Why Does the World Exist: An Existentia - By Jim Holt Page 0,38

cosmological model of eternity is the “Oscillating Universe,” which was first proposed in the 1920s by the Russian mathematician Alexander Friedmann. According to this model, our universe—the one that originated some 14 billion years ago with the Big Bang—emerged from the collapse of an earlier universe. And, like that earlier universe, ours too will eventually stop expanding and collapse back on itself. But when it does, the result will not be an all-annihilating Big Crunch. Instead, a new universe will rebound out of the fiery implosion, in what might be called the Big Bounce. And so on and so on, ad infinitum. In this model, time becomes an endless cycle of destruction and rebirth, rather like the dance of the god Shiva in Hindu cosmology.

Both the Steady-State Universe and the Oscillating Universe make the problem of cosmic origination go away. If the universe is infinitely old—if it has always been around, in other words—there is no “creation event” to be explained. Unfortunately for lovers of eternity, the Steady-State model is no longer taken seriously by cosmologists. It was done in by the detection, in 1965, of the background radiation left over from the Big Bang, which furnished decisive evidence that our universe had a fiery beginning after all. The Oscillating model has fared better, but it is plagued by theoretical gaps. So far, no one has been able to explain exactly what sort of unknown repulsive force could overcome the attractive pull of gravity at the last moment of collapse and cause the universe to “bounce” rather than “crunch.”

So at the moment, anyway, the odds seem to favor a finite past for our universe. But what if our universe is not all there is? What if it is a part of some greater ensemble?

One of the great lessons of the history of science is that reality always turns out to be more encompassing than anyone imagined. At the beginning of the twentieth century, our universe was thought to consist of just the Milky Way galaxy, sitting all by itself in an infinite space. Since then, we have learned that the Milky Way is merely one of a hundred billion or so similar galaxies. And that’s just the observable universe. The current theory that best explains the Big Bang is called the “new inflationary cosmology.” As it happens, this theory predicts that universe-engendering explosions like the Big Bang should be a fairly routine occurrence. (As one friend of mine observed, it would be very odd if the Big Bang came with a label that said, “THIS MECHANISM OPERATED ONLY ONCE.”)

In the inflationary scenario, our universe—the one that suddenly popped into existence some 14 billion years ago—bubbled out of the spacetime of a preexisting universe. Instead of being all of physical reality, it’s just an infinitesimal part of an ever-reproducing “multiverse.” Although each of the bubble universes within this multiverse had a definite beginning in time, the entire self-replicating ensemble may be infinitely old. The eternity that seemed lost with the discovery of the Big Bang is thus regained.

With an eternal world—whether of the inflationary variety or some other—there is no inexplicable “creation moment.” There is no role for a “first cause.” There are no arbitrary “initial conditions.” An eternal world thus seems to satisfy the Principle of Sufficient Reason. The way it is at any moment can be explained by the way it was the previous moment. Indeed, its existence at any moment can be explained by its existence the previous moment. Should that be enough to dispel any lingering sense of mystery?

Many have thought so—prominently among them, David Hume. In Hume’s Dialogues Concerning Natural Religion, the character Cleanthes, who comes closest to being the author’s mouthpiece, gives two arguments that an eternal world requires no explanation for its existence. “How,” he asks, “can anything that exists from eternity have a cause, since that relation implies a priority in time and a beginning of existence?” It is assumed here that an explanation must invoke a cause, and that a cause must come before its effect. But nothing could precede a world with an infinite past, so such a world could have no prior cause and hence no possible explanation for its existence.

There are two problems with this first argument. To begin with, nothing in the concept of causation says that a cause must always precede in time its effect. Think of a locomotive pulling a caboose: the motion of the former causes the motion of the latter, yet the two are