If a tree falls and nobody is there to hear it, does it make a sound? After you’re done laughing, let’s think about this. This is not a stupid question: it brings up fundamental questions that are still fundamental, even for scientifically minded people.
Before indulging in The Matrix hypothesis and talking about how the external world doesn’t exist, I’m going to start with what’s not controversial. First, animals perceive the world differently than humans (some drastically different). Second, among humans there is variation (due to various physical and psychological causes). Conclusion: the external world and the world we actually perceive are two different things. It is interpreted, processed, constructed, measured–by our sense organs and brain. In other words, the diagram above is a fiction; we do not see an exact copy of the tree “out there”; our eyes are not giant gaping windows that “let the tree in” so to speak. Naive Realism is false. Again, not controversial so far.
And if you’re still not convinced that your eyes are playing tricks on you and that your sense organs are all sacks of shit, consider two more facts: (1) sense organs evolved (like everything) and thus survival are their main concern–truthful representation of the external world is not necessary their concern at all. Whether you see the berry as white or red, all it cares about is what works. As Williams James would say, the truth is what works. For us believing folk, a nice way to put it would be: God made you so that you would survive rather than be an astrophysicist–be happy He did. (2) sense organs detect change more than anything. Vision is not like a video camera that is always recording everything like a faithful steward, not even close. Not to mention that memory, state of mind, personality, beliefs, language, societal norms–they can all affect the way we perceive things, literally. Let’s stop here.
So what is happening here? Most common sense people will say there is a physical tree “out there”, made of physical stuff (atoms) having certain fundamental properties: size, shape, texture, mass. Those properties are “really out there” and our sense organs pick up on them the best we can. Okay, cool. But notice color is not on that list. Green is nothing more than the way light reacts with our retina/brain. Color is not “out there,” light is. The tree has the potential to be perceived as green and brown when light bounces off it and hits our eyeballs, that’s all. This isn’t controversial either. Qualities like color, heat, loud, bitter, the smell of a fart–they are all quasi-real, in limbo, secondary, dependent. I hope you feel the world crumbling. Color seems pretty fucking real to me thank you very much!
Enter the Idealists
Some people just scrap the whole idea of an external world altogether. We don’t need it. When I’m dreaming, I see green trees, I move through space, I eat cake, I cry (hell, I even have sex and ejaculate sometimes). All in the mind, mental, not caused by physical objects. There is no external tree causing my perception of a tree in the dream. So why can’t reality be the same way? Well, it can. The Matrix, although improbable, is possible. We could all be “plugged in” right now. Descartes imagined a powerful Evil Demon that might be tricking us, pulling this fake reality over our eyes just for the hell of it. George Berkeley simply replaced the external world with God. God doesn’t need physical matter, a useless middle man, when He can just implant sense experiences directly to our mind. We are living in God’s dream, God’s mind; God holds up reality. As a believer, this is a very tempting position to take. There is a simplicity to it, sort of. Kant replaced the external world not with God, but with an unknowable world, a foundation, a world that causes our perceptions but one we can know nothing about–except that it must exist.
So does a tree make a sound if nobody is there to hear it? No. Or, sure, God hears it. Or, the question itself makes no sense. That’s really the point here. What do we mean by a tree, after all? Green, brown, particular shape, particular feel, particular smells, etc. A tree is nothing but a group of sense experiences or possible sense experiences, therefore to talk about an unperceived tree makes no sense at all. To be is to be perceived in some way. Yes a tree has size, shape, texture, and mass. All those qualities are real. But notice those qualities, just like color, are qualities we perceive the tree to have. They are real because we perceive them, simple as that. Yes we can say the tree is made of atoms, but that just means if we look in a microscope we see it’s made of smaller stuff, and smaller stuff, etc. We can speculate about what’s really “out there,” but all we really have is our perceptions, all we have access to is the end product (in my diagram above, it’s the thought bubble). We can only look at the world through eyes, smell the world through noses, and feel the world through touchers. We cannot float above our body and brain to see what the world really looks like when nobody is looking at it. Human reality is human reality. There is something out there, but who knows what that is? Perhaps it’s really a pink, squishy ball that’s causing my perception of a green, hard Sugar Maple. As long as we all perceive the tree, nobody cares.