Research: Other Research Projects

The Theology and Philosophy of Creation

I am interested in questions of natural theology, or philosophical theology, especially as they regard creation. This is one of my areas of focus during my graduate studies in theology.

Along these lines, a few years ago I was part of an academic collaboration that brought together theologians to explore the doctrine of creation from nothing (CEN) in the light of modern research in Biblical studies, patristics, philosophy, systematic theology and natural science. My own role was to articulate the state of contemporary physical cosmology to give context to the metaphysical claims of CEN. The project culminated in a book published in 2018: Creation Ex Nihilo: Origins, Development, Contemporary Challenges.

Relativistic Sunyaev-Zeldovich Effect

The SZ cluster..
A 2×2 degree patch of the CMB as measured by ACT, in which a large galaxy cluster has left an imprint via the SZ effect (circled). (Image taken from Fig. 5 of Louis et al., 2017).

Clusters of galaxies, which are the largest gravitaionally-bound objects in the Universe, contain diffuse, hot gas that interacts with the cosmic microwave background (CMB) radiation, leaving a distinctive signature. This is called the Sunyaev-Zeldovich (SZ) effect. The gas in these clusters is very hot—tens of millions of degrees—which means that the electrons that cause the SZ effect are travelling at a significant fraction of the speed of light and thus, for full precision, need to be described with special relativity. This creates a small but measureable change to the SZ signal that depends on the gas temperature. With colleagues in Europe, I am attempting to measure this effect in the clusters observed by the Planck satellite.

Past Projects

The Canadian Hydrogen Intensity Mapping Experiment

Photograph of the CHIME Pathfinder.
The CHIME Pathfinder. (Credit: Andre Recnik)

For a couple of years I was heavily involved in the Canadian Hydrogen Intensity Mapping Experiment (CHIME), a radio telescope in British Columbia. It seeks to explore one of the biggest puzzlers in contemporary cosmology: the fact that not only is the Universe expanding, but that it is speeding up. Something is counteracting gravity's attraction. Typically, this mysterious force is called ‘dark energy’, but this is little more than a name for our ignorance.

CHIME is designed to shed light on the nature of dark energy. It consists of four, 100-metre-long and 20-metre-wide cylinders, populated with a total of 1024 dual-polarisation radio antennas. Using this huge collecting area—eight thousand square metres—CHIME should be able to measure the radio waves emitted by billions of years ago by the clouds of hydrogen dispersed throughout distant galaxies. This signal is an excellent proxy for the distribution of matter at a given epoch in cosmological history: in particular, it should be possible to detect a higher-than-average density of matter on physical scales of about 500 million light years. We know this length scale quite precisely, since it was fixed very early on in the universe's history and can be calculated from the well-understood physics of the sound waves in the dense plasma which emerged from the big bang. However, the observed scale on the sky depends on the history of cosmic expansion between us and the emitting hydrogen. Thus, it is in principle possible for CHIME to measure how the rate of expansion has been evolving over a significant fraction of the universe's history.

The size of the signal emitted by cosmic hydrogen is so small that the amount of energy it will impart to CHIME in one year is roughly comparable to the energy it takes to lift a paperclip one millimetre off the ground! But with modern technology it should actually be possible to detect this signal. To do so, CHIME is pushing current computational power to the brink, in order to digitise and process the two trillion samples per second that pass through its electronics.

CHIME is also an excellent telescope for many types of radio astronomy. In 2018, it detected its first fast radio burst: an example of mysterious, high energy events that is an active area of research in astronomy today.

External Links of Interest

Cross-Correlating Cosmological Datasets

The scientific value of astronomical observations is more than the sum of many parts. Maps from projects like ACT and CHIME can be compared with maps of the same region of the sky observed with other experiments at other wavelengths of light. Such a comparison can provide a rigorous way of characterising objects or classes of objects that are present in both map—for example, by correlating ACT maps with radio galaxy positions or with BLAST maps one can figure out important statistical properties of distant galaxies.

A few years ago I was involved in a project which studied the spatial correlation between clusters of galaxies and dusty galaxies. We were able to make a very high-significance measurement of this cross-spectrum using IRIS and maxBCG data.

Various and Sundry

Saturn model.
A simple model of Saturn used for measuring the average ring temperature in radio frequencies.