Late in 1979, Alan Guth, then at the Stanford Linear Accelerator Center in California, realized that a solution to the monopole problem he had recently worked out with a colleague could also solve these two major puzzles. A universe that’s almost flat after more than ten billion years is as hard to arrange as a pencil that remains balanced on its point for eons. But in standard cosmological models, any universe that starts out with a little bit of curvature, positive or negative, diverges away from flatness as the universe expands. The second puzzle was that our universe appears to be approximately “flat”–on the largest distance scales, space has little or no curvature. Why, then, does the universe look more or less the same everywhere? First, the uniformity problem: the universe has expanded so rapidly that there hasn’t been time for all regions of today’s observable universe to equalize their temperatures and densities by exchanging matter and energy. Two seemingly unrelated problems also existed in cosmology at the time. One unwanted consequence of this transition, theorists realized, was that it would create an abundance of isolated north and south magnetic poles, or monopoles–a phenomenon inconsistent with cosmic observations. Then, at a cosmic age of about 10 - 35 seconds, the strong nuclear force parted company from the still-unified electroweak force. In standard big bang models, the cosmos started out hot enough to achieve that grand unified state. In the 1970s, particle theorists began to construct grand unified theories (GUTs), which proposed that at temperatures or energies above about 10 15 billion electron-volts (GeV), the electromagnetic force and the strong and weak nuclear forces are identical. Inflation not only became a central tenet of cosmological theory it also meant that any aspiring cosmic theorist had to learn particle physics. This inflationary episode, as it was dubbed, could explain how our universe came to have its observed density and uniformity. New ideas from particle physics, the paper showed, implied that the universe might have undergone a phase of very rapid expansion in the first fractions of a second of its existence. ×įocus Landmarks feature important papers from the archives of the Physical Review.ģ0 years ago, a report in Physical Review D utterly transformed scientific thinking about the origin of the universe. Among other tasks, It will observe light from early in cosmic history and test the concept of inflation–an exponential expansion of the universe during its infancy–which was originally proposed in 1981. The James Webb Space Telescope will observe the infrared universe after its launch in 2014 or later.
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