The Leaning Myth of Pisa

Prompted to post this squib, extracted from my book Science: A History, by seeing it yet again stated that Galileo dropped things from the leaning tower.  All together now, in best panto style: Oh no he didn’t!


Another of the Galileo legends introduced by his disciple Viviani refers to Galileo’s time as Professor of Mathematics in Pisa, but is, once again, almost certainly not true. This is the famous story of how Galileo dropped different weights from the leaning tower to show that they would arrive at the ground below together. There is no evidence that he ever did any such thing, although in 1586 a Flemish engineer, Simon Stevin (1548-1620; also known as Stevinus), really did carry out such experiments, using lead weights dropped from a tower about 10 metres high. The results of these experiments had been published, and may have been known to Galileo. The connection between Galileo and weights being dropped from the leaning tower, which Viviani has confused with Galileo’s time as Professor of Mathematics in Pisa, actually dates from 1612, when one of the professors of the old Aristotelian school tried to refute Galileo’s claim that different weights fall at the same speed, by carrying out the famous experiment. The weights hit the ground at very nearly the same moment, but not exactly at the same time, which the peripatetics seized on as evidence that Galileo was wrong. He was withering in his response: Aristotle says that a hundred-pound ball falling from a height of one hundred cubits hits the ground before a one-pound ball has fallen one cubit. I say they arrive at the same time. You find, on making the test, that the larger ball beats the smaller one by two inches. Now, behind those two inches you want to hide Aristotle’s ninety-nine cubits and, speaking only of my tiny error, remain silent about his enormous mistake. The true version of the story tells us two things. First, it highlights the power of the experimental method – even though the peripatetics wanted the weights to fall at different speeds and prove Aristotle was right, the experiment they carried out proved that Aristotle was wrong. Honest experiments always tell the truth. Secondly, the quotation above gives a true flavour of Galileo’s style and personality. It is impossible to believe that if he really had carried out the famous experiment himself then there would be no mention of this triumph anywhere in his writings. For sure, he never did it.



The Meaning of Multiverse

In answer to a question posed by a friend:

According to the Oxford English Dictionary, the word “multiverse” was first used by the American psychologist William James (the brother of novelist Henry James) in 1895.  But he was interested in mysticism and religious experiences, not the nature of the physical Universe.  Similarly, although the word appears in the writings of G. K. Chesterton, John Cowper Powys, and Michael Moorcock, none of this has any relevance to its use in a scientific context.  From our point of view, the first intriguing scientific use of the word followed from an argument put forward by Alfred Russel Wallace, the man who came up with the idea of evolution by natural selection independently of Charles Darwin, that “our earth is the only inhabited planet, not only in the Solar System but in the whole stellar universe.”  Wallace wrote those words in his book Man’s Place in the Universe, published late in 1903, which developed ideas that he had previously aired in two newspaper articles.  Unlike Darwin, Wallace was of a religious persuasion, and this may have coloured his judgement when discussing “the supposed Plurality of Worlds.[1]  But as we shall see, there is something very modern about his approach to the investigation of the puzzle of our existence.  “For many years,” he wrote:

I had paid special attention to the problem of the measurement of geological time, and also that of the mild climates and generally uniform conditions that had prevailed throughout all geological epochs, and on considering the number of concurrent causes and the delicate balance of conditions required to maintain such uniformity, I became still more convinced that the evidence was exceedingly strong against the probability or possibility of any other planet being inhabited.

This was the first formal, scientific appreciation of the string of coincidences necessary for our existence; in that sense, Alfred Russel Wallace should be regarded as the father of what is now called “anthropic cosmology.”

Wallace’s book stirred up a flurry of controversy, and among the people who disagreed publicly with his conclusions were H. G. Wells, William Ramsay (co-discoverer of the inert gas argon), and Oliver Lodge, a physicist who made pioneering contributions to the development of radio.  It was Lodge who used the term “multiverse,” but referring to a multitude of planets, not a multitude of universes.

In scientific circles, the word was forgotten for more than half a century, then invented yet again by a Scottish amateur astronomer, Andy Nimmo.  In December 1960, Nimmo was the Vice Chairman of the Scottish branch of the British Interplanetary Society, and was preparing a talk for the branch about a relatively new version of quantum theory, which had been developed by the American Hugh Everett.  This has become known as the “many worlds interpretation” of quantum physics, with “world” now being used as a synonym for “universe.”  But Nimmo objected to the idea of many universes on etymological grounds.  The literal meaning of the word universe is “all that there is,” so, he reasoned, you can’t have more than one of them.  For the purposes of his talk, delivered in Edinburgh in February 1961, he invented the word “multiverse” – by which he meant one of the many worlds.  In his own words, he intended it to mean “an apparent Universe, a multiplicity of which go to make up the whole  .  .  .  you may live in a Universe full of multiverses, but you may not etymologically live in a Multiverse of ‘universes’.”

Alas for etymology, the term was picked up and used from time to time in exactly the opposite way to the one Nimmo had intended.  The modern usage of the word received a big boost in 1997, when David Deutsch published his book The Fabric of Reality, in which he said that the word Multiverse “has been coined to denote physical reality as a whole.”  He says that “I didn’t actually invent the word.  My recollection is that I simply picked up a term that was already in common use, informally, among Everett proponents.”  In my books, the word “Multiverse” is used in the way Deutsch defines it, which is now the way it is used by all scientists interested in the idea of other worlds.[2]  The Multiverse is everything that there is; a universe is a portion of the multiverse accessible to a particular set of observers.  “The” Universe is the one we see all around us.

[1] His emphasis.

[2] I refer any offended etymologists to the comment of Humpty Dumpty in Through the Looking Glass:  “When I use a word,’ Humpty Dumpty said, in a rather scornful tone, ‘it means just what I choose it to mean, neither more nor less.’”

Adapted from my book In Search of the Multiverse (Penguin)