Somebody told me about Dyson spheres in the mid-1970s. Maybe it was Poul Anderson. Freeman Dyson’s revolutionary construction had habitats and widgetry of any description surrounding a star. Point was, Earthly telescopes could find alien life by looking at certain stars.

I absorbed the science fiction writers’ version: a ping pong ball as big as Earth’s orbit, enclosing a sun and collecting all of its sunlight for industrial use. Colonise the inner surface.

I played with it. I’d need generated gravity – violating general relativity – and fantasy-sized funding. Without both, you’d spin it, and only the equator would be useful…

Our writers pick their favourite science fiction books of all time

We asked 51¶ŻÂţ staff to pick their favourite science fiction books. Here are the results, ranging from 19th-century classics to modern day offerings, and from Octavia E. Butler to Iain M. Banks

Why not build just the equator? Much cheaper. Spin at – I fudged numbers, because this isn’t Sol – 770 miles per second. At this size you could keep most of the atmosphere inside with 1000-mile-high walls, no roof. Leakage would be tolerable. Spread a landscape across the interior: 3 million times the area of Earth. Population: larger than you’d think, because I made another assumption: the human race evolved elsewhere, in three stages, (the adults). I’d written about them elsewhere. The Pak protectors are intelligent tool-users; breeders (Homo habilis) are not. Protectors built the Ringworld… and landscaped it, and populated it with Homo habilis. Pak protectors are not ecologists; they didn’t bring anything they didn’t like.

With breeders spread all over the Ringworld, the protectors suddenly became extinct. I assumed a war killed them off. Without protectors to cull them, breeders moved into hundreds of ecological niches. So if you assume a population such as 100 million (for a primitive Earth) times 3 million, you’d be short. Mutating breeders shaped to use ecologies vacated by the equivalent of bats, hyenas, lions, many carnivores and herbivores… , or Night People, are everywhere, keeping the Ringworld clean and often civilised…

I was a novice, a few years into a new career. These numbers were scary. Would I be laughed off the stage? New writers were giving up the sense of wonder as passé. But an engineer had written that engineers aren’t scared by big numbers.

Free newsletter

Sign up to Book Club

Sign up to newsletter

The detail I added to The Ringworld Engineers almost writes itself.

It’s always noon. I’ll have to invent night.

The back of the Ringworld is the mask of a planet. Sea bottoms are always shallow and flat, because humans use only the top of an ocean. Fjords and harbours are everywhere, for the convenience of boatfolk. Mountains show subtle stairways.

Ringworld’s success delighted me. It won several awards. It also generated feedback – which also delighted me. Over the next 10 years I got enough feedback, in letters and conversation, along with my own afterthoughts and elaborations, to require a sequel: The Ringworld Engineers. And feedback continues.

The Ringworld is a great gaudy intellectual toy. Readers are inclined to go on playing with it after they’ve finished the book. I approve completely: a person should go on thinking about a book; if they don’t, they aren’t getting their money’s worth.

A professor in England informed me that the Ringworld floor would require the tensile strength of an atomic nucleus. Otherwise, the spin would tear it apart. (So I invented .) MIT students at the World Science Fiction convention in 1971 : “The Ringworld is unstable.” (I knew that; I added attitude jets in The Ringworld Engineers.) A Florida high school class spent a semester on the Ringworld, and decided that my worst problem was that all the topsoil would wind up in the bottoms of the oceans. (Tough one! I put a system of pipes in the seabeds, ran them rimward and over the tops of the rim walls, and got spill mountains, and whole new breeds of hominids to occupy them.)

I wrote that protectors lose their sexual urges and sex characteristics, leaving a fierce drive to protect their genetic line. A fan pointed out that they’d need a wonderfully precise sense of smell to sense unmutated descendants. Give them big noses! (I did.)

My shadow squares, which bring night to the Ringworld, needed work. There’s too much twilight, not enough night. They need to be much longer, five of them, orbiting retrograde!

Dan Alderson, a scientist at Jet Propulsion Laboratory in California, where he was known as the “sane genius”, designed a system with four ringworlds. Three are orthogonal to each other, spinning on frictionless bearings. The fourth was built by Mesklinites. has huge gravity and extreme cold. Dan ’s, and much higher speed.

Edward M. Lerner and I wrote five books retrofitting my . I kept him off the Ringworld, but my character life became far more plausible, and Ringworld’s protagonist Louis Wu took on more detail.

Freeman Dyson thought it would all work better if smaller. At 1 million miles’ radius, a one-Earth gravity spin would take 24 hours! Orbiting the sun would give it seasons! And thousands of such objects in solar orbit would comprise… a Dyson sphere.

