Soumis par Anonymous le Juin 3, 2013 - 9:16am

I argue that quantum mechanics cannot usefully be extended to a theory of the whole universe, so the task of quantum foundations is to discover that cosmological theory which reduces to quantum mechanics when restricted to small subsystems of the universe. I argue that that cosmological theory will be based on a global notion of physical time which implies the distinction between past, present and future is real and objective. These motivate two examples of novel formulations of quantum theory: the real ensemble formulation and the principle of precedence. Each may imply departur

Soumis par Anonymous le Mai 15, 2013 - 12:23pm

One of the most obvious facts about the universe is that the past is different from the future. We can turn an egg into an omelet, but can't turn an omelet into an egg. Physicists have codified this difference into the Second Law of Thermodynamics: the entropy of a closed system always increases with time. But why? The ultimate explanation is to be found in cosmology: special conditions in the early universe are responsible for the arrow of time.

Soumis par Anonymous le Avril 17, 2013 - 5:00pm

The nature of time, probability and quantum mechanics, philosophy of physics and metaphysics, especially issues involving the role of mathematical tools like symmetry in physics, and applying this formal apparatus to the philosophy of mind.

Soumis par Anonymous le Avril 8, 2013 - 4:54pm

What is time? Is our perception of time passing an illusion which hides a deeper, timeless reality? Or is it real, indeed, the most real aspect of our experience of the world? Einstein said that "the distinction between past, present, and future is only a stubbornly persistent illusion," and many contemporary theorists agree that time emerges from a more fundamental timeless quantum universe. But, in recent cosmological speculation, this timeless picture of nature seems to have reached a dead end, populated by infinite numbers of imagined unobservable universes.

Soumis par Anonymous le Janvier 23, 2013 - 4:41pm

I give an account of the Machian approach to dynamics,

from Mach's critique of Newton to the work of Barbour, Bertotti, York and

O'Murchadha, which culminated in the theory of Shape Dynamics, a new and

original way of thinking about General Relativity. I conclude commenting on the

present research lines in Shape Dynamics, and the opportunity it offers to

solve the problem of time in quantum gravity.*Support
for this colloquium is provided by The Templeton Frontiers Program.*

Soumis par Anonymous le Novembre 3, 2012 - 9:36pm

Space and time are two of the universe's most fundamental elements. Relativity combines these two into the unified notion of space-time, but twistor theory goes beyond this replacing both by something entirely different, where the basic elements are the paths taken by particles of light or other particles without mass.

Twistor theory has already found powerful applications in the field of high-energy physics.

Soumis par Anonymous le Novembre 3, 2012 - 9:36pm

Using the Deutsch approach, we show that the no-cloning theorem can be circumvented in the presence of closed timelike curves, allowing the perfect cloning of a quantum state chosen randomly from a finite alphabet of states. Further, we show that a universal cloner can be constructed that when acting on a completely arbitrary qubit state, exceeds the no-cloning bound on fidelity.

Soumis par Anonymous le Novembre 3, 2012 - 9:36pm

The history of physics, from Galileo's spatialization of time to Einstein's block universe, and on to Julian Barbour's timeless quantum cosmology, tells a story by which time is demoted from a fundamental aspect of experience to an emergent illusion in a world held to be fundamentally timeless. The question I would like to address is, is this correct, or will the next stage in the development of physics require a rediscovery of time as a primary aspect of nature?

Soumis par Anonymous le Novembre 3, 2012 - 9:36pm

I will describe an approach to the problem of time that uses dust as a time variable. The canonical theory is such that there is a true Hamiltonian with spatial diffeomorphisms as the only gauge symmetry. This feature, and the form of the Hamiltonian, suggest a model for non-perturbative quantum gravity that is computationally accessible using the formalism of loop quantum gravity.