The expected announcement today (Monday, March 17) from Harvard’s Center for Astrophysics that the BICEP2 (Background Imaging of Cosmic Extragalactic Polarization) experiment may have found proof of inflation in the early universe comes on the heels of a March 10 report from a rival group, POLARBEAR, that similar measurements of microwave background polarization can be used to map the large scale structure of the universe, and perhaps determine the masses of neutrinos.
Both groups measured the “B-mode” polarization of microwave emissions from the early universe – the so-called cosmic microwave background (CMB). The following POLARBEAR scientists are available to speak with reporters about the BICEP2 and POLARBEAR results, and future prospects for probing conditions in the early universe and cosmic evolution:
Adrian Lee, POLARBEAR principal investigator, UC Berkeley professor of physics and faculty scientist at Lawrence Berkeley National Laboratory (LBNL): (510) 703-3221 (cell),(510) 643-4606, Adrian.firstname.lastname@example.org
Nils Halverson, POLARBEAR co-PI and associate professor of physics at the University of Colorado, Boulder: (720) 987-6145 (cell), (303) 492-6817 or (303) 492-0315, email@example.com
Uros Seljak, a UC Berkeley professor of physics and astronomy and faculty scientist at LBNL who first proposed in 1996 using polarization measurements to reconstruct details of the early universe, is also available for comment: firstname.lastname@example.org, (510) 984 8431 (cell), (510) 666-2627
BACKGROUND: While measurements of minute fluctuations in the 3 degree Kelvin cosmic microwave background radiation can tell astronomers about the evolution of structure in the universe starting about 400,000 years after the Big Bang, much more information can be gleaned from measuring variations in the polarization of these microwaves. Polarized light – that is, light vibrating in one direction only – is produced by scattering; light bouncing off the surface of a lake, for example, is polarized parallel to the surface.
In the early universe, light scattered off electrons and became polarized shortly after that recombination event 400,000 years after the Big Bang, when the universe had cooled enough to allow protons and electrons to combine into atoms. By measuring how this polarization varies across the sky, scientists can map the density of material from which the radiation came, and the distribution of material through which the radiation passed on its way to Earth.
POLARBEAR reported in a paper posted online March 10 that their instruments on the Huan Tran Telescope in Chile detected characteristic “B-mode” polarization caused by the gravitational influence of matter through which the radiation passed on its 13 billion-year trip to Earth. In the future, the team will use this so-called weak lensing to measure the clustering of dark matter and dark energy in the universe, estimate the masses of neutrinos, and determine when dark energy ‘turned on’ and began to accelerate the expansion of the universe.
“We’ve made the first demonstration that you can directly see any B-mode on the sky, that is, we can measure the basic signal that will enable very sensitive searches for neutrino mass and the evolution of dark energy,” Lee said. “Our results pave the way to use CMB polarization lensing as a cosmological probe.”
POLARBEAR’s initial focus was measuring polarization variation over small angular scales. BICEP2, based at the South Pole, looked at variation over larger angular scales, which Seljak predicted should contains the signature of gravitational waves created during the universe’s infancy. Because theorists believe that primordial gravitational waves could only have been produced during a brief and very rapid expansion of the early universe, called inflation, 10-34 seconds after the Big Bang, detection of this polarization would be a confirmation that inflation actually happened.
If BICEP2 scientists have indeed found B-mode polarization caused by these very early gravitational waves, “it would be a smoking gun for inflation, and in general a major breakthrough in the field of cosmology, and probably a Nobel Prize level discovery,” Seljak said.
He noted that inflation is a key part of many theories of cosmic evolution, including some that predict eternal inflation, that is, that inflationary events are happening all the time in some corner of our universe, continually generating new alternate universes.
In the future, POLARBEAR will also look for signals of gravitational waves in B-mode polarization to confirm BICEP2’s findings.
Recent POLARBEAR papers:
- A Measurement of the Cosmic Microwave Background B-Mode Polarization Power Spectrum at Sub-Degree Scales with POLARBEAR (submitted to Astrophysical Journal 3/10/14)
- Evidence for Gravitational Lensing of the Cosmic Microwave Background Polarization from Cross-correlation with the Cosmic Infrared Background (submitted 12/23/13, accepted 3/8/14 for publication in Physical Review Letters)
- Gravitational Lensing of Cosmic Microwave Background Polarization (submitted to Physical Review Letters 12/23/13)