"You Are Here," states the caption on a poster of a spiral galaxy suspended in space-time. The arrow points to an invisible speck embedded in a curved galactic arm composed of millions of stars. When considering ourselves on a scale of this magnitude, our planet seems like a subatomic particle in an expanding matrix 15 billion light-years wide and filled with countless galaxies.

More than any other science, cosmology stretches the human mind. It challenges the mind to consider the distance a beam of light travels in a year at its constant speed of 186,000 miles per second. This is the measure of space and time called a light year, and is equivalent to six trillion miles. Then consider that one of the Milky Way's nearest neighbors, the Andromeda Galaxy, is five million light years distant from us. It challenges our common sense to understand that in the dark reaches of space-time, subatomic particles appear from nothingness, blink a physical presence for 5.3 \\a21510p-44p seconds and then vanish -- only to return again in another 55.3 \\a21510p-44p seconds, creating an endless cycle of pulsing that may be causing the universe to expand. To learn such things, and to fit them into our scale of human events, is a humbling experience.

The men and women who contemplate nature on this scale are a special breed, and their work is a brilliant testimony to the range and flexibility of the human mind. Their ponderings have led us to examine the early moments of the universe's birth, when subatomic particles brewed in a microscopic energy cauldron. In it, all energy and all matter that would become the universe waits in potential. Then, in a hyper-instant, gravity waves and space-time inflate, and the pent up universe expands out into the budding matrix and fills it. And if our observations are correct, it is filling it still.

The accumulation and understanding of this information took time to accomplish. In many ways it was initiated by Edwin Hubble, an American cosmologist who, in 1930, woke the world to the reality that the universe is composed of millions and millions of galaxies. And these galaxies, he showed us, are traveling away from each other at near-light speeds, suggesting that the universe is expanding.

The finding took Albert Einstein, whose general theory of relativity postulated a static universe, by surprise. The findings took the whole world by surprise and set in motion an earnest start to the systematic probing of the universe for its secrets.

After some fits and starts, the big bang theory seemed to best accommodate our growing observations. Tiny temperature fluctuations found throughout the cosmic microwave background -- echoes of the universe's birth -- were one of the early hallmark proofs of the big bang. Others soon followed.

Most modern cosmological thought frames itself around the big bang theory. When its shortcomings challenged the theory's boundaries, the inflation theory was born. Borrowing from the field of particle physics, the inflation theory suggests that energy fields "seeded" the universe, and that the big bang expansion of energy and matter followed.

No theory is perfect, and human curiosity cannot help but pick at the model it has created to refine it more and more. Curious questions have arisen from this refinement process. For example, what powers the expansion of the universe? Is it some kind of mysterious matter, invisible to our current technology, that urges the universe outward in defiance of the inward pull of gravity inherent in all physical matter? In "Cosmological Antigravity," by Lawrence Krauss, a variety of possible explanations are explored. Each option carries ramifications that could alter our fundamental view of the cosmos.

One possible driver of cosmic expansion may be an energy form that varies over time. "The Quintessential Universe," by Jeremiah Ostriker and Paul Sternhardt, considers this possibility, postulating that as the conditions of the universe evolved over time, so did the nature of the energy that fills it.

That changes took place over time in the evolving universe seems certain. Specific relics from the universe's earliest moments should be, in theory, present and observable, and some important findings have been coaxed from cosmic microwave background radiation. Still illusive, however, are gravity waves, which are believed to have not only expanded out into space-time in advance of the big bang but also squeezed and stretched the raw material of the universe itself. "Echoes from the Big Bang," by Robert Caldwell and Mark Kamiankowski, considers this possibility and details their role in establishing a geometry for the universe.

How the universe expanded and what its overall shape may be is the topic of "Inflation in a Low-Density Universe," by Martin Bucher and David Spergel. What is the universe's shape: is it curved like a bubble, as predicted in some variations of the inflation theory? Bent like a potato chip? Or is the universe flat like a thin sheet of rubber? The way we view the universe has a profound impact not only on our overall conceptualization of the cosmos but also on the ultimate rise or fall of such theories that predict them.

Perhaps the most astounding insights arise when theorists employ quantum mechanics -- the study of very small particles -- to frame their perception of the macro scale of the cosmos. Suddenly, the universe becomes far more dynamic than we expected: particles pop in and out of existence, history becomes probability, and an infinite number of possible scenarios play out simultaneously in galaxies that are infinite in number. "Quantum Cosmology," by Jonathan Halliwell, takes the reader into some of these realms, then catalogs the frantic attempts of cosmologists to tame the wild theories into more manageable, testable hypotheses.

Some theories tackle the universe on such an ambitious scale that finding proof for them stretches human ingenuity to new heights. The "grand unification" notion, sometimes referred to as the theory of everything, attempts to explain the four fundamental forces of nature (gravity, electromagnetism, the weak and strong atomic forces) as manifestations of a single force. Cosmic membranes made of subatomic superstrings are a natural expression of this theory, and in "String Instruments," by George Musser, a possible suggestion for testing this idea comes to the forefront.

Observation and testing are the keys to confirmation and acceptance of any scientific theory, but sometimes observations dangle outside the framework, awaiting explanation. "Surveying Space-Time with Supernovae," by Craig Hogan, Robert Kirshner, and Nicholas Suntzeff, reveals some recent observations that are still a puzzle. The universe seems to be expanding more quickly than can be accounted for in accepted theories, and the density of matter in the universe may be far less than anyone has anticipated.

The next-generation orbital cosmological probe, dubbed MAP, should be an important tool in answering these and other questions. Its sensitive gear will point into deep space and map the universe in the microwave spectrum. With a resolution greater than any previous microwave probe, MAP, the subject of "The Cosmic Cartographer," by Charles Bennett, Gary Hinshaw, and Lyman Page, should be able to provide unprecedented detail of the cosmos, and will probably end up raising more questions than it answers.

Another next-generation tool situated on the peak of a dormant volcano in Hawaii is the Gemini North Telescope, scanning the cosmos on an infrared wavelength in conjunction with a soon to be built sister telescope, Gemini South, in Peru. The logistics of establishing such cosmological tools is, not surprisingly, a very earthly concern, littered with nuts, bolts, and the hammers of funding realities.

Within the dictates of the linear time that we experience, there is a beginning to the universe, and thus there should be an end as well. The lesson applies to the star that powers life on Earth. If it was born, it must therefore someday die. What will happen to the human species then? "The Fate of Life in the Universe" muses on the subject, and projects a scenario where human consciousness could dwell among the stars.

These questions and others are the topic of this book, culled from the pages of Scientific American magazine with the intent to trace the birth of these inquiries, to track their development, and to ponder some of the key questions facing cosmologists in the 21st century. Because we are made of the same subatomic particles of which all matter in the universe is comprised, we too are a part of the greater whole, linked to it with a connection as natural as a quasar, as mysterious as virtual particles.

-- Sandy Fritz
New York City, 2001