First Question For an Alien Scientist
In an early-morning research discussion with my colleague, Liam Connor, I noted that I have 11 interviews today. Liam wondered: “you have so many interviews with prospective PhD students?” and I explained: “no, these are interviews with television outlets in the US (here and here), Italy, Spain (here) and Israel, a newspaper in the UK and five, hour-long podcasts.” Just the beginning of another busy day after my morning jog at sunrise.
Yet, I remained optimistic about my tight itinerary. Every simple beginning holds the promise of a grand finale. Consider our Universe as a role model.
Our vast cosmos gave birth to intelligence after 13.8 billion years of cosmic history which began in a simple Big Bang. This magnificent outcome was a direct consequence of the laws of physics acting on a set of simple conditions, initiated when the Universe was a fraction of a second old.
The statistical initial conditions can be summarized on a single sheet of paper, spanning about 5 kilobytes of information. Yet, our AI systems train now on hundreds of zettabytes in the world’s digital information.
To maintain the appropriate perspective of cosmic modesty, we must keep in mind that there are of order ten billion Earth-like planets around Sun-like stars in the Milky-Way galaxy alone, and of order a trillion similar galaxies in the observable volume of the Universe. Based on the isotropy of the microwave background fluctuations, we infer that similar conditions continue out to a scale which is at least 4,000 times larger than our cosmic horizon (as discussed here). All in all, this implies an information content beyond 10^{21}*10^{10}*10^{12}*(4,000)³= 6.4x10^{53} bytes, a factor of 10^{50} larger than the statistical information encoded in the initial conditions from the Big Bang.
This complexity of details is a direct result of the primordial initial conditions and the laws of physics, as is routinely demonstrated by cosmological simulations. According to our current scientific understanding, quantum fluctuations in the early Universe translated to density inhomogeneities of matter and radiation, which grew gravitationally to make bound objects like the Milky-Way galaxy, inside of which gas cooled and fragmented into stars like the Sun, next to which the debris of dust particles coagulated to make planets like the Earth, on the surface of which the chemistry of life in liquid water created biological brains which eventually became smart enough to create artificial intelligence.
In short, the complexity we find in our world today is a natural consequence of gravity and the nearly-smooth primordial Universe. The initial conditions were statistically uniform within our cosmic horizon, yet they resulted in people with very different personalities on Earth as a result of complex circumstances and interactions with numerous coincidental details.
Why was the early Universe so simple? Perhaps because any earlier “wrinkles” in spacetime were smoothed out and diluted by “a cosmic iron” in the form of an accelerated expansion such as cosmic inflation. If cosmic inflation took place, we will never know what preceded it because inflation diluted the earlier information and left behind a set of simple initial conditions for the subsequent cosmic history.
Changing the composition or quantum fluctuation spectrum of the early Universe would have resulted in very different outcomes. If such outcomes had materialized without leading to intelligence, there would have been no brains in the cosmos to appreciate it.
In our Universe, fluctuations started to grow when matter began to dominate over radiation. If we were to sample a spherical volume within the early matter-dominated Universe, we would have noticed that it has a nearly zero net energy because the negative gravitational binding energy of matter would have been nearly balanced by the positive kinetic energy associated with cosmic expansion. This insight has two major implications. First, a small enhancement in density makes a region — like the one that created the Milky-Way — gravitationally bound and drives it towards collapse. Second, to initiate such a Universe, a quantum-gravity engineer does not need to invest any energy.
We do not know how to create a baby Universe in the laboratory. How to do so would be the first question that I would love to ask an alien scientist. If they figured out the recipe for a baby Universe like the recipe for a cake, including the ingredients and the instructions for how to put them together, then my follow-up question would be: “do you have the oven needed to bake this cake?”
Most likely, such an oven needs to reach a very high temperature, of order the Planck temperature — corresponding to 10^{32} degrees Kelvin, so even the most advanced alien scientists in our cosmic neighborhood might not have it. But it is still possible that our Universe emerged from an oven created by a higher-level being outside our cosmic horizon. Whether that is the case, we might never know.
The training data set of all siblings in our family of intelligent civilizations is limited to the same cosmic horizon and so our alien dating partners might not have further insights on this question. When physics runs into a wall of the unknowable, metaphysics may come to the rescue.
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.
Professional website:
https://lweb.cfa.harvard.edu/~loeb/
Social media:
https://avi-loeb.medium.com/
https://www.youtube.com/@ProfessorAviLoeb
https://open.spotify.com/show/1zhndXkvSY2b8FdjspFpCd
https://x.com/ProfAviLoeb
