Quantum Physicist Speaks on
Possibility of Space/Time Atoms

With fresh approaches to quantum gravity, the big questions about the beginning of the universe and the possibility of time and space as particles—once thought "existential in nature"—are now seriously being considered.

Einstein's theory of relativity might not be completely accurate, according to physicist Fotini Markopoulo Kalamara with the Perimeter Institute for Theoretical Physics, who will present a topical lecture today at the American Association for the Advancement of Science (AAAS) Annual Meeting.

Einstein claims that massive stars will collapse into black holes once they've burned up all of their energy sources. But, these black holes are still a mystery. This is where Markopoulo Kalamara's specialty, quantum gravity, comes into place.

"We need a new theory to replace the theory of general relativity, so we can understand what's going on inside the black hole," she said.

Markopoulo Kalamara, a young, up-and-coming scientist, presents a fresh approach to researching theoretical possibilities for looking inside black holes and at particles of space/time.

General relativity claims that in the universe, space and time are woven into a single fabric: space/time. Matter causes space/time to curve, but in turn, that matter's motion and properties are altered by that curvature. And, because we are part of space/time, anything we do changes the universe because, according to the theory, mass affects the shape of space/time. Therefore, according to Markopoulo Kalamara, space/time is really just a network of simple, but vast relations.

To better explain her theory of a quantum gravity-based universe, Markopoulo Kalamara depicts two circles, as shown above. The first circle has a line running along its diameter. This circle (left) represents space/time and the line running through the diameter represents space. As observers, we look at the circle as a whole. This is the worldview of a quantum theory of gravity that tries to deal with all of space at once; the most common approach to constructing a quantum theory of gravity.

An alternative worldview is in the depiction of a second circle (right). In this circle, we observe space/time and space from within it, and can see only part of the whole space.

Markopoulo Kalamara therefore proposes that an "inside" quantum theory of gravity should be the collection of all the partial observations of the inside observers.

The problem with Einstein's universe is that it lacks an underlying quantum theory. Physicists now believe that quantum physics is more fundamental than classical physics. As with all forces in nature, except for gravity, there is a classical theory and a fundamental quantum theory.

For example, electromagnetism is a classical theory, and underlying electromagnetism, is quantum electrodynamics. Markopoulo Kalamara and her colleagues do not think that gravity should be exempt from this pattern. Classically, Einstein's theory of general relativity describes gravity, but what is yet to be found is the underlying theory, quantum gravity.

Current attempts to construct a quantum theory of gravity spoil the neatly packaged property of relativity that holds that all physics should describe observations made by observers inside the universe. Instead, creating a theory of quantum gravity seems to pull an observer outside the universe.

Markopoulo Kalamara proposes a way to solve this by constructing a universe that is a collection of all the observations of all the observers inside it, which works best if atoms of space/time exist.

"Space and time are not at all our daily intuitive notions of three-dimensional space surrounding us and the time of our clocks; scientists want to know what space and time really are, and we do not yet know that," she said.

The tiny scale at which the microscopic structure of space and time becomes observable is the Planck scale. To get an idea of how small that is, imagine the ratio between the size of the earth and the size of a nucleus. The nucleus is a 100 trillion trillion times smaller than the earth. Now go down another 100 trillion trillion times: this is the Planck scale, where our understanding of space and time breaks down.

Yes in spite of the amazingly tiny scale, researchers can still do testable science. "Consider matter; we know that matter is made of atoms," she said. "However, scientists in the 1900s did not know that and were doubtful that we could ever test atomic theories of matter. The situation is similar with space and time. Are there atoms of space/time, and if so, can we 'see' them?"

Fotini Markopoulo Kalamara received her Ph.D. from Imperial College in 1998 and recently shared First Prize in the Young Researchers competition at the Ultimate Reality Symposium in Princeton, New Jersey. Previous postdoctoral positions were held at the Albert Einstein Institute, Imperial College London, and Penn State University.

15 February 2003