PBS Space Time Season 2019 Episode 39 The Doomsday Argument

PBS Space Time is a fascinating science documentary series that dives deep into cutting-edge discoveries in astrophysics, cosmology, and beyond. In season 2019 episode 39, titled "The Doomsday Argument," we explore an intriguing theory about the future of humanity on planet Earth and the cosmos at large.

At the heart of this episode is a paradoxical question: How can we predict the likelihood of a catastrophic event that could wipe out human civilization, when we don't know how many humans will exist in the future? To make matters more complicated, we also don't know how long our civilization will survive before facing such an event. These are the kinds of questions that keep scientists and philosophers up at night, and they are the focus of "The Doomsday Argument."

The episode begins by introducing the titular argument, which is based on Bayesian probability theory. Put simply, Bayesian probability is a mathematical framework for updating beliefs in the face of new evidence. In the case of the Doomsday Argument, the "evidence" is the fact that we exist at a certain point in history, and we can use that fact to infer something about the likelihood of our future extinction.

As the episode explains, the basic idea behind the Doomsday Argument is that if we assume that there will be a certain total number of people who will ever exist, and we assume that we are a random sample from that population, then the fact that we exist today implies that we are more likely to be living in the earlier rather than the later part of human history. This is because if there are, say, 100 billion humans who will ever exist, and we are born around the 7 billionth mark, then it is more likely that we are closer to the beginning of human history than the end.

This may seem counterintuitive, but as the episode explains, it has some serious implications for our future. If we assume that there will be a total of, say, 10 trillion humans who will ever exist, and we are born around the 7 billionth mark, then the Doomsday Argument suggests that there is a high probability that humanity will face some kind of catastrophic event that wipes us out before we reach that total number. This is because the probability of our being born at the beginning of human history is much higher than the probability of our being born close to the end.

Of course, there are many assumptions behind the Doomsday Argument, and the episode does a great job of exploring some of the critiques and counterarguments that have been raised over the years. For example, some critics argue that our position in history may not be a random sample, since our existence could be influenced by various factors like the habitability of our planet or the likelihood of intelligent life in the universe. Others point out that the total number of humans who will ever exist is a highly uncertain and unknowable quantity, so it's not clear what we should infer from our position in history.

Despite these objections, the Doomsday Argument remains a fascinating and thought-provoking idea, and the episode does an excellent job of presenting it in a clear and accessible way. The visuals and animations are top-notch, and the explanations are accompanied by helpful diagrams and analogies that make the complex concepts easier to understand.

Overall, "The Doomsday Argument" is a must-watch episode of PBS Space Time for anyone interested in the big questions of our existence and the fate of humanity in the cosmos. It's an engaging and intellectually stimulating exploration of a fascinating idea, and it's sure to leave viewers with plenty to think about long after the episode is over.