How we see is an intriguing question - especially for quantum physics. Photo: Mark Mainz/Getty Images
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What does it mean to see something? Take a look at Schrödinger’s cat

It takes only a few photons to trigger our visual sense. Tantalisingly, a few photons can exist in superposition.

What does it mean to see something? It’s a surprisingly philosophical question, especially where quantum physics is concerned.

Quantum physics describes the world at the level of single atoms and smaller, looking at things such as photons, particles of light. These objects are able to be in two places at once, or to spin clockwise and anticlockwise at the same time, a phenomenon known as superposition. Something happens to stop bigger stuff being in two places at once, even though it is composed of atoms and molecules that can exhibit superposition. In experiments, we have achieved superpositions of molecules composed of about 800 atoms but these collapse very quickly. Something about increasing size (or weight) seems to stop the weirdness in its tracks.

Intriguingly, our eyes may help to unravel this. At a meeting of the American Physical Society in Columbus, Ohio, researchers reported that our eyes can register things at the level where quantum weirdness remains. It takes only a few photons to trigger our visual sense. Tantalisingly, a few photons can exist in superposition. The next step is to see whether we notice anything weird when photons in superposition enter our eyes.

This is ambitious. Our unconscious perception is important even to establish whether we see a few photons. The experiments reported in Ohio put subjects in a blacked-out room. When photons were flashed at their eyes, they had to say whether the flash came from their left or their right. Because of the low light intensity, few of the flashes were registered consciously: the subjects couldn’t remember seeing the flash but had to report their gut instinct. They got it right enough of the time to suggest that their brains had registered the photons.

Conscious perception has long been of interest to those who study quantum physics because observation can disturb quantum weirdness. Fire a photon at a double aperture and it will go into a superposition and pass through both apertures simultaneously – but only if no one is looking. Put a detector on the apparatus and the superposition disappears. This is the source of Erwin Schrödinger’s well-known thought experiment. He conceived a situation in which quantum physics leaves a cat both dead and alive, as long as no one observes it.

What is particularly interesting about real-world experiments is that the detector’s presence seems to determine whether the photon behaves like a wave or a particle. It does not require that a person consciously register the result. There is a mystery here about the nature of observation and measurement and what effect it has on the way the microscopic world manifests in our experiments.

No one understands how an atom or photon “knows” that it is – or might be – being tracked. That is what makes the new proposal so exciting. If you cut out the detection apparatus and go straight to the human eye, a slew of questions and opportunities arises. Does a future collision with the molecular apparatus of the retina count as a detection? Is there a difference between human and electronic photon detection? Does it make a difference whether we are conscious or unconscious of the photon’s arrival?

We may have to wait a couple of years for answers. These experiments are beyond our present capabilities, but our horizons are expanding. They promise insight into issues that have been bothering quantum philosophers for a century.

Michael Brooks holds a PhD in quantum physics. He writes a weekly science column for the New Statesman, and his most recent book is At the Edge of Uncertainty: 11 Discoveries Taking Science by Surprise.

This article first appeared in the 19 June 2015 issue of the New Statesman, Mini Mao

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Conjuring the ghost: the "shape-shifting, queer, violent, hippie genuis" of David Litvinoff

A new biography tracks down the elusive Kray confidant who became a friend of Mick Jagger and Keith Richards.

David Litvinoff is a mythic character to anyone with an interest in London during the Sixties. An intimate of the Krays, he was a tough and violent Jew from the East End. He was also a musical genius with an unrivalled knowledge of jazz, the blues and rock that made him a valued friend of Mick Jagger and Keith Richards. It was his ability to move from the East End to Chelsea, from the dives of Soho to Notting Hill, that was the critical factor in the extraordinary vision of London that Donald Cammell and Nicolas Roeg conjured into the film Performance, for which Litvinoff is credited as dialogue coach. And yet, even though all this is known and recorded, he remains a ghost, a figure who wrote nothing and who systematically destroyed all the records of his life he could lay his hands on. Even his exact role in Performance is shrouded in mystery. He is said to have dictated much of the script to Cammell. This biography claims that Jagger’s mesmerising song on the soundtrack, “Memo from Turner”, was in fact a memo from Litvinoff.

Multiple reports describe him as the most brilliant talker London had known since Coleridge, but although there are rumours of tapes they have always been just rumours. I’d have thought he was a figure who would defeat any biographer – a shape-shifting, queer, violent, hippie genius lost in a mist of hallucinogens – but Keiron Pim’s account of this extraordinary character is a magisterial work of scholarship. He tracks down all the living witnesses; he has also unearthed letters, and even some of those long-lost tapes.

The story that emerges is even harder to believe than the legend. Litvinoff came out of the Jewish East End but he was from one of its most talented families. His name was not even Litvinoff: his mother’s first husband went by that name but David was the son of her second, Solomon Levy. Long before he met the Krays or the Stones, he was a gossip columnist on the Daily Express, practically inventing the Chelsea set that shocked the prim Fifties. By that time he had met Lucian Freud, who painted him in an astonishing study, the working title of which was Portrait of a Jew. Litvinoff was furious when Freud exhibited it with the new description of The Procurer, and the bad blood between these two men, both of whom inhabited the drinking clubs of Soho and the Krays’ gambling joints, remained for the rest of their lives. In fact, it is Freud who comes over as the villain of the book, fingered by Pim as the man behind the most violent assault on Litvinoff: he was knocked unconscious at the door to his own flat, on the top floor, and awoke to find himself naked and tied to a chair suspended from the balcony, nose broken and head shaved bald.

I learned much from this book: a period working for Peter Rachman before he became involved with the Krays; sojourns in Wales and Australia when he was fleeing threats of violence. The big discovery for me, however, was Litvinoff’s encyclopaedic knowledge of the jazz and blues traditions that gave birth to rock’n’roll. He taught the Stones a lot but he taught Eric Clapton even more – they were both living at the Pheasantry building on the King’s Road, and Litvinoff seems to have had unlimited access to the most recherché back catalogues and the most recent unreleased recordings. The book traces, but does not comment on, a transformation from an amphetamine-fuelled hard man in the Fifties and early Sixties to the oddest of hallucinogen hippies by the Summer of Love in 1967.

But, for all Litvinoff’s knowledge, wit and gift for friendship, his tale is a tragedy. A man who could talk but couldn’t write; an out gay man long before it was acceptable, who seems never to have been at ease with his sexuality; a proud Jew without any tradition of Judaism to which he could affiliate. Above all, this was a man who lived to the full the extraordinary moment when London dreamed, in Harold Wilson’s Sixties, that class was a thing of the past. Back from Australia in the early Seventies, Litvinoff awoke again to find that it had indeed been a dream. His suicide in 1975 was cold and deliberate. He had outlived his time. 

Colin MacCabe edits Critical Quarterly

Jumpin’ Jack Flash: David Litvinoff and the Rock’n’Roll Underworld by Keiron Pim is publisyhed by Jonathan Cape (416pp, £16.99)

This article first appeared in the 25 August 2016 issue of the New Statesman, Cameron: the legacy of a loser