My research interests is in the Cosmic Microwave Background (i.e. CMB) Anisotropies as a testbed for Cosmological and High Energy Physics phenomenology.
Studies of the CMB anisotropies will help answer questions in:
- Large Scale Structure
- Beyond the Standard Model of Particle Physics
- Standard Model of Cosmology
- Dark Energy and Dark Matter
- New Physics at GeV Energies
Cosmology is the study of the Universe and its origins. For a long time cosmology has bordered on being a philosophy expressed in mathematics. However, the 1965 discovery of the Cosmic Microwave Background (CMB) by Arno Penzias and Robert Wilson gave the field of cosmology observational evidence to support its theories. The discovery of the CMB supported the Big Bang Theory of cosmology. The idea that our Universe evolved from a single point in space and time. That at one point in time all that can be viewed in the night sky was once compacted into a space smaller than a grain of salt. Observational Cosmology has continued since 1965 to make new discoveries in our understanding of the Universe. With new space based, balloon-borne, and ground-base instruments (e.g. COBE, WMAP, and now Planck) our understanding of the early Universe has become an era of precision.
The CMB is the after glow of the largest explosion our Universe has ever been witness too. The Big Bang occurred approximately 13.7 billion years ago. That is 3 times the age of the Earth at 4.5 billion years. Despite this event occurring before the Earth was even a thought in the Universe we can still measure the light radiating from this massive explosion today. If you were to measure the temperature of outer-space it would not be zero as one might think. In fact outer-space is 2.725 Kelvins in temperature, which is -270.425 degrees below the freezing point of water. Outer-space is an extremely cold environment, but its not at an absolute zero temperature either. This non-zero temperature is the main evidence for the Big Bang model of the early Universe, which could not be explain by other popular models of the Universe before 1965 such as the Steady State model (i.e. an eternal Universe).
Further studies of this cosmic background of light showed that its intensity over a range of wavelengths (i.e. different colors of light) forms almost a perfect blackbody radiating at a temperature of 2.725 Kelvins that has a spectral peak at approximatly 1 millimeter. Light at 1 millimeter is not visible with the naked eye (i.e. the eye’s peak response to light is at a wavelength of 0.00055 millimeters or green light) which is why outer-space still looks black even in the presence of this Big Bang after glow. In 1989 the first cosmological space telescope, the Cosmic Background Explorer (i.e. COBE), was launched to measure the temperature across the observable Universe. It was discovered that the temperature across the Universe was not perfectly 2.725 Kelvins everywhere, but the temperature differed on the order of 1 part in a 1000 Kelvins from one point in the sky to another. These small differences in temperature from one point on the sky to another are called anisotropies. The temperature differences are interpreted as being cause by spatial differences in density and pressure of the components of the early Universe: Baryonic plasma (i.e. protons and neutrons), Photons, Cold Dark Matter, and Neutrinos.
Intensity is not the only characteristic of light. Light comes in two flavors (i.e. helicity), a property commonly referred to as polarization. As light scatters off a medium it will become polarized to a degree. The light from the CMB is also polarized. One mode of polarization, called E-mode (i.e. even parity or gradient component), is caused by light scattering off the various components of the early Universe and gravitational waves (i.e. ripples in spacetime). The other mode of polarization, called B-mode (i.e. odd parity or curl component), is caused by light scattering off gravitational waves only. Therefore the B-mode polarized light in the CMB is an independent metric for measuring gravitational waves.
The current popular theory for the source of the gravitational waves is inflation. Inflation is the idea that during the early moments of the Universe there was a period of rapid expansion. The Universe grew so rapidly that spacetime itself expanded faster than the speed of light. This expansion of the Universe would have caused gravitational waves that would still be present at the time of the CMB. The light from the CMB is from a period approximately 300,000 years after the Big Bang. Since the Big Bang is a model of a Universe that expands as one moves forward in time therefore if you go backwards in time the Universe would be contracting. The further you go back in time the smaller the Universe gets therefore stars and galaxies get closer and closer to each other to the point where the probability of a light particle (i.e. photon) running into something increases the further you go back in time. If a photon is running into the individual components of stars and galaxies (i.e. protons, neutrons, electrons, etc.) because the space between objects is getting smaller and smaller then the photon doesn’t have a chance to reach our telescopes. So there is a limit to how far back in time we can look using light and a telescope before the Universe becomes to dense to see through. However gravitational waves don’t have this same limit and can be used to make measurements and observations of the early moments of the Universe. Therefore a measurement of the B-mode polarization in the CMB can act as a probe for new discoveries in the few moments after the Big Bang and make advances in physics at energy scales of GeV energies. In comparison, the new particle accelerator to come online at CERN will reach energy levels up to 14,000 GeV. With observations of the CMB polarization we will be able to study physics at energies scales orders larger than what will be studied at CERN.
To date the B-mode polarization in the CMB has not been detected. This experiment is not without its complications primarily because the expected signal for B-mode polarization is on the order of 1 part in 50,000,000 Kelvins. The CMB is also not the only source emitting millimeter wavelength light in the Universe. Sources in our Galaxy and extra-galactic include Galactic synchrotron, bremsstrahlung, and dust emission. These foreground signals have to be differentiated from the background signal of the CMB by making measurements at multiple wavelengths of light. The anisotropies can also be caused by secondary effects. These secondary effects would have occurred sometime after the 430,000 years after the Big Bang. These secondary effects are caused by gravitational lensing, re-ionization, and the Sunyaev-Zel’dovich effect, which in their own right reveal interesting physics about our Universe. Continued research is being done to understand the foreground and secondary anisotropy effects so as to be able to distinguish them from the primary anisotropy effects caused by the early Universe. New technology and instrumentation is pushing experimentation to higher levels of precision paving the way for new discovers in the seconds after the Big Bang. This blog will serve to document these future developments in observational cosmology and the theories that support our interpretations of the data.