I put the alien Kzinti in many stories. When James Patrick Baen invited me to open Known Space to other writers, I told him Known Space was mine. But since I don’t write war stories, he could publish the era of The Man-Kzin Wars (but stay off the Ringworld). We had 15 volumes of the , a few of which are mine, before we closed it down.

I have the alien as paintings, statuettes, origami, pipe cleaners… and

There’s been little feedback on Ringworld’s Teela Brown, who was bred for luck. Hers is the ultimate psychic power – author control, which teachers of writing say should never show – or else she’s a statistical fluke. In a big enough population you must find a person who has been consistently lucky. I never decided which description holds. I had Wu playing the eternally optimistic Doctor Pangloss (from Voltaire’s Candide) throughout all four Ringworld books. Whatever happens to Teela, a reader can see it as the best of all possible worlds.

Larry Niven’s  is the latest pick for the 51¶ŻÂţ Book Club. Sign up and read along with us here.

IN THE NIGHT-TIME heart of Beirut, in one of a row of general-address transfer booths, Louis Wu flicked into reality.

His foot-length queue was as white and shiny as artificial snow. His skin and depilated scalp were chrome yellow; the irises of his eyes were gold; his robe was royal blue with a golden steroptic dragon superimposed. In the instant he appeared, he was smiling widely, showing pearly, perfect, perfectly standard teeth. Smiling and waving. But the smile was already fading, and in a moment it was gone, and the sag of his face was like a rubber mask melting. Louis Wu showed his age.

For a few moments, he watched Beirut stream past him: the people flickering into the booths from unknown places; the crowds flowing past him on foot, now that the slidewalks had been turned off for the night. Then the clocks began to strike twenty-three. Louis Wu straightened his shoulders and stepped out to join the world.

Our writers pick their favourite science fiction books of all time

We asked 51¶ŻÂţ staff to pick their favourite science fiction books. Here are the results, ranging from 19th-century classics to modern day offerings, and from Octavia E. Butler to Iain M. Banks

In Resht, where his party was still going full blast, it was already the morning after his birthday. Here in Beirut it was an hour earlier. In a balmy outdoor restaurant Louis bought rounds of raki and encouraged the singing of songs in Arabic and lnterworld. He left before midnight for Budapest.

Had they realized yet that he had walked out on his own party? They would assume that a woman had gone with him, that he would be back in a couple of hours. But Louis Wu had gone alone, jumping ahead of the midnight line, hotly pursued by the new day. Twenty-four hours was not long enough for a man’s two hundredth birthday.

They could get along without him. Louis’s friends could take care of themselves. In this respect, Louis’s standards were inflexible.

Free newsletter

Sign up to Book Club

Sign up to newsletter

In Budapest were wine and athletic dances, natives who tolerated him as a tourist with money, tourists who thought he was a wealthy native. He danced the dances and he drank the wines, and he left before midnight.

In Munich he walked.

The air was warm and clean; it cleared some of the fumes from his head. He walked the brightly lighted slidewalks, adding his own pace to their ten-miles-per-hour speed. It occurred to him then that every city in the world had slidewalks, and that they all moved at ten miles per hour.

The thought was intolerable. Not new; just intolerable. Louis Wu saw how thoroughly Beirut resembled Munich and Resht

… and San Francisco and Topeka and London and Amsterdam. The stores along the slidewalks sold the same products in all the cities of the world. These citizens who passed him tonight looked all alike, dressed all alike. Not Americans or Germans or Egyptians, but mere flatlanders.

In three and a half centuries the transfer booths had done this to the infinite variety of Earth. They covered the world in a net of instantaneous travel. The difference between Moskva and Sydney was a moment of time and a tenth-star coin. Inevitably the cities had blended over the centuries, until place­ names were only relics of the past.

San Francisco and San Diego were the northern and southern ends of one sprawling coastal city. But how many people knew which end was which? Tanj few, these days.

Pessimistic thinking, for a man’s two hundredth birthday.

But the blending of the cities was real. Louis had watched it happen. All the irrationalities of place and time and custom, blending into one big rationality of City, worldwide, like a dull grey paste. Did anyone today speak deutsch, English, francais, espafiol? Everyone spoke lnterworld. Style in body paints changed all at once, all over the world, in one monstrous surge. Time for another sabbatical? Into the unknown, alone in a singleship, with his skin and eyes and hair their own colour, a beard growing randomly over his face …

“Nuts,” said Louis to himself. “I just got back from a sabbatical.” Twenty years ago.

But it was wearing on towards midnight. Louis Wu found a transfer booth, inserted his credit card in the slot and dialled for Sevilla.

He emerged in a sunlit room.

This extract is reproduced with permission from by Larry Niven, published by Gollancz. This novel is the latest pick for the 51¶ŻÂţ Book Club. Sign up and read along with us here.