The Navy crew had toured the continent in the twain, and had sent up sounding-rockets for a higher-altitude view. There was even a clutch of simple orbiting satellites, though they had yet to complete a full planetary survey. There were various ways of viewing the result; they had maps on paper, electronic images, photographic surveys. Jha’s favourite was a globe you could handle: a basketball borrowed from the crew on to which a projected photographic mosaic had been glued. It looked pretty much like a globe of any stepwise Earth, save for a peculiar local readjustment of the continents: that gap between South and North America, the global seaway that ran from the Atlantic coast through the Mediterranean and out through Arabia to the south. That and the ubiquitous green of forests that stretched all the way to the polar regions, north and south.
But on this globe there were also false-colour markings of anomalies. Lurid orange bands around the coasts of the continents showed tsunami damage. Peculiar fractures circled the Pacific, divided the Atlantic lengthways, and spanned the southern oceans from northeast Africa south and east towards Australasia: the planet looked like a cracked vase, Jha thought. The cracks were huge tectonic flaws, bands of volcanoes and quakes. And most striking of all were the spidery bands of silver that followed the equator, and the lines of latitude to north and south.
Abrahams picked up the basketball and traced the silver lines with a finger. ‘I have seen some of these. I took my own twain journey to the south; I saw enough for me to infer the rest. You’ll be able to look it up for yourself. Freeman Dyson was a twentieth-century engineer who thought big. He worked on Project Orion, on how to use military-specification H-bombs to drive a spacecraft. And he came up with at least one conceptual scheme of how to spin up a world.’ He pointed to the latitudinal bands. ‘You wrap the world in conducting straps, and run an electrical current through them to generate a shaped magnetic field around the planet, a field shaped like a toroid, a doughnut. You have another electric current running pole to pole through the planet, and you close the loop with an arc through the magnetosphere. That causes the auroras we’ve been seeing from the ground. And then you throw in a stream of spacecraft, starting in high orbits and spiralling down through the toroidal field.’
‘Spacecraft?’
‘They need only be simple. Massive, but simple. Lumps of moon rock, for example, wrapped in some kind of conducting blanket. On my own twain journey, we reached the equator. I saw such rocks in the sky. You must have too.’
‘Yes. We’ve also been observing the moon, from where projectiles of that type are evidently being launched.’
‘And have been for years – since my wife and I first arrived here. The physics is trivial. The flyby rocks come in, they are dragged by the Earth’s new magnetic field, and, thus coupled, they pull at the Earth. Each rock speeds up the planet’s spin, just by a fraction. Then, when they reach their lowest orbit, they start to push against the planet’s magnetic field to spiral back out of there again – and, again, they give the planet another minute shove. Theoretically, it’s as if the Earth has been made the armature of a huge electric motor.’ He looked at their faces, seeking understanding.
Jha said, ‘I think I get it. Metaphorically anyhow. I have a daughter. When she was little, in the park in our home town back on West 5, there was a roundabout, a simple thing, a wooden disc with hand rails spinning on a pivot. The kids liked to run by it; each one grabbed a rail and let it go, and with every tug the roundabout spun a little faster.’
‘That’s the idea.’
Bowring sucked his teeth. ‘So the world’s spinning faster. What about the conservation of momentum? Where’s the extra spin coming from?’
‘I don’t have the facilities to observe properly,’ Abrahams said. ‘Perhaps you do. It appears that the flyby objects stream off towards the sun. There they are probably deflected at closest approach by a gravitational assist – or maybe they use solar sails – and that way they harvest angular momentum from the sun, and return for another pass. It’s a slow process for an individual rock; it must take months or years to make a full orbit, from Earth to sun and back again. But with a stream of such rocks the accelerating effect becomes continuous.’
‘So let’s see if I’ve got this straight,’ Jha said. ‘The latitude bands, the magnetic field they create, are ways of coupling these flyby rocks to the Earth. But what’s really happening is that through the rock stream some of the sun’s spin is being transferred to the Earth.’
‘The sun’s angular momentum, yes. And its angular kinetic energy.’
‘Yeah. A hell of a lot of energy,’ Bowring said dubiously.
Abrahams smiled wistfully. ‘That depends on your perspective. Suppose you doubled this Earth’s spin rate – brought the day down to twelve hours. You’d need four times its original angular energy. But to top up the spin to that rate would take just thirty minutes of the sun’s total fusion-energy output. It’s a lot to us, but if you can tap a source as vast as the sun …’