In a new Joe Rogan podcast, the British physicist Brian Cox argued that we hold a great responsibility for prolonging our civilization because it might be the only source of meaning in the cosmos.
However, in the big scheme of the cosmos, the future existence of humans might not matter, for the same reason that the extinction of dinosaurs did not attract cosmic attention. Humans arrived at the cosmic scene only over the last percent of a percent of cosmic history and nobody at cosmological distances might care about it. Other cosmic players may have no interest in making their presence known to us because our terrestrial brag sheet does not amount to much on the cosmic dating scene.
Given the hundred billion older habitable planets in the Milky-Way galaxy alone, it is likely that beings like us existed in the past on exoplanets. Their electromagnetic signals might be long gone, since it takes merely tens of thousands of years to cross the Milky-Way galaxy at the speed of light, and that is a few millionths out of the full span of cosmic history.
Whether anything was left from dead civilizations depends on how forceful they were in venturing to interstellar space. Our own interstellar probes: Voyager 1 & 2, Pioneer 10 & 11 and New Horizons, will exit the Solar system’s Oort cloud within twenty thousand years and will constitute at that time a quadrillionth of the population of interstellar objects with the same mass. We know very little about space trash from other civilizations because astronomers detected the first interstellar objects only over the past decade.
Brian is not engaged in seeking scientific evidence for interstellar space probes. His opinions on the possible existence of extraterrestrials are not better informed than those of a lay person. The only way for science to make a difference is by seeking new evidence as to whether extraterrestrials exist. This is my day job as a practicing astrophysicist. The Galileo Project under my leadership aims to collect observational data on anomalous extraterrestrial objects near Earth. It follows the scientific method of relying on evidence rather than on prejudice. In addition to the analysis of materials retrieved from the Pacific Ocean site of the first interstellar meteor, the Galileo Project research team will release next month new data on half a million near-Earth objects monitored by its new observatory at Harvard University.
A fundamental question is what should we adopt as the default assumption. Brian advocates the traditional choice that we are alone until proven otherwise. This obviously gives us a sense of self-importance and removes the urgency to invest funds in the search for evidence.
But physicists like Brian do not insist that dark matter does not exist until discovered. Since we had not detected dark matter particles so far, the most conservative view should have been to assume that known matter and radiation are the only cosmic constituents. Instead, physicists invested billions of dollars in searching for specific types of dark matter particles. This was motivated by indirect evidence for the existence of dark matter, based on its gravitational influence on the dynamics of visible matter and radiation. Nevertheless, if gravity happens to be modified at low accelerations, this indirect evidence is incorrectly interpreted.
The existence of habitable Earth-size planets around other stars is circumstantial evidence that life-bearing conditions might be common. Yet, mainstream folklore prefers to adopt the default assumption that aliens might not exist. One argument raised by Brian is that we would have detected them by now if they had existed. As I explained in a podcast today with Deepak Chopra, our own technological signatures such as city lights, industrial pollution or space rockets, are difficult to notice through the vast expanse of interstellar space. We must also keep in mind that the search for extraterrestrial technological signatures was funded at less than a percent of the search for dark matter. If so, why should we insist that dark matter exists and gravity is not modified while arguing that extraterrestrials might not exist without engaging in an elaborate attempt to detect their space probes?
Science is exciting because it offers the opportunity to seek evidence. Expressing an opinion on a scientific question without investing time or effort to answer it, is unscientific.
The biggest advances in our scientific knowledge were surprises. This includes the experimental discovery of quantum mechanics a century ago, which no theorist expected. It also includes pioneering theoretical ideas, such as Stephen Hawking’s realization that black holes evaporate, inspired by Jacob Bekenstein’s insights on black hole entropy — which Hawking initiated attempted to disprove, and by Yacov Zel’dovich’s insights on vacuum fluctuations — which Hawking learned about during a trip to Moscow. The latter inspiration was mentioned by Kip Thorne in a public lecture he gave last week at Harvard’s Black Hole Initiative, for which I served as the founding director and where the first images of black holes were derived.
Stephen Hawking was very interested in the possible existence of extraterrestrials when he visited my home for the inauguration of the Black Hole Initiative in 2016. Stephen was particularly concerned about the existential risk from alien predators. Here again, my take is different from the Brits: aliens probably do not care about us. Since most stars formed billions of years before the Sun, aliens may have embarked on interstellar journeys long before humans distinguished themselves from nature through modern science and technology. We should search for aliens not out of fear but because their scientific insights might endow us with a quantum leap in our scientific knowledge. The inspiration we may draw from advanced alien scientists could echo Hawking’s inspiration from Bekenstein and Zel’dovich on steroids.
Rather than stay trapped in an echo chamber that amplifies our prejudice on our privileged cosmic status, it would make more sense to assume that we are typical students in the class of intelligent civilizations. After all, the Copernican Principle proved more sensible than the alternative in the past. It offers a more modest default assumption than the notion that we are privileged.
Here’s hoping that our observatories will eventually connect us to our cosmic neighbors. Copernicus and Galileo used observational data to argue against the geocentric model of the cosmos and the Vatican finally admitted that they were right in 1992. Now, a new type of clergy advocates for an egocentric model of the cosmos without pursuing scientific evidence. In the long run, we will all do much better with a curious mindset about the cosmos. Science at its best is a learning experience, driven by curiosity and the humility to admit that we are not as important on the cosmic stage as we are tempted to think.
ABOUT THE AUTHOR
Avi Loeb is the head of the Galileo Project, founding director of Harvard University’s — Black Hole Initiative, director of the Institute for Theory and Computation at the Harvard-Smithsonian Center for Astrophysics, and the former chair of the astronomy department at Harvard University (2011–2020). He is a former member of the President’s Council of Advisors on Science and Technology and a former chair of the Board on Physics and Astronomy of the National Academies. He is the bestselling author of “Extraterrestrial: The First Sign of Intelligent Life Beyond Earth” and a co-author of the textbook “Life in the Cosmos”, both published in 2021. The paperback edition of his new book, titled “Interstellar”, was published in August 2024.
