Consider this: You are sitting on a chair in an otherwise empty room. You go out of the room and close the door behind you, so that you have no way of knowing what is happening inside. A little while later, you go inside again. The chair is exactly as you had left it; the room completely unchanged. Pretty normal, right? After all, nobody else went in after you, and inanimate objects don’t just move about on their own. (Or do they?! I’m looking at you, Toy Story!)
But just stop for a moment and consider. How do you know that while you were gone, the roof didn’t fall and break the chair, and then magically repair itself before you came in? Or that the chair didn’t do a little dance on its wobbly wooden legs before becoming inanimate upon your entrance? How do you know for sure? But that’s absurd, you say. Things like that don’t just happen! Chairs don’t dance, roofs don’t repair, and potatoes don’t potate!
This whole scenario strikes us as absurd, or at best, magical, because it doesn’t fit in with our version of reality. In our mundane world, inanimate objects remain inanimate, entropy doesn’t reverse itself, and the whole world goes along nice and well within specific rules. We do not think the chair will move because the laws of physics and our understanding of them says it can’t. And how have we arrived at these laws? By observation, experimentation, and reasoning. Every time we drop an apple on earth, it goes down. Every time we check the time, it is moving forward (unless the watch is broken, of course). Everything in the world we know follows the laws of reality, with no exceptions whatsoever.
However, it is worth remembering how these laws, or our interpretations of them, have come about. We observe that when we throw a ball at our friend’s face, it moves forward and hits him, instead of moving backwards and hitting us. We observe that every time we drop an object, it goes down. We observe a number of such commonplace phenomenon, and so we try to come up with theories to explain them. We explain it by the means of the theory of gravity, projectile motion, entropy, and similar scientific mumbo jumbo. These theories explain practically everything we commonly see, and so we accept them as laws after rigorous experimentation. In the case of objects falling downwards, it has happened every time in the same manner, so it is safe to assume that it will happen in the same manner every time in the future. This is known as “Model dependent realism”, i.e. we create a model of reality based on our observations and use it to explain the stuff we see.
The problem which arises now is this- the model that we have created is based on our observations. So how can we know what all is happening or not happening if we aren’t observing it? We do not observe anything of what is happening inside the room, so hypothetically speaking, an infinite number of things could have happened. Our model of reality dictates that none of it should be happening, but that is only because every time we have observed a similar situation, nothing extraordinary has happened. We thus take it to assume that since nothing weird has ever happened, nothing weird will ever happen. Every time we leave a room, we do not think that anything bizarre will happen, precisely because it has never happened before. For all we know, there could be a ghost aggressively break dancing, or the chair transforming into a fire-breathing dragon in the room. But we don’t think this will happen because the laws of our reality, based on previous observations, say that it can’t happen.
The conclusion logically follows that all of our reality depends on what we observe, whether by our biological senses or with the help of machines. So there could be an infinite number of things going on right now, but we would never know because we aren’t observing, or cannot observe, them. The question now arises, is there any Reality (with a capital R) at all? And even if there are innumerable strange things going on right now, if we can’t observe them and they can’t affect us, does it even matter?
Further reading -
The Grand Design by Leonard Mlodinow and Stephen Hawking
Scientific Perspectivism by Ronald N. Giere