Above is a screenshot of the GL Matrix screensaver, part of the XScreenSaver suite written by jwz.
Is life a simulation? Back in the age of Greek antiquities, minds like Plato pondered about the Cave Allegory. He wasn’t particularly interested in computation, but how perception is inherently indirect. And Descartes’ “I think, therefore I am” is just an affirmation that one’s consciousness defines one’s reality. This later gives rise to the Brain in a Vat thought experiment which stipulates that what the brain perceives is indistinguishable from reality, no matter how detached it is.
The Matrix (1999 film) popularized the idea that life could be a simulation inside a computer. Since then, contemporary philosophers and scientists have also been looking for clues.
Proposition 1: A universal computer can simulate the universe, and the universe is a universal computer.
It is true that a man-made Turing Machine can simulate the universe to arbitrary precision for an arbitrary length of time, subject to resource limitations such as the length of tape and how many steps it is allowed to run. The speed at which the simulation runs does not matter because the simulation determines its own time scale. It is also true that laws of the universe exhibit computability traits at the quantum scale. This means that for all intents and purposes, we can consider the universe that we live in is actually a computer. But one computer does not a simulation make.
So, what is a simulation?
Proposition 2: A simulation implies there exists a Source of Truth.
A simulation implies that there is a “source of truth” that the simulation is designed to imitate, and that the simulation is an approximation of that truth. If we say we live in a simulation, we need to have an understanding of what is the ultimate truth that our universe is trying to imitate. For example, the National Weather Service uses computers to simulate the earth’s atmospheric conditions for weather forecast. The source of truth is if the weather goes according to forecast.
Proposition 3: The Simulator does not have to look like the Simulation.
Although a simulation likely means there exists a simulator “host” computer in an outer universe, it is important to note that the simulated “guest” inner universe does not have to bear any resemblance to the host’s universe at all. We often run computer simulations to see what happens if we changed some rules, such as the gravity or even the speed of light. The guest universe can also be as simple as Conway’s Game of Life, which does not look very much like our own universe, but is still a universe in its own right—including being Turing complete, which means it can be used to simulate yet another universe inside.
Proposition 4: The Simulation must be a closed, isolated system that is consequence-free.
What really makes a computer a computer is that you have states and well-defined rules that change these states, and that applies to simulations as well. Normally, under a simulation, guest states are isolated and not allowed to interact with the host states. If the guest were allowed to interact with the host’s universe, then they might as well coexist in the same universe due to the breach of state isolation, and it stopped being a simulation. Such is the premise of The Thirteenth Floor (1999 film) where characters from the simulation escaped. This is why virtual reality that has real-world consequences isn’t virtual at all: if you can die in real life for being killed in virtual reality, then the virtual world is just as real.
Indeed, the hallmark of a simulation is that what happens in the guest ought to be consequence-free as far as the host is concerned. The host may even pause, reset, and rerun a simulation like how you can save and load a game. It may seem like Groundhog Day (1993 film), but the premise of the movie is not really consequence-free. Although the protagonist kept living the same day over and over, he had knowledge of what happened in the previous days. That is an accumulation of state, so his days did not completely reset. If the resets were perfectly stateless, he would never break the cycle, and he would not even be cognizant that he was in a loop. Though it was funny that he could try to commit a suicide, and he would simply be resurrected to begin another same day.
Proposition 5: The Simulation cannot be isolated from the Simulator.
But is it really possible to run a consequence-free simulation? Even if the guest does not have a loophole to breach into the host, the guest is still not consequence-free if the host as an observer changes its behavior due to the observations it made on its guest. Weather simulation seems benign enough, but it changes how people make their plans in the real world, so it has real-world consequences. The supercomputer that runs weather simulation may itself produce enough heat in the data center and throughout the energy grid system that alters the weather pattern in the real world.
Let’s reflect on the propositions we have so far:
Propositions 4 and 5 seem at odds with each another: if a simulation is closed, how could it affect the simulator?
There is something remarkably religious about these propositions. The universe is our world, and we can imagine that God is the one who designed the simulator. These propositions would become:
The idea of a resurrection is probably the earliest notion that we might be living in a simulation, such that a snapshot of our likeness may be recorded and reanimated on the Day of Judgment. If we really are living in a simulation and still have to face judgment, then it is certainly not consequence-free.
And I saw the dead, great and small, standing before the throne, and books were opened. Another book was opened, which is the book of life. The dead were judged according to what they had done as recorded in the books. The sea gave up the dead that were in it, and death and Hades gave up the dead that were in them, and each person was judged according to what they had done.
——Revelation 20:12-13 (NIV)
Except, it would seem that believing in the forgiveness of sins takes away the consequences of sin.
I confess one Baptism for the forgiveness of sins
and I look forward to the resurrection of the dead
and the life of the world to come. Amen.
——Nicene Creed (451 CE)
So it doesn’t really matter if we live in a simulation or not. There is no way to keep the states of the simulator and the simulated completely isolated, so they are still in the same universe. Even if we were simulated, it would simply mean that we can potentially play by a different set of rules for better or worse. It could really be that believing in the forgiveness of sins will determine which rules your simulation will play by, and that changes the outcome of your reality.