OK, so the topic today is Great Filters. These are things that could get in the way of a civilization leaving its home planet and colonizing the galaxy. Actually, there’s a lot of types of great filters, from the emergence of life through various stages of evolution, and stuff like that, but these filters aren’t generally one-off events. A great filter would be something so catastrophic to any species or civilization that they prevent anyone from colonizing the galaxy. And why do we say that? Because we don’t see any evidence of galactic colonization anywhere. Now I know the first thing you’re going to say is, ‘Tony, how the hell can you say that? We’ve only just begun looking! Give it time!’ I know, and you’re right, we have only just started looking and we should absolutely continue looking, but what I can say with some level of confidence is that there are no obvious signs of other civilizations within our galaxy. Whatever or whomever is out there, is not making it easy to find them. So, the question is reasonable, where the hell is everybody? Now over the course of the years I’ve been doing this, people get really impatient with me and think that the idea of a great filter preventing any civilization from colonizing the stars is too limiting, that we’re not thinking outside the box enough. Many people have pointed out, and we’ve even done hangouts on things like this, that von neumann probes could visit a sizeable fraction of the galaxy in just a few million years and that it’s not that hard to expand out to the stars. Those arguments actually support my view that we are probably the only ones in our galaxy, not dispute it. If it’s so easy to go to the stars, especially with robotic spacecraft, then given the fact that the milky way galaxy is almost as old as the universe - some of the stars in our galaxy are 13 and a half billion years old - then there has been plenty of time to send out your probes several times over and still we see nothing. So before you start saying great filters are a waste of time to talk about, you really need to come up with good answers to the question of where the hell everybody is. So, for now, grant me that the idea of a great filter is at least a possibility and that there may be different ones that present themselves in the course of the evolution of a species and consider that one of them may just be the effect an advancing technological civilization has on the host planet it’s living on. That’s the topic of the paper we were going to discuss today with Adam Frank and his collaborators and I promise we’ll go into the modelling details they used when we reschedule, but for today, let’s just take a layman’s view of the problem. I am by no means an expert on this, but I do think I have a beginner’s level knowledge of the topic. So, here’s the basic question: what if sustainability is not possible in the universe? What if all species ran through all of their natural resources before they could reach for the stars? Think about it, we don’t actually know if sustainability is something that can happen in nature. Equilibria go out all the time when things are left on their own and they correct, but usually only to become unsustainable again. Can life in the universe live sustainably within the galaxy? The answer isn’t necessarily yes. So far as we know today, we are the only civilization in the galaxy. We may also be the first of many, but I find that somewhat unlikely given how much time has passed before we got here, but it’s possible. So what do you guys think? Is sustainability possible in the universe? Why? Lemme know in the comments. Also let me just say real quick that this topic, the paper written by Dr. Frank nor this hangout is any kind of veiled attempt to put forth a political agenda on the climate change topic. Whether you think human induced climate change is occurring right now on this planet or not, try to think of the problem in more generic terms. I’m not going to get into a pissing contest over whether climate change on Earth is real or not. What I want from you is to think for a minute. As a general rule, it’s hard to argue that resource depletion can go on forever, it has to stop or slow down at some point in a civilizations development, and whether we’re faced with that right now, today, isn’t really the point for today, so I’m not gonna debate that here. The point is that AT SOME STAGE civilizations are faced with the problem of resource depletion, and what effect does that have on their ability to colonize the stars? Is it enough to prevent it entirely? Is it a Great Filter? Based on population studies done on our planet, one concept we have to become familiar with is carrying capacity. I’ll just read wikipedia’s definition, “The carrying capacity of a biological species in an environment is the maximum population size of the species that the environment can sustain indefinitely, given the food, habitat, water, and other necessities available in the environment. In population biology, carrying capacity is defined as the environment's maximal load,[1] which is different from the concept of population equilibrium. Its effect on population dynamics may be approximated in a logistic model, although this simplification ignores the possibility of overshoot which real systems may exhibit.” So that’s a good point, we need to be careful when talking about this not to oversimplify the problem, but it’s not unreasonable to think that there’s only so much a planet can give to a host population before something has to change. Population and resource consumption can’t just go on indefinitely when the resources are finite. And the graphs in Frank’s paper didn’t seem to exhibit any overshoot in population, which as the wikipedia definition pointed out, we do see in real systems. So there are some caveats to this discussion, but let’s just go on an see where this leads. So this study went through four possible outcomes of a simulation they ran based on population studies and examples, like Easter Island, on our own planet. I’m not gonna go into them all today, just watch the SFN episode I did on Monday for a summary. We’re also going to go into that in depth when Dr. Frank can join us. But basically, three of the four outcomes were bad, with only one way entering into a stable equilibrium. Most of the research seemed to pin the outcomes on the advancing civilization realizing the problem in time. The one scenario that didn’t was the first outcome, the Die Off one, they just went on consuming, but the others had lesser and varying impacts. Finally, before I open this up for discussion, I want to mention that those of you who think that the Easter Islanders, and by extension humanity as a whole can just go find more resources, are also oversimplifying the problem. Notwithstanding the fact that the thinking of “let’s just go get more resources to consume” is basically just thinking like a virus, it’s never been easy to do that. Sure some Easter Islanders left via emigration, but think about it, the nearest island was 1200 miles away. You didn’t just get on a boat and leave, it was a really big deal. So after they consumed the forests and most of the natural resources, the population of Easter Island went from a peak of 10,000 to as little as 100 in the mid-1800’s. So for humanity, going to another planet is not necessarily the answer and there’s by no means an easy solution. Just go get more stuff to eat is a problem that has plagued humanity from day one. It’s also not clear we can even survive in space. It may actually kill us. I’ve done many hangouts last year with Arnauld Nicogossian about human physiology in space, and if we’ve learned anything it’s that being up there is very detrimental to our health. I already know what you’re going to say next because you’re a big fan of Ray Kurzweil and Mark Zuckerberg and all those guys who say we’ll just put our personalities into androids and go into space that way. OK fine, I’ll grant that that is possible. Not easy certainly, but possible. But if it’s possible for us, then it is surely possible for any other civilizations out there and they apparently didn’t do it. Why? Again folks, come up with a reasonable answer to the question, Where the hell is everybody? OK enough of me talking, it’s time to hear from you. Leave me some questions and comments and let’s solve this thing.