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From Subatomic Quantum Fuzz to the Largest Structures in the Universe

Cosmic inflation, introduced in 1980 by Alan Guth and turned into a workable model a year later by Andrei Linde, Andreas Albrecht and Paul Steinhardt, has revolutionized the way cosmologists think about the Universe. Inflation is probably the most important idea in cosmology since the big bang itself.

Simply put, cosmic inflation is a gigantic growth spurt during which the Universe expanded by a factor of more than 1030 in a fraction of a second. As a result, all that we can see today originated from a region of space smaller than an atom and any curvature of space or lumpiness is smoothed out. Inflation thereby explains the homogeneity of the Universe and the uniformity of the cosmic microwave background and predicts that we live in uncurved space (a flat Universe). The latter prediction was confirmed last year by measurements of the cosmic microwave background made by the Boomerang and Maxima experiments. It has now been independently confirmed by today’s results from the Degree Angular Scale Interferometer.

An even more remarkable prediction of inflation is that the largest structures observed today, from the smallest galaxies to clusters containing thousands of galaxies, began as fuzziness in the subatomic world. The tremendous stretching of the size of the Universe during inflation also stretched the graininess of the subatomic world, to astrophysical scales, where it manifests itself as tiny (0.001%) lumpiness in the distribution of matter on cosmic scales, and tiny variations in the temperature of the Universe from place to place.

Over the past 14 billion years, gravity has amplified the lumpy matter into the structure that we see today in the Universe, from galaxies to superclusters. If inflation is correct, the intrinsic graininess of the subatomic world is responsible for the largest structures we see in the Universe today.

The tiny (10 micro Kelvin) variations in the temperature are linked to the matter lumpiness and provide a diagnostic to test this idea. This is a beautiful, elegant –and unexpected –connection between the microworld of subatomic particles and the vastness of the cosmos.

Because of its resolution and sensitivity, the DASI experiment was able to more precisely characterize the temperature variations and show that they are exactly what inflation predicts. In particular, the experiment revealed a series of characteristic peaks in the power spectrum as predicted by inflation.

The idea that the largest structures grew from quantum fuzz involved University of Chicago faculty member Michael Turner and others who attended a landmark conference organized by Stephen Hawking in Cambridge during the summer of 1982 (the 1982 Nuffield Workshop). While at the conference, living in College dormitory rooms, the workshop participants fleshed out the mathematical details and corrected each other’s errors. There was a lot of burning of the midnight oil and post-midnight visits to each other’s rooms for sometimes heated discussions. It was the most exciting time of Turner’s scientific career. Hawking was kept busy as the organizer and host, holding dinners at his home and a garden party (to distract the workshop participants), but he also worked late at night.

At the end of the two-week conference, four very different calculations arrived at the same amazing conclusion: if the Universe inflated, then the largest structures grew up from the intrinsic fuzziness of the quantum world. The workshop participants also realized that this idea could be tested by measurements of the cosmic microwave background radiation, though experiments were then far from being able to do so. (The four papers were authored by Jim Bardeen, Paul Steinhardt and Michael Turner; Stephan Hawking; Alexi Starobinsky; and Alan Guth and So-Young Pi, refs 1-4).

Almost 19 years later, the DASI results have produced the first confirmation of this profound connection between the subatomic world and the cosmos. At the time, several of Hawking’s colleagues chided him on spending so much money on the Nuffield Conference to bring together scientists from around the world to ponder inflation. No one is likely to hear such complaints now. Today’s DASI results put a big exclamation point on the significance of the Nuffield Workshop.

 

The standard references to density perterbations from inflation:

  1. J. Bardeen, P. Steinhardt and M.S. Turner, Physical Review D 28, 697 (1983).
  2. A. H. Guth and S.-Y. Pi, Phys. Rev. Lett. 49, 1110 (1982).
  3. S. W. Hawking, Phys. Lett. B 115, 295 (1982).
  4. A. A. Starobinskii, Phys. Lett. B 117, 175 (1982).

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http://www-news.uchicago.edu/releases/01/dasi/010427.dasi-background2.shtml
Last modified at 01:55 PM CST on Friday, September 12, 2003.

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