Welcome back to our Fermi Paradox series, where we take a look at possible resolutions to Enrico Fermis famous question, Where Is Everybody? Today, we examine the possibility that we cant see them because they have us all inside a massive simulation!

In 1950, Italian-American physicist Enrico Fermi sat down to lunch with some of his colleagues at the Los Alamos National Laboratory, where he had worked five years prior as part of the Manhattan Project. According to various accounts, the conversation turned to aliens and the recent spate of UFOs. Into this, Fermi issued a statement that would go down in the annals of history: Where is everybody?

This became the basis of the Fermi Paradox, which refers to the disparity between high probability estimates for the existence of extraterrestrial intelligence (ETI) and the apparent lack of evidence. Seventy years later, we are still trying to answer that question, which has led to some interesting theories about why we havent. A particularly mind-bending suggestion comes in the form of the Planetarium Hypothesis!

To break it down, this hypothesis states that the reason we are not seeing aliens is that humanity is in a simulation, and the aliens are the ones running it! In order to ensure that human beings do not become aware of this fact, they ensure that the simulation presents us with a Great Silence whenever we look out and listen to the depths of space.

Given the sheer size of the Universe and its age, the Search for Extraterrestrial Intelligence (SETI) seems like a valid enterprise. Consider the following: there are 200 to 400 billion stars in our galaxy and as many as 2 trillion galaxies in the Universe. Within our galaxy alone, there are an estimated 6 billion Earth-like planets, which means that there could be as many as 12 quintillion Earth-like planets in the Universe.

Meanwhile, it took humanity about 4.5 billion years to emerge on Earth, and the Universe has been around for 13.8 billion years. As such, its not farfetched at all to assume that intelligent life has had countless opportunities to emerge somewhere else in the Universe and plenty of time to evolve. In 1961, American physicist and SETI researcher Dr. Frank Drake illustrated this point during a meeting at the Green Bank Observatory.

In preparation for the meeting, Drake created an equation that summed up the probability of finding ETIs in our galaxy. Thereafter known as the Drake Equation, this probabilistic argument is expressed mathematically as:

The purpose of this argument was to summarize the challenges of SETI (i.e. the sheer number of unknowns) and put it into context. At the same time, it demonstrated that the odds of findings ETIs are quite good. Even employing the most conservative estimates for every parameter, the Equation indicates that there should be at least a few ETIs in our galaxy that we could communicate with at any given time.

Moreover, given the age of the Universe itself, there should be many species in our Universe that have evolved to the point where they could explore space and perform feats of engineering that would dwarf anything we can dream of. Which brings us to

In 1964, Soviet/Russian astrophysicist Nikolai Kardashev proposed that extraterrestrial civilizations could be classified based on the amount of energy its able to harness. In an essay detailing this idea, titled Transmission of Information by Extraterrestrial Civilizations, Kardashev proposed a three-tiered scheme the Kardashev Scale that stated the following:

From the standpoint of SETI, civilizations that fall into any of these three categories could be identified in a number of ways. For example, a Type I civilization is likely to have grown to occupy its entire planet and colonize Low Earth Orbit (LEO) with satellites and space stations. This cloud of artificial objects (aka. Clarke Belts) could be visible from the way it reflects the stars light during planetary transits.

A Type II civilization, according to Kardashev, is one that would be capable of building a megastructure around their star (i.e. a Dyson Sphere). This would allow the civilization to harness all of the energy produced by its sun, as well as multiplying the amount of habitable space in its home system exponentially. As Dyson himself stated in his original paper, these megastructures could be spotted by looking for their infrared signatures.

As for Type III civilizations, it is possible that a civilization capable of harnessing all the energy of its galaxy would do so by building an apparatus that encloses it. Or, its possible they would choose to enclose just a part of it, around its core region perhaps, and the supermassive black hole (SMBH) at its center. Regardless, it stands to reason that such an advanced civilization would be impossible not to notice.

Hence Fermis why famous question endures. To date, most attempts to resolve the Fermi Paradox focus on how aliens could exist but be unable to communicate with us. In contrast, the Simulation Hypothesis suggests that they are deliberately not communicating with us, and even taking great pains to hide their existence. Their method of choice consists of keeping us in a simulated reality so that we are blind to their existence.

In 2001, famed science fiction author and mathematician/engineer Stephen Baxter wrote a seminal essay titled, The Planetarium Hypothesis A Resolution of the Fermi Paradox. In response to Fermis question, Baxter postulated that humanitys astronomical observations are actually an illusion created by a Type III Civilization who are keeping humanity in a giant planetarium. Or as he put it:

A possible resolution to the Fermi Paradox is that we are living in an artificial universe, perhaps a form of virtual- reality `planetarium, designed to give us the illusion that the universe is empty. Quantum-physical and thermo-dynamic considerations inform estimates of the energy required to generate such simulations of varying sizes and quality.

This concept is similar to the Simulation Hypothesis, a theory originally put forth by Niklas Bostrom of the Oxford Future of Humanity Institute (FHI). In a 2001 paper, titled Are You Living In A Computer Simulation?, he addressed the idea that what humanity considers the observable Universe is actually a massive virtual environment. This idea, where the very nature of reality is questioned, has deep roots in many philosophical traditions.

In this case, however, it is suggested that the purpose of keeping humanity in a simulation is to protect us, our hosts, and perhaps other species from the dangers associated with contact. Using human history as a template, we see countless examples of how two cultures meeting for the first time can easily end in war, conquest, slavery, and genocide.

