This series covers all areas of research at Perimeter Institute, as well as those outside of PI's scope.
I
will discuss some basic notions in the theory of phonology (sound systems
in language). The sounds of a language are generally assumed to be
composed of smaller constituents, called features. The features that
make up a sound cannot be directly obtained from its pronunciation, but
rather must be inferred from the system of contrasts that are at play
in a particular language. How to determine which features are contrastive
presents a logical and empirical puzzle that may be interesting
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.
Gravity
in string theory is a generalized version of Einstein's theory with some
universal features that call for a reformulation
The Rosenbluth Method is a classical kinetic growth Monte
Carlo algorithm for growing a self-avoiding walk by appending steps to its
endpoint.
This algorithm
A revolution is underway in the construction of ‘artificial atoms’ out
of superconducting electrical circuits.
These macroscopic ‘atoms’ have quantized energy levels and can emit and
absorb quanta of light (in this case microwave photons), just like ordinary
atoms. Unlike ‘real’ atoms, the
properties of these artificial atoms can be engineered to suit various
particular applications, and they can be connected together by wires to form
quantum ‘computer chips.’ This so-called
The solutions to
the cosmological constant problems may involve modifying the very long-range
dynamics of gravity by adding new degrees of freedom. As an example of a conservative and minimal
such modification, we consider the possibility that the graviton has a very
small mass. Massive gravity has received
renewed interest due to recent advances which have resolved its traditional
problems. This kind of modification has
some peculiar and unexpected features, and it points us towards a universe
which looks quite unfamiliar.
A quantum communication channel can be put to many uses: it can transmit
classical information, private classical information, or quantum information.
It can be used alone, with shared entanglement, or together with other
channels. For each of these settings there is a capacity that quantifies a
channel's fundamental potential for communication. In this introductory
talk, I will discuss what we known about the various capacities of a quantum
channel, including a discussion of synergies between different channels and
Some recent searches for quantum gravity signatures using
observations of distant astrophysical sources will be discussed, focusing on
the search for Lorentz invariance violation (LIV) in the form of a dependence
of the photon propagation speed on its energy. Fermi gamma-ray space telescope
observations of ~8 keV to ~30 GeV photons from a short (
burst (GRB 090510) at a cosmological distance (z = 0.903), enabled for the
first time to put a direct time of flight limit on a possible linear variation of
Astronomical hydrodynamics is usually almost ideal in the sense that the Reynolds number (Re) is enormous and any effective viscosity must be due to shocks or turbulence. Astronomical magnetohydrodynamics (MHD) is often also nearly ideal, so that magnetic fields and plasma are well coupled. In particular, dissipation of orbital energy in accretion disks around black holes is readily explained by MHD turbulence. On the other hand, the planet-bearing disks around protostars are magnetically far from ideal because of very low fractional ionization. MHD turbulence is at best marginal