Welcome to the Multiverse
The multiverse, as this vast cosmos is called, is one of the most polarizing concepts to have emerged from physics in decades, inspiring heated arguments between those who propose that it is the next phase in our understanding of reality, and those who claim that it is utter nonsense, a travesty born of theoreticians letting their imaginations run wild.
So which is it? And why should we care? Grasping the answer requires that we first come to grips with the big bang.
In Search of the Bang
In 1915, Einstein published the most important of all his works, the general theory of relativity, which was the culmination of a 10-year search to understand the force of gravity. The theory was a marvel of mathematical beauty, providing equations that could explain everything from the motion of planets to the trajectory of starlight with stupendous accuracy.
Within a few short years, additional mathematical analyses concluded that space itself is expanding, dragging each galaxy away from every other. Though Einstein at first strongly resisted this startling implication of his own theory, observations of deep space made by the great American astronomer Edwin Hubble in 1929 confirmed it. And before long, scientists reasoned that if space is now expanding, then at ever earlier times the universe must have been ever smaller. At some moment in the distant past, everything we now see—the ingredients responsible for every planet, every star, every galaxy, even space itself—must have been compressed to an infinitesimal speck that then swelled outward, evolving into the universe as we know it.
The big-bang theory was born. During the decades that followed, the theory would receive overwhelming observational support. Yet scientists were aware that the big-bang theory suffered from a significant shortcoming. Of all things, it leaves out the bang. Einstein’s equations do a wonderful job of describing how the universe evolved from a split second after the bang, but the equations break down (similar to the error message returned by a calculator when you try to divide 1 by 0?) when applied to the extreme environment of the universe’s earliest moment. The big bang thus provides no insight into what might have powered the bang itself.
Fuel for the Fire
In the 1980s, physicist Alan Guth offered an enhanced version of the big-bang theory, called inflationary cosmology, which promised to fill this critical gap. The centerpiece of the proposal is a hypothetical cosmic fuel that, if concentrated in a tiny region, would drive a brief but stupendous outward rush of space—a bang, and a big one at that. In fact, mathematical calculations showed that the burst would have been so intense that tiny jitters from the quantum realm would have been stretched enormously and smeared clear across space. Like overextended spandex showing the pattern of its weave, this would yield a precise pattern of miniscule temperature variations, slightly hotter spots and slightly colder spots dotting the night sky. In the early 1990s, NASA’s Cosmic Microwave Background Explorer satellite first detected these temperature variations, garnering Nobel Prizes for team leaders John Mather and George Smoot.
By Brian Greene