What Are the Chances That We Are Visited by Aliens?
Below is a set of questions that I addressed today about alien visitation near Earth:
Do you believe the Drake Equation is obsolete, or does it still have scientific value as a framework for discussing extraterrestrial intelligence?
Based on the latest census of exoplanets, there should be billions of Earth-Sun analogs in the Milky-Way galaxy — equivalent to billions of houses in our town. We do not know how many of them had residents since the town was constructed, 10 billion years ago.
Mainstream astrobiologists define their highest priority to build the space-based Habitable World Observatory and search remotely for the chemical fingerprints of microbes in some of these houses. This may not be as easy as identifying a prominent technological signature of an alien visitor, akin to a package in our mailbox or a knock on the front door of our house.
Traditionally, the SETI community followed Frank Drake and defined its goal to search for an electromagnetic signal, akin to a phone call from one of the residents of our town. Whether they decided to call us remains to be seen. The Drake equation factors, through 7 parameters, the uncertainty about the number of neighbors that might transmit detectable communication signals.
Radio communication is an old technology, which was recently accompanied by optical laser communication in NASA’s Artemis II mission to the Moon. Lasers might replace radio communication in our future. To save power, a technological transmitter might beam its signal in the direction of the receiver rather than Earth, and might only transmit sporadically. Interestingly, the anomalous “Wow! Signal” — detected on August 15, 1977, came from a direction which is aligned to within 9 degrees from the arrival direction of the interstellar object 3I/ATLAS into the inner Solar System, but a similar signal was never detected again.
In contrast to fleeting communication signals that travel at the speed of light, physical interstellar objects are trapped by the Milky-Way gravity and accumulate over time. Technological devices might cluster around the habitable zones of stars for the same reason that bees seek resources around flowers. The chance of finding bees around flowers depends on how many bees exist per flower. Interstellar probes could outlast the age of their senders. The number of packages in our mailbox is not simply related to the number of phone calls we receive, because most senders of these slow packages might have died by now whereas their communication signals are billions of light years away and not detectable on Earth.
Therefore, the Drake equation does not address the likelihood of detecting extraterrestrial technological probes near Earth.
Is it currently possible to estimate the probability that intelligent life exists elsewhere in the universe? If so, what do you consider to be the most reasonable estimate based on present scientific knowledge?
All we know is that about a tenth of the Sun-like stars have an Earth-mass planet roughly at the same separation (as summarized in Figure 2 here). If a substantial portion of these planets have an atmosphere and liquid water on their surface, these are likely to develop the chemistry of life-as-we-know-it leading to intelligent beings like us after about 5 billion years.
Most stars formed billions of years before the Sun. As a result, most extraterrestrial civilizations could have launched interstellar probes billions of years ago. It takes Voyager-like probes less than a billion years to cross the Milky-Way disk. Therefore, it is completely reasonable for us to find near Earth interstellar objects of technological origin that targeted the habitable zone of the Sun.
What percentage of scientists, astronomers, astrophysicists, or astrobiologists would you estimate believe that intelligent extraterrestrial life exists somewhere in the cosmos?
Most astronomers are willing to admit publicly that microbial life is probably abundant but at the same time they are in favor of sidelining any allocation of major resources to the search for intelligent extraterrestrial life.
There used to be a U.S. congressman who prominently advocated for anti-gay legislation. After retiring, he confessed that he was in fact gay and was just trying to be popular among his constituents. The same might happen to most astronomers after the first disclosure of alien visitation.
In your view, is interstellar visitation by extraterrestrial civilizations physically plausible?
Yes, even with Voyager-like technologies from the 1970s.
If the Alcubierre warp drive concept were ultimately shown to be physically realizable, would it significantly reduce the travel time between stars and make interstellar exploration or visitation more feasible?
Yes, a warp drive which surfs on a spacetime distortion would significantly reduce travel time, but it is highly uncertain whether such a drive is physically possible to construct with known constituents.
Finally, do you believe that the study of UAPs and related phenomena may become more accepted within academia as more researchers apply rigorous scientific methods and empirical standards to the subject?
Once the first indisputable evidence will be revealed on alien visitation, the study of related phenomena will become the hottest frontier within academia as more researchers apply rigorous scientific methods and empirical standards to the subject, similarly to the Galileo Project under my leadership right now.
ABOUT THE AUTHOR
Avi Loeb is the head of the Galileo Project, founding director of Harvard University’s — Black Hole Initiative, former 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.
Professional website:
https://lweb.cfa.harvard.edu/~loeb/
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