David Chalmers

Speaking for myself, I don’t think there’s anything special about thinking per se. Descartes could have said, “I feel, therefore I am,” or “I see, therefore I am,” or “I worry, therefore I am.” All of these are claims about his mind that he can be certain of and that aren’t threatened by the evil demon. At least, he can be certain about these claims if they’re understood as states of consciousness, or subjective experience.

In my view, the best statement of the cogito is “I am conscious, therefore I am.”

Faced with an argument that we have knowledge of the external world, the Riposte counters: That’s what someone in a simulation would say.

First, you don’t know you’re not in a simulation. (This amounts to saying no to the Knowledge Question.)

Virtual reality involves an immersive, interactive, computer-generated space.

At this point, we can ask, “How do you know you’re not in a computer simulation right now?”

How do you know anything at all about the reality outside you?

How do you know that your perception of the world is not an illusion?

Thinking about virtual reality gave me a new perspective.

The central thesis of this book is: Virtual reality is genuine reality. Or at least, virtual realities are genuine realities. Virtual worlds need not be second-class realities. They can be first-class realities.
We can break down this thesis into three parts:
Virtual worlds are not illusions or fictions, or at least they need not be. What happens in VR really happens. The objects we interact with in VR are real.
Life in virtual worlds can be as good, in principle, as life outside virtual worlds. You can lead a fully meaningful life in a virtual world.
The world we’re living in could be a virtual world. I’m not saying it is. But it’s a possibility we can’t rule out.