You might have read that gravity has been making waves recently. The discovery of gravitational waves has apparently added substantial weight to Einstein’s general theory of relativity, truly one of the the ground breaking theories on how our universe operates. Nevertheless, it is has been a long road to get to our current understanding of the universe, and there is no reason to think we’re anywhere near the end of it. In fact, the road is so long and winding that I’m going to split this history of the theory of gravity over two weeks.

Strangely enough, I can’t seem to find a reference on when people first started to notice that things held up in the air would drop to the ground if you let them go. Nevertheless, for a long time in the West at least, Aristotle was considered the foremost authority on gravity (keeping in mind the term “gravity” itself wouldn’t be coined for over one and a half thousand years by Newton). Aristotle held that everything in the world was composed of four elements: earth, water, air and fire. Each of these elements wanted to be in its proper place, with earth wanting to occupy the centre of the universe below and fire the heavens above. According to Aristotle, everything was made up of these elements in differing quantities, and it was their relative compositions that determined whether they wished to rise or fall.

Interestingly, the fact that a falling object accelerates as it “nears its proper place” (ie. falls), rather than slows down or remains constant, was well known to Aristotle, but he managed to avoid this critique of his theory by using one of the most traditional discursive strategies of the Ancient Greeks: he ignored it. It is also worth noting that in Ancient Greece, there was also a competing theory of gravitation from atomists—those who believed everything was composed of tiny particles—that posited that all atoms attracted each other on some level and therefore everything had some type of gravity. Therefore going from the Ancient Era to the Middle Ages we had two competing theories of gravity—one over a thousand years ahead of its time and one that almost could not have been more wrong—I’ll let you guess which one we chose.

One the most curiously logical and yet mind-bending paradoxes in the history of gravitational theory is that for the majority of human history it did not seem to occur to anyone that what made objects fall to the floor and what kept the planets sailing around the sun (or earth, as it was believed for a long time) was the same thing. Aristotle seems strangely reticent on why the planets wander around the sky, but he maintained that the universe consisted of perfect symmetry and therefore they must orbit in perfect circles, while the Earth sat still at the centre of the universe. A beautiful model of the universe it may have provided, but unfortunately it failed to describe the movements of the planets as they were actually observed. The issue was that the planets would move forward across the sky for many months of the year, conduct funny little reversals, and then proceed forward like nothing had happened. Aristotle took his usual approach to explaining such inconsistencies—he ignored it.

Fortunately, Ptolemy stepped in to the rescue. To solve this conundrum, he introduced epicycles and a deferent. In essence, to correct for this backwards movement, the planets didn’t simply rotate around the earth, they traced small circles around a point—an epicycle—and that point traced a large circle around the Earth, along the deferent. There were even other aspects, such as equant and eccentric, because the model clearly wasn’t complicated enough already.

Again, as seems to so often be the case, there were Ancient Greeks who pointed out that if the planets and the earth revolved around the Sun, it explained many of these inconsistencies. But on the authority of that great thinker Aristotle, the model was rejected.

Credit where credit’s due, Aristotle was not without reason. There were problems with a heliocentric model of the solar-system. If the Earth were spinning, for instance, why don’t we all just go flying off? Similarly, why don’t objects dropped from a great height fall westwards? Why didn’t the stars appear to move around the sky? And finally, it needs to be kept in mind that whilst assuming the planets all revolves around the sun explains many of the inconsistencies, the model still does not entirely line up with observations.

However, for those answers, we need to wait about one and a half thousand years. Or at least until next week.

Academic Sources

Applebaum, W 2005, The Scientific Revolution and the Foundations of Modern Science, Greenwood Press,Connecticut.

Ede, A & Cormack LB 2012, A History of Science in Society: From Philosophy to Utility, 2nd ed., University of Toronto Press, Toronto.

Grant, E 1996, The Foundations of Modern Science in the Middle Ages: Their Religious, Institutional and Intellectual Contexts, Cambridge University Press, Cambridge.

Horvitz, LA 2002, Eureka!: Scientific Breakthroughs that Changed the World, John Wiley & Sons, New Jersey.

Huff, TE 2003, The Rise of Early Modern Science: Islam, China and the West, Cambridge University Press Cambridge.

Krebbs, RE 1999, Scientific Development and Misconceptions Through the Ages: A Reference Guide, Greenwood Publishing Group, Connecticut.