The essence of quantum physics. Fundamentals of quantum physics in five experiments for "dummies"

Physics is the most mysterious of all sciences. Physics gives us an understanding of the world around us. The laws of physics are absolute and apply to everyone without exception, regardless of person and social status.

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Fundamental discoveries in quantum physics

Isaac Newton, Nikola Tesla, Albert Einstein and many others are the great guides of mankind in the wonderful world of physics, who, like prophets, revealed to mankind the greatest secrets of the universe and the ability to control physical phenomena. Their bright heads cut through the darkness of ignorance of the unreasonable majority and, like a guiding star, showed the way to humanity in the darkness of the night. One of these conductors in the world of physics was Max Planck, the father of quantum physics.

Max Planck is not only the founder of quantum physics, but also the author of the world famous quantum theory. Quantum theory is the most important component of quantum physics. In simple terms, this theory describes the movement, behavior and interaction of microparticles. The founder of quantum physics also brought us many other scientific works that have become the cornerstones of modern physics:

theory of thermal radiation;
special theory of relativity;
research in the field of thermodynamics;
research in the field of optics.

The theory of quantum physics about the behavior and interaction of microparticles became the basis for condensed matter physics, elementary particle physics and high energy physics. Quantum theory explains to us the essence of many phenomena of our world - from the functioning of electronic computers to the structure and behavior of celestial bodies. Max Planck, the creator of this theory, thanks to his discovery allowed us to comprehend the true essence of many things at the level of elementary particles. But the creation of this theory is far from the only merit of the scientist. He was the first to discover the fundamental law of the universe - the law of conservation of energy. The contribution to science of Max Planck is difficult to overestimate. In short, his discoveries are priceless for physics, chemistry, history, methodology and philosophy.

quantum field theory

In a nutshell, quantum field theory is a theory of the description of microparticles, as well as their behavior in space, interaction with each other and mutual transformations. This theory studies the behavior of quantum systems within the so-called degrees of freedom. This beautiful and romantic name says nothing to many of us. For dummies, degrees of freedom are the number of independent coordinates that are needed to indicate the motion of a mechanical system. In simple terms, degrees of freedom are characteristics of motion. Interesting discoveries in the field of interaction of elementary particles were made by Steven Weinberg. He discovered the so-called neutral current - the principle of interaction between quarks and leptons, for which he received the Nobel Prize in 1979.

The Quantum Theory of Max Planck

In the nineties of the eighteenth century, the German physicist Max Planck took up the study of thermal radiation and eventually received a formula for the distribution of energy. The quantum hypothesis, which was born in the course of these studies, marked the beginning of quantum physics, as well as quantum field theory, discovered in the 1900th year. Planck's quantum theory is that during thermal radiation, the energy produced is emitted and absorbed not constantly, but episodically, quantumly. The year 1900, thanks to this discovery made by Max Planck, became the year of the birth of quantum mechanics. It is also worth mentioning Planck's formula. In short, its essence is as follows - it is based on the ratio of body temperature and its radiation.

Quantum-mechanical theory of the structure of the atom

The quantum mechanical theory of the structure of the atom is one of the basic theories of concepts in quantum physics, and indeed in physics in general. This theory allows us to understand the structure of everything material and opens the veil of secrecy over what things actually consist of. And the conclusions based on this theory are very unexpected. Consider the structure of the atom briefly. So what is an atom really made of? An atom consists of a nucleus and a cloud of electrons. The basis of the atom, its nucleus, contains almost the entire mass of the atom itself - more than 99 percent. The nucleus always has a positive charge, and it determines the chemical element of which the atom is a part. The most interesting thing about the nucleus of an atom is that it contains almost the entire mass of the atom, but at the same time it occupies only one ten-thousandth of its volume. What follows from this? And the conclusion is very unexpected. This means that the dense matter in the atom is only one ten-thousandth. And what about everything else? Everything else in the atom is an electron cloud.

The electron cloud is not a permanent and even, in fact, not a material substance. An electron cloud is just the probability of electrons appearing in an atom. That is, the nucleus occupies only one ten thousandth in the atom, and everything else is emptiness. And if we take into account that all the objects around us, from dust particles to celestial bodies, planets and stars, consist of atoms, it turns out that everything material in fact consists of more than 99 percent of emptiness. This theory seems completely unbelievable, and its author, at least, a deluded person, because the things that exist around have a solid consistency, have weight and can be felt. How can it consist of emptiness? Has a mistake crept into this theory of the structure of matter? But there is no error here.

