Adam Frank

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Introduction

If we don't ask how long they last, but instead ask what's the probability that there have been any civilizations at all, now matter how long they lasted. I'm not asking whether they exist now or not, I'm just asking in general about probabilities to make a technological civilization anywhere and at any time in the history of the university. That, we're able to constrain. What we found was basically that there have been 10 billion trillion habitable zone planets in the universe. What that means is those are 10 billion trillion experiments that have been run. The only way that we're the only time that this whole process from abiogenesis to a civilization has occurred is if everyone one of those experiments failed. Therefore, you could put a probability, we called it the Pessimism Line. We don't really know what nature sets for the probability of making intelligent civilizations, but we could set a limit using this. We could say, look, if the probability per habitable zone planet is less than 10 to the minus-22, one in 10 billion trillion, then yeah, we're alone. If it's anywhere larger than that, then we're not the first. It's happened somewhere else. To me, that was mind-blowing. It doesn't tell me there's anybody nearby, the galaxy could be sterile. It just told me that unless nature's really has some bias against civilizations, we're not the first time this has happened. This has happened elsewhere over the course of cosmic history.