The Origin of the Big Bang

ACCORDING TO THE BOSHONGO PEOPLE of central Africa, in the beginning there was only darkness, water, and the great god Bumba. One day Bumba, in pain from a stomachache, vomited up the sun.

In time the sun dried up some of the water, leaving land. But Bumba was still in pain, and vomited some more. Up came the moon, the stars, and then some animals: the leopard, the crocodile, the turtle, and finally man.

The Mayans of Mexico and Central America tell of a similar time before creation when all that existed were the sea, the sky, and the Maker.

In the Mayan legend the Maker, unhappy because there was no one to praise him, created the earth, mountains, trees, and most animals. But the animals could not speak, and so he decided to create humans.

First he made them of mud and earth, but they only spoke nonsense. He let them dissolve away and tried again, this time fashioning people from wood.

Those people were dull. He decided to destroy them, but they escaped into the forest, sustaining damage along the way that altered them slightly, creating what we today know as monkeys. After that fiasco, the Maker finally came upon a formula that worked, and constructed the first humans from white and yellow corn.

Today we make ethanol from corn, but so far haven’t matched the Maker’s feat of constructing the people who drink it.

Creation myths like these all attempt to answer the questions we address in this book: Why is there a universe, and why is the universe the way it is? Our ability to address such questions has grown steadily in the centuries since the ancient Greeks, most profoundly over the past century.

Armed with the background of the previous chapters, we are now ready to offer a possible answer to these questions.

One thing that may have been apparent even in early times was that either the universe was a very recent creation or else human beings have existed for only a small fraction of cosmic history.

That’s because the human race has been improving so rapidly in knowledge and technology that if people had been around for millions of years, the human race would be much further along in its mastery.

According to the Old Testament, God created Adam and Eve only 6 days into creation.

Bishop Ussher, primate of all Ireland from 1625 to 1656, placed the origin of the world even more precisely, at nine in the morning on October 27, 4004 BC. We take a different view: that humans are a recent creation but that the universe itself began much earlier, about 13.7 billion years ago.

The first actual scientific evidence that the universe had a beginning came in the 1920s. As we said in Chapter 3, that was a time when most scientists believed in a static universe that had always existed. The evidence to the contrary was indirect, based upon the observations Edwin Hubble made with the 100-inch telescope on Mount Wilson, in the hills above Pasadena, California.

By analyzing the spectrum of light they emit, Hubble determined that nearly all galaxies are moving away from us, and the farther away they are, the faster they are moving. In 1929 he published a law relating their rate of recession to their distance from us, and concluded that the universe is expanding.

If that is true, then the universe must have been smaller in the past. In fact, if we extrapolate to the distant past, all the matter and energy in the universe would have been concentrated in a very tiny region of unimaginable density and temperature, and if we go back far enough, there would be a time when it all began—the event we now call the big bang.

The idea that the universe is expanding involves a bit of subtlety. For example, we don’t mean the universe is expanding in the manner that, say, one might expand one’s house, by knocking out a wall and positioning a new bathroom where once there stood a majestic oak. Rather than space extending itself, it is the distance between any two points within the universe that is growing.

That idea emerged in the 1930s amid much controversy, but one of the best ways to visualize it is still a metaphor enunciated in 1931 by Cambridge University astronomer Arthur Eddington.

Eddington visualized the universe as the surface of an expanding balloon, and all the galaxies as points on that surface. This picture clearly illustrates why far galaxies recede more quickly than nearby ones.

For example, if the radius of the balloon doubled each hour, then the distance between any two galaxies on the balloon would double each hour. If at some time two galaxies were 1 inch apart, an hour later they would be 2 inches apart, and they would appear to be moving relative to each other at a rate of 1 inch per hour. But if they started 2 inches apart, an hour later they would be separated by 4 inches and would appear to be moving away from each other at a rate of 2 inches per hour.

That is just what Hubble found: the farther away a galaxy, the faster it was moving away from us. It is important to realize that the expansion of space does not affect the size of material objects such as galaxies, stars, apples, atoms, or other objects held together by some sort of force.

For example, if we circled a cluster of galaxies on the balloon, that circle would not expand as the balloon expanded. Rather, because the galaxies are bound by gravitational forces, the circle and the galaxies within it would keep their size and configuration as the balloon enlarged.

This is important because we can detect expansion only if our measuring instruments have fixed sizes. If everything were free to expand, then we, our yardsticks, our laboratories, and so on would all expand proportionately and we would not notice any difference.

That the universe is expanding was news to Einstein. But the possibility that the galaxies are moving away from each other had been proposed a few years before Hubble’s papers on theoretical grounds arising from Einstein’s own equations.

