The theory according to which everything. Quantum physics for dummies: the essence in simple words
The golden foliage of the trees shone brightly. The rays of the evening sun touched the thinned tops. Light broke through the branches and staged a spectacle of bizarre figures flickering on the wall of the university "kapterka".
Sir Hamilton's pensive gaze moved slowly, watching the play of chiaroscuro. In the head of the Irish mathematician there was a real melting pot of thoughts, ideas and conclusions. He was well aware that the explanation of many phenomena with the help of Newtonian mechanics is like the play of shadows on the wall, deceptively intertwining figures and leaving many questions unanswered. “Maybe it's a wave… or maybe it's a stream of particles,” the scientist mused, “or light is a manifestation of both phenomena. Like figures woven from shadow and light.
The beginning of quantum physics
It is interesting to watch great people and try to understand how great ideas are born that change the course of evolution of all mankind. Hamilton is one of those who stood at the origins of quantum physics. Fifty years later, at the beginning of the twentieth century, many scientists were engaged in the study of elementary particles. The knowledge gained was inconsistent and uncompiled. However, the first shaky steps were taken.
Understanding the microworld at the beginning of the 20th century
In 1901, the first model of the atom was presented and its failure was shown, from the standpoint of ordinary electrodynamics. During the same period, Max Planck and Niels Bohr published many works on the nature of the atom. Despite their complete understanding of the structure of the atom did not exist.
A few years later, in 1905, a little-known German scientist Albert Einstein published a report on the possibility of the existence of a light quantum in two states - wave and corpuscular (particles). In his work, arguments were given explaining the reason for the failure of the model. However, Einstein's vision was limited by the old understanding of the model of the atom.
After numerous works by Niels Bohr and his colleagues in 1925, a new direction was born - a kind of quantum mechanics. A common expression - "quantum mechanics" appeared thirty years later.
What do we know about quanta and their quirks?
Today, quantum physics has gone far enough. Many different phenomena have been discovered. But what do we really know? The answer is presented by one modern scientist. "One can either believe in quantum physics or not understand it," is the definition. Think about it for yourself. It will suffice to mention such a phenomenon as quantum entanglement of particles. This phenomenon has plunged the scientific world into a position of complete bewilderment. Even more shocking was that the resulting paradox is incompatible with Einstein.
The effect of quantum entanglement of photons was first discussed in 1927 at the fifth Solvay Congress. A heated argument arose between Niels Bohr and Einstein. The paradox of quantum entanglement has completely changed the understanding of the essence of the material world.
It is known that all bodies consist of elementary particles. Accordingly, all the phenomena of quantum mechanics are reflected in the ordinary world. Niels Bohr said that if we do not look at the moon, then it does not exist. Einstein considered this unreasonable and believed that the object exists independently of the observer.
When studying the problems of quantum mechanics, one should understand that its mechanisms and laws are interconnected and do not obey classical physics. Let's try to understand the most controversial area - the quantum entanglement of particles.
The theory of quantum entanglement
To begin with, it is worth understanding that quantum physics is like a bottomless well in which you can find anything you want. The phenomenon of quantum entanglement at the beginning of the last century was studied by Einstein, Bohr, Maxwell, Boyle, Bell, Planck and many other physicists. Throughout the twentieth century, thousands of scientists around the world actively studied it and experimented.
The world is subject to the strict laws of physics
Why such an interest in the paradoxes of quantum mechanics? Everything is very simple: we live, obeying certain laws of the physical world. The ability to “bypass” predestination opens a magical door behind which everything becomes possible. For example, the concept of "Schrödinger's Cat" leads to the control of matter. It will also become possible to teleport information, which causes quantum entanglement. The transmission of information will become instantaneous, regardless of distance.
This issue is still under study, but has a positive trend.
Analogy and understanding
What is unique about quantum entanglement, how to understand it, and what happens with it? Let's try to figure it out. This will require some thought experiment. Imagine that you have two boxes in your hands. Each of them contains one ball with a stripe. Now we give one box to the astronaut, and he flies to Mars. As soon as you open the box and see that the stripe on the ball is horizontal, then in the other box the ball will automatically have a vertical stripe. This will be quantum entanglement expressed in simple words: one object predetermines the position of another.
However, it should be understood that this is only a superficial explanation. In order to get quantum entanglement, it is necessary that the particles have the same origin, like twins.
It is very important to understand that the experiment will be disrupted if someone before you had the opportunity to look at at least one of the objects.
Where can quantum entanglement be used?
The principle of quantum entanglement can be used to transmit information over long distances instantly. Such a conclusion contradicts Einstein's theory of relativity. It says that the maximum speed of movement is inherent only in light - three hundred thousand kilometers per second. Such transfer of information makes possible the existence of physical teleportation.
Everything in the world is information, including matter. Quantum physicists came to this conclusion. In 2008, based on a theoretical database, it was possible to see quantum entanglement with the naked eye.
This once again indicates that we are on the verge of great discoveries - movement in space and time. Time in the Universe is discrete, so instantaneous movement over vast distances makes it possible to get into different time densities (based on the hypotheses of Einstein, Bohr). Perhaps in the future it will be a reality just like the mobile phone is today.
Aether dynamics and quantum entanglement
According to some leading scientists, quantum entanglement is explained by the fact that space is filled with some kind of ether - black matter. Any elementary particle, as we know, exists in the form of a wave and a corpuscle (particle). Some scientists believe that all particles are on the "canvas" of dark energy. This is not easy to understand. Let's try to figure it out in another way - the association method.
Imagine yourself at the seaside. Light breeze and a slight breeze. See the waves? And somewhere in the distance, in the reflections of the rays of the sun, a sailboat is visible.
The ship will be our elementary particle, and the sea will be ether (dark energy).
The sea can be in motion in the form of visible waves and drops of water. In the same way, all elementary particles can be just a sea (its integral part) or a separate particle - a drop.
This is a simplified example, everything is somewhat more complicated. Particles without the presence of an observer are in the form of a wave and do not have a specific location.
The white sailboat is a distinguished object, it differs from the surface and structure of the sea water. In the same way, there are "peaks" in the ocean of energy that we can perceive as a manifestation of the forces known to us that have shaped the material part of the world.
The microworld lives by its own laws
The principle of quantum entanglement can be understood if we take into account the fact that elementary particles are in the form of waves. Without a specific location and characteristics, both particles are in an ocean of energy. At the moment the observer appears, the wave “turns” into an object accessible to touch. The second particle, observing the system of equilibrium, acquires opposite properties.
The described article is not aimed at capacious scientific descriptions of the quantum world. The ability to comprehend an ordinary person is based on the availability of understanding of the material presented.
Physics of elementary particles studies the entanglement of quantum states based on the spin (rotation) of an elementary particle.
In scientific language (simplified) - quantum entanglement is defined by different spins. In the process of observing objects, scientists saw that only two spins can exist - along and across. Oddly enough, in other positions, the particles do not “pose” to the observer.
New hypothesis - a new view of the world
The study of the microcosm - the space of elementary particles - gave rise to many hypotheses and assumptions. The effect of quantum entanglement prompted scientists to think about the existence of some kind of quantum microlattice. In their opinion, at each node - the point of intersection - there is a quantum. All energy is an integral lattice, and the manifestation and movement of particles is possible only through the nodes of the lattice.
