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.
We will review the uncertainty principle of quantum mechanics, first formulated by Werner Heisenberg in 1927, and the role they played in the famous debate between Einstein and Bohr on the meaning of quantum theory. Along the way we will focus on questions like: what do we mean by "uncertainty", and how do we express that in the theory? What, in fact, is a physical property? Does a theory like quantum mechanics provide a description of physical reality? Interestingly, some of these questions do not have a unique answer.
Put two physicists in a room and ask them to talk about the interpretation of quantum mechanics. This is a recipe for disagreement; the mysteries of quantum theory run so deep that it’s hard to find any interpretive claims that are immune to controversy. Therefore, when thinking about quantum theory, it is a useful tactic to first focus on the macroscopic facts it predicts while ignoring the formalism and what it might suggest about the constitution of reality. I will adopt this tactic in my talk to describe the strange features of sequences of Stern-Gerlach measurements.
Put two physicists in a room and ask them to talk about the interpretation of quantum mechanics. This is a recipe for disagreement; the mysteries of quantum theory run so deep that it’s hard to find any interpretive claims that are immune to controversy. Therefore, when thinking about quantum theory, it is a useful tactic to first focus on the macroscopic facts it predicts while ignoring the formalism and what it might suggest about the constitution of reality. I will adopt this tactic in my talk to describe the strange features of sequences of Stern-Gerlach measurements.
The speculation that Dark Energy can be explained by the backreaction of present inhomogeneities on the evolution of the background cosmology has been increasingly debated in the recent literature. We demonstrate quantitively that the backreaction of linear perturbations on the Friedmann equations is small but is nevertheless non-vanishing. This indicates the need for an improved averaging procedure capable of averaging tensor quantities in a generally covariant way.
One of the quintessential features of quantum information is its exclusivity, the inability of strong quantum correlations to be shared by many physical systems. Likewise, complementarity has a similar status in quantum mechanics as the sine qua non of quantum phenomena. We show that this is no coincidence, and that the central role of exclusivity in quantum information theory stems from the phenomenon of complementarity.
A discussion of how the zero point energy of atoms is what makes possible their existence in our universe – atoms are purely quantum mechanical objects.
Learning Outcomes:
• Continuation of QM-9: A calculus-based derivation of the zero point energy of the quantum harmonic oscillator.
• How our previous understanding of energy quantization and zero point energy can be applied also to the hydrogen atom.
Understanding the zero point energy of the quantum harmonic oscillator as a consequence of the Heisenberg Uncertainty Principle.
Learning Outcomes:
• Understanding why the minimum energy of a ball in a bowl must be greater than zero based on the Heisenberg Uncertainty Principle.
• How the Heisenberg Uncertainty Principle adds a purely quantum mechanical kinetic energy to the ball, in addition to its classical potential energy.