In 1922, Russian physicist and mathematician Alexander Friedmann investigated what would happen in a model universe based on two assumptions that greatly simplified the mathematics: that the universe looks identical in every direction, and that it looks that way from every observation point.

We know that Friedmann’s first assumption is not exactly true—the universe fortunately is not uniform everywhere! If we gaze upward in one direction, we might see the sun; in another, the moon or a colony of migrating vampire bats. But the universe does appear to be roughly the same in every direction when viewed on a scale that is far larger—larger even than the distance between galaxies.

It is something like looking down at a forest. If you are close enough, you can make out individual leaves, or at least trees, and the spaces between them. But if you are so high up that if you hold out your thumb it covers a square mile of trees, the forest will appear to be a uniform shade of green.

We would say that, on that scale, the forest is uniform.

Based on his assumptions Friedmann was able to discover a solution to Einstein’s equations in which the universe expanded in the manner that Hubble would soon discover to be true.

In particular, Friedmann’s model universe begins with zero size and expands until gravitational attraction slows it down, and eventually causes it to collapse in upon itself. (There are, it turns out, two other types of solutions to Einstein’s equations that also satisfy the assumptions of Friedmann’s model, one corresponding to a universe in which the expansion continues forever, though it does slow a bit, and another to a universe in which the rate of expansion slows toward zero, but never quite reaches it.) Friedmann died a few years after producing this work, and his ideas remained largely unknown until after Hubble’s discovery.

In 1927, a physics professor and Roman Catholic priest named Georges Lemaître proposed a similar idea: If you trace the history of the universe backward into the past, it gets tinier and tinier until you come upon a creation event—what we now call the big bang.

Not everyone liked the big bang picture.

In fact, the term “big bang” was coined in 1949 by Cambridge astrophysicist Fred Hoyle, who believed in a universe that expanded forever, and meant the term as a derisive description.

The first direct observations supporting the idea didn’t come until 1965, with the discovery that there is a faint background of microwaves throughout space.

This cosmic microwave background radiation, or CMBR, is the same as that in your microwave oven, but much less powerful.

You can observe the CMBR yourself by tuning your television to an unused channel—a few percent of the snow you see on the screen will be caused by it.

The radiation was discovered by accident by two Bell Labs scientists trying to eliminate such static from their microwave antenna.

At first, they thought the static might be coming from the droppings of pigeons roosting in their apparatus. But it turned out that it was radiation left over from the very hot and dense early universe that would have existed shortly after the big bang.

As the universe expanded, it cooled until the radiation became just the faint remnant we now observe.

At present, these microwaves could heat your food to only about −270 degrees Centigrade—3 degrees above absolute zero, and not very useful for popping corn.

Astronomers have also found other fingerprints supporting the big bang picture of a hot, tiny early universe.

For example, during the first minute or so, the universe would have been hotter than the center of a typical star. During that period the entire universe would have acted as a nuclear fusion reactor.

The reactions would have ceased when the universe expanded and cooled sufficiently, but the theory predicts that this should have left a universe composed mainly of hydrogen, but also about 23 percent helium, with traces of lithium (all heavier elements were made later, inside stars).

The calculation is in good accordance with the amounts of helium, hydrogen, and lithium we observe.

Measurements of helium abundance and the CMBR provided convincing evidence in favor of the big bang picture of the very early universe, but although one can think of the big bang picture as a valid description of early times, it is wrong to take the big bang literally, that is, to think of Einstein’s theory as providing a true picture of the origin of the universe.

That is because general relativity predicts there to be a point in time at which the temperature, density, and curvature of the universe are all infinite, a situation mathematicians call a singularity.

To a physicist, this means that Einstein’s theory breaks down at that point and therefore cannot be used to predict how the universe began, only how it evolved afterward.

So although we can employ the equations of general relativity and our observations of the heavens to learn about the universe at a very young age, it is not correct to carry the big bang picture all the way back to the beginning.

We will get to the issue of the origin of the universe shortly, but first a few words about the first phase of the expansion. Physicists call it inflation. Unless you’ve lived in Zimbabwe, where currency inflation recently exceeded 200,000,000 percent, the term may not sound very explosive.

But according to even conservative estimates, during this cosmological inflation, the universe expanded by a factor of 1,000,000,000,000,000,000,000,000,000,000 in .00000000000000000000000000000000001 second. It was as if a coin 1 centimeter in diameter suddenly blew up to ten million times the width of the Milky Way.

That may seem to violate relativity, which dictates that nothing can move faster than light, but that speed limit does not apply to the expansion of space itself.