David Wands

I am Professor of Cosmology and Director of the Institute of Cosmology and Gravitation at the University of Portsmouth.

I am interested in the physics of the very early universe, less than a second after the Big Bang. My research investigates what primordial fluctuations in the density and metric of spacetime can tell us about the physical processes at work at such early times and high energies.

I teach undergraduate courses in the Faculty of Technology and on the Applied Physics degree in the Faculty of Science.

In a new paper out in Physical Review Letters this week, we show how we can include the effect of quantum fluctuations, which contribute to cosmological inflation in the very early universe, in calculations of primordial density waves.

Physicists do not know yet how to combine theories of gravity and of the quantum world. Yet both play a crucial role in the very early Universe where the expansion of space is driven by gravity and cosmological structures arise from quantum fluctuations. An effective description can be derived where each patch of space experiences a random expansion history. In this approach, known as stochastic inflation, we show how to calculate observable quantities such as primordial density waves in the Universe. We identify a phenomena which we term infinite inflation where the average expansion in each patch can be infinite. However we show that there is a robust procedure through which observable predictions can be derived and tested against astronomical data so long as the energy density of the Universe remains below the quantum gravity scale. This reveals quantum imprints left on cosmological structures in the very early Universe and sheds light on what we may expect from a full quantum theory of gravity.

Our work is led by one of our bright young postdoctoral researchers, Vincent Vennin (above), working with Hooshyar Assadullahi and me in Portsmouth, and our collaborators, Hassan Firouzjahi and Mahdiyar Noorbala, at the Institute for Fundamental Research in Tehran.

The press release has been picked up by a number of organisations including phys.org.

Today, at 3.30pm UK time, scientists from the Laser Interferometric Gravitational Observatory (LIGO) are expected to announce the first direct detection of gravitational waves.

Gravitational waves are ripples in the fabric of spacetime, a key prediction of Einstein's theory of general relativity. Their discovery would prove that Einstein really was right and spacetime is a dynamic framework.

Rumour has it that LIGO has detected a signal from the merger of two black holes, many times heavier than our Sun. Just like an earthquake sends ripples through the Earth's crust, this colossal space-quake would send ripples through spacetime which for the first time have been felt by LIGO.

Have we seen the first direct evidence for inflation in the very, very early universe? Never mind inflation, have we seen gravitational waves on cosmic scales?

The BICEP2 experiment has presented evidence of primordial gravitational waves, revealed in the pattern of polarised radiation coming from the edge of our observable universe (the cosmic microwave background). The existence of such ripples in the cosmological fabric had been predicted as a "smoking gun" for a period of rapid, accelerated expansion ("inflation") in the very early universe.

Gravitational waves imprint a distinctive curl in the polarisation ("B-modes") which are not produced by other primordial sources, such as density waves. The surprisingly large signal seen by BICEP2 indicates that these primordial ripples were produced by cosmic inflation occurring at fantastically high energy scales, more than a million, million times larger than the energy of particles produced at the LHC in CERN.

The results are surprising because at fist glance they appear to be in tension with data from the ESA Planck satellite released a year ago. Both results quote the size of the gravitational wave signal in terms of a parameter "r". BICEP report a central value of r=0.2 while the Planck collaboration quoted an upper bound of r<0.12. There are uncertainties in both numbers coming from modelling either foregrounds or inflationary parameters. So cosmologists will wait anxiously for the Planck team to release their own polarisation data, expected by the end of this year.

In the meantime the BICEP2 team have staked their claim to be the first to have discovered direct evidence of both primordial gravitational waves and cosmic inflation.

Note added:Here is an interview I gave on the BBC News channel the same day.

Postscript: Sad to say, but the BICEP signal seems to have been an unexpectedly large signal from dust in our Galaxy and not primordial gravitational waves. It really was too good to be true.

Sandi Toksvig is the new chancellor of the University of Portsmouth and she came to visit the ICG last month. We told her a bit about the research that goes on in Portsmouth and showed her some of the public outreach activities we do. Here she is with ICG researchers holding an inflatable cosmic microwave background sky. We also showed her how to build a lego universe - a sure-fire hit with any Danish visitors!

Just finished recording a short interview for Radio Solent about the announcement at CERN earlier today of the discovery of a new particle, almost certainly the elusive Higgs boson. I was asked if today is a historic day in the annals of science? I reckon so. The discovery of a new fundamental particle is big news, and the Higgs is the final block (until today the missing link) in the standard model of particle physics. The particle physics community has invested many years, a few billion euros and a lot of credibility in the Large Hadron Collider specifically to discover the Higgs particle. So congratulations to the international community of scientists and engineers at CERN who delivered the goods.

This September the ICG hosted the annual 2-day UK Particle Cosmology meeting, and a Cosmic Superstrings meeting, and an extended cosmology workshop over the following week. The UK Cosmo meetings started 20 years ago with a small group of researchers from Cambridge, Sussex and Imperial meeting in Tom Kibble's office at Imperial College, London. For this meeting we welcomed 90 researchers from around the UK and around the globe, with researchers from the US, Mexico, South Africa and Japan, but we try to keep the same relaxed and informal style, giving students and young postdocs the chance to present their research in a friendly environment.

On Thursday 17th March I am being interviewed on Ronnie Barbour's afternoon show ("The Other One Show") on BBC Three Counties Radio. I think this probably has more to do with the fact that it is National Science and Engineering Week rather than that it is St Patrick's Day (and my Aunt Patricia's birthday). In case you were wondering, the Three Counties are Beds, Herts and Bucks. It just so happens that I grew up in Amersham, Buckinghamshire. The photo above is of the distinctive Market Hall (1682) in Old Amersham.