Keanu Reeves as Neo in The Matrix Reloaded

Imagine tomorrow the sky suddenly cracked open and a couple of giant teenage nerds poked their spotty heads out from behind its broken blue shell. Imagine they explained to you that everything you’d ever thought was real was actually a computer simulation and they had the code to prove it. Imagine, even, that they gave you a quick peek behind the scenes — before dropping you back into the simulated world and glueing up the heavens behind you. Wouldn’t your life be, in a flash, rendered utterly meaningless?

David Chalmers, a professor of philosophy and neural science at New York University, thinks not. In his fascinating new book, Reality+, he makes the seemingly outlandish case that virtual worlds — simulated universes, mega-corporate metaverses, even simple slay-the-dragon VR games — should be considered just as real as physical, analogue worlds. If — as he considers entirely possible — our universe turns out to be nothing but a schoolchild’s plaything, our lives will still matter just the same. Even if, as in the film The Matrix, we’re unknowingly plugged in to some replica world while superintelligent machines harvest our bodies for energy, our lives within that world would be just as metaphysically real as our analogue lives without it.

Chalmers knows he’s being provocative, quoting Bertrand Russell’s dictum: “The point of philosophy is to start with something so simple as not to seem worth stating, and to end with something so paradoxical that no one will believe it.” Chalmers flips this round. He starts with the seemingly absurd — that “virtual realities are genuine . . . first-class realities” — then retraces his steps back to the reasonable. Thankfully, by philosophers’ standards, he’s also unusually committed to trying to change his readers’ minds and proves a thoughtful, clear and funny companion — if not, in the end, an altogether convincing one.

Much of Reality+ hinges on the central question of how to define “real”. Chalmers offers a few approaches. One is to discern what features of a thing make it real. Chalmers suggests five criteria, among them mind-independence (a chair is real if it continues to exist when nobody is perceiving it) and causal power (a chair is real if it affects the world around it, most obviously by supporting the buttocks of whoever sits on it). By these criteria, he argues, virtual objects can be just as real as physical objects (the virtual chair remains when you look away, and supports the virtual buttocks of your goblin avatar).

Another approach is simply to say that reality is whatever can be captured by truthful statements — what is true, after all, is surely what is real, and vice versa. Sure enough, Chalmers concludes that statements made in and about virtual worlds can be just as truthful as those made in and about analogue worlds. Drawing on the work of the linguistic philosopher Hilary Putnam, he argues that words derive their meaning not just from the intentions of the speaker, but the conditions of their environment. When virtual Jeff in virtual Vancouver says, “It’s raining”, “raining” refers not to analogue rain but the virtual rain around him. If it is indeed virtually raining, then what virtual Jeff says is true.

Surely, though, we could define reality much more simply. Could we not just say, for instance, that the truly real world is the final, outermost, physical, analogue shell of the cosmos within which any and all other simulated or virtual worlds are contained?

Chalmers says no. While he concedes that there must be some “top-level universe”, a “base reality at the top of the chain”, a “single outer-world physics” that ultimately sets the final limits for all simulated universes within it, he still thinks it’s a mistake to consider it inherently more real.

To explain, he appeals to a metaphysical theory he calls “it-from-bit”. This essentially states that even the very outermost cosmos that encompasses all other realities is, at its most fundamental level, digital: built up from nothing more than 1s and 0s. Below atoms we find electrons. Below electrons we find quarks. Eventually, at the very bottom, we find just bits: 1 or 0, on or off, something or nothing.

If “it-from-bit” is correct, then there would be no reason to treat a simulated digital reality as any less real than the overarching digital reality within which it existed — just as an individual house made of bricks is no less real than the brick terrace within which it stands.

More pertinently, if digital and analogue metaphysics could, in principle, achieve the same outcome (creating the universe around us), then it does not ultimately matter which one produced ours — they are functionally interchangeable and thus equally real.

Chalmers admits that “it-from-bit” isn’t taken seriously by philosophers, but even if it were true, it still doesn’t quite achieve what he is after. Yes, if everything is ultimately reducible to bits, then, sure, everything is “equally real” in the unremarkable sense that it is composed of the same fundamental stuff. But all that really means is that we need a better term to describe the type of realness we’re getting at. A feverish hallucination and sober observation might be both reducible to 1s and 0s, but we can still clearly make a hierarchical distinction between the two. The same goes for different realities.

So: are we in a simulation? Chalmers, drawing on the probabilistic work of the philosopher Nick Bostrom, says it’s quite likely that we are. Bostrom’s theory goes something like this: if computer processing power continues to increase at present rates, we’ll soon reach a point where even a bog-standard laptop can simulate universes as complex as our own. Perhaps 50 years from now we’ll be running billions of digital but otherwise perfectly “realistic” universes on our phones and tablets. At that point the likelihood of any single one of the total universes in existence being the ultimate “base reality” becomes vanishingly small. Isn’t it probable, then, that we too are actually inside one of billions of simulated universes created by beings in the next reality up, who are just a little further ahead, technologically, than we are?

Thankfully, this is where Reality+ is at its least convincing. For starters, Chalmers’s claim that “it’s more likely than not that conscious humanlike simulations are possible” depends on the dubious assumption that consciousness simply emerges from purely physical processes. However, this is a position of faith — nobody yet has the foggiest idea how the material brain produces the immaterial mind.

Worse, his argument relies mostly on probabilistic analyses of what we would do with the power to produce full-universe simulations (his conclusion: we’d create millions of them). But can we really extrapolate from what we would do to what our unseen simulators might do? Can we be sure that their minds or physical laws are like our own? On the contrary, it seems to me that statistics about our world can’t really tell us anything fruitful about other worlds beyond.

In the end, Reality+ is a gripping act of philosophical escapology — a remarkable, if ultimately unsuccessful, attempt by Chalmers to wriggle free from the wild implications of his opening thesis. Just shy of 500 pages, it’s a sprawling, brain-tenderising beast of a book — but a hugely entertaining one at that. Reality+: Virtual Worlds and the Problems of Philosophy by David J Chalmers, Allen Lane, 544pp; £25