When time began: mapping the earliest moments of our universe
Dr Sam Wong (Croucher Fellowship 2017) studies cosmology and particle theory. Between the two fields, his research extends from the smallest known particles in existence to the massive system they have created: our entire universe.
Wong’s interest in the universe was sparked by childhood curiosity. “I recall asking my kindergarten teacher where the earth came from,” he said. He was disappointed not to get an answer, and years later decided to pursue the question himself, as a theoretical physicist.
“I am always amazed by how physics describes the world with precise and quantitative theories,” he said.
After receiving a PhD in theoretical physics from Hong Kong University of Science and Technology, Wong undertook post-doctoral research at Columbia University in the United States. Since 2019, he has continued his post-doctoral research into cosmology and black holes, at the University of Pennsylvania.
“Broadly speaking, I study the early universe,” Wong explained. “The first thing we ask is, where did we come from? What is this entire universe made of?”
Theoretical physics is a balance of creating new theories and proving others. As a researcher, Wong is interested in pursuing both. “On the one hand it is always exciting to build up new physical theories but, on the other hand, we are always thrilled to see experiments verifying predictions of theories,” he said.
While archeologists can reimagine the past from fragments of pottery and bone, Wong depends on mathematical deduction and theorising to reconstruct our universe’s beginning, some 13.8 billion years ago. What most people call the Big Bang is known to physicists as the “inflation”, Wong said, “because the universe was expanding very rapidly in the beginning”.
Most of the scientific community has accepted the following sequence of events, Wong explained. “At the beginning, our entire universe was even smaller than an atom. Fuelled by vacuum energy, this tiny point explodes and cools down into our entire universe.”
The closer to the Big Bang, the stronger the gravity. In scientific terms, spacetime is strongly curved during inflation. An analogous environment is the vicinity of black holes in which gravity is extremely strong, such that even light cannot escape. “Simply speaking, we can use black hole physics to study fundamental laws of nature,” Wong said.
Wong’s work to comprehend the early universe includes examining the impact on the laws of physics and the four known fundamental forces: gravity, electromagnetic pull, strong interactions, and weak interactions.
“Gravity is the earliest discovered fundamental force and yet it is the least understood among [them],” he said. “Strong gravity regions like black holes and the Big Bang provide a great environment to study gravity and [its] effects on fundamental particles.”
Based on Einstein’s general theory of relativity, black holes are recognisable from three basic categories of data: mass; electric charge; and angular momentum. Otherwise, there is nothing to tell one black hole apart from another.
Wong’s work with researchers at Columbia University has focused on finding differentiating characteristics that separate black holes from one another. “We want to see if there is a special signature from the type of gravitational wave emitted from a black hole so we can distinguish different types of fundamental theory,” he added.
Last year, Wong and fellow researchers at Columbia University showed how black holes develop something known as “scalar hair”, by studying a supermassive black hole at the centre of the M87 galaxy. This “hair” is information about the individual black hole beyond the three data categories. The work was published in the Journal of Cosmology and Astroparticle Physics.
“Another project I did at Columbia [involved] extracting signatures from these correlation functions to learn about properties of the underlying fundamental theory,” Wong said. “We came up with a test for the symmetries of these theories.”
For physicists, fundamental theory is the one explanation that encompasses everything in the universe and provides all the answers to our questions. “There are different types of fundamental theories,” Wong noted. “But they all try to explain what we see in the cosmic microwave background.”
The cosmic microwave background, known as CMB, is electromagnetic residue from the start of the universe. It is a legacy written in radiation of the first flash of light to illuminate the early universe during the Big Bang. The flash has since been warped and stretched by space’s steady expansion.
All other information about how black holes are formed and what they consume has been lost to the void. “Black holes are very heavy and dense,” Wong said. “You can imagine 10 times the mass of the earth condensed into a region that is smaller than a basketball.” In this dark space, even light falls into the black hole’s gravitational pull.
Studying black holes is one way to learn more about our origins. Learning about the particles that make up the universe is another. “The study of the early universe is actually very promising in telling us about new particles,” Wong said.
New particles must exist because scientists have documented phenomena that cannot occur without interactions with particles other than the ones we already know. "If we believe that everything is built from fundamental particles, dark matter must be built from some kind of fundamental particles as well," Wong explained. "But we just don’t know what they are."
Researching these particles is an exercise in theory and deduction. By subtracting all the matter made from known particles in the universe, physicists are left with a quantity that is presumed to be a placeholder for as yet undiscovered types of particles. As technology advances, researchers hope that their identities will be uncovered.
In the meantime, questions abound, some being tackled with the help of the world’s largest and most powerful particle accelerator - CERN’s Swiss-based Large Hadron Collider. “We know that we are all made of matter but whenever we collide particles in the LHC, we produce matter and antimatter in equal quantities. In our universe, five per cent of matter is visible while the amount of antimatter is actually negligibly small so that leaves us with the question: what happened in the early universe? Why do we have so much more matter today compared to antimatter today?”
There should be a particle theory to explain this inequality, but it hasn’t been found – yet. As Wong and his colleagues continue their studies of black holes, who knows what answers lie at their centres?
Dr Sam Wong received his BSc in Physics from Hong Kong University of Science and Technology (HKUST) in 2011. He undertook a PhD in theoretical physics at HKUST, working with Professor Henry Tye, a pioneering string cosmologist. After receiving his PhD in 2017, he became a postdoctoral researcher at Columbia University, US. Since 2019, he has continued his explorations of the universe as a post-doctoral researcher in the Department of Physics and Astronomy at the University of Pennsylvania. He received his Croucher Fellowship in 2017.
To view Dr Wong’s Croucher profile, please click here.