![]() The key to this assertion, much as with Fermi’s original insight, lies in the relatively short amount of time it would apparently take for a species to spread across the Milky Way’s 100,000-light-year girth even using modest, far-slower-than-light propulsion systems.Ĭredit: Nadieh Bremer Source: Jonathan Carroll-Nellenback, University of Rochester That unassailable fact (for most level-headed people) led Hart to the conclusion that no other technological civilizations currently exist-or have ever existed-in our galaxy. In 1975 astrophysicist Michael Hart produced the first properly quantitative and nuanced study of this idea, in which he put forward what has become known as Hart’s “fact A.” This refers to the absence of aliens on Earth today. Fermi, renowned for his ability to carry out so-called back-of-the-envelope calculations in his head, had figured out in approximate terms that the Milky Way could be settled in the blink of a cosmic eye when each tick of the galactic clock accounts for millions of years. Most famously, over a lunch in 1950 with fellow scientists, physicist Enrico Fermi first recognized this fact and-as the story goes-blurted out, “Don’t you ever wonder where everybody is?” The “everybody” in this case was any spacefaring species, and the question developed over time into the equally famous, albeit somewhat mislabeled, Fermi paradox: unless technologically proficient species are vanishingly rare, they should have spread practically everywhere across the galaxy by now, yet we see no evidence for them. ![]() Just as Western Europeans eventually realized that the peoples of the southern Pacific had spread across its thousands of miles of ocean on simple vessels gliding along at just a few knots, we can now see that spreading across our galaxy need not require much more than persistence and a modest amount of cosmic time. And that is where things get really interesting. Like the islands of Earth, these exoplanetary specks might both generate and support living systems and could provide a network of waypoints for any species determined to migrate across interstellar space. The best estimates from exoplanet-hunting efforts, such as those undertaken with NASA’s Kepler space telescope, suggest that within this ocean of stellar bodies there may be more than 10 billion small, rocky worlds in orbital configurations conducive to temperate surface conditions. In the Milky Way galaxy, there are perhaps as many as 300 billion stars. The parallels between this unmistakably terrestrial environment and our cosmic surroundings are striking. But taken together, they represent a vast landscape of potential settlement and civilization for people motivated to navigate across Earth’s watery depths. Many are barely more than a protuberance of rock and coral, and even the habitable spots are not all inhabited at any given time. Within the regions of Polynesia, Micronesia and Melanesia, there are tens of thousands of islands scattered across millions of square miles of ocean. ![]() The story of Pitcairn is just one extreme example of the unusual dynamics of human occupation across the southern Pacific. Remarkably, it took another 18 years for any other ship to drop anchor at Pitcairn, even though the settlers recorded sightings of vessels passing in the distance. What was, at least superficially, a habitable place had become unsustainable, until the arrival of the Bounty on that fateful day in 1790. That community perhaps existed for centuries-centuries that seem to have culminated with a depletion of natural resources, as well as conflicts on other, distant islands that cut off lines of trade and supply, leading to the effective extinction of Pitcairn’s human occupants. Surrounded by the southern Pacific Ocean and with hundreds of miles of open water between it and the nearest other islands, Pitcairn is the epitome of solitude.īefore the Bounty escapees showed up, the island may not have seen human occupation of any kind since the 1400s, when it was still inhabited by Polynesians. On the 15th of January in 1790, nine mutineers from HMS Bounty, 18 people from Tahiti and one baby arrived on Pitcairn Island-one of the most isolated habitable places on the planet.
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