Two Types of Future Filters
In principle, any piece of simple dead matter in the universe could give rise to simple life, then to advanced life, then to an expanding visible civilization. In practice, however, this has not yet happened anywhere in the visible universe. The “great filter” is sum total of all the obstacles that prevent this transition, and our observation of a dead universe tells us that this filter must be enormous.
Life and humans here on Earth have so far progressed some distance along this filter, and we now face the ominous question: how much still lies ahead? If the future filter is large, our changes of starting an expanding visible civilization are slim. While being interviewed on the great filter recently, I was asked what I see as the most likely future filter. And in trying to answer, I realized that I have changed my mind.
The easiest kind of future filter to imagine is a big external disaster that kills all life on Earth. Like a big asteroid or nearby supernovae. But when you think about it, it is very hard to kill all life on Earth. Given how long Earth as gone without such an event, the odds of it happening in the next millions years seems quite small. And yet a million years seems plenty of time for us to start an expanding visible civilization, if we were going to do that.
Yes, compared to killing all life, we can far more easily imagine events that destroy civilization, or kill all humans. But the window for Earth to support life apparently extends another 1.5 billion years into our future. As that window duration should roughly equal the typical duration between great filter steps in the past, it seems unlikely that any such steps have occurred since a half billion years ago, when multicellular life started becoming visible in the fossil record. For example, the trend toward big brains seems steady enough over that period to make big brains unlikely as a big filter step.
Thus even a disaster that kills most all multicellular life on Earth seems unlikely to push life back past the most recent great filter step. Life would still likely retain sex, Eukaryotes, and much more. And with 1.5 billion years to putter, life seems likely to revive multicellular animals, big brains, and something as advanced as humans. In which case there would be a future delay of advanced expanding life, but not a net future filter.
Yes, this analysis is regarding “try-try” filter steps, where the world can just keep repeatedly trying until it succeeds. In principle there can also be “first or never” steps, such as standards that could in principle go many ways, but which lock in forever once they pick a particular way. But it still seems hard to imagine such steps in the last half billion years.
So far we’ve talked about big disasters due to external causes. And yes, big internal disasters like wars are likely to be more frequent. But again the problem is: a disaster that still leaves enough life around could evolve advanced life again in 1.5 billion years, resulting in only a delay, not a filter.
The kinds of disasters we’ve been considering so far might be described as “too little coordination” disasters. That is, you might imagine empowering some sort of world government to coordinate to prevent them. And once such a government became possible, if it were not actually created or used, you might blame such a disaster in part on our failing to empower a world government to prevent them.
Another class of disasters, however, might be described as “too much coordination” disasters. In these scenarios, a powerful world government (or equivalent global coalition) actively prevents life from expanding visibly into the universe. And it continues to do so for as long as life survives. This government might actively prevent the development of technology that would allow such a visible expansion, or it might allow such technology but prevent its application to expansion.
For example, a world government limited to our star system might fear becoming eclipsed by interstellar colonists. It might fear that colonists would travel so far away as to escape the control of our local world government, and then they might collectively grow to become more powerful than the world government around our star.
Yes, this is not a terribly likely scenario, and it does seem hard to imagine such a lockdown lasting for as long as does advanced civilization capable of traveling to other stars. But then scenarios where all life on Earth gets killed off also seem pretty unlikely. It isn’t at all obvious to me that the too little coordination disasters are more likely than the too much coordination disasters.
And so I conclude that I should be in-the-ballpark-of similarly worried about both categories of disaster scenarios. Future filters could result from either too little or too much coordination. To prevent future filters, I don’t know if it is better to have more or less world government.