To answer John Wheeler's ``Really Big Question,'' ``Why the quantum?'' via quantum information theory according to Bub, one must explain both why the world is quantum rather than classical and why the world is quantum rather than superquantum, i.e., ``Why the Tsirelson bound?'' We propose an answer to these questions based on the assumption that the world is not ``quantum rather than classical'' (reductionism) but is fundamentally both (quantum-classical contextuality), as constrained by conservation principles from the spacetime symmetry group. We illustrate this using the spin singlet state and the `Mermin photon state', which uniquely produce the Tsirelson bound for the Clauser-Horne-Shimony-Holt (CHSH) quantity, showing how quantum correlations satisfy conservation of angular momentum for binary (quantum) outcomes while both classical and superquantum correlations violate this constraint. Accordingly, as Unnikrishnan has pointed out, expecting the Bell inequality to be satisfied for quantum outcomes per classical probability theory means abandoning the conservation of angular momentum. Thus, that experiments have produced violations of the Bell inequality up to the Tsirelson bound and not beyond can be explained by conservation of angular momentum for quantum outcomes per quantum-classical reality as constrained by the spacetime symmetry group.
This is a link to our OUP Blog post, "Ascending to the god's-eye view of reality."
A recurring theme in natural philosophy is the tension between the God's-eye view of reality comprehended as a whole and the ant's-eye view of human consciousness, which senses a succession of events in time. Since the days of Isaac Newton, the ant's-eye view has dominated fundamental physics. We divide our description of the world into dynamical laws that, paradoxically, exist outside of time according to some, and initial conditions on which those laws act. The dynamical laws do not determine which initial conditions describe reality. That division has been enormously useful and successful pragmatically, but it leaves us far short of a full scientific account of the world as we know it. The account it gives – things are what they are because they were what they were – raises the question, Why were things that way and not any other? The God’s-eye view seems, in the light of relativity theory, to be far more natural. Relativity teaches us to consider spacetime as an organic whole whose different aspects are related by symmetries that are awkward to express if we insist on carving experience into time slices. Hermann Weyl expressed the organic view memorably in his 1949 book Philosophy of Mathematics and Natural Science (Princeton University Press, page 116):
"The objective world simply is, it does not happen. Only to the gaze of my consciousness, crawling upward along the life line of my body, does a section of this world come to life as a fleeting image in space which continuously changes in time."
To me, ascending from the ant’s-eye view to the God’s-eye view of physical reality is the most profound challenge for fundamental physics in the next 100 years.
Frank Wilczek: Physics in 100 Years. Physics Today 69(4), 32-39 (2016).
Theoretical physics and foundations of physics have not made much progress in the last few decades. Whether we are talking about unifying general relativity and quantum field theory (quantum gravity), explaining so-called dark energy and dark matter (cosmology), or the interpretation and implications of quantum mechanics and relativity, there is no consensus in sight. In addition, both enterprises are deeply puzzled about various facets of time including above all, time as experienced. The authors argue that, across the board, this impasse is the result of the “dynamical universe paradigm,” the idea that reality is fundamentally made up of physical entities that evolve in time from some initial state according to dynamical laws. Thus, in the dynamical universe, the initial conditions plus the dynamical laws explain everything else going exclusively forward in time. In cosmology, for example, the initial conditions reside in the Big Bang and the dynamical law is supplied by general relativity. Accordingly, the present state of the universe is explained exclusively by its past. This book offers a completely new paradigm (called Relational Blockworld), whereby the past, present and future co-determine each other via “adynamical global constraints,” such as the least action principle. Accordingly, the future is just as important for explaining the present as is the past. Most of the book is devoted to showing how Relational Blockworld resolves many of the current conundrums of both theoretical physics and foundations of physics, including the mystery of time as experienced and how that experience relates to the block universe.