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MODERN TIMES by Art Hobson [email protected] Our Incredible Universe Stonehenge and other prehistoric sites testify to the age-old human thirst to understand the universe. Today science is in the midst of a revolutionary burst of cosmological discovery. We live in fact in the golden age of cosmology—the study of the structure, origin and evolution of the large-scale universe. The Cosmic Background Explorer (COBE), an observing satellite able to map the details of the faded afterglow of the big bang creation of the universe, ushered in this golden age in 1992. This year, another satellite known as the Microwave Anisotropy Probe (MAP) reported further details that confirmed the picture that has been developing since COBE. We now know fairly precisely when the big bang occurred: 13.4 billion years ago. More importantly, we have a fairly well-confirmed theory, called “inflation,” as to what caused the big bang. It has to do with quantum physics, the theory that describes how nature behaves at the microscopic level. A major principle of quantum physics is that most microscopic events are inherently unpredictable, or uncertain. One consequence of these uncertainties is that the amount of energy in every microscopic region of space fluctuates unpredictably from very small amounts up to occasional large amounts. Our universe began from a huge--and therefore highly improbable—quantum fluctuation in the energy of a tiny part of the emptiness that existed before there was a universe. This unusually large energy fluctuation within an unbelievably small region of space—far smaller than an atom or an atomic nucleus--unleashed new microscopic forces that created the universe. These forces actually created space and time along with all that we see around us today. During a tiny fraction of the first second, the universe went through a short period of rapidly accelerating faster-than-light expansion called “inflation.” This initial expansion stretched the universe enormously (although its overall size was still smaller than 1 millimeter) and permanently imprinted the patterns of the microscopic quantum fluctuations that occurred just after the original energy fluctuation. COBE and MAP recorded these stretched-out patterns as they appeared 300,000 years later, when the universe had cooled sufficiently to allow the light from the big bang’s flash to be released and travel through space. The universe has been expanding at the speed of light ever since, simply because there is nothing to stop it. By today, the quantum fluctuations that were imprinted on the early universe have been shaped by the force of gravity into the giant clusters of galaxies (a galaxy, such as our own Milky Way galaxy, is a collection of billions of stars) that characterize the large-scale universe. In other words, the weird and wonderful microscopic principles of quantum physics are magnified and writ large in the heavens probed by our largest telescopes. If you are wondering how all this can possibly be, you aren’t alone. I warned you that it’s incredible--but backed by substantial evidence. We now know that the universe is not made of the stuff we had always thought it was made of. The “ordinary” matter and radiation that make up everything you can see (stars etc.) or feel (tables etc.) form only about 4 percent of the universe’s total mass (or “weight”). Another 23 percent is made of “dark matter”--but “invisible” or “transparent” matter would be better terms. There have been hints of dark matter for decades, but MAP provided conclusive details. Dark matter seems to show itself only through the gravitational forces that it exerts on ordinary matter. It might also exert a subtle sub-atomic force known as the “weak force.” It is truly ghostlike: It does not shine, it can pass right through ordinary objects without a trace (many particles of “ordinary” matter do this too), and nobody knows quite what it is. It is probably made of microscopic particles, it is widespread throughout the universe and probably all around us on Earth, and it was probably created in the big bang and has remained nearly unchanged since that time. It’s played an important role in the scheme of things. Our universe could not have “condensed” from the hot gases of the big bang into anything like the galaxies, stars, planets and people that we see around us were it not for the gravitational influence of dark matter. There’s more. The remaining 73 percent of the universe was only discovered during the past decade. It is called “dark (or invisible, or transparent) energy.” It is strange stuff indeed. Dark energy is a so-called “field,” a little like the gravitational field that pulls things down to Earth and holds the solar system together. It seems to be spread smoothly throughout the universe, and to be related to gravity. But it is an odd kind of gravity, because gravity pulls while dark energy pushes. In fact, it pushes on every bit of space within the universe, and causes it to actually accelerate (speed up) in its expansion. Nobody knows what it is or how it originated. The big bang, inflation, dark matter, dark energy, and the expanding accelerating universe have all fallen into place during the past decade to form a striking and probably enduring picture of our cosmic home. There is both scientific and poetic truth here. The new cosmology presents an awe-inspiring epic that in beauty and inspirational power surely does justice to the poets of old who were likewise moved by the glories of the heavens and Earth. It is a joy and a privilege to live in such an incredible universe.