One of the strange things about dreams is that, most of the time, we aren’t aware we’re dreaming. Typically, our memory and our reflective ability are substantially limited within dreams (Fosse et al. 2003; Hobson et al. 1998), causing us not to notice incongruencies within the dream and to take for granted that what we experience is real. It simply doesn’t occur to us to consider whether it might not be.
Perhaps even more strangely, even when we do on occasion become aware that we’re dreaming—and according to various surveys carried out around the world, anywhere from 26% to 92% of people have had at least one lucid dream (Stepansky et al. 1998; Erlacher et al. 2008; Palmer 1979; Yu 2008)—the “sensory” experiences of the dream can remain just as convincingly real. I remember in one of my own dreams realizing that it was a dream and then marveling at how solid and real the cell phone in my hand still felt.
The ability of the dream world to appear real has led many thinkers—philosopher René Descartes (1641) being the most prominent Western example—to wonder whether the world we experience while awake might itself be a dream. If the dream world feels just as real as the waking one (at least while we are in it), how can we know for sure that we’re not currently living in a dream—a dream from which we may one day wake up?
One way that philosophers have tried to dispel such worries is by appealing to differences between the dream world and the waking one. For instance, our waking world has a coherence that the dream world often lacks. (For an example of a coherence-based argument against the skeptical hypothesis, see Norman Malcolm (1959).) You may recall that, in the feature film Inception, the characters learn to recognize that they’re dreaming by asking themselves how they came to be in a certain situation, then realizing that they can’t remember, because the dream just dropped them there.
But does the coherence of our waking world guarantee that it’s real?
I believe the coherence of our waking world does give us evidence that it is not merely a figment of our imagination. Specifically, it gives us evidence that, when we are awake, something is causing our experience that is independent of the experience itself. For instance, the relative permanence of the objects and environments we experience in waking life would appear to be best explained by there being something real and enduring that our experiences are reflecting.
However, the relative permanence of the objects and environments we encounter in the waking world is no guarantee that the waking world is as real as it gets. After all, a high degree of permanence is also found in the worlds of video games, in which the “environments” and “objects” one interacts with are merely the creations of computer code. So, while perceived permanence does seem to point to there being something objective/enduring out there, the true nature of whatever is “out there” might resemble our experience of it as little as computer code resembles the images we see when we play a video game.
In fact, physics teaches us that the objects we experience as being solid are actually made up almost entirely of empty space. And the results of quantum mechanical experiments indicate that, under certain conditions, the building blocks of matter do not behave as discrete particles at all, but rather as waves of probability. If we nevertheless experience the world as full of enduring, solid objects, this is due to the usual way that our senses interact with it and to the way these interactions are represented in consciousness.