How did the universe begin?

 

How did the universe begin?

 According to the Boshongo people of central Africa, before us there was only darkness, water and the great god Bumba. One day Bumba, in pain from a stomach ache, vomited up the Sun. The Sun evaporated some of the water, leaving land. Still in discomfort, Bumba vomited up the Moon, the stars and then the leopard, the crocodile, the turtle and, finally, humans.

This creation myth, like many others, wrestles with the kinds of questions that we all still ask today. Fortunately, as will become clear, we now have a tool to provide the answers: science. When it comes to these mysteries of existence, the first scientific evidence was discovered in the 1920s, when Edwin Hubble began to make observations with a telescope on Mount Wilson in California. To his surprise, Hubble found that nearly all the galaxies were moving away from us. Moreover, the more distant the galaxies, the faster they were moving away. The expansion of the universe was one of the most important discoveries of all time. This finding transformed the debate about whether the universe had a beginning.

If galaxies are moving apart at the present time, they must therefore have been closer together in the past. If their speed had been constant, then they would all have been on top of one another billions of years ago. Was this how the universe began? At that time many scientists were unhappy with the universe having a beginning because it seemed to imply that physics had broken down. One would have to invoke an outside agency, which for convenience one can call god, to determine how the universe began. They therefore advanced theories in which the universe was expanding at the present time but didn’t have a beginning.

Perhaps the best known was proposed in 1948. It was called the steady state theory, and it suggested that the universe had existed for ever and would have looked the same at all times. This last property had the great virtue of being a prediction that could be tested, a critical ingredient of the scientific method. And it was found lacking.

Observational evidence to confirm the idea that the universe had a very dense beginning came in October 1965, with the discovery of a faint background of microwaves throughout space. The only reasonable interpretation is that this “cosmic microwave background” is radiation left over from an early hot and dense state. As the universe expanded, the radiation cooled until it became just the remnant we see today. Theory soon backed up this idea.

With Roger Penrose of Oxford University, I showed that if Albert Einstein’s general theory of relativity is correct, then there would be a singularity, a point of infinite density and space-time curvature, where time has a beginning. The universe started off in the Big Bang and expanded quickly. This is called “inflation” and it was extremely rapid: the universe doubled in size many times in a tiny fraction of a second. Inflation made the universe very large, very smooth and very flat. However, it was not completely smooth: there were tiny variations from place to place. These variations eventually gave rise to galaxies, stars and solar systems. We owe our existence to these variations. If the early universe had been completely smooth, there would be no stars and so life could not have developed. We are the product of primordial quantum fluctuations. As will become clear, many huge mysteries remain. Still, we are steadily edging closer to answering the age-old questions: Where did we come from? And are we the only beings in the universe who can ask these questions?

This story by Stephen Hawking was originally published as the introduction of the New Scientist book The Origin of (Almost) Everything.