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Inflation’s Smoking Gun

Beginning in the early 1980s, scientists started developing inflationary models to solve problems in standard big bang cosmology. Since then, the search has focused on independent evidence of an inflationary epoch in the universe’s early history. The recent discovery of “B-mode polarization” in the cosmic microwave background radiation provides a strong signature for that epoch. This result confirms inflationary models and strengthens the case for a beginning—and, thus, a Beginner—of the universe.

Last month’s announcement that the BICEP2 Collaboration had discovered the “smoking gun” that proves inflation happened early in the history of the universe made headlines and caused a lot of discussion (you can listen to RTB’s initial thoughts on the discovery here). This finding has important implications for ongoing research and for understanding how the universe came into existence.

In the 1960s, the discovery of the cosmic microwave background radiation (CMBR)turned scientific consensus away from steady-state cosmology and toward big bang models, which postulate a singular beginning of space, matter, time, and energy. However, standard big bang models faced a number of difficult issues (specifically, the “flatness-oldness,” horizon, and monopole problems) before they could pass scientific testing.

Scientists hypothesized that an epoch of extremely rapid expansion in the earliest moments of the universe (i.e., inflation) would solve all these problems. So, they set about developing big bang models that incorporate inflation. Yet any good model must rest on evidence independent of problems the model was designed to solve—which is where the BICEP2 Collaboration’s research comes in.

Inflation’s Signatures

Researchers expected inflation to leave a number of signatures in the CMBR. During the inflationary epoch, quantum fluctuations produced regions of higher and lower density in the universe. The rapid expansion caused these regions to increase to macroscopic scales and resulted in the fluctuations that COBE, WMAP, and Planck have detected in the CMBR. Given this picture, scientists expect the fluctuations to be highly adiabatic, Gaussian, and nearly scale-invariant (for details on these expected characteristics see here). Sensitive observations of the CMBR affirm all of these properties (and others). However, other mechanisms besides inflation could account for them. Thus, scientists needed to find a signature unique to inflation.

Inflation does produce a nearly unique signature via the generation of gravitational waves. Although no instruments currently possess the sensitivity to detect gravitational waves themselves, scientists have developed microwave telescopes capable of finding the polarization that the gravitational waves induce in the CMBR. In 2008, one research team conducted an experiment known as BICEP to measure E-modes, an expected form of polarization. After upgrading the telescope, the BICEP2 team announced (in March 2014) the detection of inflationary gravitational wave polarization (B-modes), thus confirming the existence of an inflationary epoch early in the universe’s history.1

Implications of the Discovery

This new research highlights several ramifications. First, the existence of inflationary gravitational waves (if affirmed by future research) would eliminate certain models of inflation. Most notably, the spectrum of B-mode polarization detected by BICEP2 differs from that predicted by ekpyrotic models developed by Paul Steinhardt and Neil Turok. Second, the BICEP2 results show that the energy scale of inflation resides only two orders of magnitude below the Planck scale. Consequently, future probes of inflationary mechanisms will permit scientists to explore the Planck epoch and hopefully understand what the proper quantum theory of gravity looks like. Third, these results affirm that inflationary models lead, in all likelihood, to the generation of a multiverse. (I’ve addressed multiverse theory’s compatibility with the big bang and the Christian worldview in previous articles and in my booklet Who’s Afraid of the Multiverse?

Scientists continue to gain deeper understanding of the remarkable universe in which we live. The smoking gun B-mode polarization of the CMBR validates the current inflationary big bang model, which, in turn, demonstrates that our universe began to exist and requires a cause or Beginner. A further quest involves identifying what or who that Beginner is.

  1. BICEP2 Collaboration, “BICEP2 I: Detection of B-mode Polarization of at Degree Angular Scales,” submitted March 17, 2014, last updated March 18, 2014,