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Even when you understand the science, its quite hard to accept that rainbows are not real. You can think you can see one, and the person standing next to you agrees. But you are both being fooled. A rainbow is the pattern of coloured light that you perceive when you look out on a very specific set of atmospheric conditions. Because each of your eyes looks out at a slightly different angle, you actually perceive two different rainbows, one in each eye. And the person next to you sees a different rainbow again. None of those rainbows exist out there, outside of a mind.

If you can accept this, maybe you can accept the Italian physicist Carlo Rovellis perception of the universe. His new book, Helgoland, is an argument that nothing we see and experience actually exists. Just as the rainbow is a manifestation of the angle between you, some water droplets in the sky, and the sun, Rovelli tells us that the atoms, electrons, photons of light and other stuff of the universe manifest only in their interactions with each other. Individual objects are the way in which they interact, he says. Reality is a vast web of interacting entities, of which we are a part.

This relational reality is Rovellis favoured way of interpreting quantum theory, physicists best mathematical description of how the universe behaves at its most fundamental level. Quantum physics invites such interpretations because it doesnt actually have anything to say about the nature of reality. It was cobbled together, a somewhat Heath Robinson affair, on the back of late 19th-century attempts to make better electric light bulbs.

First came the assertion from the German physicist Max Planck that energy is emitted by atoms in lumps: it pours out like cereal from a packet, not like milk from a bottle. Planck could not justify his idea he called it an act of desperation. Nonetheless, it enabled him to explain the ratio of heat to visible light given out by electric light bulb filaments. After this problem was solved, one ingenious hack was forced on top of another until we ended up with a theory that could accurately describe the outcomes of any experiment involving atoms and their ilk.

Its been a huge success; developments of quantum theory have given us innumerable technological and scientific breakthroughs. At the same time, though, the theory has never been able to tell us what the constituents of the universe actually are.

This wouldnt have been a problem if a small cadre of physicists didnt insist that it should be. Early in the quantum story the 1920s and 1930s the Danish physicist Niels Bohr tried his best to stem this tide. When Einstein objected to the apparent randomness at the heart of quantum theory, Bohr allegedly told him to, Stop telling God what to do. In the face of efforts to describe what atoms were, Bohr warned that, when it comes to atoms, language can be used only as in poetry.

Bohr might as well have saved his breath. We now have myriad interpretations of quantum theory, each one an attempt to describe an underlying reality that gives rise to the results we obtain in quantum experiments. And they are, essentially, guesswork.

[see also:The moonshot delusion]

You might be familiar with some of the guesses. Theres the many worlds interpretation, for instance, which claims that you are reading this in one of a near-infinite number of alternate universes. Each one is the host of a different outcome of a single event in the quantum world. Another famous interpretation is the hidden variables idea favoured by Einstein, where an atom is not a particle as we tend to think of it, but consists of a particle and an invisible, undetectable quantum wave that guides the particles behaviour.

Rovellis relational interpretation, the central subject of his book, has its roots in the work of a young physicist called Werner Heisenberg. In the summer of 1925, Heisenberg took himself on a retreat to the small, near-treeless North Sea island of Helgoland. Here, he dedicated himself to creating a new mathematical approach to quantum theory: matrix mechanics.

You probably wont have heard of matrix mechanics because it has been suffocated by the popularity of an alternative: Erwin Schrdingers wave equation. Schrdinger treated isolated quantum entities, such as atoms, as if they were waves. When different quantum waves come together, they create what seem like otherworldly influences between quantum stuff, and strange behaviours such as one entity simultaneously existing in multiple places, or simultaneously moving in multiple directions.

In the commonly accepted view, Schrdingers waves eventually crash on the shores of their environment (such as our laboratory measuring apparatus), leaving imprints that we have generally taken as evidence for the existence of quantum particles. However, these imprints often reveal a wave-like past to these particles existence, confounding our understanding of what these things actually are. Hence the American physicist Richard Feynmans evergreen assertion that quantum physics is not actually comprehensible.

Heisenberg appreciated this far earlier than most, declaring Schrdingers quantum waves to be repulsive and crap, and offering his matrix mechanics the pure, unadorned mathematics of how one state of an atom relates to another state in the moment of a measurement of its properties as an alternative. Even Schrdinger conceded that this was more accurate. It is better, he admitted, to consider a particle not as a permanent entity but rather as an instantaneous event.

And according to Rovelli, this series of fortunate events is all there is. The properties of a quantum object are only real with respect to some other object at some moment, just as a rainbow is only real in the mind of an observer at the moment of its observation. Whats more, a third quantum object might not perceive those same properties at all. Putting it another way, reality is relative and truth is subjective. Is it possible that a fact might be real with respect to you and not real with respect to me? Rovelli asks. Quantum theory, I believe, is the discovery that the answer is yes.

Rovelli doesnt really push things much further than that; you wont come away from Helgoland with a sense that you finally understand the true nature of reality. He doesnt explain, for instance, what it is that is doing the interacting, if the entities are nothing but their interactions. But it is a pleasure to travel in his company regardless.

Thats partly because, as with Rovellis previous books, the prose is translated from his Italian by the writer Erica Segre and Simon Carnell, a poet, who have made it a delight to read. They describe reality as a luxuriant stratification: snow-covered mountains and forests, the smile of friends, the rumble of the underground on dirty winter mornings With phrasing like this, who cares if there are no real answers?

And lets not pretend that any books on quantum physics can contain satisfying answers about what reality is. How could they, when the theory is not designed to give any? Using it as a guide to the nature of reality leaves us stranded in the mist, like Heisenberg lost in his thoughts on Helgoland.

Aware of the inadequacy of the science, Rovelli offers a second source for his intuitions. In the last third of the book we are seated with him at the feet of the Buddhist philosopher Nagarjuna, who teaches that there is nothing that exists in itself, independently from something else. For me as a human being, Rovelli says, Nagarjuna teaches the serenity, the lightness and the shining beauty of the world: we are nothing but images of images. Reality, including our selves, is nothing but a thin and fragile veil, beyond which there is nothing. Much like that damned rainbow.

Michael Brookss books include The Quantum Astrologers Handbook (Scribe)

HelgolandCarlo RovelliAllen Lane, 208pp, 20

[see also:This risks creating an arms race: inside Europes battle over the future of quantum computing]

Read more here:

Carlo Rovelli's Helgoland argues that all reality is relative - New Statesman