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Read more: 鈥�Existence special: Cosmic mysteries, human questions鈥�

IN A nutshell, you don鈥檛 know.

Philosopher Ren茅 Descartes hit the nail on the head when he wrote 鈥渃ogito ergo sum鈥�. The only evidence you have that you exist as a self-aware being is your conscious experience of thinking about your existence. Beyond that you鈥檙e on your own. You cannot access anyone else鈥檚 conscious thoughts, so you will never know if they are self-aware.

That was in 1644 and little progress has been made since. If anything, we are even less sure about the reality of our own existence.

It is not so long ago that computers became powerful enough to let us create alternative worlds. We have countless games and simulations that are, effectively, worlds within our world. As technology improves, these simulated worlds will become ever more sophisticated. The 鈥渙riginal鈥� universe will eventually be populated by a near-infinite number of advanced, virtual civilisations. It is hard to imagine that they will not contain autonomous, conscious beings. Beings like you and me.

According to , a philosopher at the University of Oxford who first made this argument, this simple fact makes it entirely plausible that our reality is in fact a simulation run by entities from a more advanced civilisation.

How would we know? Bostrom points out that the only way we could be sure is if a message popped up in front of our eyes saying: 鈥淵ou are living in a computer simulation.鈥� Or, he says, if the operators transported you to their reality (which, of course, may itself be a simulation).

Although we are unlikely to get proof, we might find some hints about our reality. 鈥淚 think it might be feasible to get evidence that would at least give weak clues,鈥� says Bostrom.

Economist Robin Hanson of George Mason University in Fairfax, Virginia, is not so sure. If we did find anything out, the operators could just rewind everything back to a point where the clue could be erased. 鈥淲e won鈥檛 ever notice if they don鈥檛 want us to,鈥� Hanson says. Anyway, seeking the truth might even be asking for trouble. We could be accused of ruining our creators鈥� fun and cause them to pull the plug.

Zombie invasion

Hanson has a slightly different take on the argument. 鈥淪mall simulations should be far more numerous than large ones,鈥� he says. That鈥檚 why he thinks it is far more likely that he lives in a simulation where he is the only conscious, interesting being. In other words, everyone else is an extra: a zombie, if you will. However, he would have no way of knowing, which brings us back to Descartes.

Of course, we do have access to a technology that would have looked like sorcery in Descartes鈥檚 day: the ability to peer inside someone鈥檚 head and read their thoughts. Unfortunately, that doesn鈥檛 take us any nearer to knowing whether they are sentient. 鈥淓ven if you measure brainwaves, you can never know exactly what experience they represent,鈥� says psychologist Bruce Hood at the University of Bristol, UK.

If anything, brain scanning has undermined Descartes鈥檚 maxim. You, too, might be a zombie. 鈥淚 happen to be one myself,鈥� says Stanford University philosopher Paul Skokowski. 鈥淎nd so, even if you don鈥檛 realise it, are you.鈥�

鈥淚 happen to be a zombie myself and even if you don鈥檛 realise it, so are you鈥�

Skokowski鈥檚 assertion is based on the belief, particularly common among neuroscientists who study brain scans, that we do not have free will. There is no ghost in the machine; our actions are driven by brain states that lie entirely beyond our control. 鈥淚 think, therefore I am鈥� might be an illusion.

So, it may well be that you live in a computer simulation in which you are the only self-aware creature. I could well be a zombie and so could you. Have an interesting day.

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