Is the Earth flat, spherical or hollow? There are varying theories on the plant's shape and size presented by different scientists over the years, who have even backed up their opinions with logical and scientific evidence, but the debate continues.

According to a small group of theorists termed as hollow Earthers, our planet is hollow — somewhat like a donut, with the core inhabited by aliens, Nazis and Vikings. Rodney Cluff, a self-proclaimed "scientist" and a hollow-Earth theorist himself, has recently penned a book detailing the doughnut-shaped "hollow Earth" and its hidden residents.

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Dianne Robbins, another hollow Earth theorist, believes that the creatures living at the centre are immortal. "They are physical humans like we are, but they live in peace, isolation and seclusion, and through this they have gained their immortality."

Cluff claimed that the pseudoscientific theory has already gained popularity and the number of hollow Earthers has been increasing progressively. "More and more people are coming to terms with the fact that the Earth is hollow. I get emails from people learning about it every day," Cluff told the paper. "It's definitely growing in popularity - certainly not in the millions but maybe in the thousands."