Cosmic acceleration: connecting theory and observation.
Lead Research Organisation:
University College London
Department Name: Physics and Astronomy
Abstract
Current cosmological data are, for the first time, precise enough to allow detailed observational tests of our models of the very early universe. The initial conditions of the Big-Bang are thought to have been set during ``inflation'', an era of almost exponential expansion in the primordial universe. Usually modelled as a slowly rolling potential-dominated scalar field, it provides a mechanism to generate the primordial fluctuations which are seen today in the cosmic microwave background (CMB) radiation, the left-over heat from the Big Bang. The microphysics of inflation is presently unknown, but accessible because the different inflationary models make distinctive predictions about the statistical properties of the CMB anisotropies. Moreover, because inflationary models have their basis in theoretical high energy physics, the early universe is effectively a unique laboratory for testing particle physics at energies far beyond the reach of any conceivable Earth-bound experiments. Intriguingly, the cosmological expansion may be accelerating once again, not slowing down as expected in a universe filled with matter only. Independent data from supernovae, the CMB and galaxy surveys all support this surprising result. These observations can be explained if the universe is dominated by a negative-pressure component, coined ``dark energy'', which makes up roughly two-thirds of the cosmological energy density. Theoretical models for the dark energy include vacuum energy (the ``cosmological constant''); and a time-varying, spatially inhomogeneous component modelled by a rolling scalar field (``quintessence''). I propose to develop and apply new tools to pin down the precise mechanism of inflation and the nature of dark energy. The enormous difference in energy scales makes it unlikely that the same underlying mechanism is responsible for both effects. However, a unified framework is the most efficient way to approach these two problems, as they share many similarities in terms of the physics and astrophysics at hand. The number of theoretical models proposed for inflation and dark energy is very large, and it is not profitable to analyse each in turn. Instead, the basic philosophy of my proposed research programme is to identify and systematically confront broad classes of models with precision cosmological data and well-motivated theoretical priors. The data will be analysed robustly so that the final constraints do not have significant unknown contributions from imprecise models or systematic errors, and the competing theories will be compared against each other using advanced model-comparison techniques to identify the simplest models that are consistent with the data. The research is certain to improve our understanding of the microphysics of inflation and dark energy if the universe corresponds to the most ``minimal'' current ideas, but also flexible enough to exploit the data fully if it contains statistically significant hints of more exotic physics. The dual mysteries of cosmic acceleration at early and late times are two of the biggest questions confronting cosmologists today, and the results of this research will help to answer important questions about both Inflation: - Does inflationary physics have more than one degree of freedom? - Did inflation take place at the Grand Unified Theory-scale or at lower energies? - What inflationary initial conditions are consistent with the data? - Was the inflationary potential smooth? and Dark Energy: - Can we rule out a cosmological constant in favour of scalar fields? - Does dark energy cluster? - Is dark energy coupled to matter? This work thus has the potential to exploit measurements of the CMB, large scale structure and gravitational waves -- all of which are the target of major projects funded by PPARC -- in order to increase our understanding of fundamental physics.
Publications
Peiris H
(2010)
The shape of the primordial power spectrum: A last stand before Planck data
in Physical Review D
Pontzen A
(2010)
The cut-sky cosmic microwave background is not anomalous
in Physical Review D
Mortlock D
(2009)
Photometric constraints on white dwarfs and the identification of extreme objects
in Monthly Notices of the Royal Astronomical Society
Pontzen Andrew
(2010)
Cosmology's not broken
in NEW SCIENTIST
Pontzen A
(2010)
Cosmology's not broken
in New Scientist
Baumann D
(2009)
Cosmological Inflation: Theory and Observations
in Advanced Science Letters
Mortonson M
(2009)
CMB polarization features from inflation versus reionization
in Physical Review D
Peiris H
(2010)
CMB isotropy anomalies and the local kinetic Sunyaev-Zel'dovich effect
in Physical Review D
Bird S
(2009)
Brane inflation and the overshoot problem
in Physical Review D
Mortonson M
(2011)
Bayesian analysis of inflation: Parameter estimation for single field models
in Physical Review D
Description | The research funded on the grant centres on connecting cosmological observations to fundamental physics. In achieving this I worked with data from large cosmological datasets at a variety of wavelengths, including the cosmic microwave background (CMB) and large galaxy and quasar surveys. I carried out interdisciplinary research with theoretical physicists to sharpen the predictions of fundamental theory for cosmological observations, and develop innovative algorithms and statistical techniques to test these theories with data. I have been at the forefront of a large international effort to understand the physical origin of cosmological structure in the first moments of our universe. |
Exploitation Route | The findings are already influencing the future directions of my academic research area, and have been featured in the media attracting strong interest from the public. |
Sectors | Digital/Communication/Information Technologies (including Software),Education,Culture, Heritage, Museums and Collections |
URL | http://www.earlyuniverse.org |
