In the 19th century, scientists proposed the existence of luminiferous aether, a medium believed to fill space and allow the propagation of light waves. Its existence was disproven by the Michelson-Morley experiment.
Scientists once believed in phlogiston, a hypothetical substance thought to be released during combustion. It was later replaced by the oxygen theory of combustion.
Before the germ theory of disease, scientists believed illnesses were caused by foul-smelling air, or "miasma," emanating from decaying organic matter.
Contrary to popular belief, ancient scientists like Aristotle understood the Earth was round. However, during the Middle Ages, some cultures, including European ones, entertained the idea of a flat Earth.
There was a time when scientists thought living organisms could arise spontaneously from non-living matter, leading to beliefs like maggots spontaneously generating from rotting meat.
Geocentrism was the belief that the Earth was the center of the universe, with celestial bodies orbiting around it. This was later replaced by the heliocentric model proposed by Copernicus.
Ancient Greek and Roman physicians believed that health was governed by the balance of four bodily fluids or "humors": blood, phlegm, black bile, and yellow bile.
Before the Big Bang theory gained widespread acceptance, the steady state theory proposed that the universe had always existed and would continue to exist indefinitely, with new matter continually.