Physically speaking all we have access to are the signals that go into our brains. When we look at how a perception makes its way to the brain there is nothing special about the visual input that makes it interpretable as visual alone. If we were to connect a display to the input of the senses it would just look like so much data. But from the “inside” of this system this is not the way it seems at all. We don’t feel like we are receiving arbitrary data, but rather seeing and hearing. And moreover our senses seem to have only one possible interpretation, they tell us about a world that exists independently of us, that contains all sorts of things, that behave according to their own laws.
Obviously the fact that we don’t interpret our senses as arbitrary data is a fact that can be explained by how our brains work. Our brains are simply set up to interpret data from different senses as being of fundamentally different kinds of things. And moreover it seems that our brain naturally interprets and structures this data, unconsciously, in terms of an independently existing world. But this solves only part of the mystery. We might accept the fact that we, by no choice of our own, interpret our senses in a certain way. But is this interpretation justified?
Now previously I have shown that the best explanation for our senses is that an external world, independent of us, exist, on the basis that a) no matter how hard you try you can’t affect the contents of that world without acting, and that b) the external world contains things that you didn’t know, but couldn’t be otherwise (like complicated mathematical proofs), showing that even if the world is not as it appears whatever is behind it is more complex than you mind. And this is part of the answer that we are looking for. The other part is to show that the interpretation we naturally give to our senses, about a three dimensional world that contains various everyday objects, ect is the correct one.
I have bad news; the interpretation that we give our everyday senses is not correct. The best science shows that the world, fundamentally, works in ways that are completely alien to us, for example of the quantum world. We live in this world, and although the data that our senses contain doesn’t directly point to this unusual structure, it is still what ultimately is behind our perceptions (or at least it is an approximation of some even more fundamental reality, which can certainly be only more strange). And it isn’t quantum physics alone that has brought us to this realization, although it is the most obvious example. We perceive the world as being made up of objects, when in reality there is no such thing as an object, simply an uneven distribution of matter. Much of our intuitive conception of the world revolves around these nonexistent objects, we give them properties, we expect them to interact in certain ways, and we conduct our lives as if objects were the most fundamental part of the world. Usually this is a workable description of the world, but it doesn’t explain everything, and the explanations that do don’t include objects (only X, where X is what the current theory says is the fundamental constituent of nature). So the world we perceive doesn’t really exist, at least not as we perceive it.
But the world we perceive isn’t a total illusion either. For example, if you see a train coming you should probably get out of the way, otherwise you will have an unpleasant experience. Although the world as we perceive it may not reflect the underlying reality perfectly it does a very good job, especially in the situations we usually find ourselves in. The world we perceive should be thus best thought of then as a good approximation, or a convenient and useful model, of the real facts. Let me put it another way. The data we receive from our senses can be interpreted in many ways. One model is the world we are used to living in, but surely there are other, much more complicated, ways as well. But the world, as we conceive of it, is by far the simplest of these, and the most reliable for generating predictions as to what will happen next.
Thus I think that we can trust our experience of the world to be a decent, although imperfect, reflection of what is really out there. But it is also important to remember that we can’t trust it completely. Because our model of the world contains objects of various kinds, and their properties, we can’t really trust it in full. Believing that the world really is exactly as it seems leads to bad science, and bad philosophy. A good example of this problem is ancient Greek philosophy. The Greeks were good reasoners, but unfortunately the philosophy that came to dominate their thought (post-Socrates) only rarely took into account the possibility that the world might be other than it appeared (with a few notable exceptions), and thus we ended up with forms and categories. Of course this problem still crops up again occasionally in modern philosophy. We should be suspicious whenever we are told that something is obviously one way or another, except when it is something that we construct (not part of the objective world) or when it couldn’t possibly be otherwise.