Suppose both A and B are asked to prepare a meal. They each choose their favorite recipes, buy the ingredients at their local specialty stores, and follow the instructions carefully.

Assume that both A and B are asked to prepare a meal. A likes Chinese food, B likes Italian food. They each choose their favorite recipes, buy the ingredients at their local specialty stores, and follow the instructions carefully. But when they took the plate out of the oven, they were surprised that the meal they made was the same. We can imagine that A and B will definitely have questions. How can different ingredients make the same dish? What does it mean to even make Chinese or Italian cuisine? Is their way of preparing food completely wrong?

This is exactly the confusion that quantum physics scientists have experienced. They found many examples of two completely different descriptions of the same physical system. In physics, seasonings are particles and forces; recipes are mathematical formulas that interact with each other; cooking processes are quantization programs that convert equations into physical phenomena. Just like A and B, quantum physicists want to know how different recipes lead to the same results.

. Are there any choices naturally when formulating basic laws? Albert Einstein once had a famous idea: given some common principles, there is essentially a unique way to build a consistent, functioning universe. In the Einstein 's view, if we are deep enough about the essence of physics, we will find that there is and only one way to combine matter, radiation, force, time and space into a real world, just like the unique combination of the gears, springs, dials and hands of the clock to make the clock move accurately.

Currently, the standard model of particle physics is a strict construction mechanism with a small amount of components. However, the universe seems not to be the only one, but one of the infinite possibilities. We don't know why this particular combination of particles and forces is the basis of natural structure. Why are there six "flavors" quark , three "generations" neutrino and one Higgs boson ? In addition, the standard model has 19 natural constants, such as the mass and charge of electrons, which must be measured experimentally. The values ​​of these free parameters do not seem to have any deeper meaning. On the one hand, particle physics is an elegant miracle; on the other hand, it is a hypothetical content.

If our universe is just one of many universes, how do we face other universes? The current view can be seen as the opposite of Einstein's only cosmic dream. Modern physicists have accepted possibilities and tried to understand their all-encompassing logic and interconnections. They went from gold diggers to geographers and geologists, portraying the physical landscape in detail and studying the forces that shape it.

The game changer that leads to a change in perspective is string theory . At this moment, it is the only viable candidate for natural unity theory, able to describe all particles and forces, including gravity, while following the strict logic rules of quantum mechanics and relativity . The good news is that string theory has no free parameters. It doesn't make sense to ask which string theory can describe our universe, because there is only one. No additional properties lead to a fundamental result, and all numbers in nature should be determined by physics itself, they are not "natural constants" but just variables fixed by equations.

But this also has its disadvantages, the answers to string theory are broad and complex. This is not uncommon in physics. We traditionally use mathematical equations, and the solutions of these equations to distinguish basic laws. Usually, there are only a few laws, but there are countless solutions. Take Newton's law as an example. They are clear and beautiful, but they describe very broad phenomena, from gravity to the orbit of the moon. If you know the initial conditions of a particular system, these laws allow you to solve equations and predict what will happen next. We do not expect nor demand a single priority solution that describes everything.

In string theory, certain characteristics of physics, such as specific particles and forces, are actually solutions. They are determined by the shape and size of the hidden extra dimensions. The space for all these solutions is often referred to as "landscape".Even the most amazing landscapes look pale compared to this vast space. Although the geographical location of this landscape is only understood a little bit, we know it has a huge dimension to the continent. One of the most attractive features is that maybe everything is connected, with each two models connected by an uninterrupted path. By shaking the universe enough, we will be able to move from one possible world to another, changing what we think is immutable laws of nature and the special combination of fundamental particles that make up reality.

But how do we explore cosmic physics models that are likely to have hundreds of dimensions? It would be helpful to imagine a landscape as a largely undeveloped wilderness, which is mostly hidden under a thick layer of tricky complexity. Only at the edge can we find a place to live, everything is simple and beautiful. Here we find the basic model we fully understand. They have little value for describing the real world, but can serve as a convenient starting point for exploring local neighborhoods.

Quantum electrodynamics (QED) is a good example of how matter interacts with light. This model has a separate parameter called the fine structure constant α, which measures the intensity of the force between two electrons. Nearly 1/137 on the number. In QED, all processes can be regarded as a result of basic interactions. For example, the repulsion between two electrons can be imagined as the exchange of photons . QED requires us to consider all possible ways in which two electrons may exchange photons, which actually means that physicists must solve extremely complex problems. But this theory also provides a way out: each additional photon exchange adds a term, including α to an additional amount. Since this is a relatively small number, terms with many exchanges will only make a little difference. They can be ignored, approximate the actual values.

We found these weak coupling theories at the edge of the landscape. The intensity of forces in theory is small, making it meaningful to discuss elementary particles and calculate their interactions. But if we leave the environment in front of us and explore deeper into the wilderness, then the coupling becomes large and each additional item becomes more important. Now we can no longer distinguish individual particles. Instead, they will dissolve into an entangled energy net, just like the ingredients of cakes in a hot oven.

However, not everything disappeared. Sometimes, the road through the dark wilderness reaches another edge. That is, there is another well-controlled model consisting of completely different particles and forces. In this case, for the same basic physics, there are two different recipes, just like A and B dishes. These complementary descriptions are called dual models, and the relationship between them is duality. We can regard these dualities as a general summary of the famous wave-particle dualities found in Heisenberg .

standard model

Why is this so exciting for physics? First, many models are part of a huge interconnected space, and this conclusion is one of the most amazing results of modern quantum physics . This is a change of opinion that can be expressed by the term "paradigm shift". It tells us that instead of exploring individual islands, we discovered a huge continent. In a sense, by studying one model in depth enough, we can understand all models. We can explore how these models are correlated and shed light on their common structure. What is important is that this phenomenon is largely independent of whether string theory describes the real world. It is an inherent characteristic left by quantum physics, and it exists no matter what the future theory of everything is.

A more compelling conclusion is that all traditional descriptions of basic physics must be abandoned. Particles, fields, forces, and symmetry are all products of a simple existence at the edge of this extremely complex landscape. Thinking about physics from the basic building blocks seems wrong, or at least limited.Perhaps there is a fundamental new framework that unifies the basic laws of nature and ignores all familiar concepts. The mathematical complexity and consistency of string theory are powerful motivations for this compelling view. But to quote the words of Niels Bohr, a master of quantum physics, there are very few ideas about replacing particles and fields that are true at present. But physics is ready to throw away old recipes and embrace modern fusion cooking.