Simulation Hypothesis

February, 2017 (Edited on August, 2023)

Numerous writers, technologists, and futurologists have predicted that the computational power available in the future will be staggering. If so, civilizations may have the capability to create highly detailed simulations. These would replicate the universe and its governing laws, enabling the emergence of self-aware entities that could communicate with one another. The simulations could be of that civilization's forebears, and due to the formidable computing resources, run a great many of them.^{[1, 2]}

This concept, known as the Simulation Argument or Simulation Hypothesis, explores the idea that our universe is a software process running on some deeper computational substrate. The philosopher Nick Bostrom has presented a compelling argument for this thesis, which has garnered the attention of philosophers and even physicists who are suggesting practical means to validate it.^{[3, 4, 5]}

Simulation Argument

In 2003, Nick Bostrom of the University of Oxford rigorously explored the simulation argument for the first time. It’s important to note that the type of simulations he discussed differed from those depicted in movies like “The Matrix.” In that film, the world is simulated, but the conscious minds are not. Conversely, the simulations imagined by Bostrom lack a biological component; they operate on a deeper hardware level or within virtual machines nested inside other simulations. The argument takes into account the assumption of substrate-independence, the technological limits of computation, and the indifference principle.^{[1, 4]}

Assumption of Substrate-Independence

Substrate-independence is a foundational concept in the area of philosophy of mind. It asserts that human consciousness does not rely on a biological substrate. Theoretically, it could be replicated within silicon-based processors, provided the system incorporates the appropriate computational structures and processes, with fine-grained detail like on the level of the individual synapses. The replication does not need perfection; it merely requires sufficient fidelity to generate a human-like subjective experience. While not universally accepted, this assumption enjoys widespread recognition.^{[1, 4, 6]}

Presently, there is insufficient computer power to run the computational processes needed for replicating the human brain and generating consciousness. Even if such computational resources were available, there is still no knowledge on how to program such system. Additionally, creating a highly detailed scan of a human brain would also require sophisticated techniques. These obstacles are only technical difficulties, not insurmountable physical laws or material constrains. A civilization with sufficiently advanced computing power to create conscious minds within computer hardware would be classified as posthuman.^{[4, 6]}

Technological Limits of Computation

While the creation of conscious minds in computers is still a distant prospect due to current technological limitations, some argue that continued, unhindered technological progress, will eventually overcome these restrictions. For the purposes of the simulation argument, the specific timescale at which humankind reaches a posthuman stage capable of such feats is irrelevant.^[1]

Currently, it is impossible to establish an upper bound limit on the computing power available to future posthuman civilizations. Indeed, these advanced societies might have the ability to convert planets and other astronomical resources into computers with unprecedented capabilities. In contrast, determining a lower bound for computation in a posthuman future, considering only well-understood mechanisms, is more feasible. Some authors have proposed a computing system approximately the size of a sugar cube, capable of executing 1021 instructions per second, while others have envisioned one with the mass of a planet, capable of performing 1042 operations per second.^{[1, 6]}

There are also estimates regarding the computational power required to emulate a human mind. One approximation suggests around 10¹⁴ operations per second for the entire brain, while another, based on the number of synapses and their firing frequency, yields figures between 10¹⁶ and 10¹⁷ operations per second. Adding environmental elements to a simulation will increase the necessary computing power, with the extent of increase contingent on the simulation’s scope and granularity. To achieve a realistic simulation of human experience, it is unnecessary to model the universe at the quantum level, which might prove unfeasible unless a radically new physics paradigm emerges. However, what is essential is that the simulated humans interact normally within their simulated environment without noticing any irregularities. According to Bostrom (2003), “a posthuman simulator would have enough computing power to keep track of the detailed belief‐states in all human brains at all times. Therefore, when it saw that a human was about to make an observation of the microscopic world, it could fill in sufficient detail in the simulation in the appropriate domain on an as needed basis. Should any error occur, the director could easily edit the states of any brains that have become aware of an anomaly before it spoils the simulation. Alternatively, the director could skip back a few seconds and rerun the simulation in a way that avoids the problem.”^[1]