The size of the "window" of such a grating is quite small, and measurement with modern equipment is impossible. However, in order to confirm or refute this hypothesis, scientists decided to study the motion of photons in a spatial quantum lattice. The bottom line is that a photon can move either straight or in zigzags - along the diagonal of the lattice. In the second case, having overcome a greater distance, he will spend more energy. Accordingly, it will differ from a photon moving in a straight line.
Perhaps, over time, we will learn that we live in a spatial quantum grid. Or it might turn out to be wrong. However, it is the principle of quantum entanglement that indicates the possibility of the existence of a lattice.
In simple terms, in a hypothetical spatial “cube”, the definition of one facet carries with it a clear opposite meaning of the other. This is the principle of preserving the structure of space - time.
Epilogue
To understand the magical and mysterious world of quantum physics, it is worth taking a close look at the development of science over the past five hundred years. It used to be that the Earth was flat, not spherical. The reason is obvious: if you take its shape as round, then water and people will not be able to resist.
As we can see, the problem existed in the absence of a complete vision of all acting forces. It is possible that modern science lacks a vision of all acting forces to understand quantum physics. Vision gaps give rise to a system of contradictions and paradoxes. Perhaps the magical world of quantum mechanics contains the answers to the questions posed.
Welcome to the blog! I am very glad to you!
Surely you have heard many times about the inexplicable mysteries of quantum physics and quantum mechanics. Its laws fascinate with mysticism, and even the physicists themselves admit that they do not fully understand them. On the one hand, it is curious to understand these laws, but on the other hand, there is no time to read multi-volume and complex books on physics. I understand you very much, because I also love knowledge and the search for truth, but there is sorely not enough time for all the books. You are not alone, so many inquisitive people type in the search line: “quantum physics for dummies, quantum mechanics for dummies, quantum physics for beginners, quantum mechanics for beginners, basics of quantum physics, basics of quantum mechanics, quantum physics for children, what is quantum Mechanics". This post is for you.
You will understand the basic concepts and paradoxes of quantum physics. From the article you will learn:
- What is interference?
- What is spin and superposition?
- What is "measurement" or "wavefunction collapse"?
- What is quantum entanglement (or quantum teleportation for dummies)? (see article)
- What is the Schrödinger's Cat thought experiment? (see article)
What is quantum physics and quantum mechanics?
Quantum mechanics is part of quantum physics.
Why is it so difficult to understand these sciences? The answer is simple: quantum physics and quantum mechanics (a part of quantum physics) study the laws of the microworld. And these laws are absolutely different from the laws of our macrocosm. Therefore, it is difficult for us to imagine what happens to electrons and photons in the microcosm.
An example of the difference between the laws of macro- and microworlds: in our macrocosm, if you put a ball into one of the 2 boxes, then one of them will be empty, and the other - a ball. But in the microcosm (if instead of a ball - an atom), an atom can be simultaneously in two boxes. This has been repeatedly confirmed experimentally. Isn't it hard to put it in your head? But you can't argue with the facts.
One more example. You photographed a fast racing red sports car and in the photo you saw a blurry horizontal strip, as if the car at the time of the photo was from several points in space. Despite what you see in the photo, you are still sure that the car was at the moment when you photographed it. in one specific place in space. Not so in the micro world. An electron that revolves around the nucleus of an atom does not actually revolve, but located simultaneously at all points of the sphere around the nucleus of an atom. Like a loosely wound ball of fluffy wool. This concept in physics is called "electronic cloud" .
A small digression into history. For the first time, scientists thought about the quantum world when, in 1900, the German physicist Max Planck tried to find out why metals change color when heated. It was he who introduced the concept of quantum. Before that, scientists thought that light traveled continuously. The first person to take Planck's discovery seriously was the then unknown Albert Einstein. He realized that light is not only a wave. Sometimes it behaves like a particle. Einstein received the Nobel Prize for his discovery that light is emitted in portions, quanta. A quantum of light is called a photon ( photon, Wikipedia) .
In order to make it easier to understand the laws of quantum physics And mechanics (Wikipedia), it is necessary, in a certain sense, to abstract from the laws of classical physics familiar to us. And imagine that you dived, like Alice, down the rabbit hole, into Wonderland.
And here is a cartoon for children and adults. Talks about the fundamental experiment of quantum mechanics with 2 slits and an observer. Lasts only 5 minutes. Watch it before we delve into the basic questions and concepts of quantum physics.
Quantum physics for dummies video. In the cartoon, pay attention to the "eye" of the observer. It has become a serious mystery for physicists.
What is interference?
At the beginning of the cartoon, using the example of a liquid, it was shown how waves behave - alternating dark and light vertical stripes appear on the screen behind a plate with slots. And in the case when discrete particles (for example, pebbles) are “shot” at the plate, they fly through 2 slots and hit the screen directly opposite the slots. And "draw" on the screen only 2 vertical stripes.
Light interference- This is the "wave" behavior of light, when a lot of alternating bright and dark vertical stripes are displayed on the screen. And those vertical stripes called an interference pattern.
In our macrocosm, we often observe that light behaves like a wave. If you put your hand in front of the candle, then on the wall there will be not a clear shadow from the hand, but with blurry contours.
So, it's not all that difficult! It is now quite clear to us that light has a wave nature, and if 2 slits are illuminated with light, then on the screen behind them we will see an interference pattern. Now consider the 2nd experiment. This is the famous Stern-Gerlach experiment (which was carried out in the 20s of the last century).
In the installation described in the cartoon, they did not shine with light, but “shot” with electrons (as separate particles). Then, at the beginning of the last century, physicists around the world believed that electrons are elementary particles of matter and should not have a wave nature, but the same as pebbles. After all, electrons are elementary particles of matter, right? That is, if they are “thrown” into 2 slots, like pebbles, then on the screen behind the slots we should see 2 vertical stripes.
But… The result was stunning. Scientists saw an interference pattern - a lot of vertical stripes. That is, electrons, like light, can also have a wave nature, they can interfere. On the other hand, it became clear that light is not only a wave, but also a particle - a photon (from the historical background at the beginning of the article we learned that Einstein received the Nobel Prize for this discovery).
You may remember that at school we were told in physics about "particle-wave dualism"? It means that when it comes to very small particles (atoms, electrons) of the microworld, then they are both waves and particles
It is today that you and I are so smart and understand that the 2 experiments described above - firing electrons and illuminating slots with light - are one and the same. Because we're firing quantum particles at the slits. Now we know that both light and electrons are of quantum nature, they are both waves and particles at the same time. And at the beginning of the 20th century, the results of this experiment were a sensation.
Attention! Now let's move on to a more subtle issue.
We shine on our slits with a stream of photons (electrons) - and we see an interference pattern (vertical stripes) behind the slits on the screen. It is clear. But we are interested to see how each of the electrons flies through the slit.
Presumably, one electron flies to the left slit, the other to the right. But then 2 vertical stripes should appear on the screen directly opposite the slots. Why is an interference pattern obtained? Maybe the electrons somehow interact with each other already on the screen after flying through the slits. And the result is such a wave pattern. How can we follow this?
We will throw electrons not in a beam, but one at a time. Drop it, wait, drop the next one. Now, when the electron flies alone, it will no longer be able to interact on the screen with other electrons. We will register on the screen each electron after the throw. One or two, of course, will not “paint” a clear picture for us. But when one by one we send a lot of them into the slots, we will notice ... oh horror - they again “drawn” an interference wave pattern!
