the sequence of events and reduce the possible endgames down to one.

Sure there were open questions, but mainstream cosmologists saw these as refinements. Most researchers believed in a clear-cut model of the universe that had little room for change after the first few moments of its history. Much debate was centered on pinning down what happened during the initial ticks of the cosmic clock.

A few of us pondered alternatives to the canon—theories of the universe that strayed from the simplest version of the Big Bang. Like the standard model, these were legitimate mathematical solutions— albeit of variations, reinterpretations, or extensions—of Einstein’s equations. Mainstream cosmologists knew about such alternatives but tended to treat them as mere curiosities. In the absence of evidence to the contrary, these researchers advised, why reach beyond conventional approaches?

The situation was akin, in some ways, to the state of affairs before the age of Johannes Kepler and Galileo Galilei. From the 2nd century until the 16th century AD, astronomy relied on the coarse measurements of planetary motion recorded by the Alexandrian thinker Claudius Ptolemy (born circa 85 AD). In his pivotal text, the Almagest, Ptolemy developed a clockwork model of the solar system that corresponded well to his data. Consisting of wheels within wheels ultimately turning around Earth, Ptolemy’s model showed how planets could follow distinct patterns as they moved across the sky. Because his scheme explained all known facts and fit in well with religious views, scholars found little reason to dispute it. True, it could be simplified, as the Polish astronomer Nicholas Copernicus pointed out, by placing the Sun at the center instead of Earth. But even Copernicus had no new data to back up his proposition.

What changed matters at the turn of the 17th century—as well as at the turn of the 21st century—were substantial improvements in astronomical measuring techniques that led to an enhanced understanding of the movements of celestial bodies. Superior naked-eye

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