The story of modern cosmology is a convoluted one. At its core, cosmology attempts to describe an epic tale of evolution-to answer questions about the beginning, growth and possible end of the universe as we know it. Not surprisingly, such knowledge doesn’t come easily. The line between observable reality and fantastically abstract theory is often blurred and constantly shifting. The path to established fact is inevitably strewn with quarks, leptons, supernovae, and black holes.
And according to U of T cosmologist Richard Bond, an internationally respected figure in theoretical astrophysics, there is a recent addition to that list of usual suspects; one that might pave the way to a more coherent understanding of the structure of the universe. Despite its semantic emptiness, the concept of a vacuum is becoming the focus for astrophysicists worldwide.
“The vacuum is at the heart of our lack of understanding about the universe,” noted Bond in a lecture given last week as part of U of T’s University Professor Lecture Series. According to Bond, a mysterious energy thought to be associated with the emptiness of space may be driving the fate of the universe. “If there is a physicist who says he truly understands a vacuum, what he is really saying is that he is not a physicist.”
Known as Omega-Lambda, the tiny and poorly-understood vacuum energy is hoped to help solve a fundamental conundrum in cosmology: is the universe eternally expanding or eventually collapsing? If it is continually expanding, our long-term descendents might not have much to look forward to. “Our ultimate fate would be a cold, cold, cold death,” Bond puts it.
The question is fundamental to understanding the mechanics of the cosmos. A coherent answer will shed light on not only the future, but also on our beginnings. Particularly, how the universe got to be so complex since the early moments of the Big Bang. Over that 14 billion year time period, astronomers know that matter has clumped together to form galaxies, stars, planets and humans. What is less clear is how exactly this has happened.
According to Bond, the answers may reside in an elusive pair: dark matter and dark energy.
Only about five per cent of the universe consists of observable matter. A proportion of the remainder is comprised of so-called dark matter, which invisible to our eyes as it does not emit or reflect light, and is detectable only through its gravitational effects. Fundamentally, “dark matter is holding the universe together,” remarked Bond. It accounts for a significant amount of hidden gravity in the universe, and helps keep current cosmological theories in line with astronomical observation.
But, there are other factors at play. If only observable matter and dark matter existed, the universe should be decelerating in its expansion. But in fact recent observational evidence, particularly high-tech snapshots of supernovae in distant galaxies, is leading astronomers to conclude that the universe is not only expanding but accelerating. This acceleration is often referred to as the cosmological constant, and apparently results from an elusive “dark energy” that seems to be prevalent across the universe.
“Dark energy is distinct from dark matter,” pointed out U of T physicist Amanda Peet, who is working at the frontiers of astrophysics to understand the mechanisms behind dark energy and the accelerating universe. According to Peet, dark energy’s significance to our cosmological understanding can’t be overestimated. “It makes up 70 per cent of the universe,” she noted, and it may be causing the universe to inflate indefinitely.
Peet is an expert in a new field known as string theory, which sees matter and energy as made up of tiny vibrating strings, as opposed to more traditional particles. It is hoped that string theory can help bridge a cosmological ingenuity gap that stubbornly resides at the interface of observational astronomy, mathematics, physics, and computational theory. “[String theory] is the best hope for understanding the fundamental structure of gravity-and gravity is the basis of cosmology,” noted Peet.
Over the next year, U of T will be at the international forefront of string theory research and the quest for cosmological understanding. The Fields Institute at U of T and the Perimeter Institute at the University of Waterloo will be co-hosting a year-long program dedicated to string theory research. Known as The Year of the String, the program will run from September 2004 to June 2005 and will attract speakers and researchers worldwide to contemplate the boundaries of our understanding.
So, just when you were about to concede to confusion and acknowledge ( la Douglas Adams) that The Answer really is 42, cosmologists are now telling us that it just may be Omega-Lambda. But, what was The Question anyway?
The beauty of the cosmological pursuit of knowledge is that, to quote Bond, “the meaning is up to you.”
