Space. Stephen Baxter
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– helium fusion reaction is about as low-energy and clunky as you can get. There are much more productive alternatives, like reactions involving boron or lithium. I think I always imagined that when Eetie finally showed up, she would have technology beyond our wildest dreams – beyond our imagining. Well, the flower-ships are pretty, but they aren’t the way we’d choose to travel to the stars –’
‘Especially not in this region,’ Nemoto said evenly.
Maura said, ‘What do you mean?’
Nemoto smiled thinly, the bones of her face showing through papery skin. ‘Now that we are, like it or not, part of an interstellar community, it pays to understand the geography of our new terrain. The interstellar medium, the gases that would power a ramjet, is not uniform. The sun happens not to be in a very, umm, cloudy corner of the Orion Spiral Arm. We are moving, in fact, through what is called the ICM – the intercloud medium. Not a good resource for a ramjet. But of course the flower-ships are not interstellar craft.’ She eyed Maura. ‘You seem surprised. Isn’t that obvious? These ships, with their small fraction of lightspeed, would take many decades even to reach Alpha Centauri.’
Maura said, ‘But time dilation – clocks slowing down as you speed up –’
Nemoto shook her head. ‘Ten per cent of lightspeed is much too slow for such effects to become significant. The flower-ships are interplanetary cruisers, designed for travel at speeds well below that of light, within the relatively dense medium close to a star. The Gaijin are interplanetary voyagers; only accidentally did they become interstellar pioneers.’
‘Then,’ asked Maura reasonably, ‘how did they get here?’
Nemoto smiled. ‘The same way Malenfant has departed the system.’
‘Just tell me.’
‘Teleportation.’
Maura had brought Sally Brind here because she’d grown frustrated, even worried, by the passage of a full year since Malenfant’s disappearance: a year in which nothing had happened.
Nothing obvious had changed about the Gaijin’s behaviour. The whole thing had long vanished from the mental maps of most of the public and commentators, who had dismissed Malenfant’s remarkable jaunt as just another odd subplot in a slow, rather dull saga that already spanned decades. The philosophers continued to debate and agonize over the meaning of the reality of the Gaijin for human existence. The military were, as always, wargaming their way through various lurid scenarios, mostly involving the Gaijin invasion of Earth and Moon, huge armed flower-ships hurling lumps of asteroid rock at the helpless worlds.
Meanwhile, the various governments and other responsible authorities were consumed by indecision.
Truthfully, the facts were still too sparse, questions still proliferating faster than answers were being obtained, mankind’s image of these alien intruders still informed more by old fictional images than any hard science. The picture was not converging, Maura realized with dismay, and history was drifting away from meaningful engagement with the Gaijin.
Which was why she had set up this meeting. Nemoto had, after all, been the first to detect the Gaijin – she had quickly understood the implications of her discovery – and she had immediately selected the one person, Reid Malenfant, who had, in retrospect, been best placed to help articulate her discovery to the world, and even to do something about it.
If anybody could help Maura think through the jungle of possibilities of the future, it was surely Nemoto.
But still – teleportation?
Maura closed her eyes. So I have to imagine these Gaijin e-mailing themselves from star to star. She suppressed a foolish laugh.
Nemoto continued to tinker with her apparatus, her plants.
Sally Brind said slowly, ‘Let’s be clear. You think the hoop Malenfant found was some kind of teleportation node. Then why not locate this – gateway – in the asteroid belt? Why place it all the way out on the rim of the system, with all the trouble and effort that causes? …’
Nemoto kept her counsel, letting the younger woman think it through.
Sally snapped her fingers. ‘But if you teleport from another star you must basically fire a stream of complex information by conventional signal channels – that is, light or radio waves – at the solar system, the target. And the place to pick that up with greatest fidelity is the star’s solar focus, where the signal gain is in the hundreds of millions … But Malenfant can’t have known this. He can’t have deduced the mechanism of teleportation.’
‘But his intuition is strong,’ Nemoto said, smiling. ‘He recognized a gateway, and he stepped through it. Contact had been his purpose, after all.’
‘I thought,’ Maura said doggedly, ‘teleportation was impossible. Because you’d need to map the position and velocity of every particle making up the artefact you want to transmit. And that violates the Uncertainty Principle.’ The notion that, because of quantum fuzziness, it was impossible to map precisely the position and momentum of a particle. And if you couldn’t make such a map, how could you encode, transmit and reconstruct such a complex object as a human being?
‘If you did it so crudely as that, yes,’ Nemoto said. ‘In a quantum universe, no such classical process could possibly work. Even in principle we know only one way to do this, to teleport. An unknown quantum state can be disassembled into, then later reconstructed from, purely classical information and purely non-classical correlations …’
Maura said tightly, ‘Nemoto, please.’
‘This is a teleport machine,’ Nemoto said, waving her hand at her strung-out junk. ‘Sadly I can only teleport one photon, one grain of light, at a time. For the moment.’
‘Sally, do you understand any of this?’
‘I think so,’ Sally said. ‘Look, quantum mechanics allows for the long-range correlation of particles. Once two objects have been in contact, they’re never truly separated. There is a kind of spooky entanglement, called EPR correlation.’
‘EPR?’
‘For Einstein – Podolsky – Rosen, the physicists who came up with the notion.’
‘I do not transport the photon,’ Nemoto said. ‘I transmit a description of the photon. The quantum description.’ She tapped two boxes. ‘Transmitter and receiver. These contain a store of EPR-correlated states – that is, they were once in contact, and so are forever entangled, as Sally puts it.
‘I allow my photon to, umm, interact with ancillary particles in the receiver. The photon is absorbed, its description destroyed. But the information I extract about the interaction can then be transmitted over to the receiver. There I can use the other half of my entangled pair to reconstruct the original quantum state.’
Sally said, still figuring it out, ‘The receiver has to be entangled with the transmitter. What the builders must have done is send over the receiver gate – the hoop Malenfant found – by some conventional means, a slower-than-light craft like a flower-ship. The gate is EPR-correlated with another object back home, a transmitter. The transmitter makes a joint measurement on itself and the unknown quantum system of the object to be teleported. The transmitter then sends the receiver gate the classical result of the measurement. Knowing this, the receiver can convert the state of its EPR twin into an exact replica of the unknown quantum state at the transmitter …’
‘So now you have two photons,’ Maura said slowly to Nemoto. ‘The original and the version you’ve reconstructed.’
‘No,’ said Nemoto, with strained patience. ‘I explained this. The original photon is destroyed when it yields up its information.’
Sally said, ‘Maura, quantum information isn’t like classical information, the stuff you’re used to. Quantum information can be transformed, but not duplicated.’