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.
The de Broglie waves we have been using thus far were assumed to be real functions; we discuss why this is wrong and how to fix the problem.
Learning Outcomes:
• Understanding why there is a serious flaw with using real de Broglie waves, and how using a complex wave (one with both a real and an imaginary part) solves the problem.
• Understanding how the de Broglie wave corresponding to a free particle is like a moving corkscrew, with a magnitude that is uniform across space and constant in time.
Learning Outcomes:
• How the complex standing wave states of an electron in a one-dimensional box are “stationary states” in that the electron probability pattern is static (not changing with time).
• However, if the electron is put in a superposition of two such stationary states (with different energies), its probability pattern is not static, but rather oscillates back and forth; understanding how this oscillation is connected with photon emission and absorption.
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.
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.