This is the question posed - seriously - by a growing number of contemporary physicists and philosophers. I present here researchers and their ideas from an article published in September 2016 on the BBC website and part of the "best-of" articles on the site.
More and more physicists, cosmologists and philosophers think today that we live in a vast simulation, like the famous "matrix" of the eponymous film, which we mistakenly take for an objective physical reality. Just as computers now allow to simulate realities called virtual increasingly realistic, the three-dimensional reality in which we are immersed could well be part of the same process, namely to be the projection of a more fundamental reality, which eludes our ordinary perception, that allowed by our five senses.
What are the possible scenarios?
For entrepreneur Elon Musk, there is a one in a billion chance for our reality to be what it seems to be.
The expert on artificial intelligence Ray Kurzweil proposed that our entire universe could be a scientific experiment performed by a simple college student in another universe. Several physicists discussed this theme in April 2016 at the Museum of Natural History in New York. But their ideas do not just fit the "Matrix model" because there are other ways to think about the problem. Cosmologist Alan Guth of the Massachusetts Institute of Technology suggested that our universe as a whole could be real while proceeding from a kind of scientific experiment, that is, it would have been created by a super -intelligence. According to Guth, nothing in principle precludes the possibility of making a universe from an artificial big-bang that is filled with real matter and energy. This new universe would create its own space-time bubble, separate from the one in which it hatched. This bubble would cut quickly from his parent universe and lose contact with him. This scenario does not change much for us, because even if our universe was born in a kind of specimen manipulated by a super-being, it would be just as "real" as if it were born "naturally".
A second scenario is proposed, and it is the one that gets more attention because it seems to compromise our idea of reality. For Musk, it is conceivable that we are fully simulated beings, that is to say that we would be chains of information (lines of code) in a huge computer, like the characters of a video game. Our brains themselves being simulated, they respond to simulated sensory stimuli. In this conception, there is no "matrix" from which it would be necessary to extract oneself. This is where we live and it is our only chance to live (at least in this physical form).
What are the arguments that support such a vision?
First, that we ourselves are capable of making simulations. By extending technological progress, we can consider becoming capable of creating a simulation that conscious agents immersed in the interior would take for the one and only reality. Computer simulations are not only used in video games but also in research to simulate certain aspects of the world from the subatomic level to the scale of galaxies and beyond. For example, computer simulations make it possible to understand how some animals develop complex behaviors such as schools of fish or swarms of insects. Other simulations allow us to understand how planets, stars and galaxies are formed. We are also able to simulate human societies using simple "agents" who make choices according to certain rules. This provides information on how cooperation is taking place, how cities are changing, how cars and the economy work, and more.
These simulations become more complex as computers become more powerful. Some simulations of human behavior begin to use crude descriptions of cognition. The researchers envision a not-so-distant future in which agents' decision-making will not rest solely on "if ... then ..." basic rules.
On the contrary, they will give these agents simplified models of the brain and observe how they respond. This line of research, however, is based on the "emergentist" idea that such virtual beings will eventually show signs of consciousness, which is an uncertain bet to date.
Do we live in a gigantic simulation?
If humanity is able to reach such a stage, many simulations can be created and end up obscuring the "real" reality. These researchers therefore push the reasoning by considering that it is quite probable that another form of intelligence somewhere in the universe has already reached this stage. If we follow this reasoning to the end, given the size and age of the universe, it is ultimately more likely that we live in a simulated reality.
For the philosopher Nick Bostrom, from Oxford University, this scenario splits into three possibilities.
1) either no intelligent civilization has ever reached the stage at which it can produce such simulations, perhaps because it has extinguished before.
2) some have reached it but then chose for one reason or another not to perform such simulations.
3) Or it is more than extremely likely that we are in such a simulation.
Astrophysicist and Nobel laureate George Smoot felt that there is no strong enough reason to hold assumptions 1 and 2. Surely, the world is going badly now and we could ourselves head for mass extinction ... or not. Thus, option 1 is missing. Moreover, there are no convincing arguments to suggest that very detailed simulations in which agents would consider themselves as real and free are, in principle, impossible. Smoot believes that the discovery of many exoplanets makes us think that we should be extremely arrogant to believe that we are the peak of intelligence in the universe. With regard to Option 2, we could indeed refrain from conducting such simulations for ethical reasons, as it would seem inappropriate to create simulated beings who believe that they exist on their own and enjoy full autonomy. But Smoot thinks it's unlikely, because the reason we're producing simulations today is precisely to better understand the "real" world we live in, which is right. So, no matter the ethical issues, is not it? There remains option 3: we are probably living in a simulation. In my turn, I point out that the question of who would be the source of such a simulation is still dizzying and that if Smoot blames it on a higher intelligence that exists in our physical universe, then it makes a mistake of reasoning, since this universe would be a simulation and that it is necessary to envisage another order of reality from which it would be simulated.
