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“Meta-level” Physics: How Constructor Theory Explains Life, Universe and Quantum Computing



News from November 5, Beijing time, you can think of physics as a way to explain the behavior of things like black holes, particle collisions, where apples fall, and quantum computers. But a theory that some physicists are studying today is not just about individual phenomena; it’s a new way of describing the universe itself.This theory can solve many questions, such as why biological evolution is possible, and how abstract things like thoughts and information have characteristics independent of any physical system. Researchers call this theory “constructor theory.”However, although this is a very fascinating theory, a prominent question is: how to verify it?

“When I first studied Constructor Theory, it seemed too bold to be true,” said Abel Jansma, a graduate student in physics and genetics at the University of Edinburgh in the United Kingdom. “Early The thesis covers life, thermodynamics and informatics. For such a young theory, the basic work seems to be too much. However, it may be natural to study this theory in this way. As an outsider, it is very awful to be able to witness all this. People excited.”

Chiara Marletto (Chiara Marletto) is a young physics researcher who is very interested in biological processes. The laws of physics do not state the possibility of life, but any slight change in the physical constants may make the life we ​​know no longer exist. So, why was the evolution of natural selection possible in the first place? No matter how long you stare at the physical equations, you will never understand why they allow biological evolution; however, it is clear that they do make biological evolution possible.

Maleto was dissatisfied with this contradiction. She wanted to explain why the emergence and evolution of life is possible when the laws of physics do not imply that life should exist. She found a 2013 paper, written by David Deutsch, a physicist and quantum computing pioneer at the University of Oxford, that laid the foundation for the constructor theory. The basic principle of the theory is: “All the laws of physics can be expressed as a set of statements, that is, which tasks (physical transformations) are possible, which tasks are impossible, and why are they so.”

Maleto stated that she speculates that “constructor theory has a set of useful tools to solve this problem”, that is, even though the laws of physics do not explicitly encode the design of biological adaptation, why evolution is still possible. Out of curiosity about these possibilities, Marletto quickly turned her doctoral research focus to constructon theory.

Many theories are concerned with what has already happened, while the constructor theory is concerned with what may happen. For example, in the current physics paradigm, people try to predict the trajectory of a comet based on its initial state and the motion equation of general relativity. In contrast, the Constructor Theory is more holistic, trying to explain the possible trajectories of the comet in principle. For example, a comet whose speed exceeds the speed of light is impossible, but a trajectory whose speed is lower than the speed of light is possible as long as they also conform to the law of relativity.

Today’s mainstream physics theories can explain violent phenomena like the collision of two black holes, but it is difficult to explain how and why a tree exists. Constructor theory focuses on what may happen, so it can explain the rules of fields that are inherently unpredictable—such as evolution—that is, any patterns that need to be explained.

Constructor theory can also capture the attributes of information, which do not depend on the physical system in which they exist. For example, the same lyrics can be sent over radio waves, can be imagined in a person’s mind, or written on a piece of paper. The Information Constructor Theory also puts forward new principles to explain which information transformation is possible, which is impossible, and why.

The laws of thermodynamics have also been accurately expressed in the constructivist theory; before that, these laws were only stated as approximations and applied within specific scales. For example, when trying to describe the second law of thermodynamics (that is, the entropy of an isolated system will never decrease over time), some models show that a physical system will reach its final equilibrium (maximum entropy) because this is the system’s Possible” configuration. However, the measurement scale of these models is traditionally arbitrary. Is this model suitable for nano-scale systems or only for systems composed of one particle? Constructor theory reinterprets the laws of thermodynamics through possible and impossible transformations, rather than the evolution of a physical system over time; in this process, the theory also uses precise, scale-independent statements to formulate these laws. Description: The second law of thermodynamics allows some transformations from X to Y to be possible, but not the other way around-work can be completely converted into heat, but heat cannot be completely converted into work without side effects.

