HOW SMALL, DID YOU SAY?

No matter how hard you try you will never be able to grasp just how tiny, how spatially unassuming, is a proton. It is just way too small. A proton is a very, very small part of an atom, which is itsell of course an insubstantial thing. Protons are so small that a little dib of ink like the dot on this i can hold something in the region of 500,000,000,000 of them-that's rather more than the number of seconds contained in half a million years. So protons are exceedingly microscopic, to say the very least.

Now imagine if you can (and of course vou cant) shrinking one of those protons down to a billionth of its normal size into a space so small that it would make a proton look enormous. Now pack into that tiny, tiny space about an ounce of matter. Excellent. You are ready to start a universe.

I'm assuming of course that you wish to build an inflationary universe. If you'd prefer instead to build a more old-fashioned, "standard Big Bang" universe, you'll need additional material. In fact, you will need to gather up everything there is-every last mote and particle of matter between here and the edge of creation-and squeeze it into a spot so infinitesimally compact that it has no dimensions at all. It is known as a singularity.

In either case, get ready for a really big bang. Naturally, you will wish to retire to a safe place to observe the spectacle. Unfortunately, there is no where to retire to because outside the singularity there is no where. When the universe begins to expand, it won't be spreading out to fill a larger emptiness. The only space that exists is the space it creates as it goes.

It is natural but wrong to visualize the singularity as a kind of pregnant dot hanging in a dark, boundless void. But there is no space, no darkness. The singularity has no "around" around it. There is no space for it to occupy, no place for it to be. We can't even ask how long it has been there-whether it has just lately popped into being, like a good idea, or whether it has been there forever, quiedy awaiting the right moment. Tune doesn't exist. There is no past for it emerge from.

And so, from nothing, our universe begins.

HOW FAST, DID YOU SAY?

In a single blinding pulse, a moment of glory much too swift and expansive for any form of words, the singularity assumes heavenly dimensions, space beyond conception. In the first lively second (a second that many cosmologists will devote careers to shaving into ever-finer wafers) is produced gravity and the other forces that govern physics. In less than a minute the universe is a million billion miles across and growing fast. There is a lot of heat now, 10 billion degrees of it, enough to begin the nuclear reactions that create the lighter elements-principally hydrogen and helium, with a dash (about one atom in a hundred million) of lithium. In three minutes, 98 percent of all the matter there is or will ever be has been produced. We have a universe. It is a place of the most wondrous and gratifying possibility, and beautiful, too. And it was all done in about the time it takes to make a sandwich.

Most of what we know, or believe we know, about the early moments of the universe is thanks to an idea called inflation theory. Inflation theory holds that a fraction of a moment after the dawn of creation, the universe underwent a sudden dramatic expansion. It inflated-in effect ran away with itself, doubling in size every 10^sup -34^ seconds. The whole episode may have lasted no more than 10^sup -30^ seconds-that's one million million million million millionths of a second-but it changed the universe from something you could hold in your hand to something at least 10,000,000,00 0,000,000,000,000,000 times bigger. Inflation theory explains the ripples and eddies that make our universe possible. Without it, there would be no clumps of matter and thus no stars, just q drifting gas and everlasting darkness.

According to inflation theory, at one 10 millionth of a trillionth of a trillionth of a trillion th of a second(or 10^sup -43^ seconds), gravity emerged. After another ludicrously brief interval it was joined by electromagnetism and the strong and weak nuclear forces-the stuff of physics. These were joined an instant later by swarms of elementary particles-the stuff of stuff. From nothing at all, suddenly were swarms of photons, protons, electrons, neutrons, and much else-between 10^sup 79^ and 10^sup 89^ of each, according to the standard Big Bang theory. Such quantities are of course ungraspable. It is enough to know that in a single cracking instant we were endowed with a universe that was vast-at least a hundred billion light-years across, according to the theory, but possibly any size up to infinite-and perfectly arrayed for the creation of stars, galaxies, and other complex systems.

HOW BIG, DID YOU SAY?

Now the question that has occurred to all of us at some point is: what would happen if you traveled out to the edge of the universe and, as it were, put your head through the curtain? Where would your head be if it were no longer in the universe? What would you find beyond?

The answer, disappointingly, is that you can never get to the edge of the universe. That's not because it would take too long to get there-though of course it would-but because even if you traveled outward and outward in a straight line, indefinitely and pugnaciously, you would never arrive at an outer boundary. Instead, you would come back to where you began (at which point, presumably, you would rather lose heart in the exercise and give up). The reason for this is that the universe bends, in a way we can't adequately imagine, in conformance with Einstein's theory of relativity. We are not adrift in some large, everexpanding bubble. Rather, space curves, in a way that allows it to be boundless but finite. Space cannot even properly be said to be expanding because, as the physicist and Nobel laureate Steven Weinberg notes, "solar systems and galaxies are not expanding, and space itself is not expanding." Rather, the galaxies are rushing apart. It is all something of a challenge to intuition.

The analogy that is usually given for explaining the curvature of space is to try to imagine someone from a universe of flat surfaces, who had never seen a sphere, being brought to Earth. No matter how far he roamed across the planet's surface, he would never find an edge. He might eventually return to the spot where he had started, and would of course be utterly confounded to explain how that had happened. Well, we are in the same position in space as our puzzled flatlander-he is flummoxed by a higher dimension than two, while we are flummoxed by a higher dimension than three.

For us, the universe goes only as far as light has traveled in the billions of years since the universe was formed. This visible universe-the universe we know and all talk about-is a million million million million (that's 1,000, 000,000,000,000,000,000,000) miles across. But according to most theories, the universe at large-the meta-universe, as it is sometimes called-is vastly roomier still. According to Martin Rees, Britain's astronomer royal, the number of light-years to the edge of this larger, unseen universe would be written not "with 10 zeroes, not even with a hundred, but with millions." In short, there's more space than you can imagine already without going to the trouble of trying to envision some additional beyond. As the biologist J. B. S. Haldane once famously observed: " The universe is not only queerer that we suppose; it is queerer that we can suppose."

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