6 The “Hollow Earth Theory” was once seriously considered by scientists and politicians. It is a concept that planet Earth is hollow on the inside or has a substantial interior space. The notion was disproved around the late 17th century but was occasionally brought up throughout the 19th century. 

Edmond Halley in the 17th century notably did studies on the Hollow Earth concept. Many expeditions were planned to the North Pole to find the entrance to the hollow part of the planet.

Some even stranger theories, like the inside of the Earth, might have inner sun and even a subterranean kingdom, also became widely disputed but also accepted by many during the early 16th to 20th century. 

While some claimed that humans lived outside Hollow Earth, some claimed we lived inside the surface of a hollow, spherical world. The Egyptian mathematician, Mostafa Abdelkader, is known for the papers he has written on this theory. It was even clear on some historical documentation that even Adolf Hitler was influenced by Hollow Earth ideas. (Source)

7 “Icepick lobotomy” was one of the most brutal medical procedures of all time. The patient ended up in a vegetative state after an icepick was inserted through an eye socket for treating mental illness. President John F. Kennedy’s sister Rosemary was the most famous patient in the world having to undergo the procedure. 

In 1974, Walter Freeman, a psychiatrist from Washington, D.C., launched treatment for mental illness. His theory was mental illness can be treated by cutting the brain to remove such feelings.

Before his death, he had performed around 2,500 “icepick lobotomies” in 23 states. The treatment stemmed from the leucotomy process that started in 1935 in Portugal where a hole is drilled into the skull to help fix the patient’s brain. 

Freeman convinced everyone that his 10-minute procedure was set to help transform the history of medicine. Through the orbit of the eye, the ice pick was inserted through a patient’s eyeball to the frontal lobes of the brain. The icepick is moved back and forth to make the adjustment. The procedure caught on, and he lobotomized patients across the country. (1, 2)

8 “Lamarckism” is a theory that an organism can pass on the physical characteristics it acquired during its lifetime. It is also called “soft inheritance,” and many scientists worked with it in the 1860s to find evidence. Even Charles Darwin supported the idea which turned out to be just an assumption of Lamarck’s idea of heredity and not about evolution. 

Lamarck was considered an important personality in the history of science. He put forward a new notion of evolution with very little scientific evidence. The theory itself was more based on speculations than facts. Lamarck said small changes that happen in an animal’s body as they strove for food will be shown on their offspring. 

Even though he explained his theory in materialistic terms, the scientists eventually began questioning the authenticity and his lab results. Darwin’s concept was well articulated, but Lamarck’s was not. His idea about the evolution of giraffes to have long necks was passed on to school textbooks but eventually taken down due to less scientific backup. (1, 2)

9 Scientists, including Charles Darwin, used to believe in the theory that Earth is expanding. The theory is now considered pseudoscience after the plate tectonics theory. Data analysis has helped prove that the Earth has not expanded in around 600 million years. 

A Growing Earth or Expanding Earth hypothesis had eventually had problems when new geological evidence came up and the results did not match. Due to the lack of enough scientific material and research, geologists of the time believed in the theory that planets changed dimensions.

The debates also included expansionism, mobilism, and fixed dimension planets. Contracting Earth and Expanding Earth theories got rapidly replaced after the plate tectonics theory was introduced.

The supporters, even after the theory of plate tectonics had been accepted, continued believing by selectively picking the data that supports expansion even after several inconsistencies. It is now considered a falsified hypothesis and one of the most absurd theories ever. (1, 2)

10 According to Newton, the reason for the wobbling of the planet Mercury was believed to be due to the existence of a planet called “Vulcan” which orbited between Mercury and Venus. It was first observed in 1859 by Urbain Le Verrier. It was eventually proven wrong in the 19th century and confirmed by Einstein that Vulcan did not exist. 

There was a belief that there was a planet orbiting next to Mercury that cannot be found because it is lost in Sun’s glare. The belief that humans can discover a planet without any fundamental proof and self-deceive a huge mass into believing it is what happened when the planet “Vulcan” was introduced to the planetary system to help explain the orbit and gravitational influence on Mercury. 

The theory made absolute sense with Newton’s mathematical framework, and for 20 years, people believed such a planet existed. Since the wobbling of Uranus led to the discovery of Neptune, this logic seemed clear to the scientists when they couldn’t explain the same influence on Mars.

Scientists even got U.S.-government-funded stations set up to watch the 1878 great eclipse to find more clues on Vulcan. Later, the relativity theory fundamentally changed the idea of gravity and disproved the existence of Vulcan. (1, 2)