Nobel laureate Leon Lederman and modern cosmology share a common goal - to understand how symmetry governs the universe, writes Dick Ahlstrom.
Apples falling from a tree, the rise and fall of the tide and the interaction between galaxies are all part of a symmetry that makes our universe what it is. Symmetry represents simplicity and simplicity is a beautiful concept, stated Nobel laureate for physics, Prof Leon Lederman.
"What symmetry does for you ultimately is give you an understanding of complexity," he said last night during his Academy Times lecture in the arts block of Trinity College Dublin. His talk, jointly organised by The Irish Times and the Royal Irish Academy, and sponsored by DEPFA Bank, perfectly reflected its title, "The Search for Simplicity in the Universe".
His mission was to ask the fundamental question, "how does the world work?", a short question with a difficult answer.
Lederman took his appreciative audience on a tour of the universe and also on a visit to the inside of an atom, two parts of a greater symmetry, he suggested. His goal was to demonstrate "inner space, outer space connections", a topic of considerable interest to modern physicists.
Researchers around the world study cosmology and astrophysics in the search for answers to questions about the origins of the universe and how it all started after the big bang. The same answers are sought on the other side of this coin, in particle physics research centres such as Fermilab in the US and CERN in Europe. Atom smashers are used to create the kinds of energies and resultant particles seen moments after the big bang occurred and space-time began.
"There is a connection that is important between the two," he said. "Cosmologists need a bit of help modelling the beginning of the universe."
But his talk returned again and again to one word: symmetry. "What it means is if I made an operation on a system, it doesn't change."
He used gravity as an example, noting that an apple falling from a tree and the interactions between galaxies must all obey the demands of gravity and respond accordingly.
"All of these things are explained by the single statement which is Newton's law of gravity. There is complexity out of simplicity and gravity is symmetry," he stated. "Symmetry is invariant. If it is variant it changes, if it is invariant it has symmetry."
Symmetry now "dominates all thinking" in modern physics research, according to Lederman, a former director of the Fermi National Accelerator Lab, and winner of a Nobel Prize in 1988. "It is a search for simplicity and beauty," but it remains a challenge given there are different forms of symmetry.
Matter and antimatter form a symmetry. They are very different but together they form a system that has symmetry.
There is also mirror symmetry seen when you hold a mirror up to apparently produce an alternative mirror world. Mirror symmetry brings with it a "handedness" that is opposite but equal to the real world.
Many advances in physics grew from discoveries that a system somehow apparently violated symmetry. He recollected "one exciting weekend" when T.D. Lee and C.N. "Frank" Yang, then at Princeton in the US, proposed that in certain situations mirror world symmetry might not exist. If applied, the proposition allowed them to solve problems that had previously been insoluble.
They suggested that the symmetry between physical phenomena occurring in right-handed and left-handed co-ordinate systems is violated when certain elementary atomic particles decay. "We discovered that there were particles that didn't obey mirror symmetry," said Lederman. "They tried to recover the beauty by getting back the symmetry." Since then, the challenge has been to find and understand these apparent violations of symmetry.
Lederman concluded his talk with current examples of this puzzle faced by cosmologists trying to explain what we know about the universe. The issue is not to discover how things are, but rather why they are that way, he says. One of the greatest conundrums is the so-called "dark energy" that is driving the continual expansion of the universe. "Nobody has a clue as to what it is," says Lederman.