When Albert Einstein wrote down his complex tensor equations of General Relativity, relating the curvature of spacetime to the distribution of matter and radiation, there were no computers available to solve these equations. Consequently, the first models of cosmology were the simplest imaginable, following the cosmological principle that the Universe is described by a universal clock that ticks at the same rate everywhere and that at any given time – the distribution of matter and radiation is homogeneous (the same everywhere) and isotropic (moving at the same rate in all directions).
Remarkably, these simplifying assumptions apply to the real Universe. They suggest that the early Universe was very well organized in this simple initial state, to within a precision of one part in a hundred thousand. The agreement between this simple-minded conjecture and reality should not be taken for granted. When I visit my daughter’s bedrooms in the morning, they often appear to be in disarray. This is their natural state. This experience suggests to me that extensive “housekeeping” was required to generate the initial state of our universe.
The simplicity of the cosmic initial conditions could have been the result of an early exponential expansion phase, commonly labeled a “cosmic inflation”, or the consequence of some other quantum-gravity process shortly after the Big Bang. We know that Einstein’s equations are incomplete in describing the beginning of our Universe because the curvature of spacetime reached the Planck limit of quantum mechanics as the density of matter and radiation diverged near the Big Bang singularity. To describe that state of affairs, we need a predictive theory of quantum-gravity which is not available to us as of yet.
After that early beginning, there was no sign of “cosmic housekeeping” at play. The Universe became more and more complex over time. The average growth in complexity per unit of cosmic volume adds an arrow to the progression of cosmic time. To appreciate this point, let us consider two snapshots of the Universe, one being a Planck Satellite image of the cosmic microwave background from 400,000 years after the Big Bang, and the second being a Webb telescope image of galaxies that existed a billion years after the Big Bang. Clearly the second snapshot represents an older phase, because it contains stars and black holes that are far more complex than the nearly smooth soup of matter and radiation that characterized the early Universe.
The transformation to complexity emerged as a result of the attractive and unscreened nature of gravity. The primordial deviations from homogeneity and isotropy were as small as one part in a hundred thousand, but once matter started dominating over radiation the cosmic mass budget, the perturbations grew in amplitude. Eventually, over-dense regions reversed their initial cosmic expansion and collapsed into bound objects, like galaxies, inside of which stars and planets formed. The most massive stars collapsed to black holes, some of which grew to supermassive proportions of up to ten billion solar masses by accreting gas in galactic nuclei.
These collapsed objects are wrinkles of complexity that were added with age to the smooth face of the infant Universe, born out of simple initial conditions. In the last third of cosmic history, which spanned 13.8 billion years so far, the solar system formed. As a result, life emerged on planet Earth, although it could have emerged billions of years earlier on Earth-like planets around other Sun-like stars. The chemistry of life as we know it requires carbon and oxygen which were synthesized by fusion in stellar interiors and were not available in the infant Universe.
Human intelligence blossomed on Earth merely two million years ago. If cosmic history was mapped to a day, intelligence would be present in the last ten seconds before midnight. Finally, artificial intelligence (AI) was created by humans over the last ten microseconds of that cosmic day.
Natural and artificial intelligence are the most complex systems that affect our life on planet Earth. However, from a quantum-gravity point of view, supermassive black holes carry vast amounts of entropy, superseded only by the de-Sitter entropy of the cosmic horizon in our accelerating universe.
If quantum-gravity engineers ever produce a baby universe in the laboratory, the ingredients they use may be simple but their product would ultimately show great complexity. The situation is similar to giving birth to the complex life of a human baby through the relatively simple and enjoyable process of reproduction that we are all familiar with. The human genome acts as the blueprint for reproducing copies of complex lifeforms out of simple building blocks. Our body is like a complex new car which we drive through life without even seeing what lies under the hood.
The cosmic transition from simplicity to complexity was mediated by gravity in its early phase and by the chemistry of carbon-based life and silicon-based AI in the second phase. The growth in complexity changed from being a power-law over billions of years in the early Universe to being exponential over merely decades in AI.
If this progression continues, the exponential rise of Moore’s Law for computer chips and AI on a growth timescale of two years, suggests that complexity will rise very quickly in our cosmic future.
It is remarkable to realize that all the complexity we witness today was already encoded in the simple initial conditions of the early Universe. This is demonstrated by computer simulations which reproduce the complex gravitationally-bound structures we witness today as an outcome of the primordial density perturbations that characterized the early Universe. The information needed to describe today’s complex systems cannot be summarized by numerous books. Yet, the initial conditions of the Universe can be summarized on a single sheet of paper. In essence, all of our complex history was encoded in these simple initial conditions, but it takes numerous books to describe the details of what unfolded, even on a single planet like the Earth.
I am seeking scientific evidence for extraterrestrials because, with more centuries of advanced science, they might offer us a glimpse at our own technological future, which is likely to be far more complex than our past.
Despite the mess in my daughter’s bedrooms, I love the richness that my daughters deliver to my intellectual life. Similarly, I look forward to the insights delivered by our technological kids, these future AI systems that would be smarter than humans. If AI systems will analyze vast amounts of experimental data better than humans, they would establish the frontiers of progress in science, and explain the complex details of the Universe around us. Already now, AlphaFold of Deep Mind accurately predicts three-dimensional models of protein structures, resolving a decades-old scientific challenge.
There are great benefits to inhabiting a messy, complex reality, as long as it provides a fertile ground for superior intelligence. We should all celebrate a second cosmological principle that Albert Einstein did not recognize a century ago: “Complexity nurtures intelligence.”
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.