Einstein’s
theory of gravity with quantum mechanics—to create a simple model
of the universe. Loop quantum cosmology was born, and with it, a
theory that managed to do something even Einstein’s general theory
of relativity had failed to do—illuminate the very birth of the
universe.
Ever since, loop quantum cosmology, or LQC, has
been tantalizing physicists with the idea that our universe could
conceivably have emerged from the collapse of a previous one. Now
the theory is poised to formulate hypotheses we can actually test.
If they are verified, the big bang will give way to the big bounce.
Instead of a universe that emerged from a point of infinite
density, we will have one that recycles, possibly through an
eternal series of expansions and contractions, with no beginning
and no end.
Bojowald’s major realization was that unlike
general relativity, the physics of LQC do not break down at the big
bang. The greatest mystery surrounding the origin of the universe
is what cosmologists call the big bang “singularity”—the point at
the beginning of the universe, prior to the existence of space and
time, when gravity, along with the temperature and density of the
universe, becomes infinite. The equations of general relativity
can’t cope with such infinities, and as a result big bang theory
has never been able to give any explanation for the initial
condition of our universe, succeeding only in describing and
explaining the evolution of the universe from that instant onward.
Bojowald’s theory takes us right up to the first moment of the
universe—and then back, even before the big bang itself.
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