Extrait du Journal des Jeunes

Throwing Einstein for a Loop

Physicist Fotini Markopoulou Kalamara has developed a way to connect relativity with quantum theory--while making sure that cause still precedes effect

By Amanda Gefter

She talks about physics like it's cooking. "My strength is to put things together out of nothing," she says, "to take this ingredient and another one there and stick something together." The art is figuring out which ones to use and how to combine them so that when the oven bell dings, the universe comes out just right.

At 31 years old, Fotini Markopoulou Kalamara is hailed as one of the world's most promising young physicists. She recently accepted a position at the Perimeter Institute for Theoretical Physics in Waterloo, Ontario (Canada's answer to the Institute for Advanced Study in Princeton, N.J.). There she works alongside such prominent physicists as Robert Myers and Lee Smolin, hoping to blend Einstein's general relativity with quantum theory to explain the nature of space and time.

This unification is probably the single greatest challenge of modern physics. String theory has been the predominant contender. It proposes that the building blocks of matter are tiny, one-dimensional strings and that various vibrations of strings play the familiar medley of particles as if they were musical notes.

Although string theory finds a way to incorporate gravity into a quantum description of matter, some physicists believe that it has shortcomings that prevent it from being the ultimate theory of everything. For one, the theory presupposes up to 26 spatial dimensions, many more than have yet to be experimentally discovered. More fundamental still, whereas strings are fine for describing matter, they do not explain the space in which they wiggle. Newer versions of string theory may fix this problem. But a small band of physicists, including Smolin, Abhay Ashtekar of Pennsylvania State University and Carlo Rovelli of the Theoretical Physics Center in Marseilles, France, place greater stock in a different approach: loop quantum gravity, or LQG.

In LQG, reality is built of loops that interact and combine to form so-called spin networks-- first envisioned by English mathematician Roger Penrose in the 1960s as abstract graphs. Smolin and Rovelli used standard techniques to quantize the equations of general relativity and in doing so discovered Penrose's networks buried in the math. The nodes and edges of these graphs carry discrete units of area and volume, giving rise to three-dimensional quantum space. But because the theorists started with relativity, they were still left with some semblance of a space outside the quantum networks.

That was the state of LQG in the late 1990s, when Markopoulou Kalamara began tackling it. Serendipity actually led her to the subject. "I only decided on physics when I was 16 or 17," says the theorist, who is from Athens, Greece. "Before that, I wanted to be all sorts of things: an archaeologist, an astronaut, a painter." While she was an undergraduate at the University of London, a friend taking theoretical physics recommended lectures being given by quantum-gravity theorist Chris Isham of Imperial College London. "It was on my way home, so I went once a week, and I loved it." She convinced Isham to be her adviser and wound up with a Ph.D. in quantum gravity. She then joined Smolin at Penn State as a postdoctoral fellow.

Markopoulou Kalamara approached LQG's extraneous space problem by asking, Why not start with Penrose's spin networks (which are not embedded in any preexisting space), mix in some of the results of LQG, and see what comes out? The result was networks that do not live in space and are not made of matter. Rather their very architecture gives rise to space and matter. In this picture, there are no things, only geometric relationships. Space ceases to be a place where objects such as particles bump and jitter and instead becomes a kaleidoscope of ever changing patterns and processes.

Each spin network resembles a snapshot, a frozen moment in the universe. Off paper, the spin networks evolve and change based on simple mathematical rules and become bigger and more complex, eventually developing into the large-scale space we inhabit.