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Women, priests, and astronomy
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23-07-2018 5:16am#1Last week Google did a Doodle for Georges Lemaître's 124th birthday.
I think Lemaître is sometimes viewed a bit suspiciously as the Catholic priest who came up with a theory of creation. In fact he was a hard-nosed scientist who warned the Pope against any over-enthusiastic philosophical speculation. A few newspapers did blurbs in his honour last week ...
https://www.express.co.uk/news/world/989888/Google-Doodle-Georges-Lema-tre-124th-birthday-Big-Bang-theory-universe-Albert-Einstein
Lemaître's story reminded me of what seemed like one of the great milestone achievements of my youth -- figuring out how to balance a sweeping brush upside down on the palm of your hand, and to prevent it from toppling by constant small adjustments of hand position. Imagine if instead of a sweeping brush you were trying to hold up the entire contents of the universe. That was the situation in the static universe proposed by Einstein in 1917, two years after his publication of the General Theory of Relativity. He found his equations permitted the addition of a cosmological constant, representing a kind of anti-gravity that would support a changeless universe and keep it from collapsing under its own weight.
The "sweeping brush problem", as one might call it, was pointed out by Georges Lemaître in 1927. While the static universe was possible, it required very special conditions and was hopelessly unstable under the most general assumptions. Rather than try to rescue Einstein's universe, Lemaître pointed out that an expanding universe avoided the problem altogether. The rest, as they say, is history. Well, except it isn't ... Hubble's discovery of the cosmic expansion in 1929 should have been Lemaître's crowning glory, but in fact practically nobody had heard of him. His 1927 paper was published in an obscure journal that was little read outside Belgium.
In 1930 Sir Arthur Eddington, the giant of British astrophysics, wrote an English language article about Lemaître's ideas in the Monthly Notices of the Royal Astronomical Society. I haven't read Lemaître's paper, but Eddington's is available here and I was motivated to read it since Google stuck up their Lemaître doodle last week. It's a fascinating read even if you have to skip a lot of the maths. A primary insight is that the clumping together of galaxies would cause any initially stable configuration to destabilise. It's also interesting to note that Hubble's measurement of the cosmic expansion the previous year was too high by a factor of seven compared to modern accepted values. This gave -- to use Eddington's words -- an uncomfortably recent beginning of the universe, no more than one or two billion years ago.
Albert Einstein, Georges Lemaître, Agnes Mary Clerke, William and Caroline Herschel.
Much of Eddington's paper would not be out of place in a modern textbook but it is also interesting from a historical perspective. Sometimes science can be presented as too much of a fait accompli when in fact its development is invariably a mishmash of often mutually incompatible ideas. These grow up side by side, only for some to flourish while others wither. So recently I listened to the audio book version of Agnes Mary Clerke's Popular History of Astronomy in the 19th Century. I can't recommend it highly enough, although it's not a beginner's book and you'll need a passing knowledge of the subject material in order to appreciate which ideas have been subsequently refined or superseded. The first edition of the book came out in 1885, but the audio book version is the 4th edition from 1902. In the short span of time between those editions, physics had made considerable leaps. The preface mentions that "Clerk Maxwell's medium no longer figures as an indispensable factotum", a reference to null results of experiments to detect the aether which was supposed to fill all of space.
Other major problems in astronomy were nowhere near a resolution in 1902. As an example, the processes that powered the Sun were completely unknown. Conversion of mass into energy as a result of Einstein's Special Relativity was still some years away, but even then it was treated as a curiosity with Einstein doubting that it was a physical possibility. The detailed reactions were not worked out by Hans Bethe until 1939 and he didn't get his Nobel prize for it until 1967!
Meanwhile, in the 19th century there were some interesting theories doing the rounds. The possibility that the Sun was actually burning like a lump of coal was considered, although calculations showed it would have difficulty persisting over geological time which was already known to be vast. Compressional heating by friction -- which we now understand is how stars get started -- was similarly known to have problems explaining sustained energy output. An ingenious extension of the nebular theory of star formation was conceived. The idea was that the Sun continued to accrete material to the present day, in the form of comets falling into it. Nowadays we know the rate of such accretion is much too low to sustain the Sun, but it was a reasonable guess for 19th century astronomy.
And let's face it, there were much wackier ideas floating around. For a 19th century writer, the preeminent astronomer had to be William Herschel, the discoverer of the planet Uranus. He dominated British astronomy for half a century, including the first quarter of the 19th, and his son John took up the standard thereafter. William was born only a decade or so after the death of Isaac Newton (who was born the year Galileo died). Even in Herschel's time, you got hints of pre-scientific ideas still floating around. So Herschel believed the Sun was a planet like our own, with people living on it. He reckoned that if the solar inhabitants looked at our own planet, they would perceive it as a fiery ball, like we do the Sun. The roots of this idea, of course, are in the classical Greek elements. Even though Earth had been displaced from the centre of the universe, fire still had a tendency to rise heavenward, and this was where the great Herschel got his unscientific idea.
There is lots more fascinating stuff in Clerke's book which I recommend you read or listen to yourself. The author is an interesting person in her own right. She wrote several other books on astrophysics and cosmology, and is one of the foremost science popularisers of the 19th century in spite of having no university degree or even any formal schooling. But then, orthodox routes to learning were very limited for women of the time. She was the daughter of a bank manager in Skibbereen and got interested in astronomy as a child, while the elder Herschel was still alive. She was home schooled by her parents, her father being a graduate of TCD, and an amateur astronomer. He owned a transit telescope which would have provided a time service to the townsfolk of Skibbereen in the days long before standardised time zones. The younger Clerke got to view the planets through this instrument and studied astronomy at home in addition to Latin, Greek, and maths. In her twenties she lived in Italy where she was also able to study science (though her first published article was on the Sicilian mafia!).
Later in London Clerke became a successful popular science writer. This gained her many connections with scientists of the time, and her circle grew to include astronomers from across Europe as well as South Africa, and major universities and observatories in the USA. She got to spend time at observatories and became something of an expert on spectroscopy.She was a founding member of the British Astronomical Association, but later became a member of the Royal Astronomical Society and the Royal Institution. She was only the third female member of the RAS, after astronomer Caroline Herschel (brother of William and aunt of John) and Mary Somerville, another self-motivated student and friend of the Herschels. And that reminds me, my next reading or listening project has to be the Memoir and Correspondence of Caroline Herschel, written by John's wife Margaret Herschel in 1879.10
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