Short:
- why modern physics has reached a dead end.
- that Einstein and Hawking did not have time to explore.
- how to combine quantum mechanics and general relativity.
With the help of the Internet, you can learn everything - from the design of an internal combustion engine to the speed of expansion of the Universe. But there are questions, the answers to which are not known not only by Google, but even the greatest scientists of our time.
If you are suddenly lucky enough to talk with the latest Nobel Prize winners in physics, do not ask them about exoplanets and dark matter, they have already said this hundreds of times.
Better ask why different objects in our world obey different laws of physics. For example, why planets, stars and other large objects interact with each other, following certain laws, and particles at the smallest level, like atoms, obey only themselves.
Such a question will baffle the layman, and an educated person, answering it, will tell why modern science has come to a standstill, what is the difference between the Standard Model of physics and general theory of relativity (hereinafter - GR), and also why the meaning of Higgs bosons and string theory is actually the case is overrated.
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Despite these explanations, no one, including the resurrected Albert Einstein, will be able to explain to you the different nature of physical phenomena at the micro and macro levels. If you yourself can solve this problem - congratulations, you are the first author of the theory of everything, the greatest brain in the history of mankind, the laureate of all possible awards and the father (or mother) of the new physics.
But, before presenting to the world a revolutionary discovery, it is better to understand what the theory of everything means, what questions it should answer, and who came closest to its discovery.
The theory of everything is a combination of two of the most famous concepts of modern physics - the general relativity of Albert Einstein and quantum mechanics. The first theory describes everything that surrounds us in the form of space-time, as well as the interaction of all objects in the Universe using only gravity. Quantum mechanics, in turn, describes the interaction of elementary particles using three indicators at once - electromagnetic, and strong / weak nuclear interaction.
Thus, it talks about gravity and large objects like planets and stars, and quantum mechanics talks about elementary particles and their electromagnetic and weak / strong nuclear interactions. We will return to this a little later.
Newton's heir
For the first time, general relativity was voiced by Albert Einstein. At that time, a young employee of the Austrian Patent Office supplemented Newton's classical theory of gravitation and described all the unknowns in it. In particular, thanks to this discovery, people learned what gravity really is, and how it determines the interaction not only between the apple and the Earth, but also between the Sun and all the planets in the solar system.
Einstein suggested that space and time are interconnected and form a single space-time continuum - the basis for the emergence of the gravitational forces of all objects. Unlike Newton's theory, this continuum (or space-time) is flexible and can change its shape depending on the mass of objects and, accordingly, their energy.
Einstein's conjectures were only confirmed in practice a few years ago, when they noticed how light - and, accordingly, space-time - bends, passing near a massive object - the Sun - due to the influence of gravity. Even without this evidence, general relativity has long become the basis for modern physics, and so far no one has been able to offer a more substantiated explanation of the gravity of bodies and fields in space.
Despite this, space-time itself is still poorly understood, and scientists do not know how it is formed and what it consists of. Answers to these questions are just beginning to be sought in quantum mechanics - a theoretical branch of physics that describes the nature of physical phenomena at the level of molecules, atoms, electrons, photons and other tiny particles.
Quantum mechanics
According to Einstein's theory, absolutely all objects in the Universe should succumb to gravity. But, simultaneously with the discovery of general relativity, other scientists investigated how objects interact at the subatomic level.
It turned out that gravity on such a scale is completely useless. Instead, electromagnetic and weak / strong nuclear interactions became defining. With the help of these forces, the smallest particles interact with each other - photons, gluons and bosons.
But, scientists still do not know by what principles these particles interact, because they can have an extremely high energy density, and still do not lend themselves to gravity. Hence - such inexplicable phenomena as wave-particle dualism (manifestation of the properties of a wave by a particle), as well as the effect of an observer with the resulting in the form of a living and dead Schrödinger's cat.
Because of this, two worlds of physics collided with their foreheads - Einstein's, where all objects have certain properties, lend themselves to gravity, can be described and predictable, and quantum, where a completely different, unpredictable life rages, in which everything is constantly changing and levels the concept of space - time as such.
What needs to be done to unite these two worlds? We talked about gravity in general relativity and about the electromagnetic, strong / weak nuclear interaction in the Standard Model of physics. So, gravity is almost perfect, it allows us to understand almost everything that surrounds us, but it does not take into account the very inexplicable behavior of particles at the smallest level. Electromagnetic and strong / weak nuclear interaction is an alternative part of physics that hides new discoveries and represents a huge reservoir for research, but does not take into account the gravitational laws of general relativity.
The last stage in Albert Einstein's research and life was the creation of the theory of quantum gravity, which would unite all possible interactions of objects at the macro and micro levels, and also explain why they behave differently. Einstein was never able to find answers to these questions, and after him the possible unification of general relativity and quantum mechanics began to be called the theory of everything.
The theory of everything
In their quest for a theory of everything, scientists have investigated some of the most unusual objects in the universe - black holes. They are so heavy that they lend themselves to gravity, and so compressed that quantum effects can theoretically be observed when falling into a black hole. But, unfortunately, so far, apart from Hawking radiation, which is contrary to quantum mechanics, and a recent photo of the event horizon, black holes have helped little to modern science. Even if they do exist, reaching them is an almost impossible task for humans.
They began to search for a theory of everything on Earth using various thought experiments and properties of quantum mechanics and general relativity, which could potentially complement each other.
Today, perhaps the most popular and closest to the truth version of the theory of everything is string theory. It says that any particle is a one-dimensional string that vibrates in an 11-dimensional reality, and, depending on these vibrations, its mass and charge are determined.
Among others, the main property of a string is that it can transfer gravity at a quantum level. If such a theory were confirmed in practice, strings could be the first step towards the unification of quantum mechanics with general relativity. But, unfortunately, so far no one has been able to prove it and declare that the strings are the bearer of gravity at the subatomic level. Just like the recently discovered Higgs boson did not become the desired graviton.
Yes, we still do not know where the mass of many elementary particles comes from and by what principle they interact with each other, but this does not prevent modern physicists from proposing more and more new "theories of everything."
Recently, for example, physicists from China, Germany and Canada tested Wojciech Zurek's theory of quantum Darwinism, which supposedly explains how quantum particles leave their traces in the macrocosm available to us. But even in the case of confirmation that particles are in two states at the same time, this is only a confirmation of the interaction of quantum mechanics of general relativity, and in no way an explanation of this.
Another American theoretical physicist from the University of Maryland, Brian Swingle, undertook to describe the nature of the origin of space-time and decided that quantum entanglement could form the Einstein continuum. Swingle suggested that the four-dimensional structure of spacetime (length, width, depth, and time) could be encoded in three-dimensional quantum physics (with the same dimensions, only without time). According to the physicist, gravity and general relativity should be explained through the properties of quantum mechanics, and not vice versa, which made this experiment rather contradictory.
There are dozens of similar complex and even well-reasoned theories, but none of them can yet be called a theory of everything. Perhaps this is good, since man has been trying to understand how atoms and stars interact only for the last century, and the Universe has existed for almost 14 billion years.
The most famous modern researcher of the theory of everything - Stephen Hawking - at the end of his life came to the conclusion that it was impossible to find it. But, this did not become a disappointment for him, but, as he later said, on the contrary, led to the understanding that a person will develop constantly: “Now I am glad that our search for understanding will never end, and that we will always experience new discoveries … Without this, we would have stood still."
