Regardless of how well we exercise or monitor our diet, no human being has been documented living longer than Jeanne Calment, who died at the age of 122.5 years. Likewise, no matter how much we can mitigate climate change, drive away asteroids with NASA’s DART-like missions, develop mRNA vaccines for deadly viruses and avoid nuclear wars, Earth will eventually be sterilized by the sun in about a billion years.
Detailed accounts of the Sun’s evolution and the Earth’s response to it indicate that we are entering the last quarter of terrestrial life. Within a billion years, the water vapor content in the atmosphere will increase dramatically, and the oceans will begin to evaporate, leading to runaway evaporation until the oceans dry up. Water vapor in the atmosphere will make its way into the stratosphere, where solar ultraviolet rays will separate water molecules. The decomposition products will gradually leak out, until most of the water vapor in the atmosphere is lost. The subsequent dry phase of global warming will raise the surface temperature, and the Earth will become a dry, lifeless planet.
Any intelligent civilization on a habitable Earth-like planet around a sun-like star would face this existential danger. While technologically intelligent civilizations will abort their frantic planets, less advanced civilizations will show signs of distress like animals in a burning forest.
In our history of science and technology, wireless communications were developed during the same century with space travel. However, it will take some time before we can develop the infrastructure to launch spaceships large enough to transport all of humanity away from Earth under existential distress.
The most realistic scenario is similar to the biblical story of Noah’s ark, where Noah saved his family and pairs of wild animals from a flood that engulfed the world. In such a limited scenario, we would only keep a representation of what we consider valuable. Noah’s Ark, in this case, could hold an electronic archive of the DNA of all terrestrial life, as well as all human creations in the form of books, music, and valuable online content. It would be wise to leave any toxic content from social media.
In this limited scenario, most humans would be left behind. Under these conditions, radio and television stations would transmit severe distress signals as our planet warmed by the sun. Can we detect such signals from a distance?
By scanning stars that are currently transitioning through the evolutionary stage the Sun will reach in a billion years, we can look for cries for help in the form of radio communications or laser signals from other intelligent life forms that may be out there.
Instead, we can look for accelerated technological activities on a planet that is on the verge of sterilization.
If intelligent life forms elsewhere in the universe exist and do anything like us, then civilizations under stress are likely to show more city lights and industrial pollution than would be expected under normal circumstances, like ants engaged in building new colonies in anticipation of harsh weather. . Their scientists will be working frantically around the clock in sustainable bunkers beneath the surface with proper food, air and sun supplies from the increasing heat radiating from their host star. The wealthy class will be able to access this technology and build luxurious underground complexes long before the rest of the population is protected, and after sterilizing the surface, it will be difficult to detect these underground civilizations. Their lifespan will depend on how much water, food, or energy they can store or extract from the rocks around them.
Data from the Mars Reconnaissance Orbiter indicates that Mars was rippled with rivers and pools of water about 2.5 billion years ago. NASA’s MAVEN Orbiter has provided evidence that Mars lost its atmosphere around this time. So far, Perseverance has not observed any traces of Mars technology, which means it has never experienced the aforementioned technological consequences of drought. Coincidentally, around the same time that Mars dried up, Earth’s atmosphere was enriched with oxygen by cyanobacteria. There was good news and bad news about possible life in the solar system simultaneously; Too bad there were no sentient beings around to report it in the media.
Our main opportunity to collect memorabilia from potential extraterrestrials is to search for artificial objects that have been launched into interstellar space in the ultimate existential act of technological civilizations. (The Galileo Project at Harvard University, which I lead, is involved in this research.) The success of this research depends critically on the number of tools that technological civilizations sent into space in the accelerating final phase of their existence, before the lights in “head.” Canaveral sites have been shut down.
Most sun-like stars formed billions of years before the sun appeared, and they should have boiled all the oceans onto their now habitable Earth-like planets. The oldest stars have evolved beyond the red giant stage, swallowing up their closest planets and are now white dwarfs. After billions of years of cooling, this mineral remnant has roughly the surface temperature of the Sun and Earth’s radius. As a result, their habitable zone is a hundred times closer than the separation of the Earth and the Sun.
As I noted in a paper I co-authored a decade ago, a habitable Earth-like planet would cover the entire face of a white dwarf as it transited in front of it, making studying biomarkers in the planet’s atmosphere already feasible with NASA’s new James Webb Space Telescope. While oxygen or methane would refer to primitive life forms, she explained in a follow-up paper she co-authored that industrial pollution could also be detected as the fingerprint of an advanced technological civilization, if any.
If we study the technological civilizations of the habitable zone around the white dwarfs, it will be especially interesting to read the history books written by their ancestors over the past 10 billion years.
aVI TheohB He is the chair of the Harvard University’s Galileo Project, the founding director of the Harvard University’s Black Hole Initiative, the director of the Institute for Theory and Computation at the Harvard-Smithsonian Center for Astrophysics, as well as the past chair of the Harvard Department of Astronomy (2011-2020). He chairs the Breakthrough Starshot Project’s advisory board, is a former member of the President’s Council of Advisors for Science and Technology and a past chair of the Physics and Astronomy Board of the National Academies. He is the best-selling author of Extraterrestrials: The First Sign of Intelligent Extraterrestrial Life and co-author of Life in the Universe, both published in 2021.