Princeton Meeting Honors Wheeler's Contributions to Physics

"Science and Ultimate Reality," a meeting about forefront theoretical and experimental physics, was held at Princeton, 15-18 March, in honor of John Wheeler's 90th birthday and his many contributions to quantum mechanics, cosmology, and information science.

The Princeton meeting served up an impressive menu of hot topics and notable speakers, including the subject of decoherence, the process by which a quantum system converts to a classical system by subtle but often swift interactions with the surrounding environment; the many-worlds interpretation of quantum mechanics, according to which a quantum system does not suffer a "collapse of probability", but the universe itself continues to bifurcate into multiple versions corresponding to the many possible histories available to the quantum system as it moves through space-time; and the entanglement of ions in an atom trap for the purpose of forming logic gates for a future quantum computer.

At the heart of the meeting was the keynote speech by the always interesting Anton Zeilinger (Vienna), who paid tribute to John Wheeler's many physics insights. One of those ideas was a proposal for a "delayed choice" experiment in which the dissipation of wavelike interference effects brought about by the experimenter's efforts to determine which of several possible paths a particle took in going toward a detector might be avoided by delaying the observation of the path until the particle (or wave) had made its mark. Zeilinger has carried out just such an experiment with entangled photons in a setup he referred to as a "Heisenberg microscope."

Several speakers addressed the persistent problem of bringing quantum mechanics and general relativity into a single framework. Prominent issues here include the fate of information supposedly lost inside black holes; comparisons of string theory with the rival quantum loop gravity theory, which holds that space is not a mere platform for interactions but is itself a sort of dynamical thing; how gravity behaves in extra dimensions; and the effort to detect gravity waves.

One purpose of the meeting was to promote freewheeling debate on all of the above issues, including the role of human consciousness in the measurement process. Young scientists were especially encouraged to engage in this debate, for which scholarships were given for attending the meeting. In fact, a Young Researchers Competition was held for papers on quantum reality. The joint winners, from among 64 entries, were Raphael Bousso from UC Santa Barbara and Fotini Markopoulou-Kalamara from the University of Waterloo in Canada.

— Phillip F. Schewe