John S. Rigden

Why a biography of hydrogen? The book justifies itself.

Hydrogen is not only the most common element in the universe, the source of energy production in stars, and the simplest of all elements. It’s also the historical lab specimen/crash test dummy for physicists.

Theory, lab experimentation, and observation place hydrogen at a focus for the understanding of the universe from the very, very small in particle physics to the very, very large in cosmology.

Why hydrogen? Its abundance is one show more thing, at least if we just think about “normal” matter in the universe. But it’s really its simplicity — one proton and one electron. It’s as if the universe swept away the complexity so that we could see atomic structure at its cleanest and measure parameters without noise.

And deuterium, hydrogen’s heavier isotope, provides the simplest example for studying the atomic nucleus. Deuterium’s nucleus (“deuteron”) contains just one proton and one neutron, so that the relationship between the two and how they are bound together through the strong force can also be studied without complication.

The book is organized into chapters focused on landmarks in the study of hydrogen that generate more general theoretical breakthroughs in physics.

Rigden begins with William Prout’s 1815 speculations about hydrogen as the basic building block for all of the elements, a speculation that is both “wrong” but conceptually provocative. It provides a conceptual framework for the atom, taking up ancient clues from the Greek atomists. The idea of a fundamental building block, out of which all the elements are made is not obvious, and Prout’s speculation carries forward a way of thinking that, even though wrong in its particulars, provides a conceptual framework into which atomic structure later fits.

Other early chapters focus on the Balmer spectral lines for hydrogen and the Bohr model. Those two set out a basic question — how can we understand the spectral emission lines (and absorption lines) associated with hydrogen in relationship to the structure of the hydrogen atom? Hydrogen emits energy at those particular wavelengths for a reason — can we derive them from hydrogen’s atomic structure, in particular the behavior of its one electron?

Bohr’s original model of the atom did tie atomic structure to those Balmer lines. But it was specific to hydrogen. It contained ad hoc values to place transitions between electron energy levels and orbits in sync with the Balmer spectral lines.

Not until more generalized theories of the atom and the energy states of electrons (through work by Sommerfeld, Dirac, Schrodinger, and others) did this initial model of the atom, with its quantized conceptual character, evolve into what we now know as quantum theory. Rigden traces this theoretical and experimental progress through succeeding chapters of the book.

Later chapters make the transition from particle physics to cosmology and some more speculative topics. Some of these chapters made me appreciate the continuity between the study of atomic structure, understanding the energy states for hydrogen’s electron at the particle physics level, and application of that same understanding to cosmological questions.

Rigden does a good job of showing, for example, how spectral analysis of hydrogen emission lines from interstellar hydrogen gas enables astronomers to map the structure of our galaxy.

Ordinarily, in trying to understand our galaxy’s structure, our view is blocked, like someone unable to see the forest for the trees. As we look out into the sky, we see stars, gas and dust clouds, etc. — what’s right in front of us blocks our view of the whole.

Mapping the galaxy’s structure was only possible because one of the energy state transitions of hydrogen’s electron, a transition that was missed in the Bohr model but discovered as part of the “hyperfine structure” understood through quantum theory, results in an emission at 21 centimeters wavelength. That emission, in the radio spectrum, passes transparently through the objects (stars, planets, dust, gas, . . ) that would otherwise block our view of the galaxy’s structure as a whole. In the radio spectrum we can see hydrogen gas clouds emitting signals of their presence anywhere they exist in the galaxy, giving us a map of the galaxy’s structure.

Hydrogen has always provided a link between the very big and the very small. As the simplest of elements it has played this key role in the development of particle physics, and especially quantum theory. But hydrogen was also the first element to form after the Big Bang, by far the most common element in the universe, and a key to understanding the universe’s structure and geometry.

Also, hydrogen’s isotope, deuterium, provides both a validation of Big Bang cosmology and a mystery about the current makeup of the universe.

The Big Bang is the only (known) appreciable source of deuterium in the universe. From Big Bang theory, we can derive an expected abundance of deuterium relative to hydrogen per se (really the lighter isotope without deuterium’s neutron). Then by comparing that predicted abundance with the actual observed abundance, we can provide one of the validating pillars of Big Bang theory.

(I’m skipping a complication — deuterium, although it can be created only in the Big Bang, can be depleted in the fusion processes at the cores of stars, so we need “primordial” sources from which to sample deuterium’s actual abundance — fortunately quasars supply such sources).