Since the scientific revolution, physics has made great progress. In 1687, Isaac Newton proposed his theory of cosmic physics in his masterpiece “Principia Mathematica”. Newton’s theory of classical mechanics is based on his famous “Three Laws of Motion”, which means that if a person knows the time interval of the force acting on a system and also knows the initial speed and position of the system, he can use the classical mechanics. Motion equation to predict the speed and position of the system at any subsequent moment in this time interval. In the first decades of the 20th century, classical mechanics was proven wrong in both directions. Quantum mechanics overturned Newton’s theory in explaining the physics of the microcosm. Einstein’s general theory of relativity replaced classical mechanics, deepening our understanding of gravity and the nature of mass, space and time. Although these three theories—classical mechanics, quantum mechanics, and general relativity—are different in details, they can all be expressed in terms of initial conditions and dynamic laws of motion, and these laws allow people to predict the system in time. The track status. This overall framework is called the mainstream concept.

However, in many fields, our best theories cannot be expressed by the mainstream concepts of initial conditions and laws of motion. For example, the laws of quantum computing are not fundamentally about what happens to a quantum system after a certain initial state, but about which transformations of information are possible and which are impossible. The question of whether a so-called “universal quantum computer”-a quantum computer that can accurately simulate any physical system-can be built is completely different from the framework of “initial conditions plus the law of motion”. Even in the field of cosmology, it is very difficult to use mainstream concepts to explain the well-known problem of the initial conditions of the universe: we can in turn understand everything that happened after the Big Bang, but we still cannot explain why the universe appeared in its specific initial state. , But not other states. However, the constructor theory may indicate the initial conditions of the universe at the time of the Big Bang, which can be derived from the principles of the theory. If you only consider physics from the perspective of mainstream concepts, the problems of quantum computing, biology, and the birth of the universe seem impossible to solve.

The basic components of Constructor Theory are Constructor, Input Matrix and Output Matrix. Constructors are any objects that can cause specific physical transformations and retain the ability to perform such transformations again.The input matrix is ​​the physical system presented to the constructor, and the output matrix is ​​the physical system produced by the constructor transforming the input matrix

The basic components of Constructor Theory are Constructor, Input Matrix and Output Matrix. Constructors are any objects that can cause specific physical transformations and retain the ability to perform such transformations again. The input matrix is ​​the physical system presented to the constructor, and the output matrix is ​​the physical system produced by the constructor transforming the input matrix.

For how the Constructor Theory describes a system, we can use a milkshake mixer as a simple example. The device mixes ingredients such as milk, fruit and sugar to output a completely homogeneous beverage. A milkshake blender is a construct that can repeat this transformation time and time again: the input matrix is ​​a set of raw materials, and the output matrix is ​​a milkshake.

There are examples of this in the universe, such as the sun. The sun is like a nuclear fusion reactor. It takes hydrogen as an input matrix, converts it into helium, and uses light as an output matrix. The sun itself is the constructor, because it retains the ability to cause this transformation again.

In the mainstream concept, people can use the initial state of the sun to calculate through appropriate algorithms to predict the end of the sun after it runs out of fuel. In the formulation of the constructor theory, it is possible for hydrogen to be converted into helium and light; once we understand that the conversion from hydrogen to helium and then to light is possible, we can deduce that a constructor that can cause such a conversion is also possible of.

The basic principle of Constructon Theory means that all the laws of physics—general relativity, thermodynamics, quantum mechanics, and even information—can be expressed by physical transformations that are possible and impossible in principle.

This setting is very common and may be counterintuitive. We can use a chemical reaction that uses a catalyst as an example: the chemical catalyst is a constructor, the reactant is the input matrix, and the product is the output matrix. The operation of a computer is also a construction process: a computer (and its program) is a constructor, and its information input and output correspond to the input matrix and output matrix of the constructor theory. Heat engine is another constructor, as are all forms of self-replicating life. Imagine a bacterium carrying a genetic code. The cell and its genetic code are a certain construct, and the output is a progeny cell with a copy of its genetic code.

The explanation of which transformation is possible and which transformation is impossible never depends on the specific form adopted by the constructor, so it can be abstracted out, leaving the statement about transformation as the main focus of the constructor theory. This is already very advantageous. For example, we can express which computer programs or simulations are achievable and which are not in principle, without worrying about the details of the computer itself.

Why does life exist?

