An investigation of relativistic gravitational effects of use for understanding and interpreting dark energy
Lead Research Organisation:
Queen Mary University of London
Department Name: Physics
Abstract
Normal matter, such as the electrons, protons and neutrons that make up the everyday things we are familiar with, have the property of attracting each other through gravity. A universe that were filled with only matter of this type, together with radiation, neutrinos and a few other ingredients, would either slow down in its expansion as time goes by, or settle into a steady rate of constant expansion. Instead, astronomers see a Universe that appears to be accelerating in its expansion. This is a highly unexpected result, and one that requires the introduction of a highly unusual substance that must permeate the whole of the Universe and be responsible for pushing everything apart. This substance has been given the name Dark Energy, and to explain the observations it must make up approximately 2/3 of the total energy budget of the Universe. There are lots of ideas as to what Dark Energy might be, but at the moment no-one knows for sure. The research I am proposing to perform is an investigation of some of these ideas. In particular, I am planning to focus on three specific areas, which I will outline below. The first area is modifications to general relativity. General relativity is the theory that governs the behaviour of space-time, and it has been suggested by some that the apparent need for Dark Energy may be a sign that we have not understood how gravity, and hence general relativity, behave on the largest scales. A number of modifications to general relativity have been proposed, but it is not always clear what the full implications of these modifications are, and if they are compatible with all of the astrophysical and cosmological observations that we have available to us. I intend to study these modified theories, and to produce a frame-work through which they can be straightforwardly compared to observational data, in order to determine their validity. The second area is inhomogeneous models of the Universe. The usual model for the Universe is based on small deviations from a background that, at every point, looks the same in every direction. This has been very successful for understanding and explaining observations of the Universe, but it has been suggested that it may not be entirely sufficient, and that Dark Energy may be the result of interpreting data within an incorrect model. I aim to critically investigate this suggestion, either to bolster the validity of the usual model, or to provide a credible alternative. The third area is Dark Energy from string theory. Many physicists now agree that string theory does not have a single unique vacuum, but very many different possible vacua. Each of these will have different properties, including different types of Dark Energy. If the Universe expanded very rapidly early on, then these different types of vacuum will be realised in different parts of the Universe. If there are enough vacua, and the Universe is big enough, there should be at least one part with a Dark Energy that looks like ours. While this is a promising idea, there are some fundamental difficulties with understanding how likely it is for our type of Dark Energy to be realised. I intend to investigate this area to improve our understanding of these problems, and how they can be resolved. Understanding Dark Energy is of critical importance in our understanding of the Universe, and the research I aim to perform will contribute substantially towards achieving this goal. The existence of Dark Energy provides excellent motivation for improving our understanding of the foundations of our models of the Universe, and, with many new and exciting observational missions planned in the near future, now is the perfect time to perform the research programme I have outlined above.
Organisations
- Queen Mary University of London (Fellow, Lead Research Organisation)
- QUEEN MARY UNIVERSITY OF LONDON (Collaboration)
- UNIVERSITY OF OXFORD (Collaboration)
- UNIVERSITY OF NOTTINGHAM (Collaboration)
- Stockholm University (Collaboration)
- Dalhousie University (Collaboration)
- St. Francis Xavier University (Collaboration)
- University of Cape Town (Collaboration)
- UNIVERSITY OF CAMBRIDGE (Collaboration)
People |
ORCID iD |
Timothy Clifton (Principal Investigator / Fellow) |
Publications
Clifton T
(2013)
A gravitational entropy proposal
in Classical and Quantum Gravity
Clifton T
(2012)
Observational cosmology in macroscopic gravity
in Journal of Cosmology and Astroparticle Physics
Clifton T
(2013)
Exact evolution of discrete relativistic cosmological models
in Journal of Cosmology and Astroparticle Physics
Clifton T
(2012)
Isotropic blackbody cosmic microwave background radiation as evidence for a homogeneous universe.
in Physical review letters
Clifton T
(2012)
Improved treatment of optics in the Lindquist-Wheeler models
in Physical Review D
Sanghai V
(2015)
Post-Newtonian cosmological modelling
in Physical Review D
Sanghai V
(2016)
Cosmological backreaction in the presence of radiation and a cosmological constant
in Physical Review D
Description | I have discovered that a single large under-density is not sufficient to explain the observations attributed to the accelerating expansion of the universe, that cosmological models that contain arbitrarily large density contrasts can approach the behaviour of smooth cosmological models (in appropriate limits), that interaction energies in cosmological models can potentially affect the large-scale expansion of the Universe, that entropy in gravitational fields can potentially be understood in terms of the super-energy-momentum tensor of free gravitational fields, that fourth-order theories of gravity that are used to explain accelerating expansion generically have problems with embedding weak-field systems into cosmology, that the spatial curvature term that is introduced by smoothing over small-scale structure in the Universe can be constrained with observations, that collapse of structure can produce effects that mimic accelerating expansion of the universe, that the microwave background radiation can in principle be used to constrain the geometry of the universe without using the Copernican Principle, and that inhomogeneities can affect luminosity distances and redshifts of distant bodies in the universe in a non-trivial way. |
Exploitation Route | I have pioneered various different methods to explore the effects of inhomogeneity and modified gravity on the expansion of the universe. All of these methods can be explored and extended in future studies. |
Sectors | Other |
Description | My findings have been used to further the understanding of inhomogeneity and modifications to gravity on the large-scale expansion of the Universe. |
