«I think I understand. I couldn't order a chimp to carry someone into an airlock and cycle it.»

«Exactly. By itself the chimp wouldn't know that what it was doing was wrong. It lacks discrimination, that ability we call sentience. So every order is reviewed by the personality to ensure it is not harmful or illegal. Therefore, although you could tell a chimp to pick up this particular object, and point it at that person's head, then pull this small lever at the bottom, it would not perform the act. The chimp does not know the object is a pistol, or that pulling the trigger is going to fire it, nor even the consequences such an action would result in. But the habitat personality does, and its neural strata has the capacity to review every single order as it is issued. The order to murder would be erased, and the police would be informed immediately.»

«So what went wrong this time?»

«This is what I find most worrying about the incident. You understand that the habitat personality is what we call a homogenized presence?»

«I crammed biotechnology for three months before I came here, but it was just basic stuff. I know Eden has a large neural strata. But that's about all.»

Hoi Yin crossed her legs. Distracting, very distracting.

«If you look at a cross-section of the habitat shell you will see it is layered like an onion,» she said. «Each layer has a different function. On the outside we have dead polyp, several metres thick, protecting us from cosmic radiation, and gradually ablating away in the vacuum. Inside that is a layer of living polyp which gradually replaces it. Then there is a very complex mitosis layer. More polyp containing nutrient-fluid arteries. A layer for water passages. Another with waste-extraction tubules and toxin-filter glands. And so on. Until finally the innermost layer, landscaped, smeared with soil, and laced with sensitive cells. But the layer just below that surface one is what we call the neural strata. It is nearly a metre thick, and connected to the sensitive cell clusters via millions of nerve strands. Consider that, Chief Parfitt, a strata of neural cells, a brain, measuring one metre thick, and covering almost sixty-four square kilometres.»

I hadn't thought of it in quite those terms before. Too unnerving, I suppose. «It ought to be infallible.»

«Yes. But Eden's thoughts work on parallel-processing principles. A neural network this large could not function in any other fashion. There is only one personality, yet its mind is made up from millions of semi-autonomous subroutines. Think of it as analogous to a hologram; if you cut up a hologram each little piece still contains a copy of the original image; no matter how small the fragment, the whole pattern is always there. Well, that is how the personality works, complete homogeneity. It can conduct a thousand—ten thousand—conversations simultaneously, and the memory of each one is disseminated throughout its structure so that it is available as a reference everywhere in the habitat. Indeed, all its knowledge is disseminated in such a fashion. When I converse with it through affinity, I am actually talking to a subroutine operating in the neural strata more or less directly below my feet. The amount of the strata given over to running that subroutine is dependent purely on the complexity of the task it is performing. If I were to ask it an exceptionally difficult question, the subroutine would expand to utilize more and more cells until it reached a size appropriate to fulfil the request. Sometimes the subroutines are large and sophisticated enough to be considered sentient in their own right, sometimes they are little more than computer programs.»