Quantum mechanics, through the Heisenberg uncertainty principle, imposes limits on the precision of measurement. Conventional measurement techniques typically fail to reach these limits. Conventional bounds to the precision of measurements such as the shot noise limit or the standard quantum limit are not as fundamental as the Heisenberg limits and can be beaten using quantum strategies that employ “quantum tricks” such as squeezing and entanglement.

Quantum-enhanced measurements: beating the standard quantum limit.

Richard Rorty's Philosophy and the Mirror of Nature brings to light the deep sense of crisis within the profession of academic philosophy which is similar to the paralyzing pluralism in contemporary theology and the inveterate indeterminacy of literary criticism. Richard Rorty's provocative and profound meditations impel philosophers to examine the problematic status of their discipline— only to discover that modern European philosophy has come to an end. Rorty strikes a deathblow to modern European philosophy by telling a story about the emergence, development and decline of its primary props: the correspondence theory of truth, the notion of privileged representations and the idea of a self-reflective transcendental subject. Rorty's fascinating tale—his-story —is regulated by three fundamental shifts which he delineates in detail and promotes in principle: the move toward anti-realism or conventionalism in ontology, the move toward the demythologizing of the Myth of the Given or anti-foundationalism in epistemology, and the move toward detranscendentalizing the subject or dismissing the mind as a sphere of inquiry. The chief importance of Rorty's book is that it brings together in an original and intelligible narrative the major insights of the patriarchs of postmodern American philosophy—W. V. Quine, Wilfred Sellars, and Nelson Goodman— and persuasively presents the radical consequences of their views for contemporary philosophy. Rorty credits Wittgenstein, Heidegger and Dewey for having "brought us into a period of 'revolutionary' philosophy" by undermining the prevailing Cartesian and Kantian paradigms and advancing new conceptions of philosophy. And these monumental figures surely inspire Rorty. Yet, Rorty's philosophical debts—the actual sources of his particular anti-Cartesian and antiKantian arguments—are Quine's holism, Sellars' anti-foundationalism, and Goodman's pluralism. In short, despite his adamant attack on analytical philosophy—the last stage of modern European philosophy—Rorty feels most comfortable with the analytical form of philosophical argumentation (shunned by Wittgenstein and Heidegger). From the disparate figures of Wittgenstein, Heidegger, and Dewey, Rorty gets a historicist directive: to eschew the quest for certainty and the search for foundations.

Philosophy and the Mirror of Nature

LETTERS to the EDITORPhilosophy of science

The problem of reconciling general relativity and quantum theory has fascinated and bedeviled physicists for more than 70?years. Despite recent progress in string theory and loop quantum gravity, a complete solution remains out of reach. I review the status of the continuing effort to quantize gravity, emphasizing the underlying conceptual issues and the various attempts to come to grips with them.

https://cds.cern.ch/record/517743/files/0108040.pdf

Quantum Gravity: a Progress Report

The Unreality of Time

Numerous approaches to a quantum theory of gravity posit fundamental ontologies that exclude spacetime, either partially or wholly. This situation raises deep questions about how such theories could relate to the empirical realm, since arguably only entities localized in spacetime can ever be observed. Are such entities even possible in a theory without fundamental spacetime? How might they be derived, formally speaking? Moreover, since by assumption the fundamental entities can't be smaller than the derived (since relative size is a spatiotemporal notion) and so can't 'compose' them in any ordinary sense, would a formal derivation actually show the physical reality of localized entities? We address these questions via a survey of a range of theories of quantum gravity, and generally sketch how they may be answered positively.

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Emergent spacetime and empirical (in)coherence

This is the table of contents and first chapter of Physics Meets Philosophy at the Planck Scale (Cambridge University Press, 2001), edited by Craig Callender and Nick Huggett. The chapter discusses the question of why there should be a theory of quantum gravity. We tackle arguments that purport to show that the gravitational field *must* be quantized. We then introduce various programs in quantum gravity and discuss areas where quantum gravity and philosophy seem to have something to say to each other.

Physics Meets Philosophy at the Planck Scale

The quantum gravity program seeks a theory that handles quantum matter fields and gravity consistently. But is such a theory really required and must it involve quantizing the gravitational field? We give reasons for a positive answer to the first question, but dispute a widespread contention that it is inconsistent for the gravitational field to be classical while matter is quantum. In particular, we show how a popular argument (Eppley and Hannah 1997) falls short of a no-go theorem, and discuss possible counterexamples. Important issues in the foundations of physics are shown to bear crucially on all these considerations.

Why Quantize Gravity (or Any Other Field For That Matter)

Preface 1. Introduction Craig Callendar and Nick Huggett Part I. Theories of Quantum Gravity and their Philosophical Dimensions: 2. Spacetime and the philosophical challenge of quantum gravity Jeremy Butterfield and Christopher Isham 3. Naive quantum gravity Steven Weinstein 4. Quantum spacetime: what do we know? Carlo Rovelli Part II. Strings: 5. Reflections on the fate of spacetime Edward Witten 6. A philosopher looks at string theory Robert Weingard 7. Black holes, dumb holes, and entropy William G. Unruh Part III. Topological Quantum Field Theory: 8. Higher-dimensional algebra and Planck scale physics John C. Baez Part IV. Quantum Gravity and the Interpretation of General Relativity: 9. On general covariance and best matching Julian B. Barbour 10. Pre-Socratic quantum gravity Gordon Belot and John Earman 11. The origin of the spacetime metric: Bell's 'Lorentzian Pedagogy' and its significance in general relativity Harvey R. Brown and Oliver Pooley Part IV. Quantum Gravity and the Interpretation of Quantum Mechanics: 12. Quantum spacetime without observers: ontological clarity and the conceptual foundations of quantum gravity Sheldon Goldstein and Stefan Teufel 13. On gravity's role in quantum state reduction Roger Penrose 14. Why the quantum must yield to gravity Joy Christian.

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Nick Huggett

Papers

Emergent spacetime and empirical (in)coherence

Physics Meets Philosophy at the Planck Scale

Why Quantize Gravity (or Any Other Field For That Matter)

Physics Meets Philosophy at the Planck Scale: Contemporary Theories in Quantum Gravity

The Regularity Account of Relational Spacetime