Over the past century, physicists have derived a better understanding of physical reality in terms of the relativity of space and time, the curvature of spacetime as a manifestation of gravity, quantum mechanics, and the standard model of particles and their four known interactions.
Clearly, this is work in progress. The inference of dark matter, dark energy, and spacetime singularities, indicates that we have a lot more to learn about the physical world. Nevertheless, the limited scientific knowledge we have gained thus far was employed behind th advancement of computer and information technologies to levels that now allow us to simulate reality in virtual worlds with unprecedented detail.
These amazing advances gave birth to the simulation hypothesis, which postulates that our perceived world is actually a simulated reality similar to a computer simulation. Whereas this notion may apply to speculative mathematical worlds with no experimental verification, such as string theory, it stands in stark contrast to the tradition of empirical science which is founded on testing theoretical ideas by experimental data, collected by well-calibrated instruments from an external reality. The use of experimental data to gain scientific knowledge about a reality that is independent from our mind underpinned the foundation of modern science and technology.
Of course, one can argue that these experiments are also part of the simulation, but there is no added value to this notion if it cannot be distinguished from a world in which it is absent. We must keep in mind that a simulation always occurs in the background of an underlying physical reality. If our world is a simulation, what is the reality in which this simulation is embedded? Without specifying that reality, the simulation conjecture is empty of testable content.
The known laws of physics were derived by observing the physical reality with instruments, not as a result of our brain philosophically insisting that they must be this way. The history of science is full of examples where evidence provided a different answer compared to what the human brain anticipated. Examples include the duality of the waves and particles in quantum mechanics, time dilation and the equivalence of mass and energy in Special Relativity, gravity not being a force in General Relativity, and that the observable Universe contains trillions of billions of planets and is not centered on us. If the observable Universe happened to be a simulation, there is certainly a lot of wasted memory space dedicated to parts of it that we cannot see. Whoever created this simulation was very wasteful, or perhaps did not consider us important in the greater scheme of things.
The human brain is not a reliable detector and our senses are limited in sensitivity. This is why physicists use instruments. When terrestrial astronomers study the Universe with telescopes, the collected data has little to do with the human brain. Instrumental data is not hallucinations of the brain. Of course, physicists can ignore or misinterpret data by wishful thinking and be misguided by hubris or other evolutionary traits. All of these deficiencies slow down the progress of physics.
Two decades ago, Nick Bostrom suggested that if “posthuman” civilizations become capable of creating simulations, there would be so many simulated beings that a randomly chosen conscious entity will very likely be simulated.
However, we must keep in mind that even if aliens created a simulated new world on an advanced supercomputer, neighboring civilizations could still live in their physical reality. Just like in Vegas: what happens on an exoplanet, could stay on that exoplanet. Even if advanced scientific civilizations figure out how to produce a baby universe in their laboratory, this baby universe is expected to pinch off from our spacetime and not interact with us.
A conjecture must be falsifiable in order for it to be scientifically credible. If we ever discover experimental evidence for pixelization of reality or for a computer bug in the code that simulates the world, I will reconsider my stand against the simulation hypothesis.
As of now, believing in the simulation hypothesis appears to me like choosing to be high on drugs. This choice does not lead to a productive life, but there will always be people who choose this lifestyle as an escape route from our shared physical reality. Similarly, there would always be people who believe that we live in a simulation as a way of avoiding the frustrating constraints of life as we know it. My personal choice is not to belong to any of these communities.
Instead, I am dedicating my remaining time on planet Earth to the scientific search for technological relics of aliens. If extraterrestrial sentient beings chose to live in a virtual world simulated on their computers with no engagement with the physical Universe at large, then the only way to find that they exist is from the trash they disperse into interstellar space. But if aliens are truly intelligent, they would aspire to send functional gadgets that could arrive in our backyard. By discovering technological probes among the interstellar rocks that arrive near Earth, we can expand our current scientific knowledge because these probes might represent technologies of our future.
In order to learn from extraterrestrials, we must be humble and admit that there is a world out there independent of our mind. It would be self-limiting if we closed ourselves in a philosophical bubble by forgetting the curiosity and humility that advanced our scientific knowledge until now. Only those who believe that there is a real, awe-inspiring world beyond what we imagine, will be fortunate enough to learn something new.
Whereas simulated worlds are limited by the imagination of their creators, scientific curiosity is the engine that helps these creators grow beyond their limited imagination. All simulation creators are embedded in a physical reality that is bigger than their imagination. The goal of physicists is to figure out this underlying reality, whether it contains creators of simulations or not. Who cares? The creators are part of that physical reality.
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.