From a new Edge compilation of things we have believed that we’ve learned aren’t so, this on gravity. The whole set is worth reading.
Quantum Physicist, Oxford; Author, The Fabric of Reality
Surely the most extreme example is the existence of a force of gravity.
It’s hard to say when this belief began but it surely predates Newton. It must have existed from the time when concepts such as force were first formulated until the general theory of relativity superseded it in 1915.
Why did scientists hold that belief for so long? Because it was a very good explanation and there was no rival theory to explain observations such as heavy objects exerting forces on whatever they were resting on. Since 1915 we have known the true explanation, namely that when you hold your arm out horizontally, and think you are feeling it being pulled downwards by a force of gravity, the only force you are actually feeling is the upward force exerted by your own muscles in order to keep your arm accelerating continuously away from a straight path in spacetime. Even today, it is hard to discipline our intuition to conceive of what is happening in that way, but it really is.
I also like this cautionary comment from Charles Simonyi:
I think we are all too fast to label old theories “wrong” and with this we weaken the science of today — people say — with some justification from the facts as given to them — that since the old “right” is now “wrong” the “right” of today might be also tainted. I do not believe this — today’s “right” is just fine, because yesterday’s “wrong” was also much more nuanced “more right” that we are often led to believe.