Galileo Galilei’s theory of how and why the tides worked was, as we have known for hundreds of years, horribly wrong, and yet phenomenal; one that only a mind as brilliant as his could have formulated. In fact, it was a significant step towards modern science and discovery. In 1595, when Galileo first came up with his explanations for the tides, he was desperately trying to prove that the Copernican universe was true – something that the church and public would not accept at the time. In addition to this, Galileo believed that the common hypothesis of the cause of the tides at that time (that they were caused by the moon) was a ‘lamentable piece of mysticism’, as scientists who proposed it could offer no scientific explanation for it (Tyson, P. His Big Mistake, http://www.pbs.org/wgbh/nova/galileo/mistake.html). One of the main scientists of the time who supported the hypothesis of the tides being caused by the moon was Johannes Kepler, who was indeed correct in his hypothesis, which however was only based upon intuition. Interestingly, it is this way of conducting science which Galileo opposed: he believed in a more hands-on approach to science, in which one worked with what he could see and made rational and mathematical sense of his conclusions. It is because of this experimental attitude towards science that Galileo was called the ‘father of modern science’ by the likes of Albert Einstein and Steven Hawking.
At the time of Galileo Galilei, modern science did not exist – theories were formulated more mere intuition rather than hard facts and observations. Galileo supported the observations made by Copernicus in the mid 16th century which suggested that the Earth was not static, but rather that it orbited around the sun, as with other planets. This theory explained why objects in the sky seemed to move. However, at the time of Galileo (16-17th century) the Ptolemaic system was still taught and fully supported by the church. This system described that the sun orbited around a static Earth, in contrast with the Copernican heliocentric view of our system. Therefore, Galileo’s determination to prove the Copernican theory he so strongly believed in played a large part in why he got the tides wrong.
Galileo’s explanation of the tides was written in a formal letter to a cardinal, after Galileo had failed to convince the church to not ban the Copernican theory in Rome in 1616. This letter was entitled “Discorso sul flusso e il reflusso del mare”. The scientist used an interesting metaphor to describe the tides – he examined in how many different ways the water in a vase can move, in which clearly the vase represented the Earth. Firstly, the slope of the vase plays a part in the movement of the water. Furthermore, external forces such as wind can affect water movement. Lastly, and most importantly, the motion of the vase itself can influence the water movement. This final point was the root of Galileo’s theory of the tides. “The idea occurred to him while travelling on a barge that was ferrying freshwater to Venice. (Galileo lived in nearby Padua and often visited Venice.) He noticed that whenever the barge’s speed or direction altered, the freshwater inside sloshed around accordingly. If the vessel suddenly ground to a halt on a sandbar, for instance, the water pushed up towards the bow then bounced back toward the stern, doing this several times with ever decreasing agitation until it returned to a level state.” (Tyson, P. His Big Mistake, http://www.pbs.org/wgbh/nova/galileo/mistake.html).
According to the Copernican system, the Earth is affected by two circular motions – the annual revolution about the sun and the diurnal rotation. Due to these two motions, there is a change in the speed of the Earth’s rotation every 12 hours, which Galileo explained mathematically and connected this with his observations of the freshwater barge in Venice. “Thus, for 12 hours, a point on the earth’s surface will move eastward, in opposition to the global westward movement of the earth, and for 12 hours it will move westward, in the same direction as the annual motion. The composition of these motions causes on one hand a slackening (due to a subtraction of two opposite motions) and on the other hand an acceleration (due to an addition of two motions in the same direction).” (Gigli, R. Galileo’s theory of the tides, http://galileo.rice.edu/sci/observations/tides.html#4). Furthermore, he explained that differences in tidal flows are due to the differences in the physical conformations of the basins in which they flow. (Machamer, P. Galileo Galilei, http://plato.stanford.edu/entries/galileo/). Thus, Galileo thought he had explained the mystery of the tides. Moreover, this theory of his satisfied Galileo because it strongly supported the Copernican universe: the movement of the Earth accounts for the tides, and the tides account for the Earth’s movement, thus suggesting a heliocentric view of our system, which Galileo supported. In 1623 Galileo was brought to the Inquisition for suggesting in his Dialogue that the Copernican view was correct, which shows how determined the scientist was to find proof of the heliocentric universe.
At the same time in history, a contemporary scientist of Galileo’s, Johannus Kepler, argued that the water’s attraction to the moon caused the flux and reflux of the sea water, ie the tides. Galileo dismissed this idea of magic attraction between the moon and water, as no one tried to justify it by mathematical or experimental means. Instead, Galileo believed in a mechanical approach, as explained previously, which could be accounted for using mathematics and scientific facts and knowledge. Galileo, therefore, led the scientific world away from an intuitive and deductive approach – which was prominent at his time – to a modern, experimental way of conducting science, despite being completely wrong about the cause of the tides.
