Glider synthesis is the process of colliding gliders – the smallest spaceship in Conway's Game of Life – in a specific way to construct a specific object. It is one of the few areas in the Game of Life that many discoveries can still be made without using scripts.
This is an example of a glider synthesis:
Locating known glider syntheses
To locate a known glider synthesis, there are four places you should look:
- Mark Niemiec's website
- The LifeWiki, which you're looking at right now
- Chris Cain's display_synth script
- Compressed Folder of cheapest oscillator syntheses
Here is a flowchart showing which of those places you should look in, depending on what type of object you chose:
Sometimes you will not find a synthesis for a particular object in any of these places. That could be because:
- There does exist a known synthesis, but it is hidden somewhere obscure. Your best bet is to ask on the ConwayLife.com forums.
- No syntheses are known because no-one has decided to synthesise that specific object before. These are usually pretty easy to make a synthesis for yourself.
- No syntheses are known because the object is very difficult to synthesise. An example of this would be Sir Robin.
- The object has been proven impossible to synthesise. Examples of this include all Gardens of Eden as well as solutions to the grandfather problem.
In the next section we will look at how to make your own syntheses.
Making your own glider syntheses
Using Catagolue to find glider syntheses
Let's say you want to find a synthesis for block on down candlefrobra, which, according to Mark Niemiec's website, takes 12 gliders:
Select the pattern in Golly and run the script mentioned above. It should bring you to this page on Catagolue. Scroll down to the part of the page with lots of differently coloured dots. These are all sample soups for the object. The black ones are asymmetric soups, which are the easiest to make syntheses from. (However, it should not be forgotten that you can still get good syntheses from symmetric soups -- especially if the object has the same type of symmetry as the soup.)
Now run the soup until the candlefrobra appears (this should happen at generation 919). Use the goto.py script (which comes with Golly) to go 20 generations back. Watch each generation up to the candlefrobra's formation step-by-step to see which objects react to make the candlefrobra. Next, go back 20 generations, select the objects that reacted to make a candlefrobra, and paste them into a new layer.
Test to see if that pasted pattern works. If it doesn't work, go back to the layer with the soup, and select and paste a larger area. Once you've deleted any objects that don't participate in the reaction, you should get something like this:
The reaction is pi + block + boat + traffic light --> candlefrobra + some junk. We know how to make all those reactants with gliders, so we can now make a synthesis! In fact, all of the reactants can be made in two gliders (those collisions can be found in two-glider-collisions.rle in Golly's pattern collection).
However, before you start, you may notice that not all of the blinkers in the traffic light react before making the candlefrobra. So maybe we don't need all of the blinkers. In fact, the only blinker we need is the top one. Try deleting the rest of the blinkers just before the Traffic Light first reacts. This isn't necessary, but to help your understanding, I've replaced the traffic light predecessor with one that only makes a blinker to get this:
Now there is also no junk left over after the synthesis, only the candlefrobra.
Now you can start the synthesis. To do this, you should synthesise each of the reactants separately in such a way that they work when put together. You can find all the syntheses you need for this in two-glider-collisions.rle. Try to do this yourself. If you can't manage to make it work using only 2-glider collisions, look in Mark Niemiec's website to find more useful syntheses.
If you need a hint, these are the syntheses I would use (zoomed out in case you don't want the hint):
If you used the hint, note that you may need to rewind some of the syntheses to make it work.
How did you go? If you created a synthesis with less than 12 gliders then congratulations, you would have created a record-breaking synthesis! For reference, this is the synthesis I created which used 8 gliders:
In this example with the block on trans-candlefrobra, we were lucky to get a good reaction from the very first soup. Sometimes you will have to look through 20 or more soups before finding a suitable reaction.
If you want more practice for creating synthesis from a reaction, here is the reaction the current record holding synthesis of why not (8 gliders) was made with:
Using converters to make syntheses
Let’s say we want to make a synthesis for this 18-bit still-life:
So we run the pattern-to-catagolue script, and it brings us here But there (at the time of writing) are no catagolue soups! So what can we do? It is time to be introduced to the world of converters…
A converter is a collision of gliders with a still-life/oscillator, which turns it into a new still-life/oscillator. Here is an example of a converter. It turns a hook into a barge:
Converters are very useful for creating syntheses that are too large and/or rare to turn up on catagolue. For example, the duodecapole currently has no appearances on catagolue, but we can still create a synthesis from a barberpole-lengthening converter and an already known synthesis for the decapole like this:
Here are three places you will find converters:
So with this new knowledge, back to synthesising the 18-bit still life:
So what could we convert that from? We could convert it from the equivalent with a snake instead of a carrier, but I would convert it from the equivalent with a hook instead of a tub, because it is more likely to have more soups on catagolue, and the corresponding converter is cheaper:
Now, when we go to the catagolue page of the still-life with the hook, we find it has lots of soups (at the time of writing it is 43!)
So let’s try the first soup:
The soup reduces to this predecessor:
But before we start the synthesis, there are a few clever tricks we can do that will reduce the overall synthesis. The block only acts as cleanup, so perhaps it can be replaced with a glider:
1 glider less. The loaf only partly reacts before being separated from the rest of the reaction, so maybe it can be substituted with a glider. Also, the glider that we replaced a block with actually is only acting as cleanup for the loaf’s reaction, so if we replace the loaf with a glider in the right way, the other glider can be removed. Unfortunately, the loaf can’t be replaced by 1 glider, but replacing it with 2 gliders still reduces the cost:
2 gliders less. But we can do even more! Often it is possible to synthesise two nearby objects at once, instead of separately, to achieve a cheaper cost in gliders. In this example, the beehive and the traffic light can be made together in a 3-glider synthesis, instead of using 4 gliders to synthesise them separately. (More details on how these are found in a later tutorial.)
3 gliders less! See if you can complete the synthesis of the 17-bit still-life from there…
…How did you go? This in the 11 glider synthesis I got:
Now all we need to do to complete the synthesis the 18-bit still-life is to add the converter:
And we’re done! We successfully created a 14 glider synthesis of a still-life with no appearances on catagolue, by constructing it from another still-life which did have appearances on catagolue.
If you want more practice at using converters and catagolue to find syntheses, try finding a synthesis for this still-life:
Converters are used in many others ways than just assisting soup search result-based syntheses. They are used a lot in the syntheses of difficult objects like billiard tables and spaceships. For example, this is the weekender synthesis:
Using search programs to assist in creating syntheses