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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