We start to slowly go crazy. After all, we expected that there would be 2 vertical stripes opposite the slots! It turns out that when we threw photons one at a time, each of them passed, as it were, through 2 slits at the same time and interfered with itself. Fantastic! We will return to the explanation of this phenomenon in the next section.
What is spin and superposition?
We now know what interference is. This is the wave behavior of micro particles - photons, electrons, other micro particles (let's call them photons for simplicity from now on).
As a result of the experiment, when we threw 1 photon into 2 slits, we realized that it flies as if through two slits at the same time. How else to explain the interference pattern on the screen?
But how to imagine a picture that a photon flies through two slits at the same time? There are 2 options.
- 1st option: photon, like a wave (like water) "floats" through 2 slits at the same time
- 2nd option: a photon, like a particle, flies simultaneously along 2 trajectories (not even two, but all at once)
In principle, these statements are equivalent. We have arrived at the "path integral". This is Richard Feynman's formulation of quantum mechanics.
By the way, exactly Richard Feynman belongs to the well-known expression that we can confidently say that no one understands quantum mechanics
But this expression of his worked at the beginning of the century. But now we are smart and we know that a photon can behave both as a particle and as a wave. That he can fly through 2 slots at the same time in some way that is incomprehensible to us. Therefore, it will be easy for us to understand the following important statement of quantum mechanics:
Strictly speaking, quantum mechanics tells us that this photon behavior is the rule, not the exception. Any quantum particle is, as a rule, in several states or at several points in space simultaneously.
Objects of the macroworld can only be in one specific place and in one specific state. But a quantum particle exists according to its own laws. And she doesn't care that we don't understand them. This is the point.
It remains for us to simply accept as an axiom that the "superposition" of a quantum object means that it can be on 2 or more trajectories at the same time, at 2 or more points at the same time
The same applies to another photon parameter - spin (its own angular momentum). Spin is a vector. A quantum object can be thought of as a microscopic magnet. We are used to the fact that the magnet vector (spin) is either directed up or down. But the electron or photon again tells us: “Guys, we don’t care what you are used to, we can be in both spin states at once (vector up, vector down), just like we can be on 2 trajectories at the same time or at 2 points at the same time!
What is "measurement" or "wavefunction collapse"?
It remains for us a little - to understand what is "measurement" and what is "collapse of the wave function".
wave function is a description of the state of a quantum object (our photon or electron).
Suppose we have an electron, it flies to itself in an indeterminate state, its spin is directed both up and down at the same time. We need to measure his condition.
Let's measure using a magnetic field: electrons whose spin was directed in the direction of the field will deviate in one direction, and electrons whose spin is directed against the field will deviate in the other direction. Photons can also be sent to a polarizing filter. If the spin (polarization) of a photon is +1, it passes through the filter, and if it is -1, then it does not.
Stop! This is where the question inevitably arises: before the measurement, after all, the electron did not have any particular spin direction, right? Was he in all states at the same time?
This is the trick and sensation of quantum mechanics.. As long as you do not measure the state of a quantum object, it can rotate in any direction (have any direction of its own angular momentum vector - spin). But at the moment when you measured his state, he seems to be deciding which spin vector to take.
This quantum object is so cool - it makes a decision about its state. And we cannot predict in advance what decision it will make when it flies into the magnetic field in which we measure it. The probability that he decides to have a spin vector "up" or "down" is 50 to 50%. But as soon as he decides, he is in a certain state with a specific spin direction. The reason for his decision is our "dimension"!
This is called " wave function collapse". The wave function before the measurement was indefinite, i.e. the electron spin vector was simultaneously in all directions, after the measurement, the electron fixed a certain direction of its spin vector.
Attention! An excellent example-association from our macrocosm for understanding:
Spin a coin on the table like a top. While the coin is spinning, it has no specific meaning - heads or tails. But as soon as you decide to "measure" this value and slam the coin with your hand, this is where you get the specific state of the coin - heads or tails. Now imagine that this coin decides what value to "show" you - heads or tails. The electron behaves approximately the same way.
Now remember the experiment shown at the end of the cartoon. When photons were passed through the slits, they behaved like a wave and showed an interference pattern on the screen. And when the scientists wanted to fix (measure) the moment when photons passed through the slit and put an “observer” behind the screen, the photons began to behave not like waves, but like particles. And “drawn” 2 vertical stripes on the screen. Those. at the moment of measurement or observation, quantum objects themselves choose what state they should be in.
Fantastic! Is not it?
But that is not all. Finally we got to the most interesting.
But ... it seems to me that there will be an overload of information, so we will consider these 2 concepts in separate posts:
- What's happened ?
- What is a thought experiment.
And now, do you want the information to be put on the shelves? Watch a documentary produced by the Canadian Institute for Theoretical Physics. In 20 minutes, it will tell you very briefly and in chronological order about all the discoveries of quantum physics, starting with the discovery of Planck in 1900. And then they will tell you what practical developments are currently being carried out on the basis of knowledge of quantum physics: from the most accurate atomic clocks to super-fast calculations of a quantum computer. I highly recommend watching this movie.
See you!
I wish you all inspiration for all your plans and projects!
P.S.2 Write your questions and thoughts in the comments. Write, what other questions on quantum physics are you interested in?
P.S.3 Subscribe to the blog - the subscription form under the article.
I think it's safe to say that no one understands quantum mechanics.
Physicist Richard Feynman
It is no exaggeration to say that the invention of semiconductor devices was a revolution. Not only is this an impressive technological achievement, but it also paved the way for events that will change modern society forever. Semiconductor devices are used in all kinds of microelectronic devices, including computers, certain types of medical diagnostic and treatment equipment, and popular telecommunications devices.
But behind this technological revolution is even more, a revolution in general science: the field quantum theory. Without this leap in understanding the natural world, the development of semiconductor devices (and more advanced electronic devices under development) would never have succeeded. Quantum physics is an incredibly complex branch of science. This chapter only provides a brief overview. When scientists like Feynman say "nobody understands [it]", you can be sure that this is a really difficult topic. Without a basic understanding of quantum physics, or at least an understanding of the scientific discoveries that led to their development, it is impossible to understand how and why semiconductor electronic devices work. Most electronics textbooks try to explain semiconductors in terms of "classical physics", making them even more confusing to understand as a result.
Many of us have seen atomic model diagrams that look like the picture below.
Rutherford atom: negative electrons revolve around a small positive nucleus
Tiny particles of matter called protons And neutrons, make up the center of the atom; electrons revolve like planets around a star. The nucleus carries a positive electrical charge due to the presence of protons (neutrons have no electrical charge), while the balancing negative charge of an atom resides in the orbiting electrons. Negative electrons are attracted to positive protons like planets are attracted to the Sun, but the orbits are stable due to the movement of electrons. We owe this popular model of the atom to the work of Ernest Rutherford, who experimentally determined around 1911 that the positive charges of atoms are concentrated in a tiny, dense nucleus, and not evenly distributed along the diameter, as explorer J. J. Thomson had previously assumed.
Rutherford's scattering experiment consists of bombarding a thin gold foil with positively charged alpha particles, as shown in the figure below. Young graduate students H. Geiger and E. Marsden got unexpected results. The trajectory of some alpha particles was deviated by a large angle. Some alpha particles were scattered backwards, at an angle of almost 180°. Most of the particles passed through the gold foil without changing their trajectory, as if there was no foil at all. The fact that several alpha particles experienced large deviations in their trajectory indicates the presence of nuclei with a small positive charge.
