Galileo against Aristotle and the most epic redoubt to the absurd in history

Aristotle’s idea that the speed of a body in free fall depends on its weight permeated physics for centuries, until Galileo Galilei came to revolutionize this and other bases that are now part of how we understand the forces of the universe.

Already in Ancient Greece, Aristotle He developed his own conclusions about the behavior of bodies in different fluids, including air. Since then, the Greeks were wondering how objects tend to fall to the ground and what force is behind it. For this reason, Aristotle developed his primitive gravitational theory, which among many of the aspects of him here embodied that the free fall of objects depended on the ‘lightness’ or ‘gravity’ of the weights. That is, the heavier an object, the faster it would fall towards the ground. On the contrary, the free fall of lighter objects would tend to be delayed compared to heavier objects.

And this idea remained present until Galileo Galilei came out to refute it in a masterly way. To prove that Aristotle was wrong, Galileo climbed (hypothetically) to the top of the Tower of Pisa and dropped two objects, one heavy and one lighter. If Aristotle was right, then the heaviest object must fall first. And although Galileo did not appeal to practice, since there are no records that he carried out the experiment in a real way, he did appeal to logic and by mere reductio ad absurdum he deduced that Aristotle had erred. How did he do it?

reduced to the absurd

He used the absurd redoubt in a masterful way just by mentally carrying out the experiment described above. Same as mentioned in different sources, but almost never fully described and that ‘almost’ makes a huge difference in understanding why Galileo concluded that Aristotle was wrong.

In contemporary wisdom it is mentioned that Galileo dropped two objects with different weights from the tower of Pisa. What is not mentioned is that it was actually a system, not isolated objects. Thus, the Italian physicist imagined both orbs joined by a string and therefore one would influence the result of the other and vice versa. If Aristotle’s theory were correct, we would obtain two contradictory conclusions, an argument that in logic is called ‘reductio ad absurdum’.

On the one hand, we would have that the stone with the least weight would slow down its partner (just as the heaviest would accelerate the first). While on the other, the weight of both added would constitute a weight greater than that of the objects separately. So it should fall faster.

From the same event we obtain two conclusions that are contradictory: in the first case, the set should fall slower than if only the heavy object was thrown. In the second case, the whole should fall faster than if only the largest stone was thrown. This is how Galileo finally showed that Aristotle had erred in his conclusions.

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