Overall, the main computational cost to create completely realistic simulations seems to be in simulating organic brains down to the neuronal or sub-neuronal level. Given the potential for posthuman civilizations to construct a multitude of very powerful computers capable of running simulations that are indistinguishable from reality, their computational resources would be sufficient to execute a huge number of ancestor simulations.^[1]

The Central Argument

The core of the simulation argument does not attempt to prove that reality is definitely a simulation. Rather, it posits that one of three propositions should be accepted as true.^{[1, 3]} While the general concept can be understood without delving into mathematics, a formal version of the argument relies on probability theory.^[7] Although each of the propositions may seem implausible, if the simulation argument is correct, at least one of them must be true.^[6] The three propositions delineated by Bostrom (2003, 2006) are as follows:

1. Almost all civilizations at our level of development become extinct before becoming technologically mature;
2. The fraction of technologically mature civilizations interested in creating ancestor simulations is almost zero;
3. We are almost certainly living in a computer simulation.^{[1, 6, 7]}

If the first proposition is false, it implies that a substantial portion of species at our developmental level will achieve the posthuman stage, characterized by technological maturity. Conversely, if true, it does not necessarily imply imminent human extinction, but rather suggests that reaching a posthuman stage is improbable. Alternatively, a civilization could remain stagnant at the current level of technological development for a long time before facing extinction.^{[1, 6]} If the second proposition is also untrue, then it follows that a fraction of these technologically mature species will use some of their computer resources to run ancestor simulations, recreating minds like ours on a large scale. For this proposition to be true, there must exist a convergence among advanced civilizations, where almost none of them are interested in conducting simulations, or have enacted legislation to deter individuals from pursuing such endeavors. Advanced posthuman civilizations could also perceive the ethical problem of running ancestor-simulations, recognizing the suffering imposed on the inhabitants of the simulation. This ethical stance could lead to the prohibition of creating ancestor simulations. Finally, if the third proposition holds true, it suggests that reality is almost certainly a computer simulation created by an advanced civilization.^{[1, 6, 7, 8]}

If the proposition that reality is a computer simulation is true, the observed universe would constitute a small piece of the overall physical existence. The physics governing the universe in which the simulation operates may differ from our observable cosmos. Consequently, our world would not occupy the fundamental stratum of reality. Furthermore, if this proposition holds, it implies that simulated civilizations might also achieve the posthuman stage and, in turn, run their own ancestor simulations using computers built within the simulated universe. This is akin to “virtual machines”, a common concept in computer science. Moreover, virtual machines can be stacked, allowing for multiple layers of simulations within simulations. If our civilization develops ancestor simulations, this would support the third proposition, strengthening the likelihood that reality is indeed a simulation.^[1]

Living in a Simulation and its Implications

The veracity of the simulation argument would not necessarily entail a loss of rationality or significant changes in human behavior. Even within a simulated reality, individuals should continue to lead their lives as before. To predict events within the simulation, conventional methods such as extrapolating from past trends, scientific modeling, or applying common sense would be used. Furthermore, if the third proposition is indeed accurate, it would diminish the likelihood of the first proposition—namely, the risk of extinction before attaining technological maturity. Nonetheless, computational limitations could potentially result in the simulators terminating the simulation before our civilization advances to a posthuman stage.^{[1, 6, 8]}

Various suggestions have emerged regarding potential behaviors or strategies in the context of living within a simulated reality, aimed at increasing the probability of continued existence or future re-simulation.^{[2, 6]} For instance, if the simulator happened to adhere to specific religious beliefs, such as those of a Christian fundamentalist church, the simulation might incorporate these doctrines. Consequently, simulated entities could expect to be rewarded or penalized based on Christian moral criteria. In this scenario, an afterlife might become a possibility for simulated beings, where existence would continue in an alternate simulation after death, or the individual’s consciousness is uploaded into the simulator’s universe and given an artificial body.^[6] Indeed, if the simulators are actively involved in their simulations, rather than mere observers, they could assume god-like roles, having power over life and death, manipulating the simulation’s laws, and engineering anthropic fine-tuning. At any point, they can end the simulation or oversee the development of its inhabitants.^{[2, 8]}

