A history of nothing: how zero went from nil to something

From ancient trade to modern theoretical physics and computer programming, the history of mathematics closely mirrors the history of zero – first as a concept, and then ultimately as a number. Narrated by the UK mathematician Hannah Fry, this short animation explores how the evolution of the understanding of zero has helped shape our minds and our world.

The pioneering psychologist who proved that being gay isn’t a mental illness

‘What is called this year “evil” and whatever, next year may constitute the blessing of the human race.’

Throughout much of the 20th century in the United States, homosexuality was considered a mental illness by the medical establishment. This view created a cruel set of circumstances for gay people, as a lack of serious research into homosexuality allowed social institutions to discriminate on the basis of sexual orientation, and medical institutions could subject gay people to psychologically and physically damaging therapies.

This brief video essay explores the legacy of the late US psychologist Evelyn Hooker (1907-96), whose groundbreaking studies of homosexuality would help lay the groundwork for the modern gay rights movement. Inspired by her friendship with a gay student she met while teaching at the University of California, Los Angeles in the 1940s, Hooker began to study mental stability in straight and gay male populations. Ultimately, her work revealed that there was no correlation between homosexuality and psychological maladjustment. In 1973, the American Psychiatric Association finally removed homosexuality from their list of mental disorders amid pressure from gay rights activist, who cited Hooker’s pioneering work in their arguments.

How do you message an alien? Carl Sagan offers some simple suggestions

Is there a foolproof way to announce our existence to other intelligent life-forms? It’s a brainteaser with vast potential consequences, and one that scientists seem to love puzzling over – even if some, such as Stephen Hawking, have questioned the wisdom of alerting advanced beings to our humble corner of the Universe. In this short video excerpt from a 1977 lecture at the Royal Institution in London, Carl Sagan – more optimistic about the prospect of alien benevolence than Hawking – offers one possible method. First, he establishes his belief that a common language among dissimilar beings in a shared universe should, in theory, be possible. He then presents a document coded in ones and zeroes, containing a message that he hopes could be decoded by an intelligent being anywhere in the Universe. Finally, Sagan recounts an experiment in which he presented the document to what he considers a ‘reasonably clever’ life-form – some of his graduate students at Cornell University – to see if they could decipher it.

Making sauerkraut is a spiritual matter for the ‘fermentation fetishist’ Sandor Katz

The US writer and activist Sandor Katz is one of the world’s leading experts on fermentation – a process born of the collaboration between people, time and microbes that makes possible such beloved culinary staples as bread, beer, wine, kimchi and miso. A self-described ‘fermentation fetishist’, Katz views this process as a humbling means of reconnecting with nature and its foodways, and has written several books on the subject and leads fermentation workshops in the US and abroad. In Sandorkraut, the US filmmakers Emily Lobsenz and Ann Husaini explore how an HIV diagnosis in 1991 led Katz on an unexpected path from New York City to a queer community in Tennessee, where he developed a spiritual connection with all things fermented.

Step into synaesthesia’s visual soundscape, built with the music of John Coltrane

The Israeli animator and artist Michal Levy is among the roughly 3 per cent of people who experience synaesthesia – a neurological condition in which people have a recurring sensory overlap, such as ‘tasting’ words or envisioning letters and numbers each with their own inherent colour. Levy possesses one of the most common forms of the condition, chromaesthesia, in which sounds and music provoke visuals. For her short film Giant Steps, Levy set out to convey her audiovisual experience of the John Coltrane composition ‘Giant Steps’ (1959). The resulting short animation is at once an intriguing window into the sensory world of a person with synaesthesia and an audiovisual delight, as Coltrane’s rollicking notes elicit a kinetic, cascading cityscape built from colourful blocks of sound.

To read more about synaesthesia, visit visit Aeon’s sister site, Psyche, a new digital magazine that illuminates the human condition through three prisms: mental health; the perennial question of ‘how to live’; and the artistic and transcendent facets of life.