Combining precision observations of the recent Universe with laboratory and space-based experiments to test for and constrain 'new physics'.

I propose to continue the work that I began in PhD and study the cosmological implications of `new physics', such as that predicted by modern theories of quantum gravity (e.g. String Theory). I am particularly interested in the possibility that our Universe may be populated by one or more scalar fields, i.e. a new form of matter which takes one particular value at each point in space and time. These scalar fields almost always interact with normal matter, and interactions such as these lead to the variation of one or more of the traditional `constants' of Nature over cosmological scales. I intend to continue my work on developing models, or theories, that allow the `constants' of nature to vary and use these theories to make predictions which can be tested either today or in the near future. In addition to the variation of the `constants', models which feature scalar fields generally predict other small alterations to our generally accepted physical theories. These changes are only large over very small length/time scales, or at very high energies, and often they lie beyond the current reach of laboratory experiments. However, it is possible to detect the sum total of these deviations over very large time scales, such as the lifetime of our Universe. It is for this reason that precision observations of the recent Universe provide an invaluable test-bed for `new physics'. Variation of the constants has been the subject of a lot of recent interest because a) a number of recent observations of quasar seem to support the idea that at least two of the constants have indeed changed over the last 10-12 billion years, and b) it offers a mechanism to explain why the constants in our part of the universe take values that are very suited for life as we understand. Theories that allow for varying-constants make highly testable predictions. In addition to developing varying-constant theories, I intend to combine the latest precision observations of the recent Universe with the ever-improving data coming from laboratory and solar system based experiments to test the predictions of varying-constant theories and in so doing to place tighter and tighter constraints on theories that predict new physics. This is a very exciting time to study varying constants because, thanks to results that I proved in my PhD thesis, astronomical observations imply that the next generation of laboratory experiments should detect a variation in at least two of the fundamental 'constants' of nature. From the top of the tower of Pisa, Galileo famously pronounced that all objects fall at the same rate provided there is no air resistance: this is the Equivalence Principle. Another detectable prediction of new physics is that, against the expectations of Galileo, bodies fall at different rates depending on their composition and the Equivalence principle is violated. These violations would be caused by scalar fields that interact with normal matter. Since these scalar fields have never been found, scientists believe their interactions with matter to be extremely weak. Although it may seem counter-intuitive, I have recently demonstrated that the reason one has not seen these scalar fields in experiments could well be that, rather than being weak, their interaction with matter is extremely strong! This result might lead to a completely different view of the role that scalar fields play in our Universe, and I also propose to further investigate its potentially important implications.