First Year Of Impact | 2011 |
Sector | Other |
Impact Types | Societal |
Description | Alan Coley |
Organisation | Dalhousie University |
Department | Department of Mathematics and Statistics |
Country | Canada |
Sector | Academic/University |
PI Contribution | I have performed research in the areas on which we have published papers. |
Collaborator Contribution | He has performed research in the areas on which we have published papers. |
Impact | This collaboration has resulted in two publications in peer reviewed journals. |
Start Year | 2011 |
Description | Anne Marie Nzioki |
Organisation | University of Cape Town |
Country | South Africa |
Sector | Academic/University |
PI Contribution | Calculations |
Collaborator Contribution | Calculations |
Impact | DOI: 10.1103/PhysRevD.87.063517 |
Start Year | 2013 |
Description | Antonio Padilla |
Organisation | University of Nottingham |
Department | School of Physics and Astronomy |
Country | United Kingdom |
Sector | Academic/University |
PI Contribution | I have performed research in the areas on which we have published. |
Collaborator Contribution | He has performed research in the areas on which we have published. |
Impact | We published a paper in a peer reviewed journal. |
Start Year | 2010 |
Description | Chris Clarkson |
Organisation | University of Cape Town |
Department | Department of Mathematics and Applied Mathematics |
Country | South Africa |
Sector | Academic/University |
PI Contribution | I have performed research in the areas on which we have published. |
Collaborator Contribution | He has performed research in the areas on which we have published. |
Impact | We have published three papers in peer reviewed journals. |
Start Year | 2008 |
Description | Constantinos Skordis |
Organisation | University of Nottingham |
Department | School of Physics and Astronomy |
Country | United Kingdom |
Sector | Academic/University |
PI Contribution | I have performed research in the areas on which we have published. |
Collaborator Contribution | He has performed research in the areas on which we have published. |
Impact | We published a paper in a peer reviewed journal. |
Start Year | 2010 |
Description | Daniele Gregoris |
Organisation | Stockholm University |
Country | Sweden |
Sector | Academic/University |
PI Contribution | Calculations |
Collaborator Contribution | Calculations |
Impact | DOI: 10.1088/1475-7516/2013/11/010 |
Start Year | 2013 |
Description | George Ellis |
Organisation | University of Cape Town |
Country | South Africa |
Sector | Academic/University |
PI Contribution | Calculations |
Collaborator Contribution | Calculations |
Impact | DOI: 10.1088/0264-9381/30/12/125009 |
Start Year | 2013 |
Description | Kane O'Donnell |
Organisation | University of Cambridge |
Department | Department of Applied Mathematics and Theoretical Physics (DAMTP) |
Country | United Kingdom |
Sector | Academic/University |
PI Contribution | I have performed research in the areas on which we have published. |
Collaborator Contribution | He has performed research in the areas on which we have published. |
Impact | We published a paper in a peer reviewed journal. |
Start Year | 2011 |
Description | Kjell Rosquist |
Organisation | Stockholm University |
Department | Department of Physics |
Country | Sweden |
Sector | Academic/University |
PI Contribution | I have performed research in the areas on which we have published. |
Collaborator Contribution | He has performed research in the areas on which we have published. |
Impact | We have published a paper in a peer reviewed journal. |
Start Year | 2011 |
Description | Pedro Ferreira |
Organisation | University of Oxford |
Department | Department of Physics |
Country | United Kingdom |
Sector | Academic/University |
PI Contribution | I have performed research in the areas on which we have published. |
Collaborator Contribution | He has performed research in the areas on which we have published. |
Impact | We have published nine papers in peer reviewed journals |
Start Year | 2008 |
Description | Peter Dunsby |
Organisation | University of Cape Town |
Country | South Africa |
Sector | Academic/University |
PI Contribution | Calculations |
Collaborator Contribution | Calculations |
Impact | DOI: 10.1103/PhysRevD.87.063517 |
Start Year | 2012 |
Description | Philip Bull |
Organisation | University of Oxford |
Department | Department of Physics |
Country | United Kingdom |
Sector | Academic/University |
PI Contribution | I have performed research in the areas on which we have published. |
Collaborator Contribution | He has performed research in the areas on which we have published. |
Impact | We have published three papers in peer reviewed journals. |
Start Year | 2011 |
Description | Reza Tavakol |
Organisation | Queen Mary University of London |
Department | School of Physics and Astronomy |
Country | United Kingdom |
Sector | Academic/University |
PI Contribution | I have performed research in the areas on which we have published. |
Collaborator Contribution | He has performed research in the areas on which we have published. |
Impact | We have published a paper in a peer reviewed journal. |
Start Year | 2011 |
Description | Rituparno Goswami |
Organisation | University of Cape Town |
Country | South Africa |
Sector | Academic/University |
PI Contribution | Calculations |
Collaborator Contribution | Calculations |
Impact | DOI: 10.1103/PhysRevD.87.063517 |
Start Year | 2013 |
Description | Robert van den Hoogen |
Organisation | St. Francis Xavier University |
Department | Mathematics and Statistics; St Francis Xavier University |
Country | Canada |
Sector | Academic/University |
PI Contribution | I have performed research in the areas on which we have published. |
Collaborator Contribution | He has performed research in the areas on which we have published. |
Impact | We published a paper in a peer reviewed journal. |
Start Year | 2011 |
Description | Rockhee Sung |
Organisation | University of Cape Town |
Department | Department of Mathematics and Applied Mathematics |
Country | South Africa |
Sector | Academic/University |
PI Contribution | I have performed research in the areas on which we have published. |
Collaborator Contribution | She has performed research in the areas on which we have published. |
Impact | We published a paper in a peer reviewed journal. |
Start Year | 2011 |
Description | Viraj Sanghai |
Organisation | Queen Mary University of London |
Country | United Kingdom |
Sector | Academic/University |
PI Contribution | I have performed research in the areas on which we have published. |
Collaborator Contribution | He has performed research in the areas on which we have published. |
Impact | We have published one paper in a peer reviewed journal. |
Start Year | 2013 |