Another Quantum of Solstice...

Rutherford and Bohr

[this story continues in part from here.]

Ernest Rutherford discovered the atom's very kernel, the nucleus, but his tiny solar system model of the atom failed. It failed because it had a fatal flaw according to classical electromagnetic theory: Viewed side-on in the plane of the ecliptic, the orbiting electron oscillates charge from side to side and should behave like a miniature transmitter, broadcasting electromagnetic energy like a Marconi transmitter. Giving off energy, bit-by-bit, the electron should spiral into the nucleus. Rutherford never explained that away.

The Importance of Being Near Ernest

Luckily, Rutherford confided his 1909 experiments to young Niels Bohr prior to publishing them. Rutherford had invited Bohr to Manchester to study physics after a brief (and apparently unsuccessful) stint at Cambridge. Inspired,* Bohr spent the summer of 1910 and the subsequent spring (taking time off to marry and to honeymoon), devising his own theory which he published in 1913 (two years after Rutherford finally published his planetary model in 1911).

Bohr got around Rutherford's electron death spiral problem by postulating that it didn't happen! That may sound audacious and even glib, but he overcame "illogical leaps" by solving a bigger mystery which had puzzled generations of scientists: he explained the long-known but little-understood signature hydrogen lines observed in the spectra of stars (recall that stars are mostly hydrogen). According to Bohr, the lines represented quantum leaps in units of energy. He did the math for the hydrogen atom to prove it. The simplistic hope that atoms and the universe were fundamentally similar -- the too small to be seen and the too big to be noticed were whirling masses in motion or "turtles all the way down" -- shone briefly.

According to Bohr's new 1913 theory, electrons encircled a nucleus, but only in stable, fixed-distance orbits (shades of Bode's earlier but discredited planetary law?) but without the continuous death spiral energy radiation. Bohr called his quantized orbits "stationary orbits" (whence my title). A quantum of solstice or standing still.

Electrons in Bohr's stationary orbits still gained or lost energy -- but only by jumping from one orbit to a bigger orbit and vice verse. That was revolutionary. Bohr's math worked out too and depended on Planck's constant which was only 13 years old then.

Planck quantized radiation and Bohr quantized matter--viz, electrons. Scientists struggled in subsequent years with the question of whether electrons were waves or particles and whether light rays were waves or particles. They worried about the meanings of such apparent dichotomies until they gradually realized that they were fighting about language and not about science.
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*Inspired is an understatement

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My inspiration for the "Quantum of Solstice" is here at Victoria's old blog, to whom I dedicate this blog post.

The Vortex is a Downwards Death Spiral

More than 50 years before Rutherford's proof of the positively charged nucleus in 1909 (published in 1911), a physicist named Rankine had notions which today sound downright prescient. He described in 1850:

Each atom of matter consists of a nucleus, or central point, enveloped by an elastic atmosphere which is retained in its position by attractive forces, and that the elasticity due to heat arises from the centrifugal force of these atmospheres, revolving or oscillating about their nuclei or central points. link

There were no plus and minus charges in Rankine's so-called Vortex Theory.  There were no protons and electrons--there was no polarity. Things were held together presumably by gravity.  But the notion of a hard kernel having squishy orbiting clouds is intriguing in retrospect. It's reminiscent of what came later.  Or something.

Then there was Nagaota whose 1904 planetary model for the atom was in part correct.  Just as the planets circled the sun with gravity and momentum in balance...so it was at the atomic level with electrostatic forces and momentum: a tiny negative electron revolved around a positive nucleus. What gravity writ large, electrostatics writ small: electrostatic attraction countered an electron's momentum, keeping things in balance. This had the added appeal of offering a certain symmetry for the outwardly large and the inwardly small: everything was just whirling masses in motion. Turtles all the way down and up. A few remaining fundamental differences between atoms and planets remained, such as the way that electrons always circled in discrete orbits while planets did not (or did they?), but these problems were sure to be solved.  And as wrong as the model proved to be, it stuck with us:

Engraven Images

If you were a kid of a certain age who collected coins, you might recall that one unattainable possession: the 1909-s V.D.B Lincoln Cent.

The "S" stands for San Francisco where it was minted; the V.D.B. stands for the sculptor's name, Victor David Brenner. When the coin first appeared in 1909 to mark the centennial of Lincoln's birth, it was the first coin to bear the likeness of a real person.  Previously, all U.S. coins had carried the likenesses of stylized subjects like Lady Liberty, Indians, and so forth. Also, previous coin designs had had artist's initials, but VDB's were deemed too ostentatious--or too something--and were moved to the front of coin, just under Lincoln's shoulder, where they still reside. Pull out a penny and have look.

The Proof Was In The Pudding

[continued in part from here]

After Thomson discovered and defined the negative portion of the atom, his attention turned to the positive portion which was ill-defined. One problem was that there was no simple tool to probe inside atoms. Electrons could be fired at matter, but so what?  They just softly scattered off (it turns out that organized matter diffracts them but that came later).

The alpha particle was Rutherford's baby: he had named it and had shown that is was a helium atom stripped of electrons, i.e., He²⁺.  By 1909, Rutherford and his students were firing alpha particles at everything in sight, looking for any new and unusual effects, but also testing theories about the positive part of Thomson's Plum Pudding Model.

Rutherford had earlier noted the thickness of sheets of materials needed to stop alpha particles. But why did they? There was nothing about JJ Thomson's atom that should get in the way. If the positively charged portion of each atom were a uniformly thin gruel, alpha particles should sail right through.  But they noticed deflection--eppur si muove.

