I am posting some talks I gave in recent years when their PowerPoint software became available. The viewers need to click the title to download the ppt file to display the contents. This way one can take advantage of the logical sequence of the talk as constructed using the animation feature of the PowerPoint software. I have included at the end a few of the “brown-bag lunch talks”; they are short presentations lasting typically 20 minutes.

(2011)

The dominant component of matter in the universe is dark matter. The identity of such substances is still unknown; their presence is indicated by their gravitational attraction to ordinary stellar matter. The energy of the universe is mostly in an even more mysterious form called dark energy. They provide the gravitational repulsion that causes the expansion of the universe to accelerate. We discuss the observational evidence for the existence of such matter and energy. Some speculative theories of their possible origins are discussed, noting some of their shortcomings.

(2013)

Selected topics illustrating Einstein’s monumental achievements are explained and related to developments in physics since his time. We discuss Einstein vs Planck in the quantum postulate, vs Bohr on the meaning of QM, vs Lorentz in relativity, vs Newton in gravitational theory, and his influence on modern gauge theory and unification of fundamental forces.

(2015, 2022)

This is an introductory talk on the Einstein-Bohr debate on the meaning of quantum mechanics -- entanglement & nonlocality, EPR paradox, and spooky action-at-a-distance. The modern understanding started with Bell’s inequality, of which a simple derivation will be presented. We conclude with a discussion of experiments showing the weirdness of quantum mechanics.

(2017, 2020)

This talk is based on the presentation I gave in 2017 when the Physics Nobel Prize was awarded to Weiss-Thorne-Barish for the first direct detection of gravitational waves (in 2015). What are gravitational waves? What is the significance of their detection by LIGO?

(2018)

To answer a student’s question: Why should gravitational waves propagate at the same speed as light – even though there is no direct connection between gravity and electromagnetism? My answer: they all propagate at c “the Einstein speed” as dictated by relativity. It allowed me to talk about the history and significance of this universal speed in the wider physics context. Instead of just showing the similarity of these two wave equations, for instance, this equality reflects that both are long-range forces. Fundamentally, c is the conversion factor between space and time.

SHORT PRESENTATIONS

(2017, 2019)

On the 2017 solar eclipse occasion, a physics meeting was held in Missouri where I presented a pedagogical talk on Einstein’s derivations of the bending of light. It explains why Einstein’s earlier calculation based on the equivalence principle missed the final GR result he obtained in 1915 by a factor of two.

(2010)

This talk I gave at PSU in 2010 posted the possibility of spacetime having dimensions greater than four — as part of the legacies (along with relativity and gauge symmetry) of Maxwell’s equations.

(2013)

This journal club talk gives a brief history of the mysterious connection of black hole physics to thermodynamics, and the light shed on this connection by the discovery of Hawking radiation.