It is considered one of the most elegant experiments in history. A young Galileo Galilei (1564-1642) releases spheres of various masses from the top of the tower of Pisa in front of a surprised audience consisting of professors, researchers and students at his university. But it is possible that the scene never took place.
The only thing that is certain is that if it had happened it would have taken place sometime between 1589 and 1592, when Galileo was a professor of mathematics at the University of Pisa. No reference is made to these experiments in any of the Italian writings. The only source of information is a couple of lines in a biography written in 1654 (twelve years after Galileo's death and more than sixty after the assumed experiment) by Vincenzio Viviani (1622-1703), his personal assistant during his last three years of life. This was not published until 1717:
During his years as a professor in Pisa, Galileo did not publish any work on his research, even though he wrote a large number of notes on his studies on the body's fall in a medium. All this material was not published for the first time until the end of the 19th century in a text called De Motu.
In view of the existing evidence, there is no agreement among scientists in the history of science on the authenticity of the anecdote. In the past century, publications emerged that argued both for and against its veracity.
According to researcher Michael Segre, the first criticism came from two important galileo researchers: Rafaello Caverni, a Florentine priest (in an encyclopedic work with six volumes between 1891-1900) and Emil Wohlwill, engineer and historian of German science in two articles published in 1903 and 1905).
Both felt that the story of Viviani was contradictory to what arose in Galileo's writings. Caverni considered that the error was by Galileo, who lied at the time to tell Viviani, while Wohlwill considered that Viviani had invented the story and that there was no other information in the wise person who supported it. Therefore, it would never have taken place.
But in two works published in 1916 and 1917, the pupil of Galileo's life, Antonio Favaro, argued against these two authors' objections. He pointed out that his criticism was based on works that Galileo had not published, perhaps because he was not particularly pleased with the results. He pointed out that these investigations did not necessarily take place during his stay in Pisa (1589-1592), so the passages that opposed Viviani might not have been from that time.
He realizes that Viviani sometimes distorted something in his biography of the Italian genius.
On the other hand, it is also true that De Motu Galileo mentions up to seven times the ability to perform experiments from a high tower, although it does not give names or give an exact experimental description. At one point he says "it's something I've often tried." However, all this does not constitute direct evidence that the experiment took place.
This was the case for nearly twenty years, until 1935 published a book by Lane Cooper, an English professor at Cornell University. However, the probability of Viviani's history is again questioned.
The author bases his conclusions on two points: on the one hand in the analysis of the different versions circulated in history; It indicates that this is shown in a very schematic way and that there are contradictions between versions.
On the other hand, in the study of the letters exchanged between Galileo and the professor of mathematics at the University of Pisa Vincenzio Renieri in March 1641. In these letters he told him that he had lost spheres of different size and density from the top of the Tower of Pisa and who reached the ground at different times. These results contradicted the story of Viviani, who claimed they reached the ground at once. It should be noted that at this point in time Viviani was the personal assistant of older (and completely blind) Galileo, so he had access to this correspondence.
Since then, many new documents have been studied, but no one shines on the mystery. One of the last contributions to this controversy is found in the biography published in 1978 by Stillman Drake, a reference in the study of the Italian ointment.
Despite the lack of evidence, Drake believes the Pisa Tower experiment took place. Viviani left only the memories that Galileo told her when she received the letter from Ranieri, although she admits she finds it difficult to understand that Galileo suddenly remembered his age, a fact he never mentioned before.
Drake also convinces Viviani himself to write the letter of writing to Ranieri, including the tower's passage. If this letter is preserved, it would be the final proof of the veracity of history, but unfortunately this letter has not been found.
Briefly, the story is based on a phrase of two lines that arose in the biography written by his personal assistant (which is known to have falsified any information, such as date of birth) according to the alleged memory of the old man of an event that occurred half a century before . It, contrary to what is stated in the letters of Ranieri, and the lack of further evidence of time, question the authenticity of the passage.
For that reason, in a recently published book, it states without any hindrance that "the reason why none of Galileo's adopted witnesses of outstanding performance from the top of the tower mentioned it is that it did not take place".
On the other hand, the story of Viviani must be understood in the context of the eighteenth century. At the time of writing biographies, the likelihood was less important than embodying the image of the character through anecdotes, sometimes invented or adorned.
There are even authors, including the great philosopher and historian of science Alexander Koyré, who goes one step further and believes that Galileo did not perform the experiments described in De Motu. It was actually mental experiments.
If it was, the question is not only whether the Pisa Tower experiment took place or not, but the fact that Galileo Galilei in reality and unlike what is told in the books does not want to prove exactly that "body parts of different weight reach the ground at the same time "and that he was not the first to question Aristotle's ideas about the body fall.
José Manuel Montejo Bernardo: Assistant Doctor. Department of Educational Sciences, University of Oviedo
Originally published in The Conversation.