In order to conclude the Jargon Trilogy (and also because I think it will be good for my personal understanding), I would like to try to explain the substance of my thesis project under the assumption that my reader has no prior knowledge of physics. I hope to do it in less than a thousand words, starting at the end of this paragraph. I consider this to be a writing challenge to myself, so here goes:
The point of physics, as a discipline, is to describe the behaviour of nature at a fundamental level using mathematical equations known as “laws.” When we describe things that are roughly the size of Humans, these laws tend to be if not simple, then at least relatively intuitive. However, when we start to consider things that are much smaller than the human scale (like atoms), or much larger than the Human scale (like the universe) these laws become very complicated and rather counter-intuitive. The behaviour of tiny things is described by a set of laws called “quantum field theory.” The behaviour of huge things is described by a set of laws called “general relativity.” There are places (such as black holes or the dawn of time) when both sets of laws should apply, except physicists haven’t figured-out how to make this work yet since general relativity and quantum field theory do not agree with each other.
One of the hardest things in the universe to describe mathematically are the laws governing interactions between particles called “quarks” and “gluons.” What are quarks and gluons, you ask? Well consider this: your body is made of atoms; atoms are made of a cloud of “electrons” surrounding a nucleus of ‘protons’ and ‘neutrons:’ protons and neutrons are both made of quarks, with communicate with each other using particles called gluons. The set of laws governing these interactions are a branch of quantum field theory known as “quantum chromodynamics.” When quarks are very close together, physicists can approximate solutions to these equations; when they are far apart these approximations stop working.
How can we solve these equations then? It turns out that the answer may lie in an attempt to unite the physics describing very big things and the physics describing very small things. This attempt is called “string theory.” One possible consequence of string theory being true is that a set of laws describing the behaviour of very small things in a certain number of dimensions may be the same as a set of laws describing the behaviour of very big things in one more dimension. Or, more specifically, imagine a universe in which space and time are wrapped-up on themselves in such a way that it has a solid boundary. If you were living in this universe, you could drive a space ship only so far, but no further. And if you shone a light in any direction, it would eventually be reflected back at you. Now imagine that not only did time flow in this universe, but that you could move in certain directions. You could move up and down, for example, or back and forth, or side to side, or maybe even in a few extra ways. Let’s call the number of ways in which you are allowed to move in such a universe “n.” If you were living on the boundary of this universe, then obviously you could no longer move towards or away from the centre, so there would be one less direction in which you were allowed to move, so the new number of dimensions is “n minus one.” According to string theory, the set of equations which describe “general relativity” in the n-dimensional universe are the same set of equations that describe “quantum field theory” on the n-minus-one-dimensional boundary of this universe. And, as it turns out, general relativity is easier to solve than quantum field theory, so there is a chance that we may be able to solve “quantum chromodynamics” in this fashion.
But a universe is a hard thing to describe, so let us make it simpler. Let’s imagine that our universe is an enclosed, n-dimensional sphere with a “black hole” inside of it. A black hole is place where gravity is so strong that space and time become wrapped-up in each other in a ball until nothing can escape from inside; they are well-described by general relativity Due to our assumption that quantum field theory is “dual” to gravity, we can thereby compute results in quantum field theory by studying the physics of the black hole. The field theory that we describe is not exactly the same as Quantum Chromodynamics, but it is close enough that we can make qualitative predictions about how quantum chromodynamics should behave.
Now then, at this point I should say that there is a major problem here: all of this is strictly theoretical. We are using a theoretical model (of a black hole) to describe another theoretical model (of quantum chromodynamics), using a supposed implication of a third theoretical model (string theory). But science should be based upon real things; experimental observations and testable hypotheses. Right now, this picture as I have described it is untestable, as it is impossible for us to experiment upon actual black holes, as they are all off in space trillions of miles away. My proposal is to create, not a black hole, but an analogue of black hole in a rather more convenient location.
What do I mean by an analogue? Well, a black hole occurs when space and time bend until light cannot escape from within a particular radius. We can create an “accoustic analogue” of a black hole (or a “dumb hole”) if we make a fluid flow in such a way that sound cannot escape. My proposal, then, is to figure out the flow for a fluid analogue, not just of the black hole itself, but of the entire universe in which the black hole is situated (i.e, a universe with a hard boundary). In this fashion, it will become possible, in principle, to experimentally test the “duality” between ‘general relativity’ (the theory of large things) in N-dimensions and ‘quantum field theory’ (the theory of small things) in N-minus-one dimensions. Thus, for those keeping score, I am using fluids to describe black holes, to describe the behaviour of quarks and gluons. It is a very round-about way to go about it.
993 words. Now I ask you: did that make sense?