Modern flat Earth beliefs are promoted by organizations and individuals which make claims that the Earth is flat while denying the Earth's sphericity, contrary to over two millennia of scientific consensus. Flat Earth beliefs are pseudoscience; the theories and assertions are not based on scientific knowledge. Flat Earth advocates are classified by experts in philosophy and physics as science deniers.

Flat Earth groups of the modern era date from the middle of the 20th century; some adherents are serious and some are not. Those who are serious are often motivated by religion or conspiracy theories. Through the use of social media, flat Earth theories have been increasingly espoused and promoted by individuals unaffiliated with larger groups. Many believers make use of social media to spread their views.

Modern flat Earth belief originated with the English writer Samuel Rowbotham (1816-1884). Based on conclusions derived from the Bedford Level experiment, Rowbotham published a pamphlet titled Zetetic Astronomy. He later expanded this into the book Earth Not a Globe, proposing the Earth is a flat disc centered at the North Pole and bounded along its southern edge by a wall of ice, Antarctica. Rowbotham further held that the Sun and Moon were 3,000 miles (4,800 km) above Earth and that the "cosmos" was 3,100 miles (5,000 km) above the Earth. He also published a leaflet titled The Inconsistency of Modern Astronomy and its Opposition to the Scriptures, which argued that the "Bible, alongside our senses, supported the idea that the earth was flat and immovable and this essential truth should not be set aside for a system based solely on human conjecture".

Rowbotham and followers like William Carpenter gained attention by successful use of pseudoscience in public debates with leading scientists such as Alfred Russel Wallace. Rowbotham created a Zetetic Society in England and New York, shipping over a thousand copies of Zetetic Astronomy.

After Rowbotham's death, Lady Elizabeth Blount established a Universal Zetetic Society, whose objective was "the propagation of knowledge related to Natural Cosmogony in confirmation of the Holy Scriptures, based on practical scientific investigation". The society published a magazine, The Earth Not a Globe Review, and remained active well into the early 20th century. A flat Earth journal, Earth: a Monthly Magazine of Sense and Science, was published between 1901 and 1904, edited by Lady Blount.

The flat Earth model is an archaic conception of Earth's shape as a plane or disk. Many ancient cultures subscribed to a flat Earth cosmography, including Greece until the classical period, the Bronze Age and Iron Age civilizations of the Near East until the Hellenistic period, India until the Gupta period (early centuries AD), and China until the 17th century. The idea of a spherical Earth appeared in Greek philosophy with Pythagoras (6th century BC), although most pre-Socratics (6th-5th century BC) retained the flat Earth model. Aristotle provided evidence for the spherical shape of the Earth on empirical grounds by around 330 BC. Knowledge of the spherical Earth gradually began to spread beyond the Hellenistic world from then on. In the modern era, pseudoscientific flat Earth theories have been espoused by modern flat Earth societies and, increasingly, by unaffiliated individuals using social media. Read more

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