However, there are limits. According to Baxters original paper, it would be well within the abilities of a Type III civilization to contain our present civilization within a perfect simulation. However, a single culture that occupies a space measuring ~100 light-years in diameter would exceed the capacities of any conceivable simulated reality.

In this respect, it would be within the Type III civilizations best interests to create a simulation that would contain no evidence of ETIs while also placing limits on our ability to expand out into the Universe. This could be done by including physics models that limit humanitys ability to leave Earth (i.e. its high-escape velocity) and our ability to explore and colonize space (the limits imposed by Special Relativity).

Naturally, the idea that were living in a planetarium created by advanced aliens is difficult to test. However, multiple studies have been conducted on the Simulation Hypothesis that have implications for the Planetarium Hypothesis. For instance, Prof. David Kipping of Columbia University and the Flatiron Institutes Center for Computational Astrophysics recently published a study on the very subject.

In this study, titled A Bayesian Approach to the Simulation Argument, Kipping conducted a series of statistical calculations designed to test the likelihood and the uncertainty associated with Bostroms hypothesis. In sum, Kipping argued that a posthuman civilization with the ability to generate such simulations would create far more than just one, which indicates a high probability that we are not in one.

At the same time, he indicated that the odds that we could be in one of many are close to being even:

Using Bayesian model averaging, it is shown that the probability that we are sims is in fact less than 50%, tending towards that value in the limit of an infinite number of simulations. This result is broadly indifferent as to whether one conditions upon the fact that humanity has not yet birthed such simulations, or ignore it. As argued elsewhere, it is found that if humanity does start producing such simulations, then this would radically shift the odds and make it very probably we are in fact simulated.

Thanks to endorsements by public figures like Elon Musk, who once said theres a billion to one chance were living in base reality, the concept has gained mainstream attention and acceptance. At the same time, though, both the Simulation and Planetarium Hypothesis have their share of detractors and counter-studies that question the merits of this scenario.

For starters, multiple researchers have questioned whether a Universe-level simulation is even possible given our understanding of the laws of nature. In particular, some researchers have used our own failures with quantum Monte Carlo (QMC) simulations to argue that future humans (or an ETI) would not be able to generate a reality that is accurate right down to the quantum level.

Others have criticized the Simulation Hypothesis based on Ockhams Razor and what they see as the computational impossibility to simulate our something as huge as our Universe down to the granular level. Then there are arguments that use recent advancements in lattice Quantum Chromodynamics (QCD) to show how a simulated environment will inevitably be finite and vulnerable to discovery.

Of course, these criticisms can be countered by arguing that it is impossible to disprove the simulation theory based on physical arguments when the very physics we are referencing could be nothing more than the result of the simulation. But this counter-argument only reinforces the issue of how the Simulation Hypothesis is not falsifiable. In short, it can neither be proven nor disproven, so whats the point of debating it?

However, there are arguments concerning the Planetarium Hypothesis that are testable and can therefore be treated separately. For example, there are those who have argued that assuming the existence of a Level III Kardashev civilization is based on a fundamentally flawed assumption. In short, it assumes that the evolutionary path of advanced civilizations is based on expansion rather than optimization.

In a 2008 study, Against the Empire, Serbia astronomer, astrophysicist, and philosopher Milan Cirkovic argued the opposite take. In short, he tested two models for determining the behaviors of a postbiological and technologically advanced civilization the Empire-State and the City-State. In the end, he argued that advanced species would prefer to remain in spatially-compact optimized environments rather than spread outwards.

Some examples of this include the Dyson Swarm and the Matrioshka Brain, two variations on Dysons famous sphere. Whereas the former consist of smaller objects interlinked in orbits around a star, the latter consists of layers of computing material (computronium) powered by the star itself. The civilization responsible for building it could live on the many islands in space, or live out their existence as simulations within the giant brain.

At the end of the day, a species choosing to live like this would have very little incentive to venture out into the Universe and attempt to colonize other worlds or interfere with the development of other species. Nor would they consider other species a threat since they would be inclined to believe the evolutionary pathway for other intelligent life would be similar to their own i.e. in favor of optimization.

Unfortunately, such arguments require that evidence of ETIs be found such as the heat signatures produced by their megastructures in order to be considered testable. At this time, we have a hard time constraining what would be considered a sign of intelligent life and its activity (aka. technosignatures) because we know of only one species capable of doing that (simply put, us!)

Nevertheless, theories like the Planetarium Hypothesis remain fascinating food for thought as we continue to probe the Universe looking for signs of intelligent life. They also help refine the search by suggesting things to be on the lookout for. In the meantime, all we can do is keep looking, listening, and wondering if anyone is out there.

We have written many interesting articles about the Fermi Paradox, the Drake Equation, and the Search for Extraterrestrial Intelligence (SETI) here at Universe Today.

Heres Where Are All the Aliens? The Fermi Paradox, Where Are The Aliens? How The Great Filter Could Affect Tech Advances In Space, Why Finding Alien Life Would Be Bad. The Great Filter, Where Are All The Alien Robots?, How Could We Find Aliens? The Search for Extraterrestrial Intelligence (SETI), and Fraser and John Michael Godier Debate the Fermi Paradox.

Want to calculate the number of extraterrestrial species in our galaxy? Head on over to the Alien Civilization Calculator!

And be sure to check out the rest of our Beyond Fermis Paradox series:

Astronomy Cast has some interesting episodes on the subject. Heres Episode 24: The Fermi Paradox: Where Are All the Aliens?, Episode 110: The Search for Extraterrestrial Intelligence, Episode 168: Enrico Fermi, Episode 273: Solutions to the Fermi Paradox.

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Beyond Fermis Paradox VII: What it the Planetarium Hypothesis - Universe Today