The comparison confirms the Big Bang prediction. But the accuracy of the prediction poses a problem. If we now look at the actual, observable amounts of deuterium in galaxies, we can, given its expected abundance, derive some estimate of the amount of hydrogen in the galaxy, and, because we know the abundance of hydrogen itself relative to the galaxy’s mass, we can derive an estimate of the galaxy’s total mass.

When we do that, the estimate is way too low. In order for galaxies to interact gravitationally the way we see them do in galaxy clusters, and in order for galaxies to rotate and retain their observed shapes, they must have much greater masses than the estimate provides. The missing mass problem is a principal rationale for “dark matter” theories.

The final chapters concern some more esoteric work relating to antimatter (including antihydrogen), the novel state of matter known as the Bose-Einstein condensate, and “hydrogen-like atoms” (artificially assembled atomic-scale entities with similar structure to hydrogen but different components), along with technological applications.

I learned a lot from Rigden’s book. To be a bit critical, it is a little uneven in level of explanation. That, to me, is generally a problem with physics-related books for the so-called “general reader.” To explain EVERYTHING would make the book unreadable. At least with Rigden’s book, my questions were comprehensible enough that I could go off on my own to try to resolve them separately. show less

Einstein 1905 is a good book for the layman interested in understanding Einstein's miraculous year of 1905 when he produced five papers, over six months, that profoundly affected the course of science. Taking the papers one at a time, Rigden first sets the context of the issues involved, the questions or conflicts unresolved in physics, then he describes the essence of the paper itself, and outlines responses to it. The papers are:

March: the particle theory of light, which flew completely in show more the face of conventional wisdom that saw light as a wave.
April: Einstein's PhD dissertation on determination of molecular dimensions in liquids which provided support for the atomic theory of matter.
May: Einstein wanted to develop a theory of Brownian motion that would expose the atomic nature of liquids and that could be tested experimentally; the paper proved the existence of atoms.
June: the special theory of relativity that joined space and time: "The results of Part I are intellectually and emotionally stunning. Absolute space and time, the foundations of Newtonian physics, are seen to be a figment of our imagination. Absolute simultaneity is also a myth."
September: a very short (3 pages) paper that produced the famous E=mc2 that linked mass and energy through the speed of light. As Rigden puts it: "Humans distinguish between energy and mass, but Nature does not. Even more, humans have made mass into something very different from energy. ... If, however, the objective is to describe Nature accurately, humans must accept Nature on its terms and find a way to rationalize the difference between our concept of mass and our concept of energy. The factor c2 does this. Multiply m by c2, and, de facto, energy and mass become what Nature deems them to be: one and the same."

Rigden also briefly summarizes other seminal papers that Einstein produced by himself or with colleagues, dealing with the equivalence principle (uniform gravitation cannot be distinguished from uniform acceleration; and gravitational mass and inertial mass are one and the same.); his work that anticipated the development of the laser; and work that showed "spooky" action at a distance between matched pairs of photons that are said to be "entangled" (a term coined by Schrodinger in 1935).

But the jewel in the crown is Einstein's general theory of relativity, produced in 1916 in which "The concepts of space, time and gravitation are dramatically changed...the general theory of relativity has replaced the gravitation force, as described by Newtonian physics, with warped spacetime". This paper, according to Ridgen, is considered by many to be "the greatest monument to abstract thought" ever produced by a human being.

This is not a biography of Einstein. It focuses solely on the papers as described. But throughout, Rigden brings out the marvel of Einstein's thought processes, and his unwavering conviction that his predictions were right (as they were invariably proven to be) because the theories were right. Rigden touches on the fact that Einstein could never accept the basic tenets of quantum mechanics and so, after 1927, he "stood apart" from the intellectual environment of physics with his focus instead on trying to unify gravitation and electromagnetism. show less

Finished [Einstein 1905: The Standard of Greatness] by [[John S. Rigden]]. It is a short but very informative book about Einstein's five papers written in 1905, explaining on each how he came to write them, what they are about and the impact each paper had. Additionally there is an introduction to familiarize the reader with Einstein in 1905 and an excellent epilogue that discusses a few of his later papers and his overall impact on physics and the world. The book is written for the more show more intelligent layman, no math required! Highly recommended. show less

This is a good overview for the interested non-expert, but only of biographical interest to a physicist, who will want more beef.