Aristarchus of Samos was a Greek scientist famous today for being the first to suggest that the Earth revolves round the Sun. Famously, this suggestion caused major controversy, and scientists of the time generally rejected the idea. According to recent research, the reason for the controversy may not have been entirely scientific. Instead, Aristarchus may have used his theory to try to challenge the political power of the Ptolemaic kings.
Aristarchus’ theory and the controversy that resulted
Aristarchus of Samos lived from about 310 to about 230 BC. He was a scientist who studied the Earth and the movement of the celestial bodies. At the time, the prevailing theory was that the Earth sat in the centre of the universe. Around it were several concentric layers of a solid substance called aether. The celestial bodies, such as the Sun, Moon, and stars, were attached to these layers of aether, and they revolved around the Earth. This model was proposed by Aristotle in the fourth century BC.
In contrast to Aristotle’s famous and highly respected cosmological model, Aristarchus argued that the Earth was not the centre of the universe. Rather, it revolved around its axis, and it orbited the Sun. While Aristarchus still had a very incomplete and imperfect understanding of the universe, this was a major step in the right direction.
Unfortunately, most scientists of his time rejected his theories. Aristarchus was vilified for his theories by some. In particular, the Greek philosopher Cleanthes accused him of impiety.
Was the controversy scientific or political?
The most popular understanding of why Aristarchus’ heliocentric model proved so controversial is simply that it opposed the geocentric model of Aristotle. This scientist from the fourth century BC was highly respected. His model of the universe became the foundation of cosmology within Western science for nearly 2000 years. It is easy to see why a model that opposed Aristotle’s ideas would have been so vilified.
However, this is not the only explanation. New research from Dr Joshua David McDermott, from the University of Sydney, has challenged this standard viewpoint. In a paper published in Cambridge University Press on September 21, he made the case that Aristarchus was actually engaging in parrhêsia. This is an expression meaning ‘frank speech’.
In this context, McDermott is suggesting that Aristarchus was presenting his theory not just for scientific reasons, but as a way of undermining the alleged power of the Ptolemaic kings who were ruling in his time.
How Aristarchus’ heliocentric model may have challenged royal power
McDermott highlights the fact that Hellenistic writers emphasised and exaggerated the power of the Ptolemaic kings ruling from Alexandria in Egypt. Naturally, the kings of this dynasty liked to be viewed as overlords of everything. They promoted the idea that their authority as kings was divinely decreed.
Closely related to this was the idea that the heavens themselves were subject to the gods. Cleanthes, Aristarchus’ critic, highlighted this concept in his Hymn to Zeus. That being so, the fact that the universe was believed to revolve around the Earth brought everything together. The divine authority of the Ptolemaic kings, the heavens being subject to the gods, and these same heavens revolving around the Earth were three interconnected concepts.
McDermott points to a specific example of how the authority of the Ptolemaic kings supposedly encompassed the heavens. In 246 BC, an astronomer named Conon of Samos identified a constellation of stars as being a lock of hair from Queen Berenice II. According to McDermott, this is a clear example of astronomy serving a political purpose. In this case, it was to bolster the supposed divine authority of the Ptolemies by presenting it as extending into the heavens.
With this in mind, Aristarchus’ heliocentric model would certainly have undermined the authority of these Ptolemaic kings. He argued that the Earth was not the center of the universe. If this was accepted, then it would suddenly be much harder to maintain the viewpoint that the authority of the Ptolemies, ruling from the Earth, extended across the heavens.
Further implications of Aristarchus’ model
Aristarchus did not merely suggest that the Earth revolved around the Sun. He also argued that the Sun was much bigger than the Earth, and that the universe as a whole was vastly bigger than previously imagined. He noted that if the Earth was constantly in movement, then a parallax effect should be seen among the stars.
Since he could not observe any such parallax effect, this indicated that the stars were exceptionally far from the Earth. Hence, the universe as a whole must have been much larger than Aristotle’s model accounted for.
The political implications would have been immense. The Ptolemaic kings would not only have lost the foundation of being the centre of the universe, but the Earth would have suddenly become seemingly insignificant in the grand scheme of things. Certainly, this would have been an example of parrhêsia, or frank speech, towards the Ptolemaic kings. If McDermott’s argument is correct, no wonder Aristarchus was accused of impiety.
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