One of the very best things about science is that the discipline is self-correcting. A scientist makes a set of observations about nature, and then devises a theory to fit those observations.
Other scientists then test the theory, and if it withstands scrutiny it becomes widely accepted. At any point in the future, if contravening evidence emerges, the original theory is discarded. At its essence, and though in practice it’s more messy, this is how science works.
Needless to say there have been a lot of theories discarded along the way. The following represents my best efforts to select the 5 most spectacularly wrong scientific theories.
Geocentric universe: The concept that the Earth was at the center of the universe dates back to at least 600 B.C. with Greek philosophers who proposed cosmologies of the Sun, Moon and other heavenly bodies orbiting the Earth. The most famous contortion of the system was Ptolemy’s epicycles to explain the retrograde motion of Mars. This is a prime example of fitting scientific evidence into preconceived notions. The theory was disproven with the publication of Nicholas Copernicus’ De revolutionibus orbium coelestium in 1543.
Luminiferous aether: Assumed to exist for much of the 19th century, the theory held that a “medium” of aether pervaded the universe through which light could propagate. The celebrated Michelson-Morley experiment in 1887 was the first to provide hard evidence that aether did not exist, and the theory lost all popularity among scientists by the 1920s.
Immovable continents: Prior to the middle of the 20th century scientists believed the Earth’s continents were stable and did not move. This began to change in 1912 with Alfred Wegener’s formulation of the continental drift theory, and later and more properly the elucidation of plate tectonics during the 1950s and 1960s.
Stress theory of ulcers: As peptic ulcers became more common in the 20th century, doctors increasingly linked them to the stress of modern life. Medical advice during the latter half of the 20th century was, essentially, for patients to take antacids and modify their lifestyle. In the 1980s Australian clinical researcher Barry Marshal discovered that the bacterium pylori caused peptic ulcer disease, leading him to win a Nobel Prize in 2005.
Static universe: Prior to the observations made by astronomer Edwin Hubble during 1920s, scientists believed the universe was static, neither expanding nor contracting. Hubble found that distant objects in the universe were moving more quickly away than nearby ones. Very recently, in 1999, scientists unexpectedly found that not only was the universe expanding, but its expansion was accelerating.