Rutherford scattering: a beam of alpha particles is scattered by thin gold foil Although Rutherford's model of the atom was supported by experimental data better than Thomson's, it was still imperfect. Further attempts were made to determine the structure of the atom, and these efforts helped pave the way for the strange discoveries of quantum physics. Today our understanding of the atom is a bit more complex. Yet despite the revolution of quantum physics and its contribution to our understanding of the structure of the atom, Rutherford's depiction of the solar system as the structure of an atom has taken root in popular consciousness to the extent that it persists in the fields of education, even if it is misplaced.
Consider this brief description of the electrons in an atom, taken from a popular electronics textbook:
The spinning negative electrons are attracted to the positive nucleus, which leads us to the question of why the electrons don't fly into the nucleus of the atom. The answer is that the rotating electrons remain in their stable orbit due to two equal but opposite forces. The centrifugal force acting on the electrons is directed outward, and the attractive force of the charges is trying to pull the electrons towards the nucleus.
In accordance with Rutherford's model, the author considers electrons to be solid pieces of matter occupying round orbits, their inward attraction to the oppositely charged nucleus is balanced by their movement. The use of the term "centrifugal force" is technically incorrect (even for orbiting planets), but this is easily forgiven due to the popular acceptance of the model: in fact, there is no such thing as force, repulsiveany rotating body from the center of its orbit. This seems to be so because the body's inertia tends to keep it moving in a straight line, and since the orbit is a constant deviation (acceleration) from rectilinear motion, there is a constant inertial reaction to any force that attracts the body to the center of the orbit (centripetal), whether either gravity, electrostatic attraction, or even the tension of a mechanical bond.
However, the real problem with this explanation in the first place is the idea of electrons moving in circular orbits. A proven fact that accelerated electric charges emit electromagnetic radiation, this fact was known even in Rutherford's time. Since rotational motion is a form of acceleration (a rotating object in constant acceleration, pulling the object away from its normal rectilinear motion), electrons in a rotating state must emit radiation like mud from a spinning wheel. Electrons accelerated along circular paths in particle accelerators called synchrotrons are known to do this, and the result is called synchrotron radiation. If electrons were to lose energy in this way, their orbits would eventually be disrupted, and as a result they would collide with a positively charged nucleus. However, inside atoms this usually does not happen. Indeed, electronic "orbits" are surprisingly stable over a wide range of conditions.
In addition, experiments with "excited" atoms have shown that electromagnetic energy is emitted by an atom only at certain frequencies. Atoms are "excited" by external influences such as light, known to absorb energy and return electromagnetic waves at certain frequencies, much like a tuning fork that does not ring at a certain frequency until it is struck. When the light emitted by an excited atom is divided by a prism into its component frequencies (colors), individual lines of colors in the spectrum are found, the spectral line pattern is unique to a chemical element. This phenomenon is commonly used to identify chemical elements, and even to measure the proportions of each element in a compound or chemical mixture. According to the solar system of Rutherford's atomic model (relative to electrons, as pieces of matter, freely rotating in an orbit with some radius) and the laws of classical physics, excited atoms must return energy in an almost infinite range of frequencies, and not at selected frequencies. In other words, if Rutherford's model was correct, then there would be no "tuning fork" effect, and the color spectrum emitted by any atom would appear as a continuous band of colors, rather than as several separate lines.
Bohr's model of the hydrogen atom (with the orbits drawn to scale) assumes that electrons are only in discrete orbits. Electrons moving from n=3,4,5 or 6 to n=2 are displayed on a series of Balmer spectral lines A researcher named Niels Bohr tried to improve Rutherford's model after studying it in Rutherford's laboratory for several months in 1912. Trying to reconcile the results of other physicists (in particular, Max Planck and Albert Einstein), Bohr suggested that each electron had a certain, specific amount of energy, and that their orbits were distributed in such a way that each of them could occupy certain places around the nucleus, like balls. , fixed on circular paths around the nucleus, and not as free-moving satellites, as previously assumed (figure above). In deference to the laws of electromagnetism and accelerating charges, Bohr referred to "orbits" as stationary states to avoid the interpretation that they were mobile.
Although Bohr's ambitious attempt to rethink the structure of the atom, which was more consistent with experimental data, was a milestone in physics, it was not completed. His mathematical analysis predicted the results of experiments better than those performed according to previous models, but there were still unanswered questions about whether Why the electrons must behave in such a strange way. The statement that electrons existed in stationary quantum states around the nucleus correlated better with experimental data than Rutherford's model, but did not say what causes the electrons to take on these special states. The answer to this question was to come from another physicist, Louis de Broglie, some ten years later.
De Broglie suggested that electrons, like photons (particles of light), have both the properties of particles and the properties of waves. Based on this assumption, he suggested that the analysis of rotating electrons in terms of waves is better than in terms of particles, and can give more insight into their quantum nature. Indeed, another breakthrough was made in understanding.
A string vibrating at a resonant frequency between two fixed points forms a standing wave The atom, according to de Broglie, consisted of standing waves, a phenomenon well known to physicists in various forms. Like the plucked string of a musical instrument (pictured above), vibrating at a resonant frequency, with "knots" and "anti-knots" in stable places along its length. De Broglie imagined electrons around atoms as waves curved into a circle (figure below).
"Rotating" electrons like a standing wave around the nucleus, (a) two cycles in an orbit, (b) three cycles in an orbit Electrons can only exist in certain, specific "orbits" around the nucleus, because they are the only distances where the ends of the wave coincide. At any other radius, the wave will collide destructively with itself and thus cease to exist.
De Broglie's hypothesis provided both a mathematical framework and a convenient physical analogy to explain the quantum states of electrons within an atom, but his model of the atom was still incomplete. For several years, physicists Werner Heisenberg and Erwin Schrödinger, working independently, have been working on de Broglie's concept of wave-particle duality in order to create more rigorous mathematical models of subatomic particles.
This theoretical advance from de Broglie's primitive standing wave model to models of the Heisenberg matrix and the Schrödinger differential equation has been given the name of quantum mechanics, and it has introduced a rather shocking feature into the world of subatomic particles: the sign of probability, or uncertainty. According to the new quantum theory, it was impossible to determine the exact position and exact momentum of a particle at one moment. A popular explanation for this "uncertainty principle" was that there was a measurement error (that is, by trying to accurately measure the position of an electron, you interfere with its momentum, and therefore cannot know what it was before you started measuring the position, and vice versa). The sensational conclusion of quantum mechanics is that particles do not have exact positions and momenta, and because of the relationship of these two quantities, their combined uncertainty will never decrease below a certain minimum value.
This form of "uncertainty" connection also exists in fields other than quantum mechanics. As discussed in the "Mixed Frequency AC Signals" chapter in Volume 2 of this book series, there are mutually exclusive relationships between the confidence in the time domain data of a waveform and its frequency domain data. Simply put, the more we know its component frequencies, the less accurately we know its amplitude over time, and vice versa. Quoting myself:
A signal of infinite duration (an infinite number of cycles) can be analyzed with absolute accuracy, but the fewer cycles available to the computer for analysis, the less accurate the analysis ... The fewer periods of the signal, the less accurate its frequency. Taking this concept to its logical extreme, a short pulse (not even a full period of a signal) doesn't really have a defined frequency, it's an infinite range of frequencies. This principle is common to all wave phenomena, and not only to variable voltages and currents.
