Cosmologists at Perimeter Institute seek to help pin down the constituents and history of our universe, and the rules governing its origin and evolution. Many of the most interesting clues about physics beyond the standard model (e.g., dark matter, dark energy, the matter/anti-matter asymmetry, and the spectrum of primordial density perturbations], come from cosmological observations, and cosmological observations are often the best way to test or constrain a proposed modification of the laws of nature, since such observations can probe length scales, time scales, and energy scales that are beyond the reach of terrestrial laboratories.
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.
In his talk, Lee Smolin explains why he changed his mind about the nature of time. Like many fellow theorists, he used to believe time is an illusion, but he now embraces the view that time is real and everything else, including the laws of nature, evolves. Drawing from his new book, Time Reborn, Smolin explains how the great unsolved problems in physics and cosmology may be solved by adopting the view of a real time. then he will go beyond physics to explain how our view of time affects how we think of everything from our personal and family lives to how we face major problems such as climate change and economic crisis. In a world in which time is real, the future is open and there is an essential role for human agency and imagination in envisioning and shaping a good future.
Black holes are the elementary particles of gravity, the
final state of sufficiently massive stars and of energetic collisions. With a
forty-year long history, black hole physics is a fully-blossomed field which
promises to embrace several branches of theoretical physics. Here I review the
main developments in highly dynamical black holes with an emphasis on high
energy black hole collisions and probes of particle physics via superradiance.
The bimodality of gamma-ray burst (GRB) durations points
to distinct progenitor classes for the long- and short-duration GRBs. While the
progenitors of long-duration GRBs are now known to be massive stars, the
progenitors of short-duration GRBs remain unidentified. In this talk I will
discuss the discovery of short GRB afterglow and their host galaxies, detailed
studies of their environments from parsec to galactic scales, and studies of
their energetics and beaming. Taken together, these observations point to the
coalescence of NS-NS/NS-BH binaries as the most likely progenitors. With the
upcoming Advanced LIGO/VIRGO gravitational wave detectors it is therefore
possible that short GRBs will be the first detected sources, and I will discuss
various approaches to making this connection between gravitational wave and
electromagnetic sources.
An analytical understanding of large-scale matter
inhomogeneities is an important cornerstone of our cosmological model and helps
us interpreting current and future data. The standard approach, namely Eulerian
perturbation theory, is unsatisfactory for at least three reasons: there is no
clear expansion parameter since the density contrast is not small everywhere;
it does not consistently account for deviations at large scales from a perfect
pressureless fluid induced by short-scale non-linearities; for generic initial
conditions, loop corrections are UV divergent, making predictions cutoff
dependent and hence unphysical.
I will present the systematic construction of an
Effective Field Theory of Large Scale Structures and show that it successfully
addresses all of the above issues. The idea is to smooth the density and
velocity fields on a scale larger than the non-linear scale. The resulting
smoothed fields are then small everywhere and provide a well-defined small
parameter for perturbation theory. Smoothing amounts to integrating out the
short scales, whose non-linear dynamics is hard to describe analytically. Their
effects on the large scales are then determined by the symmetries of the
problems. They introduce additional terms in the fluid equations such as an
effective pressure, dissipation and stochastic noise. These terms have exactly
the right scale dependence to cancel all divergences at one loop, and this
should hold at all loops. I will present a clean example of the renormalization
of the theory in an Einstein de Sitter universe with self-similar initial
conditions and discuss the relative importance of loop and effective
corrections.
We apply the effective field theory approach to
quasi-single field inflation, which contains an additional scalar field with
Hubble scale mass other than inflaton.
Based on the time-dependent spatial diffeomorphism, which is not broken
by the time-dependent background evolution, the most generic action of
quasi-single field inflation is constructed up to third order
fluctuations. Using the obtained action,
the effects of the additional massive scalar field on the primordial curvature
perturbations are discussed. In
particular, we calculate the power spectrum and discuss the momentum-dependence
of three point functions in the squeezed limit for general settings of
quasi-single field inflation. Our
framework can be also applied to inflation models with heavy particles. We make
a qualitative discussion on the effects of heavy particles during inflation and
that of sharp turning trajectory in our framework.
This talk will begin by discussing one by one the various
reasons why cosmologists today consider the big bang inflationary cosmology to
be the leading, if not proven, theory of the universe and
then explaining
why each of these reasons is flawed. This leads
naturally to the question: what is the alternative? Understanding the flaws helps point the way.
As black holes accrete surrounding gas, they often
produce relativistic, collimated outflows, or jets. Jets are expected to form
in the black hole vicinity making them powerful probes of strong-field gravity.
However, how jet properties are connected to black hole and accretion flow
properties has been unclear. Recent progress in computer simulations of black
hole accretion enables studies of jet formation in unprecedented detail. For
the first time, 3D general relativistic magnetohydrodynamic numerical
simulations allow one to determine the maximum efficiency with which accretion
onto black holes can power relativistic jets. I will present the dependence of
this maximum efficiency on black hole spin and discuss how this dependence
allows one to probe strong-field gravity. In realistic astrophysical systems,
the angular momentum vector of the accretion flow can be tilted relative to the
spin of the black hole. I will present the first simulations of jets from such
tilted accretion systems and discuss their observational signatures.