Motivated by the observation that excursions into the history of physics often inform, and are informed by a deeper understanding of fundamental physics questions, the FHP inaugurated a new genre of session at this year’s March Meeting where speakers were invited to debate a foundational question of general interest to physicists. A natural topic for the debut of this class of session was “How Should We Interpret the Formalism of Quantum Mechanics?”

In front of a standing-room-only crowd that indicated the wide appeal of a foundational session of this type, Seth Lloyd began the presentations by elaborating on his conception of the “The Universe as Quantum Computer.” Lloyd described a generalized path integral formulation of how a universe – any universe – can evolve through all its possible quantum states in an algorithmic fashion. Lloyd pointed towards how, by understanding the ensemble of possible evolutions for these universes, how one can glean the semi-classical origins of laws of nature.

Sean Carroll, speaking remotely to the audience due to a canceled flight, explained that his intent was to distinguish between real and imagined problems with the many-worlds interpretation he advocates. Listing some conventional axioms of quantum mechanics Carroll pointed out that, despite its reputation as an ontologically profligate approach, the many-worlds view is more parsimonious than many other quantum interpretations in relying on the fewest number of axiomatic assumptions. While conceding that work needed to be done to make some of the conclusions of these reduced axioms intelligible, Carroll emphasized that certain objections to the meaning and significance of continually branching of worlds can already be met.

Recounting that most interpretations of quantum mechanics invoke the notion of an observer, Carlo Rovelli began his advocacy for a relational quantum viewpoint by reminding the audience of the many ways physicists are comfortable with relative thinking. The velocity of an object is not an absolute quantity, but one whose varying values we know how to translate from reference frame to reference frame. So also, we should not be afraid of quantum interpretations, such as information theoretic ones, where different observers can have different descriptions of the same system. In Rovelli’s approach, by formulating how to translate between such descriptions, we can then make progress towards an understanding of quantum mechanics that has no privileged role for any observer.

Wojciech Zurek used the final speaking slot to emphasize that the strides he and others have made in understanding decoherence and environmentally induced selection (“einselection”) of a measured quantum state are not enough to fully grasp what is going on in a quantum measurement. To go further, we should focus on which pieces of information a quantum mechanically described object can repeatedly imprint on the environment it interacts with. Through a process Zurek terms “quantum Darwinism” the robust information repeatedly imprinted wins out exceedingly rapidly over the other, stranger aspects of quantum states, leaving the environmental record and any observer who inspects it with only the more classical aspects of the object’s existence. Zurek touted as one major virtue of this process its compatibility with any of the commonly debated quantum interpretations.

The articles in this issue represent the views of their authors and are not necessarily those of the Forum or APS.