How can people prove that the evolution of life, as well as all the elegant adaptability and appearance design of life, are in line with the laws of physics, and the laws of physics seem to have no design at all? No amount of testing of general relativity and quantum mechanics equations will yield any results-they do not show the possibility of life. Darwin’s theory of natural selection evolution explained the emergence of internal design in the biosphere, but failed to explain why such a process was possible in the first place.

Biological evolution is now understood as a process in which genes are passed on from generation to generation through self-replication, replacing competitors, namely alternative genes called alleles. In addition, genes have evolved complex “carriers” for proliferation, such as cells and organisms, including ourselves. The biologist Richard Dawkins is known for popularizing this evolutionary view: genes are the basic unit of natural selection, and they “work hard” to replicate themselves in the form of DNA strands, using temporary protective vectors Reproduce from one generation to the next to achieve immortality. Replication is imperfect, and genetic mutations will occur, which will lead to mutations in the ability of genes to spread in fierce competition with competitors. The environment determines which genes are most suitable for transmission and which are not suitable for transmission, and therefore become a source of natural selection.

With this logic of “replicating gene carriers”, people can more accurately explain the problem of biological evolution: the laws of physics do not clearly state that the transformation required for evolution and biological adaptation is possible. With this in mind, what attributes must the laws of physics have to make such a process that requires self-replication, design, and natural selection possible?

Please note that this question cannot be answered by mainstream concepts, because mainstream concepts will force us to try to predict the emergence of life after the initial state of the universe. Constructor theory allows us to reconstruct this problem and think about why life is possible and under what conditions. As Maretto said in a 2014 paper: “…the mainstream concept can only predict at best the exact number of goats that will (or may) appear on the earth under certain initial conditions. In the Constructor Theory , The statement is whether goats are possible and why.”

Only two years after Deutsche’s original paper was published, Maleto’s paper “Constructor Theory of Life” was published. In her article, she pointed out that the evolution of life is compatible with the laws of physics, and the laws of physics themselves do not contain any design, as long as they allow the materialization of digital information (on Earth, this process occurs in the form of DNA). She also pointed out that a precise replication factor, such as a viable gene, must use a vector to evolve. In this sense, if the constructor theory is correct, then the temporary carrier is not just an accidental event of life on earth, but is regulated by natural laws. An interesting prediction related to the search for extraterrestrial life is that no matter what life you find in the universe, it must depend on replication factors and vectors. Of course, these may not be familiar DNA, cells and organisms, but replication factors and vectors will appear in some form.

So, can this theory be verified?

You can think of Constructor Theory as a theory of theory. In contrast, general relativity explains and predicts the motion of objects as they interact on the space-time stage. Such a theory can be called the “object level” theory. The constructor theory is a “meta-level” theory-its statement is about the law of the law. Therefore, the general theory of relativity stipulates the behavior of all stars, including what we have observed and what we have never seen, while the constructor theory stipulates that all object-level theories, including current and future theories, must comply with its elements. The law of hierarchy is also called “principle”. In hindsight, we can see that even before the emergence of constructon theory, scientists have taken such principles seriously. For example, physicists expect all unknown physical theories to conform to the principle of conservation of energy.

General relativity can be verified by observing the motion of stars and galaxies; quantum mechanics can be verified in experimental devices such as the Large Hadron Collider. However, since the principles of constructon theory cannot directly predict the motion of physical systems, how can people verify them? Vlatko Vedral is a physicist and professor of quantum information science at the University of Oxford. He has collaborated with Marletto to try to solve this problem through thought experiments. They imagined experiments where quantum mechanical systems can interact with gravity.

One of the most prominent problems in modern physics is the incompatibility between general relativity and quantum mechanics. General relativity cannot explain the tiny motion and interaction of atoms, while quantum mechanics cannot explain gravity and its influence on massive objects. Scientists have put forward a variety of viewpoints, trying to unify these two major fields under a deeper theory, but as we all know, these viewpoints are difficult to verify through experiments. However, we can consider the principles that these theories should follow to directly test them.

