Originally published 13 September 1999
Imagine this: A hundred billion galaxies, each galaxy with a trillion stars, each star with a family of planets as various as the planets of our own solar system, some of them perhaps harboring life and intelligence — an entire universe contained within a physical space the size of a grapefruit.
Impossible?
It must be possible because I have just summoned up this universe from my grapefruit-sized brain.
And having read the first paragraph, the same universe now actively resides in your consciousness.
What a miracle, that we can contain a hundred billion galaxies within the goldfish bowls of our skulls.
And here is the greater miracle: The universe out there, the presumed universe of actual galaxies, stars and planets, may itself once have been physically no bigger than a grapefruit. Matter, space, and time compressed to an unimaginable density, a blazing cauldron of creation the size of — a grapefruit, a lemon, a grape, a mustard seed, a…
If astronomers are right, the entire physical cosmos exploded about 15 billion years ago from an infinitely small, infinitely hot seed of energy. The Big Bang.
The mind reels. The human mind that invented the Big Bang staggers at its comprehension. Where did this outrageous and wonderful story of creation come from? This mustard seed that gives birth to light-years?
The Big Bang had its genesis in a single startling discovery, made in the 1920s with a big new telescope on Mount Wilson in California: The galaxies are racing apart from one another.
If they are moving apart, then they must have been closer together in the past. Theoretically, we can run the movie backwards, using the laws of physics to tell us what happens. The galaxies approach. The density of matter increases. Space-time curls upon itself. The temperature soars. Atoms dissolve into their constituent parts. Mass evaporates into pure energy. The whole thing collapses to a infinitely small, infinitely hot mathematical point.
How do we know that running the movie backwards gives a true picture of the early universe?
Well, for example, the calculations predict that when ordinary matter first condensed from the particle soup of the Big Bang it should have consisted almost entirely of hydrogen and helium in a ratio of about three to one. And that is exactly what we find in the universe today (Tiny amounts of heavier elements were made later on in supernovas and the hot interiors of stars).
In general, the game of theoretical cosmology is this: We do experiments here on Earth to figure out how matter and energy behave at extremely high temperatures. Using this knowledge, we calculate what sort of universe should have emerged from the Big Bang. Then we compare the calculated universe to the real one.
So far the fit is pretty good.
But cosmologists would like to draw the links between the theoretical universe and the observed universe ever tighter. Or else to prove the whole thing wrong and start over.
The best way to do this is to investigate how matter behaves at ever higher temperatures — the temperatures of the first instants of creation.
Sometime in the next few months, physicists at the Brookhaven National Laboratory on Long Island will crank up the temperature higher than ever before — to a trillion degrees. They will hurl heavy atomic nuclei in opposite directions around a powerful new $600 million accelerating machine — the Relativistic Heavy Ion Collider—until they are moving at nearly the speed of light, and then smash them into each other. Out of these titanic nuclear collisions, which last only the tiniest fraction of a second, they hope to see emerge a new kind of matter, a quark-gluon plasma, the presumed super-hot primordial soup out of which all normal particles were born.
No one has seen a naked quark before, or the gluons that supposedly bind the quarks into protons, neutrons, and electrons. If the new experiments are successful, physicists will catch a glimpse of what the universe might have been like in its first millionth of a second, before protons, neutrons, and electrons came into existence. Then they can run the theoretical movie backwards even further into the past, and compare the calculated universe with the observed universe with yet more rigor.
It’s a grand adventure, this searching for origins, and one in which we can all take pride. After all, it is human brains like our own that invent our creation story and then test it in the refining fire of experience.
What miracles. That the entire universe of galaxies might have once have been smaller than a grapefruit. And that a grapefruit-sized ball of organic tissue — my brain, your brain, right now — can contain the story.
As knowers of the story, each of us is a bit like Oliver Goldsmith’s village schoolmaster: “…and still the wonder grew that one small head could carry all he knew.”
