The Wake

Physicists and theologists, academics and armchair astronomers have long wondered what it was that sparked the beginning of the universe. Now, mathematical physicist Roger Penrose is investigating what happened before the universe began.

Two years ago, Stephen Hawking gave the conventional answer to the question—What happened before the big bang?, Hawking says the big bang was the event to begin all events so it makes no sense to ask what came before it.

Lecturing to a small audience at the University of Minnesota on February 2, Penrose admitted that his own investigation of pre-big bang events breaks with convention.

The Big Bang Theory holds that the universe began about 13.7 billion years ago when it exploded from a very dense hot state and began to expand. An illustration of the big bang would show the explosion happening at the tip of a cone, with matter moving outwards away from the tip. Questioning what happened before the explosion, though, means looking at what came before the tip of the cone.

Penrose described other physicists’ hypotheses about what happened before the big bang as “crazy ideas” put forward by “very respectable and ambitious physicists.” One speculation posits that the universe came from a black hole; another, that this universe was preceded by another universe in which the things we take for granted about our universe, such as the direction of time, may have been totally different.

Like Penrose, these physicists suspect that our universe may be just one of many incarnations. The big bang may have started our universe’s clock ticking, but the explosion could’ve been just the tolling of a grander clock.

Using analogy and accessible illustrations, Penrose described his mathematically-informed vision of how we can find out what was going on before the big bang.

An illustration by M.C. Escher, “Circle Limit IV,” provided Penrose a model universe.

This illustration, explained Penrose, represents an infinite universe. In this model universe, the very outer boundary represents infinity. But how can infinity—a theoretical description of endless space—be contained in a finite region? And how can the region beyond infinity—the black corners of the Escher illustration—also be infinity?

By a mathematical trick, explained Penrose. Describing his hypothesis, he suggested that a previous phase of the universe went on expanding and eventually joined on to the next one—the one we’re currently living in. The big bang marked the phase change, and the boundary where the universes met up was infinity.

Yet, asked Penrose, since we can’t get past infinity — in effect, the moment of the big bang — how can we know anything about what was going on during that distant, inaccessible time? Because we are able to observe directly the effects of what was happening before the big bang, said Penrose.

Imagine, he said, that our previous universe was very much like this one. Every now and again, pairs of galaxies would run into each other—as happens in our current universe—and colliding black holes would swallow each other, explode, and emit gravitational radiation, which is energy released in the form of waves from the collision.

Gravitational radiation would travel outwards to infinity, and fluctuations caused by this radiation would show up on the other side of infinity—our side. In fact, physicists can measure microwave radiation emitted by giant explosions many, many millennia in the past to gain information about those past events. Penrose suggested that we could measure radiation from events before the big bang.

Penrose illustrated his hypothesis with an analogy. Think of a pond, he said. It’s raining on the pond; each drop of water hits the pond and causes ripples on the surface of the pond. After the rain stops, we still see ripples, which appear random since we can no longer tell which drops caused which ripples. However, we could work backwards from the ripples and reconstruct the points at which individual rain drops hit the water—a bit like watching the rainstorm in reverse.

In this analogy, the ripples on the pond are microwave radiation, which Penrose proposes could be used to track the original, energy-releasing explosions. And if we track radiation back far enough, we would eventually find that the source was an event that occurred before the big bang.

About his hypothesis, Penrose said, “It’s crazy, but crazy is respectable in cosmology.”