Tag Archives: physics

Web Site Updates

I fixed some dead links and made other minor corrections and updates, but did not make any drastic changes in the longer pieces, so their style reflects the times when they were written, years or even decades ago. However, I think they are still relevant to the subjects being discussed.

Chicon 8


On Thursday, Sept. 1, Mia McDavid and I drove to Chicago for Chicon 8: The 80th World Science Fiction Convention at the Hyatt Regency Chicago . This was our 5th Chicon. Previously we had attended:

Despite some glitches, we really enjoyed the Con, and visiting downtown Chicago again.

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College Reunion

I spent the weekend of June 16-19 at Carleton College. The occasion was my 50 year class reunion, for which I was a member of the gift committee, which in turn was a part of the overall planning committee. Mia (my wife) and I had a room on the third floor of Watson Hall, “3rd Watson” was how we would have referred to it back in the day. I don’t know if the current students refer to campus locations like that. I lived on “6th Watson” my senior year.

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Electrons and Positrons

I have known about Electron–positron annihilation for at least 52 years, from my course in Atomic and Nuclear Physics at Carleton College in the spring of 1970 if not before. The reaction is

e + e+ → γ + γ

I had always assumed that the inverse reaction

γ + γ → e + e+

was also possible because of time reversal symmetry. Apparently so had everyone else, but it has only recently been observed: Matter arises from light? We finally know the answer to this question!. Even now there is a caveat about “virtual” as opposed to “real” photons.

Capricon Notes

As I wrote previously , Mia (my wife) and I spent last weekend at Capricon, a Chicagoland science fiction convention. We went to most of the Capricons in the ’80’s and ’90’s, but in our first years in Minnesota the pressures of parenthood prevented us from going. Those have eased somewhat and we have been to most of the Capricons (and Windycons) since 2009. While most Capricons have been in the Chicago suburbs, this year the convention was downtown, at the Sheraton Grand Hotel.

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Black Hole Lifetimes

Black holes are not totally black! They will evaporate by Hawking radiation. This is required by Thermodynamics and Quantum Mechanics. All properties of a Schwarzschild Black are determined by its mass, so if you know the mass the lifetime and other properties follow automatcally. Or you can start with the lifetime and determine the initial mass. Or the Schwarzschild radius, or the temperature, or the entropy, etc. For black holes comparable in mass to “normal” astronomical objects this lifetime is much longer than the current age of the universe. Viktor Toth’s Hawking radiation calculator is a convenient tool for such calculations. Here are some results:

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My First Peek at Renormalization

I have vaguely known about renormalization since the 1970’s, but had never seriously studied it. Out of curiosity I watched Renormalization and envelopes on YouTube Thursday evening. This was the final lecture of the Asymptotics and perturbation methods course by Prof. Steven Strogatz of Cornell University. I had watched the first two lectures of the course, but none of the others until this one. Fortunately, there were relatively few explicit dependencies on them, so I was able to follow this quite well. Here is the description:

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