Science is awesome – get an idea about how the world works, create an experiment to test that idea, repeat. That simple process is how mankind has come so far.
Along the way there have been several cases where the scientific process has overturned conventional “knowledge”. For example people thought that the Earth was flat because that is what came naturally to them – but that was rubbish. Don’t be so smug though, I guarantee that today we believe things that are equally untrue (about human nature, morality, and consciousness for example).
The stories of the open minded scientists who made these breakthroughs are interesting reading. Here is an article discussing 10 great experiments of history: “moments when, using the materials at hand, a curious soul figured out a way to pose a question to nature and received a crisp, unambiguous reply”.
I’ll summarise an example:
William Harvey – the heart actually pumps blood
In the 1700s conventional wisdom said that invisible spirits called “pneuma” caused the blood to “slosh back and forth like the tides” but Harvey thought the heart had something to do with it. He tested his theory but cutting open a live snake and pinching the main vein entering the heart. The heart became paler and smaller as it was starved of blood. When he pinched the main artery coming out of the heart the opposite happened, the artery swelled up with blood like a balloon. He had shown that the heart pumps blood around the body.