Three Roads to Quantum Gravity by Lee Smolin

Author:Lee Smolin [Smolin, Lee]
Language: eng
Format: epub, mobi, pdf
Publisher: Orion
Published: 0101-01-01T00:00:00+00:00

CHAPTER 10

KNOTS, LINKS AND KINKS

During the year I was working with Louis, a young postdoc named Amitaba Sen published two papers which excited and mystified many people. We read them with a great deal of interest, for what Sen was doing was attempting to make a quantum theory from supergravity. Embedded in the papers were severed remarkable formulas in which Einstein’s theory of gravity was expressed in a much simpler and more beautiful set of equations than Einstein had used. Several of us spent many hours discussing what would happen if we could somehow find a way to base quantum gravity on this much simpler formulation. But none of us did anything at the time.

The one person who took Sen’s equations seriously was Abhay Ashtekar. Abhay had been trained as a classical relativist, and early in his career had done important work in that area, but more recently he had set his sights on a quantum theory of gravity. Being mathematically inclined, Ashtekar saw that Sen’s equations contained the core of a complete reformulation of Einstein’s general theory of relativity, and by a year later he had done just that: fashioned a new formulation of general relativity. This did two things: it vastly simplified the mathematics of the theory, and expressed it in a mathematical language which was very close to that used in QCD. This was exactly what was needed to transform quantum gravity into a real subject, one in which it would in time become possible to do calculations that yielded definite predictions about the structure of space and time on the Planck scale.

I invited Abhay to give a talk about this at Yale, where I had just become an assistant professor. At the talk was a graduate student named Paul Renteln, from Harvard, who had also been studying Sen’s papers. It was clear to us that Ashtekar’s formulation would be the key to further progress. Afterwards, I drove Abhay to the airport in Hartford. On the hour’s drive between New Haven and Hartford my car had not one but two flat tyres – and Abhay still just caught his flight. He had to hitch a ride for the last few miles, while I waited on the side of the road for help.

When I finally got home I sat down immediately and began to apply to the new formalism of Sen and Ashtekar the methods Louis Crane and I had developed during our unsuccessful attempts to re-invent string theory. A few weeks later there began a semester-long workshop in quantum gravity at the Institute for Theoretical Physics in Santa Barbara. By another piece of luck, I had convinced the authorities at Yale to let me spend a semester there, just after they had hired me. As soon as I got there I recruited two friends, Ted Jacobson and Paul Renteln. We found right away that a very simple picture of the quantum structure of space emerged if we used something very like the electric superconductor picture for the flux lines of the gravitational field.

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