A Log of Our Exponential History

Avi Loeb
4 min readMay 18, 2023


A cuneiform clay tablet dating to the Early Dynastic period in Sumer, approximately 2500 B.C. (Photo credit: University of Chicago).

Our cosmic history went through periods of exponential acceleration in complexity. It is therefore appropriate to summarize it through 10 milestones separated by a factor of ten in time from each other:

  1. Five years ago, GPT-1 was introduced by OpenAI. It contained 117 million parameters. Today, GPT-4 has a million times more parameters.
  2. Fifty years ago, the final mission of NASA’s Apollo program, Apollo 17, had humans setting foot on the Moon.
  3. Five hundred year ago, Nicolaus Copernicus proposed that planets orbit the Sun, and that the Earth is not at the center of the Universe but rather a planet which, besides orbiting the Sun annually, also spins daily on its axis.
  4. Five thousand years ago, human history was recorded for the first time through the Sumerian cuneiform tablet.
  5. About fifty thousand years ago, three waves of Homo sapiens left Africa, migrated to Europe and replaced the indigenous Neanderthals, based on archaeological evidence.
  6. The genetic ancestry of Neanderthals dates to another factor of ten back in time. According to a new paper in Nature magazine, the Neanderthals originated 600,000 years ago from a small group of humans that budded off from an African community, labeled Stem1. The Neanderthals expanded across Europe and Asia.
  7. About five million years ago, the last split between the human and the chimpanzee–bonobo lineages took place. This split distinguished humans with only 23 pairs of chromosomes, compared to 24 for apes. The subsequent diversification of Hominins left only one surviving species, Homo sapiens.
  8. Ten times farther back in time, at around 66 million years ago, a ten-kilometer asteroid hit the Earth and extinguished 70–80% of all terrestrial species. Besides the non-avian dinosaurs, the event triggered the loss of all flying reptiles, most marine reptiles, more than half of land plants and insects, and hosts of other terrestrial and marine organisms. At face value, this was a devastating blow to the diversity of life on our planet. But we must keep in mind the blossoming culminating in GPT-4 after this catastrophe. If a catastrophe does not kill complexity altogether, it could make its eventual growth more impressive.
  9. Ten times farther back, half a billion years ago, Earth went through the Cambrian explosion of species, when all major animal phyla started appearing based on fossil records. Before the Cambrian diversification, most terrestrial organisms were composed of individual cells or small multicellular organisms. The accelerated diversification resulted in the complex animals we see today.
  10. About five billion years ago, the Sun formed out of the gravitational collapse of a local cloud of molecular gas. The planets, including the Earth, formed out of the debris disk left around the new star.

Fifty billion years ago, the Universe did not exist. What preceded the Big Bang is unknown.

What we do know is that the Universe started simple, in a nearly uniform state with tiny fluctuations in the density of matter and radiation that grew over time due to the unstable nature of gravity, culminating in the complexity of life-as-we-know-it and artificial intelligence (AI). The initial conditions of the Universe can be summarized statistically on a single sheet of paper. The complexity that resulted from them over time is startling.

Since most stars formed billions of years before the Sun, it is possible that complexity emerged earlier than on Earth in other pockets of the Universe. We could explore it by visiting other places. But better yet, the technological gadgets that emerged from these islands of exponential growth had enough time to reach us by now, because it takes less than a billion years for conventional chemical rockets to traverse the disk of the Milky-Way galaxy. This is the reason I lead the Galileo Project, which searches for objects from extraterrestrial technological civilizations near Earth.

Clearly, the sequence of exponential growth events punctuated by devastating catastrophes, must have been different for other Earth-like planets, depending on their individual environments. The growth rate of complexity must have depended on local circumstances.

But out of the billions of Earth-like planets, all it takes is one to exhibit equal or faster acceleration than Earth did, in order for us to encounter its GPT-N astronauts, with N much bigger than 4 — representing orders of magnitude more connections than the 600 trillion synapses in the human brain. After all, there is no reason for exponential growth to saturate at our current level of complexity. By seeing the products of earlier extraterrestrial civilizations, we can get a glimpse at the exponential growth that awaits us in our own terrestrial future.


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".