In 2014, Marletto and Deutsch published a paper outlining the theory of information constructs, in which they used possible and impossible transformations to express various quantities, such as information, calculation, measurement, and distinguishability. Importantly, they also pointed out that all recognized characteristics of quantum information follow the principles of the constructor theory they proposed. The information medium is a physical system, such as a computer or brain, in which information is verified. Observable refers to any measurable physical quantity. They defined “hyper-information medium” as an information medium with at least two information observables, and the combination of these two information observables is not one information observable. For example, in quantum theory, one can accurately measure the velocity or position of a particle, but not both. Quantum information is an example of hyperinformation. But most importantly, the concept of hyperinformation in the constructor theory is more general and is expected to be applicable to any theory that replaces quantum theory and general relativity.

In a working paper in March 2020, Marletto and Vedral pointed out that if the information principle in the constructor theory is correct, then if two quantum systems (such as two masses) pass the third Systems are entangled with each other (such as a gravitational field), and the third system itself must be quantum. Therefore, if an experiment can cause the gravitational field to produce local entanglement between two qubits, then gravity must be non-classical—it will have two observables; in quantum theory, these two observables cannot be The same accuracy is measured at the same time. If such an experiment shows that there is no entanglement between qubits, then the constructor theory needs to be completely revised, otherwise it may be completely wrong.

If this experiment shows entanglement between two masses, then all current attempts to unify general relativity and quantum mechanics (assuming gravity is classical) will be ruled out.

“There are three theories about how to unify gravity and quantum physics,” Vedral said. “One of them is complete quantum gravity.” Theories that put forward quantum gravity include loop quantum gravity theory, which believes that space is composed of circular gravity. Field composition; as well as string theory, it is believed that particles are composed of “strings”, and their different vibration modes correspond to various basic particles in nature, and some string vibration modes correspond to quantum mechanical particles carrying gravity.

“These theories will be consistent with the positive results of our experiments,” Vedral said, “and those that will be rejected are the so-called’semi-classical theories,’ such as quantum theory in curved space-time. There are many such theories. Theories. They will all be ruled out-if space-time can really entangle two massive particles, it will contradict classical space-time.”

However, the experiment proposed by Maretto and Vedral faces some major practical challenges. “I think there is a five or six orders of magnitude difference between our experiment and the current technological capabilities,” said Vedral. “One of the problems is that we need to eliminate any noise sources, such as induced electromagnetic interaction… One problem is that it is difficult to create a nearly perfect vacuum. If there are a lot of background molecules around the object you want to entangle, even a collision between a background molecule and an object you want to entangle, may be harmful , And cause decoherence. The vacuum must be very close to perfect to ensure that no atomic collisions occur during the experiment.”

As an outsider who is interested in Constructor Theory, Vedral focuses on the issue of quantum information. He sometimes thinks about the so-called “universal constructor”, a theoretical device that can perform all possible tasks permitted by the laws of physics.

“Even though we have a model of a general-purpose computer (that is, the concept needed to make a computer that can simulate any physical system),” said Vedral, “but we don’t have such a general-purpose constructor. The breakthrough to this problem may be a Group axioms can describe the meaning of universal constructs. This is a big unanswered question. What kind of machine will it be? This makes me very excited. This is also a very open field. If I were a young researcher , I will jump into this field now. This is like the next revolution.”

Samuel Kuypers is a graduate student in physics at Oxford University, working in the field of quantum information. He stated that the constructor theory “has clearly achieved great success, such as stating basic information concepts in clear physics terms, and rigorously explaining the difference between heat and work in thermodynamics, but this theory should be regarded as An ongoing project with a series of goals and problems.” Taking into account the possible future achievements, Keppers hopes that “general relativity can be rephrased in terms of constructor theory. I think that the general relativity Overall, this will bring very rich results.”

Whether the Constructor Theory is forming a revolution, time will tell us the answer. In the years after the theory appeared, only a few physicists (mainly at Oxford University) have been studying it. Constructor theory has different properties from other theories (such as string theory). This is a completely different way of thinking about the essence of reality, perhaps bolder than those more mainstream conjectures. If constructor theory can continue to solve problems, then physicists may adopt a revolutionary new worldview. They no longer imagine reality as a machine that obeys the laws of motion, but a universe and ocean full of resources, which can be transformed through suitable constructors. It will be a reality defined by possibility rather than fate. (Ren Tian)