Following a lecture on the search for extraterrestrial life, hosted by Sir Richard Branson at Necker Island, I was asked by many attendees about the impact of celestial bodies on our life on Earth.
We all know that the lunar monthly cycle and the solar yearly cycle have important imprints on the rhythms of life-as-we-know-it. In addition, global climate changes were historically triggered by giant impacts of rocks from the sky. A ten-kilometer Chicxulub impactor terminated the life of all non-avian dinosaurs 66 million years ago. Was this catastrophe part of a divine plan that enabled humans to inherit Earth in the last few million years?
Our life is short and physicists did not, as of yet, create a time machine that would allow us to experience the outcome of different branches of history before we select our favorite. In addition, life is a tumultuous journey, shaped by unpredictable circumstances that extend well beyond our control. As a result, many attendees of my lecture confessed to me that they made important life decisions, including the choice of their partner, based on astrology. Horoscopes link the positions of the Sun, the Moon and planets relative to Earth at the moment of a person’s birth to the future. My own birthday at the end of this month happens to coincide with a rare alignment of up to seven planets along an arc in the night sky. This arc is defined by the ecliptic orbital plane of the planets around the Sun. Does this alignment have consequences for our future?
Humans seek a model to explain their life and predict the future. For that reason, astronomers occupied the highest social status in the Mayan culture, as astrology was deemed important for crucial political decisions — such as the time to initiate a war. The Mayans accurately tracked changes in the positions and relative brightness of the Sun, Moon, planets and stars. They documented their astronomical data in folding books called codices, with many more quantitative details than other civilizations at the time. The astronomer-priests used observations and advanced mathematical calculations to predict eclipses, and devised a 365-day solar calendar that was off by just one month every 100 years.
As of now, our best model of physical reality is summarized by the standard model of physics. Taking account of all we know about general relativity, quantum mechanics, particle physics and cosmology, it is evident that the long-range effects of celestial bodies on life on Earth are mediated by either radiation or gravity. The radiation on Earth is dominated by the Sun which enables the chemistry of life in liquid water. For that reason, astrobiologists are searching for rocky Earth-mass planets that are similarly illuminated by their host star.
The gravitational influence of celestial bodies on terrestrial life is mediated by tides, namely the difference in gravitational acceleration for distinct locations on Earth. The tidal gravitational acceleration scales in proportion to the celestial-body mass and inversely with its distance cubed. The mass of the Moon is 27 million times smaller than that of the Sun, but its average distance is 391 times closer. As a result, the lunar tidal acceleration is 2.2 times larger than that of the Sun, dominating the gravitational shaping of the liquid-water reservoirs, like the oceans, relative to the solid crust of Earth.
The gravitational effect of Solar-system planets on Earth is dominated by Jupiter, which induces a tidal acceleration that is smaller by a factor of a hundred thousand relative to that of the Moon. Given this state of affairs, life on Earth is mostly influenced by the Sun and the Moon but not by other planets in the Solar system.
This is what the scholarship of physics teaches us about the forces that shape life on Earth. Our understanding of physics serves as the scholar’s lion, a powerful companion that helps us understand and cope with reality despite our wishful thinking.
Art complements physics in creating structures that add aesthetic pleasure to our life. As it turns out, there is a bronze sculpture named the Scholars’ Lion near Havemeyer Hall at Columbia University. The monument was crafted by the remarkable sculptor Greg Wyatt, who graduated in 1971 from Columbia College. Most recently, Greg created a new sculpture named Galileo Looking at the Four Moons of Jupiter, that will be unveiled in my office at Harvard on February 20, 2025 in celebration of the Galileo Project which searches under my leadership for extraterrestrial technological artifacts. When I invited my PhD student, Betty Hu, to this unveiling event, she noted that the Scholars’ Lion was located along the path of her daily walk to and from the physics department during her undergraduate studies at Columbia College. When Betty graduated in physics, she took a picture next to the Scholars’ Lion.
It is often argued that science and technology improve the quality of our life. But exceptional art could occasionally be more influential on our life than the tidal forces from Jupiter and other planets.
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.