To accurately determine the amplitude of a changing signal, we must measure it in a very short amount of time. However, doing this limits our knowledge of the frequency of the wave (a wave in quantum mechanics does not need to be similar to a sine wave; such similarity is a special case). On the other hand, in order to determine the frequency of a wave with great accuracy, we must measure it over a large number of periods, which means that we will lose sight of its amplitude at any given moment. Thus, we cannot simultaneously know the instantaneous amplitude and all frequencies of any wave with unlimited accuracy. Another oddity, this uncertainty is much greater than the inaccuracy of the observer; it is in the very nature of the wave. This is not the case, although it would be possible, given the appropriate technology, to provide accurate measurements of both instantaneous amplitude and frequency simultaneously. In a literal sense, a wave cannot have the exact instantaneous amplitude and the exact frequency at the same time.
The minimum uncertainty of particle position and momentum expressed by Heisenberg and Schrödinger has nothing to do with a limitation in measurement; rather, it is an intrinsic property of the nature of the wave-particle duality of the particle. Therefore, electrons do not actually exist in their "orbits" as well-defined particles of matter, or even as well-defined waveforms, but rather as "clouds" - a technical term. wave function probability distributions, as if each electron were "scattered" or "smeared out" over a range of positions and momenta.
This radical view of electrons as indeterminate clouds initially contradicts the original principle of the quantum states of electrons: electrons exist in discrete, definite "orbits" around the nucleus of an atom. This new view, after all, was the discovery that led to the formation and explanation of quantum theory. How strange it seems that a theory created to explain the discrete behavior of electrons ends up declaring that electrons exist as "clouds" and not as separate pieces of matter. However, the quantum behavior of electrons does not depend on electrons having certain values of coordinates and momentum, but on other properties called quantum numbers. In essence, quantum mechanics dispenses with the common concepts of absolute position and absolute moment, and replaces them with absolute concepts of types that have no analogues in common practice.
Even if electrons are known to exist in disembodied, "cloudy" forms of distributed probability, rather than separate pieces of matter, these "clouds" have slightly different characteristics. Any electron in an atom can be described by four numerical measures (the quantum numbers mentioned earlier), called main (radial), orbital (azimuth), magnetic And spin numbers. Below is a brief overview of the meaning of each of these numbers:
Principal (radial) quantum number: denoted by a letter n, this number describes the shell on which the electron resides. The electron "shell" is a region of space around the nucleus of an atom in which electrons can exist, corresponding to de Broglie and Bohr's stable "standing wave" models. Electrons can "jump" from shell to shell, but cannot exist between them.
The principal quantum number must be a positive integer (greater than or equal to 1). In other words, the principal quantum number of an electron cannot be 1/2 or -3. These integers were not chosen arbitrarily, but through experimental evidence of the light spectrum: the different frequencies (colors) of light emitted by excited hydrogen atoms follow a mathematical relationship depending on specific integer values, as shown in the figure below.
Each shell has the ability to hold multiple electrons. An analogy for electron shells is the concentric rows of seats in an amphitheater. Just as a person sitting in an amphitheater must choose a row to sit down (he cannot sit between the rows), electrons must "choose" a particular shell in order to "sit down". Like rows in an amphitheatre, the outer shells hold more electrons than the shells closer to the center. Also, the electrons tend to find the smallest available shell, just as people in an amphitheater look for the place closest to the central stage. The higher the shell number, the more energy the electrons have on it.
The maximum number of electrons that any shell can hold is described by the equation 2n 2 , where n is the principal quantum number. Thus, the first shell (n = 1) can contain 2 electrons; the second shell (n = 2) - 8 electrons; and the third shell (n = 3) - 18 electrons (figure below).
The main quantum number n and the maximum number of electrons are related by the formula 2(n 2). Orbits are not to scale. The electron shells in the atom were denoted by letters rather than numbers. The first shell (n = 1) was designated K, the second shell (n = 2) L, the third shell (n = 3) M, the fourth shell (n = 4) N, the fifth shell (n = 5) O, the sixth shell ( n = 6) P, and the seventh shell (n = 7) B.
Orbital (azimuth) quantum number: a shell composed of subshells. Some may find it more convenient to think of subshells as simple sections of shells, like lanes dividing a road. Subshells are much weirder. Subshells are regions of space where electron "clouds" can exist, and in fact different subshells have different shapes. The first subshell is in the shape of a ball (Figure below (s)), which makes sense when visualized as an electron cloud surrounding the nucleus of an atom in three dimensions.
The second subshell resembles a dumbbell, consisting of two "petals" connected at one point near the center of the atom (figure below (p)).
The third subshell usually resembles a set of four "petals" grouped around the nucleus of an atom. These subshell shapes resemble graphical antenna patterns with bulbous lobes extending from the antenna in various directions (Figure below (d)).
Orbitals: (s) triple symmetry;
(p) Shown: p x , one of three possible orientations (p x , p y , p z), along the respective axes;
(d) Shown: d x 2 -y 2 is similar to d xy , d yz , d xz . Shown: d z 2 . Number of possible d-orbitals: five.
Valid values for the orbital quantum number are positive integers, as for the principal quantum number, but also include zero. These quantum numbers for electrons are denoted by the letter l. The number of subshells is equal to the principal quantum number of the shell. Thus, the first shell (n = 1) has one subshell with number 0; the second shell (n = 2) has two subshells numbered 0 and 1; the third shell (n = 3) has three subshells numbered 0, 1 and 2.
The old subshell convention used letters rather than numbers. In this format, the first subshell (l = 0) was denoted s, the second subshell (l = 1) was denoted p, the third subshell (l = 2) was denoted d, and the fourth subshell (l = 3) was denoted f. The letters came from the words: sharp, principal, diffuse And Fundamental. You can still see these designations in many periodic tables used to denote the electron configuration of the outer ( valence) shells of atoms.
(a) the Bohr representation of the silver atom, (b) Orbital representation of Ag with division of shells into subshells (orbital quantum number l).
This diagram does not imply anything about the actual position of the electrons, but only represents the energy levels.
Magnetic quantum number: The magnetic quantum number for the electron classifies the orientation of the electron subshell figure. The "petals" of the subshells can be directed in several directions. These different orientations are called orbitals. For the first subshell (s; l = 0), which resembles a sphere, "direction" is not specified. For a second (p; l = 1) subshell in each shell that resembles a dumbbell pointing in three possible directions. Imagine three dumbbells intersecting at the origin, each pointing along its own axis in a triaxial coordinate system.
Valid values for a given quantum number consist of integers ranging from -l to l, and this number is denoted as m l in atomic physics and z in nuclear physics. To calculate the number of orbitals in any subshell, you need to double the number of the subshell and add 1, (2∙l + 1). For example, the first subshell (l = 0) in any shell contains one orbital numbered 0; the second subshell (l = 1) in any shell contains three orbitals with numbers -1, 0 and 1; the third subshell (l = 2) contains five orbitals numbered -2, -1, 0, 1 and 2; and so on.
Like the principal quantum number, the magnetic quantum number arose directly from experimental data: the Zeeman effect, the separation of spectral lines by exposing an ionized gas to a magnetic field, hence the name "magnetic" quantum number.
Spin quantum number: like the magnetic quantum number, this property of the electrons of an atom was discovered through experiments. Careful observation of the spectral lines showed that each line was in fact a pair of very closely spaced lines, it has been suggested that this so-called fine structure was the result of each electron "spinning" around its own axis, like a planet. Electrons with different "spins" would give off slightly different frequencies of light when excited. The spinning electron concept is now obsolete, being more appropriate for the (incorrect) view of electrons as individual particles of matter rather than as "clouds", but the name remains.