Living in a simulation could introduce uncertainty regarding the consciousness of other individuals. While certain people may be simulated with intricate detail, possessing conscious experiences, others could be represented at a more rudimentary level, presenting the appearance of real individuals but without subjective awareness. Nevertheless, according to Bostrom (2005), “some people have argued that it is necessarily true that anybody who acts sufficiently like a normal human being must also have conscious experience.”^[8]

The fact that the universe could be a simulation does not negate the existence of the world around us but rather prompts a different perspective on its fundamental nature. Ultimately, the computer running the simulation and its underlying electrical activity would be physical at the basic level of reality.^[8]

In Search of the Simulators, Glitches, and God

It is conceivable that there is no way to discern if we are living in a simulation. To the simulated inhabitants, their virtual existence would appear completely real. Yet, they would remain uncertain whether their world is genuine or a digital creation.^[6]

However, some researchers propose that simulations may have limits—that even posthuman simulators with advanced knowledge of the laws of nature may still not have a complete understanding of them. These gaps in knowledge could result in glitches. To rectify these flaws, the simulators might patch the virtual reality, resulting in gradual changes in the laws of nature. Therefore, living in a simulated reality could entail sporadic glitches and subtle drifts in the constants and laws of Nature.^{[2, 4]}

A study published in the journal ArXiv in 2012 suggests that it is conceivable for the simulated to discover the simulators. It introduces the idea that if reality is a simulation, there might be limitations on the energy levels of cosmic ray. Furthermore, it suggests that posthuman civilizations run simulations for the purpose of testing string theory. Detailed simulations could enable future researchers to test hypotheses about the universe and disprove various versions of string theory.^{[4, 5]} This would give credence to the suggestion that posthumans have an incomplete knowledge about the laws of physics, leading to gaps and flaws in their simulations.^{[2, 4]}

It is reasonable to assume that the simulators would be economical and practical in their simulated realities, especially if these were designed for entertainment. They could avoid the complexity of using a consistent set of natural laws, instead opting for “realistic” effects. These could potentially create issues that could be discerned from within the simulation. Sudden glitches might also result from the use of error-correcting codes, a technique effective for the simulation of complex systems. These codes would correct mistakes in the simulation much like the error correcting system that exists in DNA. If the genetic system did not have a correcting mechanism, it would eventually be corrupted by the build-up of mutations. The computer equivalent of this system also guards against error accumulation. With the use of error-correcting codes occasionally a correction would take place, leading to sudden changes that would appear to contravene the laws of nature present in the simulation. Ultimately, simulations would have a similar level of computational complexity, in which “the simulated creatures should have a similar complexity to the most complex simulated non-living structures.”^[2]

There is also the question of how one can trust observations about reality if it is indeed a simulation. The simulation argument relies on the assumption that a posthuman civilization possesses certain technological capabilities. However, the evidence supporting this assumption is empirical, based on current leading theories regarding the physical limits of computation. Consequently, the observations made about the world could be misleading, reflecting data about the simulated reality rather then the underlying reality where the simulation operates. Nevertheless, according to Bostrom, “the claim that we cannot have any information about the underlying reality if we are in a simulation is false.” He presents two conditional claims that can be know if reality is a simulation.^[9]

1. If we are in a simulation, then the underlying reality allows for simulations, contains at least one such simulation, and the third proposition of the argument is true.
2. If we are not in a simulation, then the empirical evidence mentioned in the simulation argument is accurate at face value, implying that a technologically mature civilization could create numerous simulations. Therefore, according to the simulation argument, there is a very high probability that at least one of the disjuncts in (1)-(3) is true.^[9]

