"Big Bang" of Cosmology

By Dr Chris Marker

Tuesday 17th March saw some extremely interesting results being announced by the BICEP2 collaboration.  

BICEP2 is a radio telescope that measures the polarisation of the cosmic microwave background (CMB). The CMB is the thermal radiation assumed to be left over from the "Big Bang" of cosmology. BICEP2 has been looking for so called B-mode polarisation in the CMB, this is a characteristic twist in the directional properties of the CMB. The team have announced that they have found a signal. Only the gravitational waves moving through the Universe in its inflationary phase could have produced such a signal. This result marks the first time that primordial gravitational waves have been detected.  Gravitational waves are ripples in the curvature of space-time that propagate as a wave. They were predicted to exist in 1916 by Albert Einstein on the basis of his theory of general relativity. They are the last prediction of this theory to be verified.

The detection of the B-mode polarisation in the CMB also provides the first direct evidence for inflation. Inflation is the expansion of space in the early universe at a rate much faster than the speed of light. The universe is thought to have started as a singularity, an incredibly small, incredibly dense space, where the laws of gravitation breakdown. This singularity then expanded outwards to become the universe, but the big bang theory alone does not explain the universe as we see it. In order to look like it does today, the universe would have to have started from very finely tuned or "special" initial conditions at the Big Bang that cannot be easily explained. Inflation does away with this fine tuning problem and explains the structure that we see in the Universe. The random quantum fluctuations that existed at the very start of the Big Bang are amplified by inflation to provide the seeds for everything that came after, the galaxies and the clusters of galaxies that we can see today.  Inflation also explains why the Universe looks so smooth on the largest scales; it would have stretched away any unevenness.

The BICEP2 team also measured the energies involved in inflation to be consistent with ideas for what is termed Grand Unified Theory (GUT).  GUT is a model of particle physics in which at high energy, the three interactions of the Standard Model; the electromagnetic, weak, and strong interactions, are merged into one single interaction.  By associating gravitational waves with the time of the universe when quantum effects were dominant, the team has improved the prospects of scientists one day pulling the fourth force - gravity itself - into a Theory of Everything.

Given the importance of these results they are likely to be heavily scrutinised by the scientific community.  The Planck satellite team has previously released preliminary results using the temperature of the CMB rather than polarisation that do not neatly fit with the new results. If however the results are confirmed either by other experiments it means a new frontier in cosmology and physics.

Inspec covers many of the topics involved in this research.

Control Terms include:

  • cosmic acceleration
  • cosmology
  • general relativity
  • grand unified theory
  • gravitation
  • gravitational waves
  • radioastronomy
  • radiofrequency cosmic radiation
  • radiotelescopes

Classifications include:

  • a0420 General relativity
  • a0430 Gravitational waves and radiation: theory
  • a0450 Unified field theories
  • a0455 Alternative theories of gravitation 
  • a0480 Experimental tests of general relativity and observations of gravitational radiation
  • a1110N Gauge field theories
  • a1210D Unified models beyond the standard model
  • a9530S Relativity and gravitation in astrophysics 
  • a9555J Radiotelescopes
  • a9870V Background cosmic radiations
  • a9880 Cosmology
  • a9880B Origin and early evolution of the Universe
  • a9880D Theoretical cosmology
  • a9880L Observational cosmology
  • b6360 Radioastronomical techniques and equipment