It takes light more time to reach us from greater distances. Hence, by detecting farther galaxies than ever before, the Webb telescope allows us to view how the infant Universe looked like. The record holder, a galaxy named JADES-GS-z14–0, has a cosmological redshift of z=14.32.
My textbooks “How Did the First Stars Form?” and “The First Galaxies in the Universe”, were published a decade ago in anticipation of the Webb telescope’s data on the farthest galaxies. Two decades before that, I was invited to serve on the first Science Advisory board that designed this `Next Generation Space Telescope’. The privilege was given to me as one of the first few cosmologists to predict theoretically the properties of the first stars and galaxies, starting in the early 1990s.
Back then, I was told by mainstream observers that galaxies are unlikely to exist beyond a redshift of a few and that my research is highly speculative. This is not the only unsubstantiated prejudice I witnessed. Before that time, most observers dismissed the possibility that a Jupiter-mass planet can reside close to a Sun-like star, because the theory used to explain the location of Jupiter in the solar system precluded a tighter system. In 1995, Michel Mayor and Didier Queloz discovered a close-in Jupiter-mass companion to the solar-type star 51 Pegasi. Of course, there are other examples of observers’ bias that slowed down the pace of discoveries. Until a few years ago, observers precluded the possibility that a stellar-mass black-hole could exist in close proximity to a Sun-like star. Nevertheless, in 2022 our ITC postdoc Kareem El-Badry and collaborators discovered Gaia BH1, a Sun-like star orbiting a black hole of 9.6 solar masses with an orbital period of half a year.
About a decade ago, I hosted the Caltech astronomer Mike Brown in my office and asked if he ever checked whether some Kuiper-belt objects might be producing their own light, as expected from extraterrestrial spacecraft. In such a case, their observed flux would fade inversely with increasing distance squared, whereas if the objects simply reflect sunlight — their flux would decrease with increasing distance to the fourth power. Mike responded: “Why should I check? They obviously should fade away with distance to the fourth power.”
Scientific inquiry is a human endeavor, and humans wish to anticipate what they may find. Since funds and telescope time are limited resources, observers tend not to take risks and sometimes miss opportunities of discovering the unknown. Young scientists tend to be more conservative because they wish to get jobs by impressing the mainstream clergy. Those who avoid being wrong and were indoctrinated to accept the popular dogma, do not have the humility to take risks in their research and make breakthrough discoveries.
The farthest known galaxy, JADES-GS-z14–0, is currently at a physical distance of 33.7 billion light-years from us. This may sound paradoxical since the age of the Universe is 13.8 billion years. However, the observed light left this galaxy 13.5 billion years ago when the Universe was merely 0.3 billion years old. Since then, the proper distance between our vantage point and that galaxy was stretched by a factor of (1+z)=15.32. The original separation was just 2.2 billion light years. But as the galaxy’s light was crossing this initial separation, JADES-GS-z14–0 receded away from us owing to the cosmic expansion. In fact, this early galaxy was outside our cosmic horizon when its light was emitted. The distance that light could have travelled since the Big Bang was merely 0.3 billion light years when the galaxy emitted its light. This distance was smaller by a factor of 7.3 than the separation between the galaxy and our location at the emission time. Since then, the Universe got older and our cosmic horizon grew in size so as to encompass this galaxy, allowing the Webb telescope to discover it.
There are many more galaxies from that time that we cannot see. They were too far away from us and hence their light will remain forever out of sight, given the accelerated expansion of the present-day Universe. The galaxies that did not enter our horizon by now, will never be visible to us because they will continue to recede faster than light away from us. According to Einstein’s equations of General Relativity, space can expand faster than light on cosmological scales. Consider photons as ants walking at some finite speed on the surface of a balloon that expands faster than their walking speed. These ants will never be able to cross the growing separations among them. The balloon’s surface is the two-dimensional analog of the three-dimensional cosmic space.
We know that the cosmic conditions are similar to those we observe out to a scale that is at least 3,900 times larger than our cosmic horizon. This is because a major deviation would have left an imprint on the temperature fluctuations of the cosmic microwave background. Therefore, there are at least (3,900)³ or equivalently sixty billion times more galaxies than those that we can observe, irrespective of how powerful our telescopes will be.
By now, there should be more than 10^{31} Earth-like planets in the habitable zone of Sun-like stars within the cosmic volume we know about. To argue that we are privileged to be the only intelligent species in the cosmos is arrogance amplified to 31 decimal places.
My academic colleagues often echo Carl Sagan’s standard: “extraordinary claims require extraordinary evidence.” In the previous paragraphs I described the evidence that makes the statement “we are alone” an extraordinary claim. Those, like Elon Musk — who suggested “we are probably alone”, do not have extraordinary evidence to support their extraordinary claim. What we actually know about the Universe argues in favor of the opposite point of view. The default assumption should be that “we are probably not alone.”
Peter Thiel argued in recent interviews: “You should never bet against Elon.” On this issue, I am willing to bet a percent of my fortune against a percent of Elon’s fortune. Let’s put this money into a common pool and use it to search for technological signatures of extraterrestrials. If we find nothing within a decade after investing this much money in the search, I will concede and give Elon a second percent of my fortune.
My new year resolution for 2025 stems from the notion that cosmic humility is more reasonable than the alternative by at least 31 orders of magnitude. How should we proceed with this realization? The answer is a matter of common sense. If we know that there are at least 10^{31} houses in our cosmic street, we should search for signatures of other residents, including any debris or packages, like the space-borne Tesla Roadster car, in our backyard.
Investing tens of billions of federal dollars in the search for microbes and less than a percent of that in the search for intelligent extraterrestrials, is not a reasonable way to hedge our bets. Yet, this is the mainstream strategy of the astronomy community. The search for extraterrestrial intelligence (SETI) is tainted as the periphery of legitimate astrophysics, and the search for extraterrestrial technological artifacts near Earth is regarded as the periphery of legitimacy by the SETI community itself. What sounds like common sense is sidelined as illegitimate squared. This is yet another example of observers’ bias, which blocks us from gaining new knowledge, a self-fulfilling prophecy that maintains our ignorance.
Here’s hoping that in 2025, the Webb telescope along with the three Galileo Observatories and the Rubin Observatory, will find evidence for technological signatures of our cosmic neighbors. Finding superhuman intelligence in space would provide us with better role-models than our politicians. It might be as easy to find the closest aliens as it is to find the farthest galaxies, if we only put our mind to the task.
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.
