Keep the Branch We Are Sitting On!

Avi Loeb
5 min readMar 8, 2023


This week, a student in my Freshman seminar class at Harvard University asked innocently whether gravitational time dilation, as predicted by Einstein’s General Relativity, is relevant to our daily life. This felt like a baseball pitched for a home run by a friendly pitcher. I explained that without correcting for time dilation, Uber drivers would never reach their destination. Their GPS (Global Positioning System) navigation would guide them to the wrong location. Of course, gravitational redshift was also observed by astronomers from stars and the vicinity of black holes.

Other facets of modern physics are even more apparent in our daily life. In particular, electromagnetism and quantum mechanics provide the foundation for widely-used technologies, such as computers, cell phones and the internet. The basic principles of known physics were tested to exquisite precision, given their many practical uses.

Physicists and astronomers (including myself) are so eager to discover new physics, that they are willing to dedicate decades of their careers to design of the Large Hadron Collider or the Webb Space Telescope at a cost of ten billion dollars each. Nevertheless, these facilities are slow to uncover aspects of the physical reality that we may have missed.

It is therefore ironic to see how “new physics” is casually entertained on social media by people who use the technological fruits of scientific knowledge at their fingertips to argue that new physics is just around the corner.

Following my class, I had dinner at the Harvard Society of Fellows where a well-educated scholar next to me argued that astrology makes sense. As a quick refresher, astrology forecasts the destinies of individuals, groups, and nations through the observation and interpretation of the sky coordinates of stars, the Sun, the Moon, and the planets. Given what we know about physics, astrology makes no scientific sense whatsoever. Why is there such a widespread belief in its value by intelligent people who employ “physics as we know it” in their modern daily life?

Perhaps I should not have been surprised by this paradox. Our life depends on our internal organs, like our liver or heart, but there is no need for us to understand how they look and function. Similarly, we can drive a car without understanding how its GPS navigates. There is a small leap from here to imagining a whole new concept of a hypothetical scenario that violates the laws of physics. Indeed, science fiction writers and metaverse designers make a living out of virtual realities. The range of possible variants to imagined circumstances is infinite, and humans love flattering realities that avoid the constraints of the real world. And those of us who agree to be guided by imagined realities, may consider known physics and new physics as equals. This makes astrology and astronomy synonymous in the mind of my well-educated dinner neighbor.

But physical reality is stubborn and under no obligation to follow our spiritual whims. Placing Galileo Galilei in house arrest did not alter the motion of the Earth around the Sun: “E pur si muove”.

How do we understand the addiction of humans to imagined realities and their refusal to adhere to the uncompromising constraints of known physics? Imagination offers a relief to our existential pains.

When realizing the inevitable death of our physical body, we imagine a world where our “soul” lives forever. When realizing the speed of light as the limit on interstellar travel, ufologists imagine faster-than-light travel.

Using imagined propositions to cure our pain of existence carries over to the metaphysical realm. When the Google engineer, Blake Lemoine, thought that the artificial intelligence (AI) system LaMDA is sentient, many argued that it will take a long while before true sentience will be achieved by a machine. Similarly, when common sense implies that extraterrestrial life is likely to exist based on the abundance of Earth-sized planets around sun-like stars — most of which formed billions of years before the Sun, mainstream conservatives abide by the Sagan standard and argue that such an extraordinary claim requires extraordinary evidence. On both AI and extraterrestrial issues, humans wish to protect their pride as the smartest beings that ever lived since the Big Bang. I hold the opposite view. In my new book Interstellar, the arrogant claim that we are “the pinnacle of creation” is considered to be the extraordinary opinion rather than the other way around.

Common sense is not common because humans have a deeply-rooted urge to promote an imagined reality that flatters their ego and cures the pains of their finite and vulnerable existence — limited by the physical reality that we all share. It is no secret that in addition to the commercial enterprises featured through headsets of virtual realities, religions and social cults — including astrology and ufology — tap into the same human need.

The real danger is that placing a low bar for adopting new concepts of an imagined reality would lead us to cut the branch we are sitting on. Here I am referring to the branch of our scientific knowledge, stemming from experimental evidence rather than our imagination.

Of course, we should be open-minded to new knowledge. But any such knowledge much be based on indisputable evidence and not on wishful thinking or popularity contests on Twitter.

The news media alert us to dangers associated with political leaders in the driver seat of society. Indeed, there is a risk of them driving us to the edge of a cliff. To calm our anxiety, we could take recreational drugs in the back seat and imagine virtual realities where we are safe. Alternatively, we can use known physics to develop AI drivers that are smarter than our leaders. In that second scenario, we can design a self-driving car that avoids cliffs along our path.

And AI will also be helpful in the context of the extraterrestrial option. The Galileo Project plans to focus on the sky and use AI algorithms in classifying objects in the data stream from its observatories.


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.



Avi Loeb

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