Eventually, they began measuring how much thin sheets of gold foil deflected beams of alpha particles. The experimental set-up involved aiming a beam of alpha particles at a gold foil and putting a detector on the other side to measure deflection angles of the "filtered" particles. In a sense, Rutherford was trying to quantify the density of the positive pudding portion. The more closely they looked, the more deflection they observed. Almost as an aside, Rutherford suggested putting the detector in front of the gold foil. When they did so, and to everyone's utter surprise, a detectable amount of alpha particles appeared to bounce off the gold foil rather than pass through it. It took Rutherford two years to digest, confirm, reconfirm and then to announce what this all meant. In Rutherford's words:

It was quite the most incredible event that has ever happened to me in my life. It was almost as incredible as if you fired a 15-inch shell at a piece of tissue paper and it came back and hit you. On consideration, I realized that this scattering backward must be the result of a single collision, and when I made calculations I saw that it was impossible to get anything of that order of magnitude unless you took a system in which the greater part of the mass of the atom was concentrated in a minute nucleus. It was then that I had the idea of an atom with a minute massive center, carrying a charge.

[Continued in part here]

Plum Pudding

The more important fundamental laws and facts of physical science have all been discovered, and these are now so firmly established that the possibility of their ever being supplanted in consequence of new discoveries is exceedingly remote.... Our future discoveries must be looked for in the sixth place of decimals.
- Albert. A. Michelson, speech at the dedication of Ryerson Physics Lab, U. of Chicago 1894

The following year, Roentgen discovered X-rays; a year later, in 1896, Becquerel discovered radioactivity; and J.J. Thomson electrified physics in 1897 when he announced that cathode "rays" were really beams of electrons or what he called "corpuscles."

Thomson knew as much as anyone about electricity and its conduction--that electricity could flow here and there like invisible water and it could even be tamed and put to use. The electron, named after the Greek word for amber, had even been proposed before but had remained safely ensconced in matter. Thomson disclosed it. Disrobed it. What the electron lost in privacy, it gained in primacy and notoriety. Alone and naked for the first time, the electron succumbed to further scrutiny--first its mass-to-charge ratio was measured by Thomson. Soon after, it was actually weighed by Millikan (ironically at the University of Chicago--see quote above). But the real shocker at the time was that atoms were divisible--they were not a-tomos. This destroyed a comfortable notion of integrity.

JJ Thomson. Note the photograph (second from right) which is an early X-ray of the hand of Frau Roentgen

Knowing that he could strip off little negative bits, but not having a working notion of the countervailing positive portion which was surely left behind, Thomson theorized that electrons were uniformly sprinkled in a positively-charged, amorphous medium. The model was dubbed Plum Pudding. And why not? Thompson went with what he knew.  He would have overreached any data to have proposed anything else. And so, for the interregnum roughly corresponding to the Edwardian era—until Ernest Rutherford undid it—the atomic model looked like this:

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Suggested reading: history of the electron

This story continues here: link

Rumford, Soddy, and The Crash

Frederick Soddy (1877-1956)

Despite years of formal education in chemistry, I'd never really heard of Frederick Soddy until I started reading about the early days of radioactivity. He wrote a book called The Interpretation Of Radium (1909) which is available free online here.  The book so influenced H.G. Wells that he dedicated his book, The World Set Free (1914), to Soddy.

Soddy seems to have had two careers--first as an accomplished physical scientist (Chemistry Nobel in 1921) and then as a sort of social scientist, but more accurately as a social activist during the Great Depression. In this way he was a prototype Linus Pauling, who won both a Chemistry Nobel and a Peace Nobel for his activism.

Soddy was a chemist by training but today he'd be called a radiochemist. He must have seen or heard firsthand many of the key discoveries in nuclear physics in the late 19th and early 20th century, first at Oxford and then as graduate student with Lord Rayleigh. Afterwards, Soddy moved to Canada around the same time Ernest Rutherford did and the two joined forces. Together they discovered the natural transmutation of elements. Soddy's Nobel Prize citation reads:

for his contributions to our knowledge of the chemistry of radioactive substances and his investigations into the origin and nature of isotopes.

His isotope work came later.

Recall that Count Rumford first paid attention to the heat given off boring cannon and thereby converted our notions of energy.  Like Rumford, Soddy first realized how much heat and energy radioactive decay gave off--orders of magnitude more energy than burning fossil fuels did and it was also seemingly inexhaustible. Soddy was so prescient regarding how much energy was locked inside uranium, radium, and thorium that he warned Britain's government about the dangers of "atomic" bombs during the First World War.

The notion of cheap and abundant atomic energy crested in 1954 with Lewis Strauss' famous too cheap to meter statement, though it appears that he was referring to hypothetical hydrogen fusion reactors.

Soddy died in 1956 in relative obscurity. This (from the Wiki bio) is intriguing:

In four books written from 1921 to 1934, Soddy carried on a 'quixotic campaign for a radical restructuring of global monetary relationships', offering a perspective on economics rooted in physics—the laws of thermodynamics, in particular—and was 'roundly dismissed as a crank'. While most of his proposals - 'to abandon the gold standard, let international exchange rates float, use federal surpluses and deficits as macroeconomic policy tools that could counter cyclical trends, and establish bureaus of economic statistics (including a consumer price index) in order to facilitate this effort' - are now conventional practice, his critique of fractional-reserve banking still 'remains outside the bounds of conventional wisdom'. Soddy wrote that financial debts grew exponentially at compound interest but the real economy was based on exhaustible stocks of fossil fuels. Energy obtained from the fossil fuels could not be used again. This criticism of economic growth is echoed by his intellectual heirs in the now emergent field of ecological economics.