Spin quantum numbers are denoted as m s in atomic physics and sz in nuclear physics. Each orbital in each subshell can have two electrons in each shell, one with spin +1/2 and the other with spin -1/2.
Physicist Wolfgang Pauli developed a principle that explains the ordering of electrons in an atom according to these quantum numbers. His principle, called Pauli exclusion principle, states that two electrons in the same atom cannot occupy the same quantum states. That is, each electron in an atom has a unique set of quantum numbers. This limits the number of electrons that can occupy any given orbital, subshell, and shell.
This shows the arrangement of electrons in a hydrogen atom:
With one proton in the nucleus, the atom accepts one electron for its electrostatic balance (the proton's positive charge is exactly balanced by the electron's negative charge). This electron is located in the lower shell (n = 1), the first subshell (l = 0), in the only orbital (spatial orientation) of this subshell (m l = 0), with a spin value of 1/2. The general method of describing this structure is by enumerating the electrons according to their shells and subshells, according to a convention called spectroscopic notation. In this notation, the shell number is shown as an integer, the subshell as a letter (s,p,d,f), and the total number of electrons in the subshell (all orbitals, all spins) as a superscript. Thus, hydrogen, with its single electron placed at the base level, is described as 1s 1 .
Moving on to the next atom (in order of atomic number), we get the element helium:
A helium atom has two protons in its nucleus, which requires two electrons to balance the double positive electrical charge. Since two electrons - one with spin 1/2 and the other with spin -1/2 - are in the same orbital, the electronic structure of helium does not require additional subshells or shells to hold the second electron.
However, an atom requiring three or more electrons will need additional subshells to hold all the electrons, since only two electrons can be on the bottom shell (n = 1). Consider the next atom in the sequence of increasing atomic numbers, lithium:
The lithium atom uses part of the capacitance L of the shell (n = 2). This shell actually has a total capacity of eight electrons (maximum shell capacity = 2n 2 electrons). If we consider the structure of an atom with a completely filled L shell, we see how all combinations of subshells, orbitals, and spins are occupied by electrons:
Often, when assigning a spectroscopic notation to an atom, any fully filled shells are skipped, and unfilled shells and top-level filled shells are denoted. For example, the element neon (shown in the figure above), which has two completely filled shells, can be described spectrally simply as 2p 6 rather than as 1s 22 s 22 p 6 . Lithium, with its fully filled K shell and a single electron in the L shell, can simply be described as 2s 1 rather than 1s 22 s 1 .
The omission of fully populated lower-level shells is not only for convenience of notation. It also illustrates a basic principle of chemistry: the chemical behavior of an element is primarily determined by its unfilled shells. Both hydrogen and lithium have one electron on their outer shells (as 1 and 2s 1, respectively), that is, both elements have similar properties. Both are highly reactive, and react in almost identical ways (binding to similar elements under similar conditions). It doesn't really matter that lithium has a fully filled K-shell under an almost free L-shell: the unfilled L-shell is the one that determines its chemical behavior.
Elements that have completely filled outer shells are classified as noble and are characterized by an almost complete lack of reaction with other elements. These elements were classified as inert when they were considered not to react at all, but they are known to form compounds with other elements under certain conditions.
Since elements with the same configuration of electrons in their outer shells have similar chemical properties, Dmitri Mendeleev organized the chemical elements in a table accordingly. This table is known as , and modern tables follow this general layout, shown in the figure below.
Periodic table of chemical elements Dmitri Mendeleev, a Russian chemist, was the first to develop the periodic table of elements. Even though Mendeleev organized his table according to atomic mass rather than atomic number, and created a table that was not as useful as modern periodic tables, his development stands as an excellent example of scientific proof. Seeing patterns of periodicity (similar chemical properties according to atomic mass), Mendeleev hypothesized that all elements must fit into this ordered pattern. When he discovered "empty" places in the table, he followed the logic of the existing order and assumed the existence of yet unknown elements. The subsequent discovery of these elements confirmed the scientific correctness of Mendeleev's hypothesis, further discoveries led to the form of the periodic table that we use now.
Like this must work science: hypotheses lead to logical conclusions and are accepted, changed or rejected depending on the consistency of experimental data with their conclusions. Any fool can formulate a hypothesis after the fact to explain the available experimental data, and many do. What distinguishes a scientific hypothesis from post hoc speculation is the prediction of future experimental data that has not yet been collected, and possibly the refutation of that data as a result. Boldly lead the hypothesis to its logical conclusion(s) and the attempt to predict the results of future experiments is not a dogmatic leap of faith, but rather a public test of this hypothesis, an open challenge to the opponents of the hypothesis. In other words, scientific hypotheses are always "risky" because of trying to predict the results of experiments that have not yet been done, and therefore can be falsified if the experiments do not go as expected. Thus, if a hypothesis correctly predicts the results of repeated experiments, it is disproven.
Quantum mechanics, first as a hypothesis and then as a theory, has been extremely successful in predicting the results of experiments, and hence has received a high degree of scientific credibility. Many scientists have reason to believe that this is an incomplete theory, since its predictions are more true at microphysical scales than macroscopic ones, but nevertheless, it is an extremely useful theory for explaining and predicting the interaction of particles and atoms.
As you have seen in this chapter, quantum physics is essential in describing and predicting many different phenomena. In the next section, we will see its significance in the electrical conductivity of solids, including semiconductors. Simply put, nothing in chemistry or solid state physics makes sense in the popular theoretical structure of electrons existing as individual particles of matter circling around the nucleus of an atom like miniature satellites. When electrons are viewed as "wave functions" existing in certain, discrete states that are regular and periodic, then the behavior of matter can be explained.
Summing up
The electrons in atoms exist in "clouds" of distributed probability, and not as discrete particles of matter revolving around the nucleus, like miniature satellites, as common examples show.
Individual electrons around the nucleus of an atom tend to unique "states" described by four quantum numbers: principal (radial) quantum number, known as shell; orbital (azimuth) quantum number, known as subshell; magnetic quantum number describing orbital(subshell orientation); And spin quantum number, or simply spin. These states are quantum, that is, “between them” there are no conditions for the existence of an electron, except for states that fit into the quantum numbering scheme.
Glanoe (radial) quantum number (n) describes the base level or shell in which the electron resides. The greater this number, the greater the radius of the electron cloud from the nucleus of the atom, and the greater the energy of the electron. Principal quantum numbers are integers (positive integers)
Orbital (azimuthal) quantum number (l) describes the shape of an electron cloud in a particular shell or level and is often known as a "subshell". In any shell, there are as many subshells (forms of an electron cloud) as the main quantum number of the shell. Azimuthal quantum numbers are positive integers starting from zero and ending with a number less than the main quantum number by one (n - 1).
Magnetic quantum number (m l) describes what orientation the subshell (electron cloud shape) has. Subshells can have as many different orientations as twice the subshell number (l) plus 1, (2l+1) (that is, for l=1, m l = -1, 0, 1), and each unique orientation is called an orbital. These numbers are integers starting from a negative value of the subshell number (l) through 0 and ending with a positive value of the subshell number.
Spin Quantum Number (m s) describes another property of the electron and can take the values +1/2 and -1/2.
