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Ancient Cosmology

Galileo's theories replaced earlier ideas, like those of Aristotle.

The ancient Greek philosopher Empedocles believed that all objects were made of a combination of fundamental elements: Earth, Water, Air and Fire.

Scientists today still believe that objects are made from basic elements, but the chemical elements of the Periodic Table are very different from the elements of the ancient world.


According to Aristotle, each element had a natural 'resting' place in the Universe. Earth naturally existed at the centre of the Earth. Water naturally rested on top of the Earth and above Earth was Air. At the top of the atmosphere existed the element of Fire. So stones 'wanted' to be at the centre of the Earth, while flames wanted to be at the top of the atmosphere.

When displaced, each element naturally moved towards its resting place. Most objects were a mixture of elements, and the different motions competed with each other. However stones would always fall and flames would always rise.

This system was sophisticated, but it failed to explain many things. In particular, the motions of the planets were difficult to explain. Aristotle believed that this meant that the planets and stars were made of an element that was completely different to anything found on Earth and moved in a completely different way. However a new system would emerge that explained the whole Universe according to a single principle.

Cosmological diagram
magnifyCosmological diagram

The periodic table
magnifyThe periodic table

Aristotle's cosmology
magnifyAristotle's cosmology
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