Was the big bang really the beginning of time? Or did the universe exist before then? Such a question seemed almost blasphemous only a decade ago. Most cosmologists insisted that it simply made no sense–that to contemplate a time before the big bang was like asking for directions to a place north of the North Pole. But developments in theoretical physics, especially the rise of string theory, have changed their perspective. The pre-bang universe has become the latest frontier of cosmology.
The new willingness to consider what might have happened before the bang is the latest swing of an intellectual pendulum that has rocked back and forth for millennia. In one form or another, the issue of the ultimate beginning has engaged philosophers and theologians in nearly every culture.
Astronomers have begun one of the most far-reaching efforts to study the cosmos. They are building giant new telescopes, while marshaling vast computational power. These technologies are part of a historic quest: to peer into space and time, to find out how the universe gave birth to galaxies and planets, to discern the amazing world of gravity and test theories by Einstein and other scientists.
Evolution of a Revolution
TODAY TWO APPROACHES stand out. One, going by the name of loop quantum gravity, retains Einstein’s theory essentially intact but changes the procedure for implementing it in quantum mechanics [see Atoms of Space and Time, by Lee Smolin, on page 82]. Practitioners of loop quantum gravity have taken great strides and achieved deep insights over the past several years. Still, their approach may not be revolutionary enough to resolve the fundamental problems of quantizing gravity. A similar problem faced particle theorists after Enrico Fermi introduced his effective theory of the weak nuclear force in 1934. All efforts to construct a quantum version of Fermi’s theory failed miserably. What was needed was not a new technique but the deep modifications brought by the electroweak theory of Sheldon L. Glashow, Steven Wein-berg and Abdus Salam in the late 1960s.
The second approach, which I consider more promising, is string theory–a truly revolutionary modification of Einstein’s theory. This article will focus on it, although proponents of loop quantum gravity claim to reach many of the same conclusions
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