Measuring tiny variations in the cosmic microwave background will enable major discoveries about the origin of the universe, including details of its early expansion and of physical phenomena at energies a trillion times greater than those of the largest earthbound accelerators.
John Carlstrom, University of Chicago
Photo credit: Jason Gallicchio
How is it possible to know in detail about things that happened nearly 14 billion years ago? The answer, remarkably, could come from new measurements of the cosmic microwave radiation that today permeates all space, but which was emitted shortly after the universe was formed.
Previous measurements of the microwave background showed that the early universe was remarkably uniform, but not perfectly so: there are small variations in the intensity (or temperature) and polarization of the background radiation. These faint patterns show close agreement with predictions from what is now the standard theoretical model of how the universe began. That model describes an extremely energetic event—the Big Bang—followed within a tiny fraction of a second by a period of very accelerated expansion of the universe called cosmic inflation. During this expansion, small quantum fluctuations were stretched to astrophysical scales, becoming the seeds that gave rise to the galaxies and other large-scale structures of the universe visible today. After the cosmic inflation ended, the expansion began to slow and the primordial plasma of radiation and high-energy sub-atomic particles began to cool. Within a few hundred thousand years, the plasma had cooled sufficiently for atoms to form, for the universe to become transparent to light, and for the first light to be released. That first light has since been shifted—its wavelengths stretched 1,000-fold into the microwave spectrum by the continuing expansion of the universe—and is what we now measure as the microwave background.
To gain an understanding of the origin of
the universe is central not only to unraveling
continuing mysteries such as dark matter
and dark energy, but also to gain a clearer
perspective on our human place within the
Recently the development of new superconducting detectors and more powerful telescopes are providing the tools to conduct an even more detailed study of the microwave background. And the payoff could be immense, including additional confirmation that cosmic inflation actually occurred, when it occurred, and how energetic it was, in addition to providing new insights into the quantum nature of gravity. Specifically the new research we propose can address a wide range of fundamental questions:
- The accelerated expansion of the universe in the first fraction of a second of its existence, as described by the inflation model, would have created a sea of gravitational waves. These distortions in space-time would in turn would have left a distinct pattern in the polarization of the microwave background. Detecting that pattern would thus provide a key test of the inflation model, because the level of the polarization links directly to the time of inflation and its energy scale.
- Investigating the cosmic gravitational wave background would build on the stunning recent discovery of gravity waves, apparently from colliding black holes, helping to further the new field of gravitational wave astronomy.
- These investigations would provide a valuable window on physics at unimaginably high energy scales, a trillion times more energetic than the reach of the most powerful Earthbased accelerators.
- The cosmic microwave background provides a backlight on all structure in the universe. Its precise measurement will illuminate the evolution of the Universe to the present day, allowing unprecedented insights and constraints on its still mysterious contents and the laws that govern them.
The origin of the universe was a fantastic event. To gain an understanding of that beginning as an inconceivably small speck of space-time and its subsequent evolution is central to unraveling continuing mysteries such as dark matter and dark energy. It can shed light on how the the two great theories of general relativity and quantum mechanics relate to each other. And it can help us gain a clearer perspective on our human place within the universe. That is the opportunity that a new generation of telescopes and detectors can unlock.