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Schelling’s Point and The Search for Extraterrestrial Intelligence

As  mentioned in Chapter 6, a coordination game is one in which the goal of both players is to coordinate on the same strategy. However, if there exists more than one Nash equilibria, then both players could fail to coordinate on choosing the same one. To help narrow down the choosing of the same Nash equilibria by both players,  Thomas Schelling introduced the idea of a focal point, also known as Schelling’s point, in 1960, where players are motivated to focus on one Nash equilibria due to natural reasons ( Networks, Crowds, and Markets by Easley).  Therefore, since both players cannot communicate with each other, they both rely on these natural decisions to choose the equilibria that will give both of them the higher payoffs. In his book, The Strategy of Conflict,  Schelling describes “focal point[s] for each person’s expectation of what the other expects him to expect to be expected to do”.

This idea can be applied in SETI’s Search for ExtraTerrestrial Intelligence. If both us and another civilization want to find each other then the same strategy must be chosen. The way we currently define an exoplanet (a planet beyond our solar system) to be habitable is through means of calculations and assumptions based off how life began on Earth, as well as distances from its star. Our current environment suggests that life is supported in main sequence stars with lifetimes of billions of years. For reference, our Sun is a G-type star with a lifetime of 10 billion years and Earth’s semi-major axis is 1 AU (astronomical unit), also known as the distance from the Sun. By obtaining the luminosity of stars in other solar systems, we can calculate the lower and upper semi-major axis bounds for a planet in its system to have life. By habitable, we do not mean a civilization; habitable simply means the planet could have water and support life. However, being that there are an estimated 2 trillion galaxies, and we have already detected about 3,700 exoplanets in our own galaxy, the potential for civilizations –even civilizations much more advanced than us that have been around for longer– is a strong possibility.

Assuming that there exists at least one civilization that is at least equally as advanced as us, we can assume that they are also searching for extraterrestrial intelligence, just as SETI is.  However, in order to find each other, we both must choose the best strategy for both parties by thinking of what each would do. If we were across the galaxy trying to detect signals from Earth, where would we look? Just how we listen to the radio in our car at different frequencies, signals also travel through frequencies in outer space. So, how do we choose the best frequency to send our signals as well as to search for signals? The electromagnetic spectrum ranges from radio waves to gamma rays; however, we look at radio waves since they can penetrate clouds of cosmic dust instead of being absorbed by them. This is true all across space, which accounts for one of the natural reasons for choosing a strategy as explained by Schelling. Additionally, we can narrow down our range of frequencies by choosing the frequency for which hydrogen atoms emit at: 1420 MHz, or the 21cm line. Hydrogen is the most abundant element in the universe, it is the element that a star’s lifetime spends the most time in during nuclear burning, and it helps us understand how the first stars and galaxies formed. This “standard of frequency must be known to every observer in the universe,” and, with our assumption that they are as advanced as us, we would both send and search for signals in that wavelength. (Cocconi and Morrison, Cornell 1959). We are playing a coordination game across the universe, and assuming that another civilization is just as eager as us to find life elsewhere, we can use game coordination to help us answer one of the most sought-after questions in the science field.




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