I read that the average speaker of English has a vocabulary of maybe 20000 words. Of those there are a great number describing things that don't exist. There are words for unicorns, dragons, griffins, minotaurs, elves (sorry Samwise), demons, gods, honest politicians and innumerable other mythical beings. Since these words refer to nothing that actually exists, why do we have them? With only 20000 words at our disposal, why waste a very significant fraction of that number on words describing things that aren't real?
It could be that people once believed that these "things" existed so they made up words to describe them. Those words have been a part of our language for so long that we're kind of stuck with them, knowing they have no explanatory value. But of all the words in this category of null content, the one that intrigues me most is, hole.
Now people have to have always known that a hole really is nothing, a description of "something" that ain't there. We can't pretend that the word hole ever pointed to anything real, it has always meant a place wherein nothing exists. Yet a hole is a real thing by virtue of the absence of whatever contains it. It is explained as a discontinuity, an interruption in whatever is supposed to be there. A hole, then, is another way of describing the thing that contains it, kind of like the linguistic analogue of a photographic negative. A hole exists because we expect something to be "there". We expect a material continuity and, since there is this interruption, our expectation is thwarted. In a way a hole is kind of creepy; something is missing. A hole should not be there. The worst kind of hole is one that goes completely through whatever contains it. A crater or a cave is really just a distortion of an otherwise regular surface; it is still contained and limited. A tunnel or a doorway penetrates all the way through so that it is most definitely not the same as what it penetrates. A hole is unexpected.
Consider that a wall exists to either keep things in or keep things out. The whole point of a wall is to distinguish "inside" from "outside". Poking a hole in a wall defeats its purpose of course but it's necessary since it's the only to get in or out of the place the wall contains. But why build a wall if you're just going to poke a hole in it? That hole is both inside and outside at the same time so the wall is made pointless. Recognizing this as a potential source of insanity, the wall builders invented the door. By using a door, the hole can still be used to let people pass through the wall, yet covered by the door to preserve the integrity of the wall. An ingenious innovation. Because of the door we don't have to think about holes anymore.
Even so there are holes that have no doors, places where you can go from one side to the other, places where there is neither inside nor outside, where every side is the other side. These kinds of holes are the ones that most disrupt our sense of order. To pass through such a hole takes us someplace that is totally different, someplace that is exactly not the place we came from. This is what happened to Alice when she chased that silly rabbit.
The word hole means that there's another side, a place that is not here. We can convince ourselves that the other side is just like this one but, since we can't be on both sides at once, we can't prove it. We tell ourselves that the other side has always been pretty much like this side so going through a hole is harmless. Even so, there is not much comfort in repeating that formula since no two holes are exactly alike. We know at some very primal level that there is a hole somewhere where the other side is radically different.
Einstein understood this. Since space is warped by objects of great mass, it becomes wrinkled like a piece of cloth. Light (and therefore information) follows the contours of the wrinkles. Where the wrinkles are large (near massive objects), the light will follow a longer path, taking longer to get from one point to another. Conventional motion through this kind of space will follow the same path as light. All this becomes interesting if we imagine that a hole can exist that bypasses the wrinkles and follows a straight line. Rather than following the contour of warped space, we can tunnel through and come out at some point unreachable by any other means.
Since the very nature of a hole prohibits knowing what's on the other side while we're on this side, there is no way we can know in advance where a hole in warped space will deposit us. Since we know that all physical phenomena exists only in warped space and not in the holes that pass through it, we will be outside of the phenomenal universe as long as we are in the hole. On the other side we will once again merge with the phenomenal universe. But the only thing we can be sure of is that the place where we end up will contain phenomena but there's no way to know what that may be. Traveling through space is equivalent to traveling through time so we can't even know when we'll end up. About the only certainty is that wherever and whenever we emerge from the hole, things will be very different.
That's what so scary about holes. You go in one end believing that when you come out on the other end things will still be pretty much the same. There are holes that lead into the distant past and others that end up somewhere in the future but we don't know which ones. Each hole carries this risk. Every time you enter a hole (including doorways), you believe that you'll come out on the other side and everything will be what you expected. This comforting delusion helps us forget the very real possibility that we may just disappear. This is why doors are made with peepholes and windows and why some are entirely glass - so we can verify that the other side is just like this one.
If I go through enough holes (doorways, etc.) I'll eventually come out in some elsewhere and find the unicorns, dragons, griffins, minotaurs, elves (hey Samwise), demons, gods, honest politicians and innumerable other mythical beings frolicking in their happy obscurity content in the knowledge that no one believes in them. I'll probably stay.