[HarHarVeryFunny]

Yes - seem a much better, more general, approach.

There was an interesting interview of Lee Cronin on Lex Fridman's podcast a while ago.

For anyone unfamiliar, Assembly Theory is based on the idea that the more structurally complex something is, such as a molecule, the less likely it was created by chance, and the more likely it was created by an assembly factory of sorts, one type of which is life in it's potentially diverse forms.

[gradus_ad]

I was never very impressed by assembly "theory" (what are its testable predictions?)... If we find a refrigerator floating in space I don't need an Assembly Theorist to tell me there's some intelligent/intentional process behind it.

Seriously, what is it other than a potent source of pop sci clickbait?

[Dr_Birdbrain]

I think assembly theory is most useful to define a spectrum of complexity.

Sure, a refrigerator requires intelligence, whereas loose carbon atoms do not.

What about everything in between? Methane? Complex hydrocarbons? Pointy sticks? Things that look like crude tools?

It’s about defining a metric that can measure complexity across a wide range of things you might encounter, to help estimate the odds that it was produced by something simple yet alive, or something complex and alive, or something alive but not very smart, or something kinda smart, or something super smart, etc

[pixl97]

No, not clickbait at all.

Take something far simpler, the methane molecule. If you find it in the atmosphere of a planet then most likely it was formed within the last 10 to 20 years. There has to be some form of process creating it. This holds true for any short time frame molecules. Now, there could be a non-biogenic source for these, but when you find something like this it points to an active planet.

[AtlasBarfed]

What sustains the methane in say, Neptune?

[HarHarVeryFunny]

The essential prediction is that complex things are made by some sort of repeatable assembly process/factory, not by chance (with increased confidence when multiple copies have been seen). There is an idea of an "assembly index" for objects (e.g. molecules) as a measure/bound of how many steps they took to assemble - the level of complexity.

There is also a prediction (or definition?) that things with a high assembly index are produced by some form of life, so if one can measure the assembly index of molecules and find ones of high index/complexity, then this indicates they were created by some form of life, and so this can be used as a test for life without having to make any assumptions of it being like life on earth (and therefore only looking for biosignatures of life we know of).

Assembly theory seems most interesting when applied to molecules, although it's not limited to that in scope. There are constraints on how complex molecules are formed in terms of what reacts with what, as well as some intuitive measure of complexity in terms of their size and variety of components and atomic bonds.

One thing that Lee Cronin has discovered/noted is that mass spectrometry can be used as a crude way to measure complexity of molecules, and hence give an idea of their "assembly index", since different chemical bonds have different fingerprints in terms of how they absorb energy (diff. frequencies of UV or IR light absorbed in the mass spec.).

There's a couple of different applications of this use of mass spectroscopy as a proxy for assembly index that Cronin mentions in his interview with Lex Fridman, which do seem to provide some proof of it's predictions of high assembly index being an indicator of life, and relative assembly index and indicator of which came first.

1) NASA, wanting Cronin to prove the value of this as a potential life-detector, gave him a variety of unlabeled organic and inorganic samples, and Cronin was able to classify them all correctly based just on their mass spec. signatures.

2) By analyzing a variety of biological samples, again via his mass spec. technique, Cronin was able to reconstruct the evolutionary tree of life in agreement with other ways of doing this. He goes into a little detail on the Lex interview, but it sounds complex and he does not fully describe the technique/analysis.

[Supermancho]

> If we find a refrigerator floating in space I don't need an Assembly Theorist to tell me there's some intelligent/intentional process behind it.

Isn't that the point? What you find obvious about a refrigerator is precisely because it's complex in a way that you understand.

I mean, the problems with the theory are pretty obvious. Anything complex is a matter of how you measure complexity. A common earth object is obvious because we can easily categorize the complexity and recognize it.