Since 2002 Perimeter Institute has been recording seminars, conference talks, and public outreach events using video cameras installed in our lecture theatres. Perimeter now has 7 formal presentation spaces for its many scientific conferences, seminars, workshops and educational outreach activities, all with advanced audio-visual technical capabilities. Recordings of events in these areas are all available On-Demand from this Video Library and on Perimeter Institute Recorded Seminar Archive (PIRSA). PIRSA is a permanent, free, searchable, and citable archive of recorded seminars from relevant bodies in physics. This resource has been partially modelled after Cornell University's arXiv.org.
Neutron stars are the collapsed cores of massive stars that went under supernova explosions. They are found with high surface magnetic fields, rapid but steady rotation and high density comparable to that inside an atomic nucleus. In the past 20 years, many different classes of neutron stars have been discovered. One of the most enigmatic classes of neutron stars is the compact central objects (CCOs). Only seven of them have been discovered and their emission process are still not well understood.
The large number of high-energy rotational lines of C18O, available via the Herschel Space Observatory, provides an unprecedented ability to model the total C18O column density in hot cores. Using the emission from all the observed lines (up to J=16-15) we use an automated algorithm to model all transitions simultaneously.
Neutron stars are collapsed remnants of massive stars. One form of neutron star, pulsars, produce clock-like radio pulses, a result of their rotation combined with a misalignment of their rotation and magnetic axes. These pulses can be used in a variety of experiments in fundamental physics, including tests of gravity theories, constraining the properties of supranuclear density matter, and gravitational wave detection. In this talk, I will describe pulsar properties and explain how the above experiments are carried out, as well as show interesting recent results.
Continuous-variable SICPOVMS seem unlikely to exist, for a variety of reasons. But that doesn't rule out the possibility of other 2-designs for the continuous-variable Hilbert space L2(R). In particular, it would be nice if the coherent states -- which form a rather nice 1-design -- could be generalized in some way to get a 2-design comprising *Gaussian* states. So the question is: "Can we build a 2-design out of Gaussian states?". The answer is "No, but in a very surprising way!" Like coherent states, Gaussian states have a natural transitive symmetry group.
If we imagine that the universe is truly eternal, special challenges arise for attempts to solve cosmological fine-tuning problems, especially the low entropy of the early universe. If the space of states is finite, the universe should spend most of its time near equilibrium. If the space of states is infinite, it becomes difficult to understand why our universe was in a particular low-entropy state.
I will discuss approaches to addressing this problem in a model-independent fashion.
"A positive cosmological constant allows arbitrarily many different quantum states, but apparently only if there can be big bangs and/or big crunches. Without any big bang or big crunch, the entropy may be limited by the Gibbons-Hawking entropy of pure deSitter, and the matter entropy might even more limited by a value roughly the three-fourths power of the Gibbons-Hawking entropy. A classical analogue of an upper limit on the entropy is the finite canonical measure for nonsingular cosmologies.
Closed systems never evolve to lower entropy states -- except when they do, which is if one waits a time that is exponential in the entropy change. Thus macroscopic decreases in entropy are 'never' observed. Yet in cosmology there are eternal systems in which downward entropy fluctuations of any magnitude eventually happen. What is the nature of such fluctuations?
Our universe may have formed via bubble nucleation in an eternally-inflating background. Furthermore, the background may have a compact dimension---the modulus of which tunnels out of a metastable minimum during bubble nucleation---which subsequently grows to become one of our three large spatial dimensions. We discuss some potential observational signatures of this scenario.
Check back for details on the next lecture in Perimeter's Public Lectures Series