## Making Waves 3

In the last couple of posts, I’ve been showing you how to go about simulating quantum effects in the comfort of your own laptop. Sound impossible? It should do.

Quantum Mechanics is usually described as mysterious, truly random, and inherently non-computable. We’re told that it’s a topic that should cause us to ask deep and difficult questions about the nature of reality, and that it might even be connected to human consciousness.

This, in my humble opinion, is hogwash. I think QM is straightforward, mundane, and something that can be understood concretely by anyone by using simple algorithms. No complex numbers. No wave equations. No Hilbert spaces. This is not to say that I have a new theory of physics to trumpet, because I don’t. My purpose is simply to demonstrate that if people are having trouble reconciling Quantum Mechanics with Relativity, it might simply be because they’re looking in the wrong place.

Last time, I got as far as showing you how to make a self-interfering excitation wave. Let’s remind ourselves what that looked like.

Mostly, at this point, this just looks like a pink smush. Not terribly impressive. So in order to show you a little more about what it can do, let’s first cover a little background about the nature of waves to make sure we’re all on the same page.

Issac Newton thought that light was made up of particles and everyone agreed with him for a while. Then Robert Young came along (as well as several others), and pointed out that light experiences diffraction, and so it had to be a wave.

Cut two slits in a cardboard sheet and shine a light through it, and you get wave interference on the other side. Here’s his famous sketch of the process.

And here’s what that looks like if you hold a second screen up to look at the pattern that the interference makes.

As you can see, we get stripes. The reason why this pattern is important is because if light is a particle, it can only be in one place at a time, and so can’t interfere with itself. So getting a pattern like this shouldn’t happen for particles.

So before we get on to talking about quantum effects, let’s first check to see how our excitation wave works when we put it through a screen with two slits in it. We do this by taking our network and cutting a line in it. Then we only allow nodes on either side of the line to join up if they’re sitting very close to a pair of points we’ve selected.

Here the wave has hit the first screen, and is just starting to peek through the two holes.

And here the waves from the two holes have started to overlap.

The results look a little fuzzy perhaps, but our method appears to be working. Try comparing it to Young’s sketch above. However, I still haven’t said anything about quantum effects. And that’s where things get interesting. So next time, I’ll make a point of revealing all.

## Making Waves 2

Last time, I promised I’d show you how to simulate quantum effects in the comfort of your own home. H0wever, I didn’t get that far. I showed you how to make simple waves that would travel across an irregular network, and that was about it. While the waves I showed you *did* allow us to think about the ways in which elements of discretized space were similar to waves or particles, they didn’t look much like the kind of waves we’re used to seeing in, say, water, let alone electromagnetism. So, this time, we’re going to start making the waves a little more realistic.

First, let’s remind ourselves what our waves from last time looked like.

Pretty, perhaps, and with many useful properties, such as the fact that the same algorithm will work in any number of dimensions. However, these waves have one obvious glaring flaw: they’re not round. So let’s fix that by using the following rule.

- Make two sets, A and B, and put a single point in A.
- Find all the points that are neighbors to the elements of set A or B, but not already in A or B.
- Make those elements the new set A, and the make the elements that were in A the new set B.
- Go back to step 2 and iterate.

As you can see. This rule is even simpler than the one we used last time, and this time the waves are always round.

Next, let’s give the wave a wavelength. To do this, let’s have several sets instead of just two. How about five? Let’s update the rule as follows.

- Make a list of five sets, numbered One to Five, and put a single point in set One.
- Find all the points that are neighbors to any of our sets, but which aren’t already in the sets.
- Make those elements the new set One, make the new set Two equal the contents of the old set One, and so on until we reach the end of the list of sets.
- Go back to step 2 and iterate.

When we run this rule, it looks like this.

However, we still have a problem, and it’s crucial. Our waves don’t interfere with each other. In this respect, they’re completely unlike the kind of waves we want for quantum effects. To solve this, we have to do something a bit clever. Rather than using a single wave, we’re going to use a *collection* of waves, or a ‘meta-wave’, if you like. Furthermore, we’re going to say that some of the points in our network are ‘special’. We’ll pick these special points at random and make the number of them just a small fraction of the total set of points in the network.

What we’re going to do at each turn is advance all the waves in our collection. But if one of the waves bumps into one of these special points, we’re going to add a new wave to our collection, starting at that point. To make things a little clearer, here’s the new rule.

- Make a set of round wave generators that use the ‘wave with wavelength’ rule listed above. Start it off with just one wave, and put just a single point in that wave.
- Advance all the waves in our collection by a single step.
- If one of the waves advanced onto a special point that isn’t in the wave, and now has a special point in its set One, start a new wave using that point, and add it to our collection.
- Go back to step 2 and iterate.

Now if we run our rule, we get something that looks rather different. In order to see what’s going on, I’m going to use a different coloring system, to let the effects of the different waves combine together.

Now we’re getting somewhere interesting. It might not look like much yet, but unlike a normal excitation wave, our meta-wave can pass through itself. This is because the individual waves that it’s comprised of don’t share any information, and each individual wave only contributes a small amount to the overall result. Furthermore, the meta-wave never loses strength. Though it becomes ever more costly to compute, it can go on growing forever. Next time we talk about waves, we’ll put this idea of interference to the test and show you some of the exciting things that it gives us.