Pauli exclusion principle says that two electrons in an atom cannot share the same set of quantum numbers. Therefore, there can be at most two electrons in each orbital (spin=1/2 and spin=-1/2), 2l+1 orbitals in each subshell, and n subshells in each shell, and no more.
Spectroscopic notation is a convention for the electronic structure of an atom. Shells are shown as integers, followed by subshell letters (s, p, d, f) with superscript numbers indicating the total number of electrons found in each respective subshell.
The chemical behavior of an atom is determined solely by electrons in unfilled shells. Low-level shells that are completely filled have little or no effect on the chemical binding characteristics of the elements.
Elements with completely filled electron shells are almost completely inert, and are called noble elements (previously known as inert).
Among the two fundamental theories that explain the reality around us, quantum theory appeals to the interaction between least particles of matter, while general relativity refers to gravity and largest structures throughout the universe. Since the time of Einstein, physicists have tried to bridge the gap between these teachings, but with mixed success.
One way to reconcile gravity with quantum mechanics was to show that gravity is based on indivisible particles of matter, quanta. This principle can be compared to how the light quanta themselves, photons, represent an electromagnetic wave. Until now, scientists have not had enough data to confirm this assumption, but Antoine Tilloy(Antoine Tilloy) from the Institute of Quantum Optics. Max Planck in Garching, Germany, attempted to describe gravity with the principles of quantum mechanics. But how did he do it?
quantum world
In quantum theory, the state of a particle is described by its wave function. It, for example, allows you to calculate the probability of finding a particle at a particular point in space. Before the measurement itself, it is unclear not only where the particle is, but also whether it exists. The very fact of measurement literally creates reality by "destroying" the wave function. But quantum mechanics rarely refers to measurements, which is why it is one of the most controversial areas of physics. Remember Schrödinger's paradox: You won't be able to resolve it until you take a measurement by opening the box and finding out if the cat is alive or not.
One solution to these paradoxes is the so-called GRW model, which was developed in the late 1980s. This theory includes such a phenomenon as " outbreaks» are spontaneous collapses of the wave function of quantum systems. The result of its application is exactly the same as if the measurements were carried out without observers as such. Tilloy modified it to show how it can be used to get to the theory of gravity. In his version, the flash that destroys the wave function and thereby forces the particle to be in one place also creates a gravitational field at that moment in space-time. The larger the quantum system, the more particles it contains and the more often flashes occur, thereby creating a fluctuating gravitational field.
The most interesting thing is that the average value of these fluctuations is the same gravitational field that Newton's theory of gravity describes. This approach to unifying gravity with quantum mechanics is called semiclassical: gravity arises from quantum processes, but remains a classical force. "There is no real reason to ignore the semiclassical approach, in which gravity is classical at a fundamental level," says Tilloy.
Gravity Phenomenon
Klaus Hornberger of the University of Duisburg-Essen in Germany, who did not take part in the development of the theory, treats it with great sympathy. However, the scientist points out that before this concept forms the basis of a unified theory that unites and explains the nature of all the fundamental aspects of the world around us, it will be necessary to solve a number of tasks. For example, Tilloy's model can certainly be used to derive Newtonian gravity, but its consistency with gravity theory still needs to be verified with the help of mathematics.
However, the scientist himself agrees that his theory needs an evidence base. For example, he predicts that gravity will behave differently depending on the scale of the objects in question: for atoms and for supermassive black holes, the rules can be very different. Be that as it may, if tests reveal that Tillroy's model indeed reflects reality, and gravity is indeed a consequence of quantum fluctuations, then this will allow physicists to comprehend the reality around us on a qualitatively different level.
The English physicist Isaac Newton published a book in which he explained the movement of objects and the principle of gravity. The "Mathematical Principles of Natural Philosophy" gave things in the world fixed places. The story goes that at the age of 23, Newton went to a garden and saw an apple fall from a tree. At that time, physicists knew that the Earth somehow attracted objects using gravity. Newton developed this idea.
According to John Conduitt, Newton's assistant, seeing an apple fall to the ground, Newton got the idea that the gravitational force "was not limited to a certain distance from the earth, but extends much further than is usually believed." According to Conduitt, Newton asked himself the question: why not even to the moon?
Inspired by his insights, Newton developed the law of universal gravitation, which worked equally well for apples on Earth and planets orbiting the Sun. All these objects, despite the differences, obey the same laws.
“People thought he explained everything that needed to be explained,” Barrow says. “His achievement was great.”
The problem is that Newton knew there were holes in his work.
For example, gravity does not explain how small objects are held together, since this force is not that great. Also, although Newton could explain what was going on, he could not explain how it worked. The theory was incomplete.
There was a bigger problem. Although Newton's laws explained the most common phenomena in the universe, in some cases objects violated his laws. These situations were rare and usually involved high speeds or heightened gravity, but they did happen.
One such situation was the orbit of Mercury, the planet closest to the Sun. Like any other planet, Mercury revolves around the Sun. Newton's laws could be applied to calculate the motions of the planets, but Mercury didn't want to play by the rules. More strangely, its orbit had no center. It became clear that the universal law of universal gravitation was not so universal, and not a law at all.
More than two centuries later, Albert Einstein came to the rescue with his theory of relativity. Einstein's idea, which in 2015 provided a deeper understanding of gravity.
Theory of relativity
The key idea is that space and time, which appear to be separate things, are in fact intertwined. Space has three dimensions: length, width and height. Time is the fourth dimension. All four are connected in the form of a giant space cell. If you've ever heard the phrase "space-time continuum", that's what it's all about.
Einstein's big idea was that heavy objects like planets or fast moving ones could warp spacetime. A bit like a tight trampoline: if you put something heavy on the fabric, a dip will form. Any other objects will roll down the slope towards the object in the valley. Therefore, according to Einstein, gravity attracts objects.
The idea is strange in its essence. But physicists are convinced that it is. She also explains the strange orbit of Mercury. According to the general theory of relativity, the giant mass of the Sun bends space and time around. Being the closest planet to the Sun, Mercury experiences much more curvature than other planets. The equations of general relativity describe how this curved space-time affects Mercury's orbit and allow the planet's position to be predicted.
However, despite its success, the theory of relativity is not the theory of everything, like Newton's theories. Just as Newton's theory does not work for truly massive objects, Einstein's theory does not work on the microscale. As soon as you start looking at atoms and anything smaller, matter starts to behave very strangely.
Until the end of the 19th century, the atom was considered the smallest unit of matter. Born from the Greek word "atomos", which means "indivisible", the atom, by its definition, should not be broken into smaller particles. But in the 1870s, scientists discovered particles that are 2,000 times lighter than atoms. By weighing beams of light in a vacuum tube, they found extremely light particles with a negative charge. Thus was discovered the first subatomic particle: the electron. In the next half century, scientists discovered that the atom has a compound nucleus around which electrons scurry. This nucleus is made up of two types of subatomic particles: neutrons, which have a neutral charge, and protons, which are positively charged.
But that's not all. Since then, scientists have found ways to divide matter into smaller and smaller parts, while continuing to refine our understanding of fundamental particles. By the 1960s, scientists had found dozens of elementary particles, making up a long list of the so-called particle zoo.
As far as we know, of the three components of the atom, the only fundamental particle is the electron. Neutrons and protons are divided into tiny quarks. These elementary particles obey a completely different set of laws, different from those that trees or planets obey. And these new laws - which were far less predictable - put the physicists in a bad mood.
