Reality Must Be Imagined, For It To Be Understood

Avi Loeb
4 min readMar 25, 2024


Near-infrared mosaic imaging of Titan’s seas and lakes from NASA’s Cassini spacecraft. (Credit: NASA/JPL)

Over the past century, astrophysicists figured out the behavior of the physical Universe at distances of billions of light years thanks to laboratory experiments on Earth. These experiments unraveled the principles of Electromagnetism for describing light and electric or magnetic fields, Chemistry for characterizing the interactions among atoms and molecules, Quantum Mechanics for describing elementary particles and their interactions, Special Relativity for their dynamics, Nuclear Physics including the strong and weak interactions, and General Relativity for describing spacetime and gravity. These principles were used to explain how stars shine, how the Universe expands, how helium, lithium and the Cosmic Microwave Background were produced after the Big Bang, and most importantly — how structure grew from small primordial inhomogeneities and resulted in galaxies like the Milky-Way in which gas fragmented to stars like the Sun, around which the debris dust coagulated to make planets like the Earth, on the surface of which life-as-we-know-it emerged.

It is remarkable that the laws of physics which were discovered experimentally on Earth, apply to the Universe at large. One could imagine another Universe in which these laws change from place to place. It would have been difficult for us to make sense of what we observe with our telescopes in such a Universe, because what we would have learned locally would not apply globally. In that case, the laws of physics would resemble the different legal systems in countries on Earth. The speed limit on the highway in Germany is higher than that in the United States. Imagine the speed of light being higher in the Andromeda galaxy than it is in the Milky Way galaxy. Astrophysicists would be baffled.

This alternative reality might apply to life in the cosmos, which may be very different in distinct environments. So far, we observed life only on one planet: the Earth. As a result, we have no idea whether the chemistry of life-as-we-know-it in liquid water is universal. Astrobiologists are therefore faced with the vast uncertainty about what to search for in extraterrestrial environments. Their mindset allows for a reality in which what we find locally does not apply globally.

One way to clear this intellectual fog is to find life beyond Earth in the Solar system. For example, Titan — Saturn’s largest moon, is the only other object in the solar system besides Earth which is known to have liquids in the form of rivers, lakes and seas on its surface as well as clouds or rain above it. As confirmed by the Cassini Orbiter, Titan’s liquids are methane and ethane, containing liquid bodies that are hundreds of feet deep and hundreds of miles wide. Under Titan’s thick crust of water ice, there is another ocean of mostly water. NASA plans to launch a rotorcraft lander named Dragonfly to Titan in 2028. If we ever study Titan’s surface oceans and find fish swimming in them, we would realize a broader scope for the chemistry of life beyond that in liquid water.

When planning a date with a human, there is little biological uncertainty because we share the genetic making of our date-partner. However, when searching for life from an alien household beyond Earth, the sky’s the limit.

Another way to expand our biological imagination is to imitate what physicists did over the past century, namely to create life in the laboratory. Similarly to baking a variety of cakes by using different ingredients or new recipes regarding the sequences of actions, the heat applied and the quantities involved, we could explore the space of possibilities beyond the examples provided by nature on Earth. With better understanding of what is possible, astrobiologists could search planets or moons for the fertility conditions that could give birth to new forms of life. This laboratory work would expand the imagination of astrobiologists in the same way that physics experiments on Earth expanded the imagination of astrophysicists.

According to Albert Einstein: “The true sign of intelligence is not knowledge but imagination.” For example, some astronomers insist that the velocity of the first interstellar meteor, as measured by sensors aboard U.S. Government satellites, was overestimated by a factor of 3 because their past knowledge allows only for solar system rocks. As it turns out, the same data could be explained by rocks from exoplanets, as we showed in a newly published paper with Morgan MacLeod. Accepting new data expands our imagination. As William Blake noted: “What is now proved was once only imagined.

Imagination is also an important tool for motivating future experiments to collect more data. For example, experiments aiming to detect dark matter are often motivated by theoretical models for weakly interacting massive particles or axions. John Steinbeck said: “Ideas are like rabbits. You get a couple and learn how to handle them, and pretty soon you have a dozen.” Experimental data is needed to select the ones that apply to reality.


Image credit: Chris Michel (October 2023)

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. His new book, titled “Interstellar”, was published in August 2023.



Avi Loeb

Avi Loeb is the Baird Professor of Science and Institute director at Harvard University and the bestselling author of “Extraterrestrial” and "Interstellar".