A technological mature civilization would be capable of running a vast number of simulations, given their expected access to abundant computational power. If our reality is a simulation then there are probably many other simulations, each varying in some detail or overall design. These may run sequentially or simultaneously. A simulation could have a civilization that advances to the posthuman stage and creates its own virtual realities. Consequently, reality may have many levels, with simulations nested within simulations, all running on virtual computers. The number of simulation layers would depend on the computational capabilities of the non-simulated, base-level computer.^{[1, 6, 8]}

From the perspective of the simulated beings, the posthuman simulators might be considered to be like gods: 1) they created the virtual world; 2) they possess superior intellect; 3) they can interfere in the everyday world, violating its physical laws (omnipotent); and 4) they can monitor everything that happens within the simulation (omniscient).^[1] The simulation argument holds intriguing theological implications. Some scholars have considered it as an interesting argument for the existence of a divine being.^[3]

If it is plausible that there can be simulations within simulations, then with each deeper level, the computers’ physical powers increase, as does the intelligence of their respective civilizations. If an infinitely deep computer exists, a divine being could be viewed as functionally equivalent to that infinitely self-programming computer, being pure hardware and not software running in another simulation. In this case, the designer of the universe would not be God; rather it would be the civilization at the deeper level. God, in this context, would be the base hardware upon which all other simulation run, functioning as the ground of being. Such a hierarchical system of simulations could support the concept of an afterlife, where simulated being are resurrected multiple times, progressively moving closer to the base-level world where the base computer operates (akin to moving closer to God).^[3]

Finally, some thinkers have explored the question of natural evil in a world supposedly created by a benevolent creator god within the context of the simulation argument. Johnson (2011) mentions that, “if we grant the theist the knowledge of God’s existence that they claim, the problem of natural evil forces the theist to choose between rejecting ‘God designed our universe’ and ‘natural disasters are evil.’ We have much more reason to reject the former than the latter and, if Bostrom is right, our being in a computer simulation is the best non-divine explanation for our universe’s design.”^[10]

If proven to be true, the simulation argument proposed by Bostrom holds profound implications for the understanding of reality and humanity’s place within it. Although current technological constraints relegate this idea to the realm of speculation, future progress may eventually shine a light into which one of the argument’s three propositions is closer to the truth.

References

1. Bostrom, N. (2003). Are You Living in a Computer Simulation? Philosophical Quarterly, 53(211): 243-255. https://simulation-argument.com/simulation.pdf
2. Barrow, J. D. (2007). Living in a Simulated Universe. In Universe or Multiverse? Cambridge University Press, pp. 481-486
3. Steinhart, E. (2010). Theological Implications of the Simulation Argument. Ars Disputandi, 10(1): 23-37. https://doi.org/10.1080/15665399.2010.10820012
4. Kones, A. Z. (2015). Are We Living in a Computer Simulation? PBS. http://www.pbs.org/wgbh/nova/blogs/physics/2015/07/are-we-living-in-a-computer-simulation/
5. Beane, S. R., Davoudi, Z. and Savage, M. J. (2012). Constraints on the Universe as a Numerical Simulation. ArXiv: 1210.1847v2 [hep-ph]. https://doi.org/10.48550/arXiv.1210.1847
6. Bostrom, N. (2003). The Simulation Argument: Why the Probability that You Are Living in a Matrix Is Quite High. Philosophical Quarterly, 53(211): 243‐255. https://simulation-argument.com/matrix
7. Bostrom, N. (2006). Do We Live in a Computer Simulation? New Scientist, 192(2579): 38-39
8. Bostrom, N. (2005). Why Make a Matrix? And Why You Might Be in One. The Simulation Argument. http://simulation-argument.com/matrix2.html
9. Bostrom, N. (2008). The Simulation Argument FAQ. The Simulation Argument. http://www.simulation-argument.com/faq.html
10. Johnson, D. K. (2011). Natural Evil and the Simulation Hypothesis. Philo, Vol. 14(2): 161-175. https://doi.org/10.5840/Philo201114212

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