In quantum physics, particles have no definite place: their location is a little blurry. As if each particle has a certain probability of being in a certain place. This means that the world is inherently a fundamentally undefined place. Quantum mechanics is even hard to understand. As Richard Feynman, an expert in quantum mechanics, once said, “I think I can safely say that no one understands quantum mechanics.”
Einstein, too, was concerned about the fuzziness of quantum mechanics. Despite the fact that he, in fact, partially invented it, Einstein himself never believed in quantum theory. But in their chambers - large and small - both quantum mechanics and quantum mechanics proved the right to undivided power, being extremely accurate.
Quantum mechanics has explained the structure and behavior of atoms, including why some of them are radioactive. It also underlies modern electronics. You couldn't read this article without her.
General relativity predicted the existence of black holes. Those massive stars that collapsed into themselves. Their gravitational attraction is so powerful that not even light can escape it.
The problem is that these two theories are incompatible and therefore cannot be true at the same time. General relativity says that the behavior of objects can be accurately predicted, whereas quantum mechanics says that you can only know the probability of what objects will do. It follows that there are some things that physicists have not yet described. Black holes, for example. They are massive enough that relativity theory can be applied to them, but also small enough that quantum mechanics can be applied. Unless you get close to a black hole, this incompatibility will not affect your daily life. But it has puzzled physicists for most of the last century. It is this incompatibility that makes one look for a theory of everything.
Einstein spent most of his life trying to find such a theory. Not being a fan of the randomness of quantum mechanics, he wanted to create a theory that would unify gravity and the rest of physics so that quantum oddities would remain secondary consequences.
His main goal was to make gravity work with electromagnetism. In the 1800s, physicists figured out that electrically charged particles could attract or repel each other. Because some metals are attracted by a magnet. Obviously, if there are two kinds of forces that objects can exert on each other, they can be attracted by gravity and attracted or repelled by electromagnetism.
Einstein wanted to combine these two forces into a "unified field theory". To do this, he stretched space-time into five dimensions. Along with three space and one time dimensions, he added a fifth dimension, which should be so small and curled up that we couldn't see it.
It didn't work, and Einstein spent 30 years looking for nothing. He died in 1955 and his unified field theory was not developed. But in the next decade, a serious rival for this theory emerged: string theory.
String theory
The idea behind string theory is quite simple. The basic ingredients of our world, like electrons, are not particles. These are tiny loops or "strings". It's just that because the strings are so small, they appear to be dots.
Like guitar strings, these loops are under tension. This means that they vibrate at different frequencies depending on the size. These vibrations determine what sort of "particle" each string will represent. Vibrating a string in one way will give you an electron. Others, something else. All the particles discovered in the 20th century are the same kind of strings, just vibrating differently.
It's quite difficult to immediately understand why this is a good idea. But it applies to all the forces in nature: gravity and electromagnetism, plus two more discovered in the 20th century. Strong and weak nuclear forces operate only within the tiny nuclei of atoms, so they could not be detected for a long time. A strong force holds the core together. A weak force usually does nothing, but if it gains enough strength, it breaks the nucleus apart: therefore, some atoms are radioactive.
Any theory of everything will have to explain all four. Fortunately, the two nuclear forces and electromagnetism are fully described by quantum mechanics. Each force is carried by a specialized particle. But there is not a single particle that would carry gravity.
Some physicists think that it is. And they call it "graviton". Gravitons have no mass, a special spin, and they move at the speed of light. Unfortunately, they haven't been found yet. This is where string theory comes into play. It describes a string that looks exactly like a graviton: has the correct spin, no mass, and moves at the speed of light. For the first time in history, the theory of relativity and quantum mechanics have found common ground.
In the mid-1980s, physicists were fascinated by string theory. “In 1985, we realized that string theory solved a lot of problems that had plagued people for the past 50 years,” says Barrow. But she also had problems.
First, "we don't understand what string theory is in the right detail," says Philip Candelas of the University of Oxford. "We don't have a good way to describe it."
In addition, some of the predictions look strange. While Einstein's unified field theory relies on an extra hidden dimension, the simplest forms of string theory need 26 dimensions. They are needed to link mathematics theory with what we already know about the universe.
More advanced versions, known as "superstring theories", get by with ten dimensions. But even this does not fit with the three dimensions that we observe on Earth.
“This can be dealt with by assuming that only three dimensions have expanded in our world and become large,” says Barrow. “Others are present but remain fantastically small.”
Because of these and other problems, many physicists dislike string theory. And they offer another theory: loop quantum gravity.
Loop quantum gravity
This theory does not aim to unify and include everything that is in particle physics. Instead, loop quantum gravity simply attempts to deduce a quantum theory of gravity. It is more limited than string theory, but not as cumbersome. Loop quantum gravity assumes that space-time is divided into small pieces. From afar, it seems that this is a smooth sheet, but upon closer inspection, you can see a bunch of dots connected by lines or loops. These little fibers that weave together offer an explanation for gravity. This idea is as incomprehensible as string theory, and has similar problems: there is no experimental evidence.
Why are these theories still being discussed? Maybe we just don't know enough. If big phenomena are discovered that we have never seen, we can try to understand the big picture, and we will fill in the missing pieces of the puzzle later.
“It's tempting to think we've discovered everything,” Barrow says. - But it would be very strange if by 2015 we had made all the necessary observations to get a theory of everything. Why should it be so?
There is another problem. These theories are difficult to test, in large part because their math is so brutal. Candelas has been trying to find a way to test string theory for years, but has never been able to.
"The main obstacle to the advancement of string theory remains the lack of development of mathematics, which should accompany physical research," says Barrow. "It's at an early stage, there's still a lot to explore."
With all this, string theory remains promising. “For years, people have been trying to integrate gravity with the rest of physics,” says Candelas. - We had theories that explained electromagnetism and other forces well, but not gravity. With string theory, we're trying to combine them."
The real problem is that the theory of everything may simply be impossible to identify.
When string theory became popular in the 1980s, there were actually five versions of it. “People started to worry,” Barrow says. “If this is the theory of everything, why are there five?” Over the next decade, physicists discovered that these theories could be converted from one to the other. They are just different ways of seeing the same thing. The result was the M-theory put forward in 1995. This is a deep version of string theory, including all earlier versions. Well, at least we are back to a unified theory. M-theory only requires 11 dimensions, which is much better than 26. However, M-theory does not offer a unified theory of everything. She offers billions of them. In total, M-theory offers us 10^500 theories, all of which will be logically consistent and capable of describing the universe.
It looks worse than useless, but many physicists believe it points to a deeper truth. Perhaps our universe is one of many, each of which is described by one of the trillions of versions of M-theory. And this gigantic collection of universes is called "".
At the beginning of time, the multiverse was like "a big foam of bubbles of all shapes and sizes," Barrow says. Each bubble then expanded and became the universe.
"We're in one of those bubbles," Barrow says. As the bubbles expanded, other bubbles could form inside them, new universes. “In the process, the geography of such a universe has become seriously complicated.”
The same physical laws operate in every bubble universe. Because in our universe everything behaves the same way. But other universes may have other laws. This leads to a strange conclusion. If string theory is indeed the best way to unify relativity and quantum mechanics, then both of them will and will not be a theory of everything at the same time.
On the one hand, string theory can give us a perfect description of our universe. But it will also inevitably lead to each of the trillions of other universes being unique. A major change in thinking will be that we stop waiting for a unified theory of everything. There can be many theories of everything, each of which will be true in its own way.
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