Simple but neat atypical calculation of energy released in fission (from Glasstone and Sesonske, “Nuclear Reactor Engineering”). It’s a nice illustration of guesstimating based on empirical data. "The amount of energy released when a nucleus undergoes fission can be calculated by determining the net decrease in mass, from the known isotopic masses, and utilizing the Einstein mass-energy relationship. A simple, but instructive although less accurate, alternative procedure is the following. Disregarding the neutrons involved, since they have a negligible effect on the present calculation, the fi ..read more

It may seem hard to believe now, but in 1865, by the time the Civil War ended, Russia was America's best friend in Europe. The two countries enjoyed a healthy diplomatic relationship, buoyed by trade and a mutual distrust of Great Britain; Russia was the only European nation to support the Union during the war. America sent formal condolences when Tsar Alexander was assassinated; Russia did the same when Lincoln was shot. By 1891 it was all over. American mistrust of Russia was so pronounced that all diplomatic relations had cooled. It has never been the same since. What changed? Many factor ..read more

Every once in a while there is a person of consummate achievement in a field, a person who while widely known to workers in that field is virtually unknown outside it and whose achievements should be known much better. One such person in the field of chemistry was Jack Dunitz. Over his long life of 98 years Dunitz inspired chemists across varied branches of chemistry. Many of his papers inspired me when I was in college and graduate school, and if the mark of a good scientific paper is that you find yourself regularly quoting it without even realizing it, then Dunitz’s papers have few rivals ..read more

  In Niels Bohr's original 1913 formulation of the quantum atom, the Bohr radius r was proportional to n^2, n being the principal quantum number. Highly excited states would correspond to very large values of n and Bohr predicted these "giant" atoms would exist. Since the volume scales as r^3 or n^6, for n=33 you should see a "hydrogenic" atom a billion times larger than a ground state hydrogen atom. However, no spectral lines corresponding to such atoms were observed. So was Bohr's theory wrong? No! Bohr pointed out that unlike physicists, *astronomers* had observed faint spectral li ..read more

As someone who loved collecting vintage books, I was stoked to acquire a first American edition of Francis Galton's pioneering book “Hereditary Genius” for the bizarrely low price of $25 - most copies in good condition like this one sell for an unaffordable few hundred dollars at the minimum. First published in 1869, “Hereditary Genius” is an important book in the history of science as well as a good example of how racist ideas are respectable in their own times. Galton was a statistician, geneticist and brilliant polymath who was one of the founders of statistics (among other idea ..read more

A book I have been enjoying recently is John Polkinghorne's "Belief in God in an Age of Science." Polkinghorne who died recently was a noted theoretical physicist who was also a theologian. Unlike Polkinghorne I am an atheist, but he makes a good case for why religion, science, poetry, art, literature should all be welcomed as sources for truth about the universe and about human beings. A quote I particularly like from it: "If we are seeking to serve the God of truth then we should really welcome truth from whatever source it comes. We shouldn’t fear the truth. Some of it will be from science ..read more

Survey of classical mechanics: Generalized coordinates and momenta. Lagrangian equations. Derivation of Hamilton’s equations from Lagrangian. Poisson brackets. Hamilton as representing invariant E under time for conservative systems. “Pull quote”: Something simple and seemingly obvious but actually deep and foundational Some notes (not checked for typos ..read more

Finally got around to making that "100 books I would want on a desert island" list. Another title would be "100 books that I consider essential reading for *my* life": thus, this is a personal selection. I don't claim to have this list cover the most important aspects of human life or the universe, nor do I expect "famous" books to be on this list (although some of them are). The list just reflects my personal traditional interests - history and philosophy of science has the most numbers, followed by science textbooks, general history, philosophy and theology and a tiny sliver of fiction (I s ..read more

Erwin Schrödinger's book, "What is Life"?, inspired many scientists like Crick, Watson and Perutz to go into molecular biology. While many of the details in the book were wrong, the book's central message that the time was ripe for a concerted attack on the structure of the genes based on physical principles strongly resonated. However, influence and importance are two things, and unfortunately the two aren't always correlated. As Sydney Brenner recounts in detail here, the founding script for molecular biology should really have been John von Neumann's 1948 talk at Caltech as part of the Hix ..read more

Two weeks ago, outside a coffee shop near Los Angeles, I discovered a beautiful creature, a moth. It was lying still on the pavement and I was afraid someone might trample on it, so I gently picked it up and carried it to a clump of garden plants on the side. Before that I showed it to my 2-year-old daughter who let it walk slowly over her arm. The moth was brown and huge, almost about the size of my hand. It had the feathery antennae typical of a moth and two black eyes on the ends of its wings. It moved slowly and gradually disappeared into the protective shadow of the plants when I put it ..read more