Our universe is a vast expanse, and while we can stare up at the night sky and wonder at the mysteries our sky holds, there is so much more that we can’t see with just our eyes. Using today’s powerful telescopes, combined with our computational ability to interpret enormous amounts of data, we are now at a time when cosmologists can do more than just look upon our skies with wonder – they can now make measurements, and calculate theoretical models of the far reaches in our observational universe.
For postdoctoral fellow Alex Krolewski, who has been awarded the 2020 AMTD Postdoctoral Fellowship in Science, analyzing the universe quantitatively is an opportunity to test some of the standard models of physics on astronomical scales.
“I’m specifically interested in testing Einstein’s theory of General Relativity because we want to see if it works on all the scales in the universe. Also, looking at General Relativity may give us clues on what is going on with dark energy.”
Krolewski is just starting his 3 year postdoctoral fellowship in physics and astronomy at the University of Waterloo, where the AMTD fellowship will make it possible to work closely with collaborators around the world. The AMTD Fellowship is a new initiative to create a unique postdoctoral program bringing together world-class scholars from top universities across the globe.
“I’m super excited about the travel support that the AMTD fellowship offers,” says Krolewski. “Astronomy depends on collaborating with a variety of people from widely separated places, and once we are able, I look forward to being able to visit collaborators around the world.”
Krolewski chose to come to Waterloo because of the countless opportunities for collaboration within the physics community in the region. Between the University of Waterloo and its newly established Centre for Astrophysics, and the Perimeter Institute, Waterloo Region is an outstanding hub for physics collaboration.
During his time at Waterloo, he will be working with physics and astronomy professor Will Percival, who is currently involved with multiple large-scale surveys of the galaxies in our universe. In particular, Krolewski plans to use data from the Dark Energy Spectroscopic Instrument (DESI), which he has already been involved with during his PhD at University of California, Berkeley. DESI is a global collaboration that is observing about 40 million different galaxies, and measuring their position and the speed at which they are moving away from the Earth.
In order to put General Relativity and other recent cosmological measurements to the test, Krolewski will be looking at the background signal of the early universe – the Cosmic Microwave Background (CMB). This is the earliest source of light we can measure because it was the first radiation to escape from the early universe. As this microwave radiation travels across the expanses of space and time, the light’s path is deflected by the gravitational fields it passes. This is known as gravitational lensing. By measuring the gravitational lensing of light, cosmologists can calculate the position and density of mass that deflected the light.
Krolewski will use DESI’s measurements of galaxies, alongside a variety of other data sets to measure the gravitational lensing that the CMB radiation experiences passing by the galaxies. Through this research, he hopes to learn about and answer the questions “What causes the universe’s expansion to accelerate” and “What is the mass of the neutrino?”. Neutrinos are small subatomic particles that do not have a charge, and usually pass through normal matter undetected. Since they are usually undetectable, one of the only ways to learn about neutrinos is to observe their impact on the distribution of matter and galaxies in the universe.
Measuring gravitational lensing will provide a large-scale system to test gravity and General Relativity, and also may resolve some inconsistencies between cosmological measurements in the distant universe and the local universe. Additionally, gravitational lensing measurements from DESI may also provide some clues to the universe’s biggest unknown component – dark energy, a force that is currently theorized to make up 70% of all the energy in the universe and causes the accelerated expansion of our universe, but is completely unknown.