Arno Penzias

A Classical View of Cosmology


Abstract

Throughout human history, the heavens above us have offered our eyes, instruments and imaginations, an immensely rich variety of objects and phenomena. In a virtuous circle, observations have provoked the creation of scientific tools, thereby increasing understanding, which suggested further observations. Astronomy, therefore, has catalyzed—and benefited from—advances in many of the principal branches of classical physics, from mechanics to General Relativity.

As we all know, the laws of classical mechanics emerged in the 17th century as a successful model of solar system dynamics. Nonetheless, when applied to that era’s “Universe” (a static infinitude of equidistant stars) these same laws produced an awkward instability—one that was to remain unresolved for some two hundred years. In the interim, progress in astronomy went hand-in-hand with progress in fields such as optics, chemistry, and thermodynamics.

In the early 20th century, Albert Einstein’s seemingly innocuous assertion of the equivalence of gravitational and inertial mass spurred far-reaching change in our notions of time and space. When applied to the then-prevailing cosmology (a static infinitude of island galaxies) this updated mechanics left Einstein facing the same problem that had vexed Newton: mutual attraction between component masses leads to universal collapse. In the end, a fully satisfactory solution to this dilemma took some fifty more years to emerge, with the now widely-accepted model of the explosive origin of the Universe from a hot initial origin in which the light chemical elements were formed, and from which a relict radiation permeates space to the present day. Here again, this advance in our astronomical understanding owes much to related progress in a terrestrial science—in this case, nuclear physics.

Until recently, quantum theory—emerging, as it did, from the study of Nature at ultra-small dimensions—has had little to do with astronomy. Now, a compelling body of evidence points to an explosive origin for our Universe. The "point" of this origin confronts astronomy with dimensions of time and space, too small for physics—at least as most of us know it—to work. Although unimaginably small by any laboratory standard, this miniscule "cosmic egg" allows ample room for imaginative and exotic extrapolations of quantum field theory. Several theories have gained adherents, but none has yet produced testable predictions.

In earlier times, cosmologists could produce theories, comfortably expecting that they would not be tested within the lifetimes of their creators. Will the same thing now happen with superstring theories, and its competitors? Current progress in observational astronomy—notably, the widening use of gravitational lensing techniques—suggests otherwise. For example, sensitive studies of small-scale irregularities in the cosmic background radiation have allowed astronomers to compare the observed angular size distribution of condensations, with calculations based upon known properties of cooling primordial gas at the time of its recombination. Much like measuring the magnifying power of a lens by looking through it at a checkerboard, the lens (in this case, the curvature of intergalactic space) turned out to have no curvature at all: thereby implying a so-called flat Universe, dominated by dark matter and dark energy.

As plans for future observations based upon these findings take shape, dark matter and dark energy will become tools, as well as targets for further observations. This, in turn will help astronomers to probe their nature, as well as to seek hints to what, if anything, future theorists can say with confidence about how Nature works in the realm of the Plank Limits.

Leaving the Universe’s first nanosecond, or so, aside, we still have much to explore and discover out here, in the more-familiar, four-dimensional portion of the Universe: the seeding, and life stories of galaxies, and the clusters they inhabit; the silent majority of matter and energy had escaped detection until recently; the myriad life cycles of stars; and (just possibly) their role in seeding the life cycles of curious creatures.


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