In a discovery that has profound implications for our understanding about the beginnings of the universe, the Harvard-Smithsonian Center for Astrophysics this morning announced evidence of so-called primordial B-modes in the cosmic microwave background (CMB). These B-modes directly show quantum gravitational waves originating during the inflationary period of cosmic evolution, from about 10-36 to 10-32 seconds after the Big Bang, and give us a direct view of physical processes taking place at 1016 GeV – a trillion times more energetic than particle collisions at the Large Hadron Collider.
BICEP2 is a project to study the polarization of the CMB, which uses a telescope located near the South Pole. The CMB cannot be studied in any detail from most locations on the Earth's surface, primarily due to absorption of microwaves by water vapor in the air. The South Pole is at an altitude of about 3 km (10,000 ft), and has winter temperatures of about -60C (-72F), making this the driest environment on the planet and the closest thing to a space-based telescope. The patch of sky measured by the 10-inch BICEP2 telescope, which is sensitive to radiation with a frequency of 150 GHz, can be observed 24/7 all year long, leading to incredibly sensitive measurements of the CMB polarization.
B-mode polarization is the twisty part of the pattern of CMB polarization. To generate B-modes requires quantum gravitational waves from the earliest moments of the Universe. The process of cosmic inflation converts quantum gravitational fluctuations (gravitons) into long wavelength gravitational waves that generate the observed B-modes.
As seen in the figure above, the observed B-modes in the cosmic microwave background are much stronger than expected from a simple model without primordial gravitational waves. The strength of the B-modes reflects that about 20 percent of the primordial excitations are in the form of quantum gravitational fluctuations.
A treasure trove of fundamental cosmological and physics information can be gathered from study of these CMB B-modes:
- Direct detection of gravitational waves
- Viewing the process of cosmic inflation
- Ultra-high energy 10^16 GeV physical processes
- Pinning down inflation models
- The gravitational field is quantized
- Symmetry properties of quantum gravity
Assuming they are correct, the BICEP2 observations clearly represent a massively historic advance in fundamental physics. Many open questions are already answered, such as the quantization of gravity, and there is an opportunity to study physics nearly at the Planck scale, something previously thought impossible. To gain understanding about the beginnings of the universe and about quantum gravity, no single set of observations have ever contained so much new information. Watching the details from such observations unfold will be as exciting and profound as the early days of quantum mechanics and relativity theory.