Obama and Probability

From The Epoch Times:

Former U.S. President Barack Obama said in a Feb. 14 podcast interview that aliens are real but that none are kept at the secretive Area 51 military base in the Nevada desert, later adding that he didn’t see any evidence indicating that extraterrestrials have contacted Earth during his presidency.

In the interview, when asked, “Are aliens real?” Obama replied, “They’re real, but I haven’t seen them—and they’re not being kept in [Area 51]. There’s no underground facility, unless there’s this enormous conspiracy and they hid it from the president of the United States.”

Obama became the first leader of the United States to affirm the existence of extraterrestrial life when questioned by progressive podcaster Brian Tyler Cohen in a video posted on YouTube.

After the interview went viral, Obama said on Instagram that he wanted to “clarify” his comments to Cohen, writing that he was “trying to stick with the spirit of the speed round” while speaking on the podcast.

“Statistically, the universe is so vast that the odds are good there’s life out there,” he wrote. “But the distances between solar systems are so great that the chances we’ve been visited by aliens is low, and I saw no evidence during my presidency that extraterrestrials have made contact with us. Really!”

Before I address Obama’s abysmal grasp of probability, I must note that he did not “affirm the existence of extraterrestrial life”. To have done that he would have offered compelling evidence of the existence of such life. He did not offer any evidence of the existence of such life, compelling or otherwise.

What he offered was an unsupported assertion: “the universe is so vast that the odds are good there’s life out there.” The assertion is unsupported because he didn’t discuss and doesn’t know (because no one does) the precise preconditions for life on Earth, or anywhere else, for that matter. It is safe to say that no one really knows the “odds” that life (of what kind?) is “out there”.

What about probability, which is implied in Obama’s invocation of “the odds”? Wikipedia offers a good starting point:

[T]here are two major competing categories of probability interpretations, whose adherents hold different views about the fundamental nature of probability:

• Objectivists assign numbers to describe some objective or physical state of affairs. The most popular version of objective probability is frequentist probability, which claims that the probability of a random event denotes the relative frequency of occurrence of an experiment’s outcome when the experiment is repeated indefinitely. This interpretation considers probability to be the relative frequency “in the long run” of outcomes….

• … The most popular version of subjective probability is Bayesian probability, which includes expert knowledge as well as experimental data to produce probabilities. The expert knowledge is represented by some (subjective) prior probability distribution…. By Aumann’s agreement theorem, Bayesian agents whose prior beliefs are similar will end up with similar posterior beliefs. However, sufficiently different priors can lead to different conclusions, regardless of how much information the agents share.

In other words, a probability is either (a) the observed frequency of an event of a given kind or (b) a guess.

There is no probability of alien life, in the frequentist interpretation of probability, because it isn’t the kind of phenomenon to which the frequentist interpretation applies.

Frequentist probability is about long-run averages, like the frequency of “heads” in a long series of coin flips. It says nothing about what might happen in the next coin flip. If the long-run average of “heads” is one-half, that tells you nothing about what will happen on the next flip. The next flip can’t be one-half of anything; it will be one of something: “heads” or “tails”.

That leaves subjective probability, which is just what it sounds like. You can make it up. Which is what Obama did. He simply asserted that “the odds” on alien life somewhere in the universe “are good” because the universe is “so vast”. He might as well have said something like this: The universe is so vast that there is someone out there who is identical to me, except that he opposes everything that I did as president.

And what does it mean to say that “the odds are good”, anyway? Nothing, actually, because you’re talking about something that might happen. A single event (e.g., the occurrence of alien life) doesn’t have a probability. It either exists or it doesn’t.

Subjective probability, as I said, is a guess. Weather forecasting is a blatant case in point. If a meteorologist says that the probability of rain in a given area is 30%, what he means is this:  There is a 30% probability that some location in the specified area will receive at least 0.01 inches of measurable precipitation during the forecast period. That’s it — not how long it will rain, not how heavy it will be, and not how much of the area will get wet.

And how does the meteorologist arrive at 30%? Forecasts rely on many model simulations. If 30 out of 100 model runs show rain, that yields a 30% chance of rain. It’s guesswork all the way down because models are nothing more than collections of guesses about the relevant variables, their values, and their relationships to each other (For more about models and modeling, see this, this, this, this, this, this, this, and this.)

Obama’s statement was in keeping with his political rhetoric: pure bull***t.