Philosophers are interested in Star Trek’s Transporter, a device that dematerializes a person in one location and rematerializes them in another. Is that really “transportation” or is it death? Derek Parfit argued that since the person being transported ostensibly ceases being, for philosophical purposes, they have died even though their memories have been preserved in a new body in a new place. Parfit’s argument is convincing to me – a copy is not so much a continuation of the original as a new being in its own right – which is part of why I find the central premise of Greg Egan’s Permutation City so difficult to wrap my head around.

In Egan’s book, humans have achieved the ability to upload their consciousnesses into virtual-reality worlds as a means of continuing life after death. The technical limitations of how Egan depicts this process are interesting; the cost of the computation determines the speed at which the simulation can run. Expensive simulations run closer to the speed of the physical world and less-well-off simulations run so slow that they have a tendency to retreat into solipsism. But can the uploaded simulation actually be considered a continuation of the original person’s life?

In this imagined future, super-computer resources for running simulations increasingly compete with a growing movement to mitigate the impact of climate-change related disasters with technology. At the outset of the narrative, virtual-reality copies anticipate a threat to their existence posed by reappropriation of computational resources. It’s the scarcity of compute that initiates the central philosophical thought experiment of the book.

The novel asks much of the reader – to keep up with head-spinning world-building and theoretical gymnastics while the central plot is only revealed a bit at a time. It weaves a richly described sci-fi world with an ensemble of characters into a reflection on the nature of consciousness and technology.

In a way, this book feels like a kind of post-human meditation on the afterlife, a religious text for the software engineer. Scarcely anyone in Permutation City seems to question whether a copy of a person’s brain is in fact a successor to their mortal existence. And since it takes place in a world where the relationship between consciousness and identity has stopped being a debate, it is left to the reader to ponder the implications.

Would I want a copy of my consciousness to live eternally in a virtual reality simulation? I feel ambivalent and I’m leaning toward no. What makes life living isn’t just the fact of my particular collection of memories and desires existing in a particular time and place but also their embodiment, their connectedness to their context. I suspect that you can’t just extract a “copy” out of a lived life and have it continue to be the same person.

I’m reminded of Alva Noë’s work on embodiment. Here’s a passage from Out of our Heads:

Human experience is a dance that unfolds in the world and with others. You are not your brain. We are not locked up in a prison of our own ideas and sensations. The phenomenon of consciousness, like that of life itself, is a world-involving dynamic process. We are already at home in the environment. We are out of our heads.

Noë’s work continually argues that our consciousness is rooted in our embodiment in the world and in our senses – not just in our neurons – and I find the argument convincing. I’m not sure if this position is in complete opposition to Egan’s model of virtual worlds. After all, maybe the virtual worlds model the physical world closely enough to incorporate this mode of embodied consciousness. But it makes me somewhat skeptical of the underlying “brain in a virtual jar” premise.

Egan gives the digital copies an escape hatch from the threat of dwindling computational resources in the form of “dust theory,” which posits that all versions of the universe simultaneously coexist, given that they have consistent underlying physics. This theory takes the premise of virtual personhood to the next level by suggesting that if human consciousness can be reconstituted in different materials at different speeds, then the underlying patterns of a mind are surely present in different states, different forms emerging from different substrates:

There’s no reason to believe that the pattern we’ve found is the only coherent way of ordering the dust. There must be billions of other universes coexisting with us, made of the very same stuff – just differently arranged. If I can perceive events thousands of kilometers and hundreds of seconds apart to be side-by-side and simultaneous, there could be worlds, and creatures, built up from what we’d think of as points in space-time scattered all over the galaxy, all over the universe. We’re one possible solution to a giant cosmic anagram… but it would be ludicrous to believe we’re the only one.

This is the protagonist in his most passionate monologue – rubbing his hands together and sounding like a cross between an acid casualty and a mad scientist. Greg Egan’s own commentary makes it clear that we’re not to take Paul Durham’s opinions at face value. But that feels like a bit of a false disavowal, the book asks us to believe in dust theory enough to read about a hundred pages that could not occur without it. The titular city is a place built out of a simulation that is somehow purely virtual, existing only as a potential permutation of a “garden of eden” formation. It is potentially infinite because it takes up no space or time, it’s nothing more than the downstream implications of one specific arrangement of electrons in a computer. The only thing that materializes it is the narrative that Egan has fabricated.

In that way, Egan’s novel is also about the power of the imagination, which is its own kind of virtual reality. We can use our imaginations to construct worlds that function as kinds of timeless simulations, playing out fantastic and alternative versions of our lives. The digital afterlife that Egan creates need not be backed by computers, since our imaginations have long harbored timeless alternate worlds.