Description | The findings have been disseminated to the public (both school-age and adults) through outreach lectures and through a variety of (old and new) media, contributing to the public understanding of science. |
Sector | Culture, Heritage, Museums and Collections,Other |
Impact Types | Cultural |
Description | FQXi Large Grant |
Amount | £70,000 (GBP) |
Organisation | Foundational Questions Institute (FQXi) |
Sector | Charity/Non Profit |
Country | United States |
Start | 01/2011 |
End | 11/2013 |
Description | IoA Theory Rolling Grant |
Amount | £2,439,000 (GBP) |
Organisation | Science and Technologies Facilities Council (STFC) |
Sector | Public |
Country | United Kingdom |
Start | 04/2009 |
End | 03/2014 |
Description | Marie Curie International Reintegration Grant |
Amount | £87,800 (GBP) |
Organisation | European Commission |
Sector | Public |
Country | European Union (EU) |
Start | 11/2007 |
End | 11/2010 |
Description | Non-stipendiary Junior Research Fellowship, King's College Cambridge |
Amount | £4,000 (GBP) |
Organisation | University of Cambridge |
Department | King's College Cambridge |
Sector | Academic/University |
Country | United Kingdom |
Start | 10/2008 |
End | 09/2009 |
Description | Support for an International Meeting |
Amount | £2,000 (GBP) |
Organisation | Royal Astronomical Society |
Sector | Academic/University |
Country | United Kingdom |
Start | 09/2010 |
End | 09/2010 |
Description | UCL Rolling Grant |
Amount | £468,086 (GBP) |
Organisation | Science and Technologies Facilities Council (STFC) |
Sector | Public |
Country | United Kingdom |
Start | 04/2011 |
End | 03/2013 |
Description | Aspen Center for Physics Dialogue: "Matter & Antimatter: The Science of Angels and Demons" |
Form Of Engagement Activity | Participation in an open day or visit at my research institution |
Part Of Official Scheme? | No |
Geographic Reach | Local |
Primary Audience | Public/other audiences |
Results and Impact | ~80 members of the public listened to my presentation followed by about 1 hr of discussion/debate. The Aspen Centre for Physics reports that this is one of the most successful Aspen Dialogues they've held |
Year(s) Of Engagement Activity | 2009 |
Description | Astronomer portrait for "Explorers of the Universe" exhibition, Royal Albert Hall |
Form Of Engagement Activity | Participation in an activity, workshop or similar |
Part Of Official Scheme? | Yes |
Geographic Reach | National |
Primary Audience | Public/other audiences |
Results and Impact | There was a huge amount of public interest in the presentation, which was reported on the BBC and elsewhere. Details of this should be available from Max Alexander, the photographer who initiated the exhibition |
Year(s) Of Engagement Activity | 2008 |
Description | Cambridge Astronomical Association talk |
Form Of Engagement Activity | A talk or presentation |
Part Of Official Scheme? | No |
Geographic Reach | Local |
Primary Audience | Public/other audiences |
Results and Impact | About 120 members of the public of all ages attended this talk, and was followed by about half an hour of Q&A/discussion CAA reported that very good feedback had been received |
Year(s) Of Engagement Activity | 2009 |
Description | Featured scientist on Guardian Science Weekly podcast |
Form Of Engagement Activity | A talk or presentation |
Part Of Official Scheme? | No |
Geographic Reach | International |
Primary Audience | Public/other audiences |
Results and Impact | http://www.guardian.co.uk/science/blog/audio/2010/jul/12/science-weekly-podcast-planck-universe Guardian Science Weekly podcast is one of the most downloaded podcasts. |
Year(s) Of Engagement Activity | 2010 |
Description | Interview and researcher profile for Research Councils UK "Impacts" publication |
Form Of Engagement Activity | A talk or presentation |
Part Of Official Scheme? | Yes |
Geographic Reach | National |
Primary Audience | Policymakers/politicians |
Results and Impact | http://www.rcuk.ac.uk/Publications/reviews/reports/impacts/Pages/PeopleandSkills.aspx see above link |
Year(s) Of Engagement Activity | 2010 |
Description | New Scientist Opinion column |
Form Of Engagement Activity | A magazine, newsletter or online publication |
Part Of Official Scheme? | No |
Geographic Reach | National |
Primary Audience | Public/other audiences |
Results and Impact | Published in Aug issue of New Scientist New Scientist is one of the highest circulation science magazines for the public. The article was reprinted in the Cambridge University Alumni magazine CAM. |
Year(s) Of Engagement Activity | 2010 |
Description | Speaker, South Hampstead High School Careers Conference |
Form Of Engagement Activity | Participation in an open day or visit at my research institution |
Part Of Official Scheme? | No |
Geographic Reach | Local |
Primary Audience | Schools |
Results and Impact | 15-20 girls attended a brief presentation followed by an extensive Q&A session on the career choices available on studying physics. Unknown at this level of detail - school sent a thank you message saying the pupils were really interested and inviting me back in future years. |
Year(s) Of Engagement Activity | 2007 |
Description | Talk to MPs and policymakers, RCUK event "Impacts: people and skills" |
Form Of Engagement Activity | A talk or presentation |
Part Of Official Scheme? | Yes |
Geographic Reach | National |
Primary Audience | Policymakers/politicians |
Results and Impact | ~50-60 MPs, policymakers and members of the media attended this presentation. RCUK reports that the event was successful in highlighting the impact of "blue skies" research. |
Year(s) Of Engagement Activity | 2010 |
Description | University of Manchester "Jodcast" |
Form Of Engagement Activity | A talk or presentation |
Part Of Official Scheme? | No |
Geographic Reach | Local |
Primary Audience | Public/other audiences |
Results and Impact | http://www.jodcast.net/archive/201102/ The Jodcast presenters send me several emails from the members of the public saying how much they had learnt from my interview. |
Year(s) Of Engagement Activity | 2010 |