What does it mean to say that consciousness exists? I agree with exchemist that consciousness isn't a substance, it's an activity in which an information processing system acquires information about its environment, performs recognition/classification tasks on that information and in some organisms on the information that the system is in the loop and doing the processing. (Some organisms not only think about the environment, they think about their thinking about the environment.) Other things are likely happening too, since the system is likely motivated in the kind of information it seeks, is assuming affective states (fear, desire etc.) and is making decisions about what kind of behavior to undertake. In your scenario, information about the surrounding environment wouldn't 'exist' in any information processing system of the sort I outlined above since ex hypothesi they wouldn't exist. Your thought experiment is about you or anything capable of awareness of its environment not existing. If nothing capable of awareness of its surroundings existed, then awareness of those surroundings wouldn't exist either -- not in the sense of a substance not existing but in the sense of a process not happening. That absence of anything capable of acquiring and processing information about its surroundings doesn't seem (to me anyway) to imply much about whether or not those surrounding exist in whatever substantial way the physical universe exists. (Another question.) I'd guess that the planet Mars has never been host to any beings capable of acquiring, processing and making use of information about the Martian environment. But that doesn't mean that the Martian environment didn't exist, only that nothing was aware of it. The Mars rovers have indeed discovered a fascinating landscape there, evidence of all kinds of geological processes have occurred and so on. All (presumably) without any sentient being being aware that any of it was happening. Put another way, when a space vehicle lands on some other body out there, we are discovering, not creating whatever it is that the cameras record.