The moment when time began

Why is it said that the Universe began with a big bang?

In the beginning, say most scientists, there was nothing. It may seem absurd to believe that something indeed, everything in the Universe, including the Earth, Sun, Moon and all the planets and stars could come from nothing, but astronomers and physicists assert this with increasing confidence.

To make the point, they start with the Universe as we understand it today. Albert Einstein believed that the Universe is static and doesn’t change. Since then, others have shown that the Universe is constantly expanding. The key to that deduction was found by the American astronomer Edwin Hubble. In 1923, he discovered that the awesome vastness of outer space contains thousands of millions of star systems similar to our Milky Way, a galaxy of 100 000 million stars.

Light from these other galaxies is what astronomers call ‘red shifted’. Light emitted by an approaching star turns bluer as its wavelength gets shorter; that from a receding star has a longer wavelength and becomes redder. Hubble knew from this principle, the Doppler effect, that most galaxies are moving away. If they are doing that, it follows that they must in the past have been much closer and the Universe much smaller.

At some moment in the far distant past the Universe began to expand. Physicists calculate this as 15 000 million years ago. Working backwards towards that precise point, they can describe what was happening just a fraction of a second after the Universe was born. At one hundredth of a second, it was something about the size of a pea, compressed in a way that is difficult for most of us to comprehend. Its temperature was so high that it defies our imagination. From that and the nothingness before it came everything we know as our Universe. With it also came the great void of space, so vast that light takes thousands of millions of years to cross it.

So far, physicists cannot say what gave birth to that initial pea sized ball of matter. Nor can they go back much farther than a moment when the Universe was only one hundredth of a second old. In their thinking, the gap between that moment and that of the actual creation, the big bang, is gigantic. More happened in that time than in the next million years.

For two decades, from the 1940s to the 1960s, many physicists believed that the Universe is in a steady state. For them, there was no big bang: the Universe has always existed and will exist for ever. They agreed that it is expanding, but held that it is not really changing because, as old galaxies die, new ones take their place.

This steady state theory was not seriously challenged until the early 1960s. Then, Martin Ryle and a team of astronomers at Cambridge University were studying powerful radio waves sent out by galaxies in distant space. The sources, known as radio galaxies, are so far away that the waves have taken thousands of millions of years to reach us. The team at Cambridge discovered that the remotest zones of outer space hold many more radio galaxies than those much closer to us. From this finding the team argued that the Universe was undoubtedly different all those years ago. If it had changed, how could anyone suggest that it is in a steady state?

In 1965, the steady state theory took another sharp blow. Two American astronomers, Arno Penzias and Robert Wilson (who later shared the Nobel prize for their work) discovered cosmic micro waves coming from outer space. Working on satellite communications at the Bell Telephone Laboratories in New Jersey, they picked up a strange signal, a form of radiation. The signal seemed to come from no single source, such as the Sun. Wherever they directed their instruments, they detected it, as if it came from a radioactive blanket stretching across the sky. What they had found, they believed and a majority of scientists now agree with them were the remains of radiation from the first big bang, the cataclysmic moment when our Universe was born.