Search for matrix bugs
Many researchers therefore think that we need to look for evidence of the existence of such a simulation and that a way would be to look for "defects", such as "bugs" in the "matrix" (in the form already seen in the movie Matrix). For example, these defects could be inconsistencies in the laws of physics. Another artificial intelligence guru, Marvin Minsky suggested that if a program creates multiple possibilities for an event, the sum of these possibilities should be equal to 1, and if not, it's that something is missing.
For other scientists, a good reason to think that our universe is a simulation is the fact that it "seems" designed. The constants of nature, such as the fundamental forces, are regulated in such a way that a minute change in their values would forbid the existence of matter and life. This argument of the "fine tuning" of the constants is well known to serve the followers of an "intelligent design," that is, of a universe actually conceived by a higher intelligence, but one that would be an intelligence of a spiritual nature God, to make it simple. Anyway, so that our universe is the fruit of a simulation by creators, it is necessary that the reality in which these creators exist also profits from a "fine adjustment", without which it can not exist.
Some people, of course, are interested in quantum physics. Matter and energy reveal a "granular" nature, and there is a limit to the resolution with which we can observe space, below which it becomes "fuzzy". According to Smoot, these are features that might be expected in a simulation, such as the pixelation of a screen that we look too closely.
Another argument is that the universe seems to be able to be described by mathematical laws, as one would expect in the context of a computer program, except that the French physicist Philippe Guillemant would make here an indispensable distinction between the language of the equations and that of the algorithms. For physicist Max Tegmark, this is indeed what to expect if the laws of physics are based on a computer algorithm. But this argument also appears circular, because if a super intelligence led simulations of its own world, it would make the physical laws rest on the same laws as its own universe, as we do ourselves. In this case, the laws of our world are mathematical not because they come from a computer program but because the "real" world also works that way. We can not therefore induce that our world is a simulation from the fact that its laws are mathematical.
Can we think outside our "box"?
However, based on his own research in fundamental physics, James Gates, of the University of Maryland, thinks there is a more specific reason to suspect that the laws of physics come from a computer simulation. Gates studies matter at the level of subatomic particles such as quarks, which make up protons and neutrons in atomic nuclei. He explains that the rules governing the behavior of these particles turn out to have characteristics that resemble codes that correct data processing errors in computers. These rules may be really computer codes. Or to interpret these physical laws in these terms is only the last example of how we always interpret nature on the basis of our most advanced technologies.
At the time of Newton, the universe was understood as a gigantic clock, and in modern times the laws of genetics, at the time of the emergence of computers, were interpreted as a kind of digital code with functions of storage and extraction of information. It is therefore quite possible that one projects the preoccupations of the moment on the laws of physics. It is likely that it will ultimately be very difficult if not impossible to find conclusive evidence that we are living in a simulation. Unless the simulation is full of errors, it will be difficult to develop a test whose results could not be explained in any other way. According to Smoot, we may never know it simply because our brains are not fit for this task. After all, we design agents in a simulation to work according to the rules of the game, not to corrupt them. It could be a box outside of which we can not think.
Matter as "bits" of information
There is still a deeper reason why we should not be worried about whether we are just information manipulated by a big machinery. In any case, this is what many physicists think about the "real" world. Quantum theory itself is increasingly described in terms of information and calculation. Some physicists believe that at its most basic level, nature might not be purely mathematical but purely informational: that is, bits like the ones and zeros of the computer binary language. The influential theoretical physicist John Wheeler has called this notion "It from Bit" (which could be translated as: everything comes from Information Units). According to this conception, everything that occurs from the interactions of elementary particles to macroscopic phenomena is the result of a kind of calculation.
"The universe can be seen as a gigantic quantum computer," said Seth Lloyd of the Massachusetts Institute of Technology. "If we look at the" guts "of the universe - the structure of matter at its smallest scale - then these guts consist only of (quantum) bits of information that are subject to local digital operations. This brings us to the heart of matter. If the reality is only information, then we are neither more nor less "real" if we are in a simulation than if it is not the case. In either case, information is everything we can be. Does it make any difference whether this information was programmed by nature or by super-intelligent creators? In principle no, except that in the second case, the creators in question would be likely to intervene in the simulation or even to delete it.
