The Nobel Prize winning physicist and cosmologist, Steven Weinberg, argued: “The more the universe seems comprehensible, the more it also seems pointless.” He referred to what we learned so far about the physical universe, namely the matter, radiation, galaxies and large-scale structure that followed the Big Bang. As a young physics student forty years ago, I learned general relativity and cosmology from Weinberg’s 1972 textbook titled “Gravitation and Cosmology”. In 2004, I had the privilege of spending time with him when he agreed to deliver the banquet lecture at a cosmology conference that I organized at Harvard, where he was faculty for a decade starting in 1973. Altogether, I greatly admire Weinberg’s seminal contributions to the standard model of physics, but I disagree with his philosophical remark about the pointlessness of the Universe. Let me explain.
By merely studying the chemical composition of paint, we cannot hope to acquire the aesthetic meaning of a Rembrandt painting. The painting might appear pointless from a chemistry perspective. Similarly, by using only black and white cameras to observe the sky, we might conclude that “The more the universe seems comprehensible, the more it also seems colorless.” Self-inflicted ignorance about reality is also captured by the tale of the physicist Hans-Peter Dürr about a fisherman who announces a new law of nature that “all fish are bigger than two inches”, until he realizes that this is the size of the holes in the fishing net. Given this perspective, the universe appears pointless to those who never seek components that might give it a meaning. Science could be a self-fulfilling prophecy. The limits on what we see depend on the blinders we use to guide our vision.
Let me pause first on what Steven Weinberg called “comprehensible”. In 1987 he advocated the notion of the multiverse to suggest that the low value of the cosmological constant is selected by the requirement that galaxies like the Milky Way are needed to allow our existence. These galaxies would not form if the cosmological constant was much larger. If spacetime regions beyond the observable region are characterized by much higher values of the cosmological constant, then they would not be inhabited by scientists. This proposal unleashed an avalanche of follow-up papers because it removed the need to explain the specific value of the cosmological constant based on fundamental principles.
But does this mean that our universe is “comprehensible” or are we demonstrating intellectual laziness in our scientific efforts to truly comprehend it? There is no demonstrated path for validating the existence of other regions of spacetime where the vacuum energy density has other values. Yet, this “explanation” is favored by mainstream theoretical physicists because string theory does not make a unique prediction for the vacuum energy density as originally hoped for. In fact, the theory allows for 10 to the power of 500 or perhaps even 10 to the power of 272,000 possible values for the cosmological constant. These are very big numbers, indistinguishable from infinity for all practical purposes. Traditionally, theories that allow for a huge number of possible answers were not considered successful as explanatory paradigms. If everything is possible, then nothing is being explained. Another way to put it is that a theory allowing everything is equivalent to a theory of nothing, if it cannot be ruled out.
We live in interesting times when mainstream physicists use untestable ideas about the multiverse, extra dimensions or anti-de-Sitter space and avoid the restrictions imposed by the properties of our observed universe in 3 spatial dimensions of de-Sitter space. This is happening while mainstream astronomers argue that the existence of extraterrestrial intelligence is an extraordinary claim that requires extraordinary evidence before we allow it to become mainstream. Paradoxically, the common sense of the general public cares more about the search for extraterrestrial intelligence than the vacuum states of the multiverse.
Can we truly claim that we comprehend the universe, a la Steven Weinberg and his followers, without actually knowing the nature of the cosmological constant, dark matter and what happened before the Big Bang?
Let me return now to the central question of why mainstream cosmologists find the universe to be pointless. My argument is simple. To acquire a sense of meaning within cosmology, we need to search for intelligent life beyond Earth. Any such finding would revolutionize our sense of cosmic meaning.
For example, if we find that life was seeded on Earth by an interstellar “gardener” or that Big Bangs can be created by a quantum-gravity engineer, then we would feel like orphans who discovered their lost parent. This would revise our perception of the cosmos from pointless to meaningful, as any orphan who went through this path of discovery will tell you. The discovery of advanced civilizations could also educate us about what might be possible in our technological future based on what others achieved before us. Such a discovery will shape humanity’s aspirations to become not only a multi-planetary species, as imagined in a 2017 paper by Elon Musk, but in fact a multi-star species.
Even if we just find microbial life on Venus, Mars, Titan, Ceres, Enceladus or Europa, the next question will be whether it originated from the same chemical network as life on Earth. If the answer is positive, the similarity may indicate that there is a favored chemical path for life or that life was shared through the exchange of rocks between neighboring sites in the solar system, commonly called panspermia.
Why would extraterrestrial life bring significance to the otherwise dead universe? Because it adds aesthetic meaning to the brush strokes of cosmic matter, a meaning to which we have kinship. Once we find sentient partners, the cosmos will not appear pointless anymore. The encounter will make humanity a member of a multi-star family.
Like in any dating experience, we will find partners only if we allow ourselves to search for them. Thinking outside the box is a must when the location of the box is not dictated by common sense.
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 chairs the advisory board for the Breakthrough Starshot project, and 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. His new book, titled “Interstellar”, is scheduled for publication in August 2023.