Chapter 11 The Real World
Physics have been looking for the ultimate theory that can unify all physics. Now it seems that they may have to stop at a set of theories and can't integrate them. Earlier, the parliament in the demon world passed a bill prohibiting the people below from raising goldfish in round fish tanks. The proponist explained that it is very cruel to lock the goldfish in a round fish tank, because the curved surface will distort the "real" world in the eyes of the goldfish. Leaving aside the well-being brought by this bill to the poor goldfish, this story also raises an interesting philosophical question: How do we know that the "reality" we perceive is real? The world seen by the goldfish is different from what we call reality, but how can we be sure that what it sees is not as real as us? As far as we know, even we may be looking at the world around us through a twisted lens for the rest of our lives.
In physics, this problem is not pure theoretical fantasy. In fact, materialists find that their current situation is similar to that of goldfish. For decades, we have been searching up and down, longing for an ultimate universal theory that can explain all aspects of reality with a set of self-consistent basic laws. But now, what we get in the end may not be a single theory, but a large family of interrelated theories. Each theory has its own description of "reality", just like observing the world through its own circular fish tank.
This view may be difficult for many people, including some scientists in the circle. Most people believe that there is an objective "reality" that directly expresses information about this material world, whether it is our perception or our science. Classical science is based on the belief that there is an external world that exists independently, and its attributes are certain and have nothing to do with the observer who perceives the world. In philosophy, this belief is called realism. However, people with fresh memories of Timothy Leary and the 1960s should know another possibility: the concept of "reality" can also depend on the mind of the perceiver. Such views are much the same, some are called anti-realism, and some are called instrumentalism or idealism.
According to these "isms", the world we know is built by the human mind based on sensory information and shaped by the explanatory structure in our brain. This view may be difficult to accept, but not difficult to understand. You can't erase the observer, that is, ourselves, from our perception of the world. With the gradual development of physics, the status of materialism is becoming precarious. In classical physics, the Sester system can describe our daily experience very accurately, and the interpretation of terms such as "object" and "position" is also largely consistent with our common sense (that is, our "reality" understanding of those concepts). However, as a measurement tool, we humans are very rough. Physicists have found that what is commonly called "objects" and the light that makes us see them are composed of objects that we cannot directly perceive (such as electrons and photons).
These objects follow not classical physics, but quantum theory. The "reality" of quantum theory is completely different from the "reality" of classical physics. In the quantum system, particles have neither a certain position nor a certain speed, and their values are determined only when an observer measures those quantities. In some cases, individual objects cannot even exist independently and can only appear as part of the whole. Quantum physics also greatly challenges our understanding of the past. In classical physics, the so-called "past" is a series of clear events that have become history, while in quantum physics, the "past" is uncertain, just the possibility of a series of events, which is no different from the "future". Even the universe as a whole does not have a clear past or history.
Therefore, quantum physics implies another "reality" different from classical physics - although classical physics is consistent with our intuition, and it can still help us design buildings, bridges and other things. These examples give us a conclusion and provide an important framework for interpreting modern science. In our view, "reality" cannot exist independently of picture or theory. On the contrary, we adopted a new view called "the idealism that depends on the model." This view is that every physical theory or world picture is a model (usually essentially a mathematical model) and a set of laws that link the elements in the model with observations. According to the truth theory that depends on the model, it is meaningless to ask whether a model itself is true, and the only meaningful thing is whether it is consistent with the observation. If both models are consistent with observations, one of them cannot be considered more real than the other.
Anyone can choose a more convenient model according to the specific situation. Don't judge the real alternative reality has become the mainstream of today's popular culture. For example, there is no need for any logic between events, no need to justify, and there is no need to follow any rules. The aliens who control this virtual world may make the world suddenly hate chocolate or eliminate war overnight to achieve world peace just because it is interesting or fun, purely to see our reactions.
The same is true of goldfish. What they see in the round glass tank is obviously different from what we see outside the fish tank, but this does not prevent them from developing a set of scientific laws to describe the movement of objects outside the fish tank they observe. For example, because light will be deflected when it enters the water from air, in our opinion, an object that moves in a straight line without external forces should move along the curve in the eyes of goldfish.
Desp being in a distorted reference system, goldfish can still sum up a set of always correct scientific laws, allowing them to predict the future movement of objects outside the fish tank. Their laws will be much more complicated than ours, but whether they are simple or not is only related to taste. If the goldfish can develop such a theory, we must admit that the goldfish's view is also a valid description of reality. There is also a famous example that occurs in the real world, which also shows that "reality" can be described differently, that is, the dispute between Ptolemy's geocentric theory and Copernicus's helith theory. Although it is usually said that Copernicus proved that Ptolemy was wrong, this is not the case. Copernicus and Ptolemyel, like us and goldfish, can choose any kind of description as a model of the universe, because whether it is assumed that the earth does not move or the sun does not move, we can well explain the celestial changes we observe. Regardless of the role of Coperniclinster's heliocentric theory in the philosophical debate about the nature of the universe, its real advantage is that the equation of motion is more concise in the sun's stationary reference system.
The truth theory that depends on the model is not only applicable to scientific models, but also effective for the conscious and subconscious mental models we create to express and understand the surrounding world. For example, the human brain receives raw information from the visual nerve, synthes the information from the eyes, enhances details and fills the lack of information such as visual blind spots. Not only that, the brain also creates a three-dimensional sense of space from the two-dimensional information received by the retina. You feel that you see a chair, but in fact, you just use the light scattered from the chair to build a mental image, or a model of the chair. The human brain is very good at building this model. If a person wears a pair of special glasses to turn the image presented in his eyes upside down, the brain will change the model to let him see objects that are not upside down - I hope this change will be completed before he wants to sit down.
In the exploration of the ultimate physical theory, there has never been a theory as promising and questionable as string theory. Although people are still trying to refer to the essence of M-theory, the single ultimate theory that seems to have been expected for a long time may not appear. To describe everything in the universe, we must choose different theories for different situations. Therefore, M theory is not a single theory in the usual sense, but a network of many theories. This is a bit similar to a map. To record the whole earth truthfully on a two-dimensional plane map, people must use a set of maps, each of which covers only one limited area.
These maps will overlap each other, and in these overlapping areas, different maps will show the same landforms. Similarly, different theories in the M-theory family may seem to be very different, but they can be regarded as some version of the same underlying theory. Where the scope of application overlaps, they will predict the same phenomenon, but no theory can cover all situations. As long as we develop a model describing the world and find it very successful, we will say that this theory describes "reality" or absolute truth.
But like the example of goldfish, M theory shows that the same physical scene can be described by different models, and each model has a different set of basic elements and basic concepts. Perhaps, to describe the whole universe, we must use different theories in different situations. Each theory may have a different understanding of "reality", but according to model-based reality, this diversity of "reality" is acceptable. It can't be said that which kind of "reality" is more real than other "reality".
This is not a unified theory traditionally expected by physicists, and it is also far from our daily understanding of reality. But this may be the true face of the universe.
Su Fei, who returned to the dormitory, finished reading the first chapter of the Axiom of Balance - the truth of the world, which shocked his cognition! The pictures about the earth in his memory are only fragments, but this does not affect his understanding of the content of this book. What is the reality of the world?