Search Talks

Theoretical models for cosmology – from standard to exotic (e.g. cosmic strings and monopoles). “Quantum creation” of multiple universes out of nothing; eternal inflation and the anthropic selection of a world that would ultimately become hospitable to life.

Cosmology of the early universe; theory and detection of gravitational waves, e.g. from the violent last stages of inspiral as two orbiting black holes coalesce. Using cutting edge quantum physics in designing practical, ultra sensitive gravitational wave detectors.

Implications of high-energy elementary particle physics for physics of the early universe and its evolution (Big Bang, creation of matter, formation of galaxies, etc). And vice-versa: implications of observable cosmological data for fundamental physics.

We present a short review of the local conformal symmetry and its anomalous violation in curved $4d$ space-time. Furthermore we discuss the ambiguities of conformal anomaly and the anomaly-induced effective actions. Despite the conformal symmetry is always broken at quantum level, it is useful for constructing the best known approximations for investigating quantum corrections to the classical action of gravity. These quantum corrections represent an appropriate basis for a number of applications in cosmology and black hole physics.

Spacelike separated classical interventions make us to rethink what is quantum and what is classical. Quantum Lorentz transformations show that identification of subsystems is a tricky business, ditto entropy, entanglement and thermodynamic quantities. Resolution of information loss problem in black hole physics is tied to a construction of a theory of quantized gravity.

Abstract: Efforts to extrapolate non-relativistic (NR) quantum mechanics to a covariant framework encounter well-known problems, implying that an alternate view of quantum states might be more compatible with relativity. This talk will reverse the usual extrapolation, and examine the NR limit of a real, classical scalar field. A complex scalar \psi that obeys the Schrodinger equation naturally falls out of the analysis. One can also replace the usual operator-based measurement theory with classical measurement theory on the scalar field, and examine the NR limit of this as well. In this limit, the local energy density of the field scales as |\psi|^2, adding credibility to this approach. With the added postulate that "all measurements correspond to boundary conditions that extremize the classical action" (see arXiv:0906.5409), additional quantitative comparisons emerge between this \psi and the standard quantum wavefunction. Uncertainty can then be introduced (along with a "collapse" due to Bayesian updating) by simply giving the classical scalar field two components instead of one, leading to an intriguing \psi-epistemic model.

Complex numbers are an intrinsic part of the mathematical formalism of quantum theory, and are perhaps its most mysterious feature. In this talk, we show how it is possible to derive the complex nature of the quantum formalism directly from the assumption that a pair of real numbers is associated with each sequence of measurement outcomes, and that the probability of this sequence is a real-valued function of this number pair. By making use of elementary symmetry and consistency conditions, and without assuming that these real number pairs have any other algebraic structure, we show that these pairs must be manipulated according to the rules of complex arithmetic. We demonstrate that these complex numbers combine according to Feynman's sum and product rules, with the modulus-squared yielding the probability of a sequence of outcomes. We then discuss how complementarity --- the key guiding idea in the derivation --- can be understood as a consequence of the intrinsically relational nature of measurement, and discuss the implications of this for our understanding of the status of the quantum state.