What Makes a Great Filter?

There are a lot of collections of Great Filter possibilities.  Many clever ideas have been expressed.  Not too much has been written about the Great Filter process, however.  This blog post is an attempt to contribute to that lack.

One of the usual arguments for a Great Filter candidate is that it took a lot of time for some particular transition to take place and therefore it is unlikely to happen and therefore it might be the Great Filter everyone is looking for.  Let’s explore this concept a bit further.  Suppose you have a planet in some state, along the presumed pathway from just rock and stuff to star-travelling lifeforms.  Someone seizes on some definition of a state, State 1, and a later state, State 2, deemed to be the next one, and notices there was a lot of time between them.  A Great Filter?  Perhaps this is just a lack of knowledge of what the intermediate states were.  If our science knew fifteen steps between the State 1 and State 2, maybe State 1a, State 1b, and so on, there would be less time between states.  The declarer of a Great State concept would have to pick one transition, say State 1g to State 1h, and show that was difficult or required unusual conditions or took almost all of the time formerly allotted to the State 1 to State 2 transition.

 

Thus, is ignorance of the details of a pathway sufficient to call something a possible Great Filter?  Hardly.  The point of the Great Filter is that many worlds wind up with the predecessor state, here State 1g, and very, very few wind up in the successor state, here State 1h.  Lack of knowledge does not translate into knowledge very easily.  Because two states are easy to describe does not mean they are particularly interesting stopping points unless we knew the details of the processes that led to each of them, and that followed from each of them.

Another argument for a Great Filter is the number of unique conditions that must simultaneously happen.  If we know the transition from State 3 to State 4, ignoring the just-discussed problems of deciding on just what those states are, we have the problem of showing that the unique conditions are really rare.  Suppose that the transition from State 3 to State 4 requires five things to be around in the neighborhood where the first exemplar of State 4 arises.  In other words, detailed knowledge of how the transition works means that each of five conditions, like temperature, pH, lack of wind, or whatever, or constituents, like Fe, Vitamin A, H₂SO₄, or whatever, or environmental changes that drive the biological  change, like drought, disappearance of cloud cover, dissolved oxygen, or whatever, or something else other than a condition, constituent or environmental change was necessary and rare.  If we don’t have detailed knowledge of the transition there is no way to get a count.  Guessing might be done in the absence of knowledge, and we will have a potential Great Filter, but some other guess might produce others and we have no Small Filter to filter out the guessed Great Filter ideas. 

For a promotion from Great Filter guess to Great Filter candidate, there would also have to be accompanying knowledge that the five, to keep with the number in the example, conditions, constituents, changes or whatever else were actually rare.  If the arguments on why something should be a Great Filter candidate depend on what we have here on Earth, we would need the rarity to be the case in space and time, in other words, while looking over the whole planet and over the whole transition time.  If these five conditions keep arising over and over, or during one shorter period all over the planet, even though it might seem to be a difficult transition, it is actually easy.   

If instead, the arguments are made that our planet is what is unique, we have at this point even less data upon which to base an argument for a Great Filter candidate.  This raises the question as to whether the concept of a Great Filter is anything more than an indication that in a string of probabilities relating to the prevalence of life, it could be true that one could be very, very small, as opposed to many of them being pretty small.  What actual benefit does the concept of the Great Filter provide?  We do not have any data to decide where the steps are, what the requirements are for each, what the statistics of the prevalence of the required conditions are, or anything else. 

There is one exception.  If a Great Filter concept relates to something we already know about or can figure out in short order, we can evaluate it and see if it is actually likely to be a Great Filter candidate.  If we are able to figure out if the concept would stop a planet from giving rise to interstellar tourists, then we can narrow down the candidates list.  Of course, there could be two or many Great Filters, but none quite as decisive as if there was only one.

This means that reasonable Great Filter candidates can come from anthropology rather than the era of the synthesis of various stages of life.  We can look at a lot of anthropology, as we are living through some, and we have records to varying degrees of failed societies, ones which might have headed off to become the originator of stellar voyagers, but which instead collapsed or dissipated away.  We might also seek Great Filter candidates from our own history, which has a fuzzy boundary with anthropology.  Here we have a chance of collecting the data needed for evaluation.

We might also use our knowledge of science and technology, limited as it is, to look for Great Filter concepts arising from these arenas.  Is there some unique invention or discovery which was done by pure chance and which made a great difference in how history developed? 

One last point is that the synthesis of life is a vital and interesting scientific question, and why it is not being pursued with great vigor and huge blocks of funding, with crowds of grad students competing to participate?   Science gets a lot of funding, but why does it go into understanding physics particles rather than our own ancestry?