Galileo’s theory, however, was not without its objections, and one can see why many were reluctant to accept it. The main problem was that his theory would call for only one high tide every day, whereas it was known already that there are about two. Galileo dismissed this anomaly as the result of several secondary causes, including the shape of the sea, its depth, and other factors. (Finocchiaro (1989), pp.127-131 and Drake (1953), pp. 432-6). Also, the tidal argument does not directly deal with the annual motion of the earth about the sun. And finally, Galileo’s theory does not suggest anything about the central position of the sun or about the periods of the planets as calculated by Copernicus. (Machamer, P. Galileo Galilei, http://plato.stanford.edu/entries/galileo/). Therefore, Galileo’s theory about the tides did not completely prove that our system is heliocentric, even though the scientist was so eager to do so. It was this eagerness, according to Einstein, that led Galileo to cling so tightly to his theory of the tides, and thus slightly mislead him.
Nevertheless, the weaknesses present in Galileo Galilei’s theory of the tides proved that it had been extremely well thought out and rationalised using mathematics, as one would not be able to point out mistakes if the theory had been based on intuition. On the other hand, Kepler was basing his theory of the tides caused by the moon on pure intuitive deduction. He wrote: “If the earth ceased to attract the waters of the sea, the seas would rise and flow into the moon…” and added “If the attractive force of the moon reaches down to the earth, it follows that the attractive force of the earth, all the more, extends to the moon and even farther…” (Fowler, M. More Kepler, http://galileoandeinstein.physics.virginia.edu/1995/lectures/morekepl.html), which were interesting arguments indeed, but Kepler did nothing in terms of physical and mathematical illustration to prove his point. Therefore, Galileo had no choice but to refuse Kepler’s ideas, despite them being ultimately indicative of the truth, due to the lack of empirical and experimental justification. How could the moon be magically attracting the water on the Earth’s surface? Newtonian gravity did not exist at the time, so an explanation was not possible. What Galileo stood against was the fact that Kepler could not even offer any plausible explanation, in words or mathematics alike, for his theory of the tides. It is this attitude towards science which made Galileo special and earned him a place as one of the greatest scientists of all time.
It wasn’t until Isaac Newton came along that the tides were explained specifically in a scientific manner. Published in 1686, his explanation of the tides was roughly the following: “Tides are periodic rises and falls of large bodies of water. Tides are caused by the gravitational interaction between the Earth and the Moon. The gravitational attraction of the moon causes the oceans to bulge out in the direction of the moon. Another bulge occurs on the opposite side, since the Earth is also being pulled toward the moon (and away from the water on the far side). Since the earth is rotating while this is happening, two tides occur each day” (Col, J. Tides, http://www.enchantedlearning.com/subjects/astronomy/moon/Tides.shtml). Newton was thus able to expand on Kepler’s intuitive theory of the tides and explain it scientifically, finally proving it. This, however, would not have been possible had Galileo not shown the world how to conduct modern science in an empirical and experimental manner, relying on observations to draw plausible, rational and mathematical conclusions.
It can hence be concluded that Galileo Galilei’s mistaken theory of the tides, his greatest blunder, served only to further demonstrate his great strength, which was the ability to conduct scientific experiments and analysis using only what he saw with his own eyes, deviating away from intuitive and deductive reasoning to a more hands on, empirical and experimental way of doing science. The world at Galileo’s time, in the 16-17th centuries, was stuck in a mentality where scientific knowledge was based on “more on closing one’s eyes than on observing through the telescope” (Gigli, R. Galileo’s theory of the tides, http://galileo.rice.edu/sci/observations/tides.html#4), which means that Galileo broke a seemingly unbreakable barrier – he fought against the Inquisition, the church and even fellow scientists to carry science to its right direction to ensure the future of modern science. It was as if Galileo knew exactly where the world of science was supposed to go, and did everything in his power to make sure it go there. It is of no historical importance that Galileo’s theory of the tides was actually wrong: what matters is the thinking and reasoning process that was behind the very plausible theory for its time. In fact, Newton’s proof that it was wrong only again goes to show exactly what Galileo Galilei so strongly stood for: basing theories on experimental observations and mathematical calculations using only facts. It is no wonder that the likes of Albert Einstein and Steven Hawking have named Galileo Galilei the ‘father of modern science’.