Weaving a web from a thread of ignorance
Max Tegmark, well aware of this possibility, recommends that we should all live and do interesting things in our lives, just in case our simulators get bored. He certainly said that by half joking. After all, there are surely better reasons for wanting to live interesting lives than the risk that they will be erased if they are not. But that reveals some problems with this global concept. The idea of super-intelligent simulators who would say at one point: "Let's see, this program is a bit boring, let's throw in another," is rather anthropomorphic and comical, because it imagines our "creators" as a band of teenagers having fun with a game console.
The discussion of Bostrom's three possibilities involves the same type of solipsism (a philosophical position that there is no other reality for the thinking subject than himself.) It is an attempt to say something. deep on the universe by extrapolating from what humans in the 21st century are capable of conceiving.The argument is reduced to: "We make video games.I bet that super-beings would do the same thing except they would be super elaborate! "
In trying to imagine what super-intelligent beings would do, or even what they would be, we have no choice but to go from ourselves. But we must not lose sight of the fact that we are only weaving a web from a thread of ignorance. It is surely not a coincidence that most advocates of this idea of "universal simulation" have admitted to having been a fan of science fiction in childhood (and even later).
Ancient philosophical sources
Certainly aware of such limitations, Harvard physicist Lisa Randall is troubled by the enthusiasm shown by some of her colleagues for these speculations about a cosmic simulation. Because it does not change the way we should understand and study reality. His perplexity is not just about saying "so what? But it raises the question of what we choose to understand by talking about "reality". It is more than likely that Elon Musk does not walk around thinking that the people he sees around him, his friends and family, are just computer constructions created by data chains that enter computer nodes. which encode his own consciousness. He does not do it because at least partly he can not keep this idea in his mind for a very long time. But we also know deep down that the only notion of reality that is valuable is the one we experience, not a hypothetical world that would be "behind". There is nothing new, however, to wonder what lies behind the appearances and sensations we experience. Philosophers have been doing this for centuries. Plato and his "cave myth", of course. Kant and the idea that we can not know "the thing in itself" which is at the source of the phenomena. Berkeley and the idea that the world is an illusion and that consciousness is the only reality (which joins the philosophy of vedanta in particular). Descartes for its part has established that the capacity to think is the only significant criterion of existence of which we can be sure.
The concept of "world as simulation" is the last avatar of this philosophical thought built from our most advanced technologies. There is nothing wrong with this philosophical enigma that leads us to examine our assumptions and preconceptions as to the nature of reality.
The holographic universe
The BBC article ends there, on philosophical considerations that carefully avoid venturing into the spiritual realm. Yet the question of the world as simulation necessarily generates two other questions: who would simulate reality and for what purpose? Spiritual traditions have answers here that it would be imprudent to ignore. Yes, the material reality may well be a simulation for the "incarnated souls" that we are who come to live a form of learning. This type of message is found both in shamanism and gnosis, and as much in Eastern philosophies as in the religions of the Book. To remain on the scientific field, the most recent reflections in this field rehabilitate the notion of holographic universe, already put forward in the years 1970-80 with Karl Pribram and Michael Talbot. The physicist Brian Greene explains that this idea comes today from data from the study of black holes. It was once thought that every object in a black hole would disappear forever. But it has been discovered that the information that constitutes the object is in fact not lost, it is found stored on the surface of the black hole, so in two dimensions. This information would help to reconstruct the object and we can also induce that all the information that is on the surface of a black hole reveals what it contains. Clifford Johnson, from the University of Southern California, confirms that "everything that has fallen into the black hole can be fully expressed on the outer surface of the black hole; so we can know what's going on inside just by referring to the outside. Now, the space inside a black hole obeys the same rules as the space on the outside; we can therefore assume that three-dimensional space as a whole is the result of the projection of information stored on a two-dimensional surface that would be all around the universe. Leonardo Susskind, from Stanford University, therefore asks the question of the illusory nature of space: "Is the three-dimensional world an illusion, in the same way that a hologram is an illusion? I am inclined to think that yes, the three-dimensional world is a kind of illusion and that the true reality is the two-dimensional reality on the surface of the universe. "