All material things appear dense only due to the interaction between atoms. Things have a solid and dense consistency only due to attraction or repulsion between atoms. This ensures the density and hardness of the crystal lattice of chemicals, of which everything material consists. But, an interesting point, when, for example, the temperature conditions of the environment change, the bonds between atoms, that is, their attraction and repulsion, can weaken, which leads to a weakening of the crystal lattice and even to its destruction. This explains the change in the physical properties of substances when heated. For example, when iron is heated, it becomes liquid and can be shaped into any shape. And when ice melts, the destruction of the crystal lattice leads to a change in the state of matter, and it turns from solid to liquid. These are clear examples of the weakening of bonds between atoms and, as a result, the weakening or destruction of the crystal lattice, and allow the substance to become amorphous. And the reason for such mysterious metamorphoses is precisely that substances consist of dense matter only by one ten-thousandth, and everything else is emptiness.

And substances seem to be solid only because of the strong bonds between atoms, with the weakening of which, the substance changes. Thus, the quantum theory of the structure of the atom allows us to take a completely different look at the world around us.

The founder of the theory of the atom, Niels Bohr, put forward an interesting concept that the electrons in the atom do not radiate energy constantly, but only at the moment of transition between the trajectories of their movement. Bohr's theory helped explain many intra-atomic processes, and also made a breakthrough in the science of chemistry, explaining the boundary of the table created by Mendeleev. According to , the last element that can exist in time and space has the serial number one hundred thirty-seven, and elements starting from one hundred and thirty-eighth cannot exist, since their existence contradicts the theory of relativity. Also, Bohr's theory explained the nature of such a physical phenomenon as atomic spectra.

These are the interaction spectra of free atoms that arise when energy is emitted between them. Such phenomena are typical for gaseous, vaporous substances and substances in the plasma state. Thus, quantum theory made a revolution in the world of physics and allowed scientists to advance not only in the field of this science, but also in the field of many related sciences: chemistry, thermodynamics, optics and philosophy. And also allowed humanity to penetrate the secrets of the nature of things.

There is still a lot to be done by humanity in its consciousness in order to realize the nature of atoms, to understand the principles of their behavior and interaction. Having understood this, we will be able to understand the nature of the world around us, because everything that surrounds us, starting with dust particles and ending with the sun itself, and we ourselves - everything consists of atoms, the nature of which is mysterious and amazing and fraught with a lot of secrets.

Hello dear readers. If you do not want to lag behind life, you want to become a truly happy and healthy person, you should know about the secrets of quantum modern physics, at least a little idea to what depths of the universe scientists have dug today. You have no time to go into deep scientific details, but you want to comprehend only the essence, but to see the beauty of the unknown world, then this article: quantum physics for ordinary dummies or, one might say, for housewives, is just for you. I will try to explain what quantum physics is, but in simple words, to show clearly.

"What is the connection between happiness, health and quantum physics?" you ask.

The fact is that it helps to answer many incomprehensible questions related to human consciousness, the influence of consciousness on the body. Unfortunately, medicine, relying on classical physics, does not always help us to be healthy. And psychology can't properly tell you how to find happiness.

Only deeper knowledge of the world will help us understand how to truly cope with illness and where happiness lives. This knowledge is found in the deep layers of the Universe. Quantum physics comes to the rescue. Soon you will know everything.

What does quantum physics study in simple words

Yes, indeed, quantum physics is very difficult to understand because it studies the laws of the microworld. That is, the world at its deeper layers, at very small distances, where it is very difficult for a person to look.

And the world, it turns out, behaves there very strangely, mysteriously and incomprehensibly, not as we are used to.

Hence all the complexity and misunderstanding of quantum physics.

But after reading this article, you will expand the horizons of your knowledge and look at the world in a completely different way.

Briefly about the history of quantum physics

It all started at the beginning of the 20th century, when Newtonian physics could not explain many things and scientists reached a dead end. Then Max Planck introduced the concept of quantum. Albert Einstein picked up this idea and proved that light does not propagate continuously, but in portions - quanta (photons). Prior to this, it was believed that light has a wave nature.

But as it turned out later, any elementary particle is not only a quantum, that is, a solid particle, but also a wave. This is how corpuscular-wave dualism appeared in quantum physics, the first paradox and the beginning of discoveries of mysterious phenomena of the microworld.

The most interesting paradoxes began when the famous double-slit experiment was carried out, after which the mysteries became much more. We can say that quantum physics began with him. Let's take a look at it.

Double slit experiment in quantum physics

Imagine a plate with two slots in the form of vertical stripes. We will put a screen behind this plate. If we direct light onto the plate, we will see an interference pattern on the screen. That is, alternating dark and bright vertical stripes. Interference is the result of the wave behavior of something, in our case light.

If you pass a wave of water through two holes located side by side, you will understand what interference is. That is, the light turns out to be sort of like it has a wave nature. But as physics, or rather Einstein, has proven, it is propagated by photon particles. Already a paradox. But it's okay, corpuscular-wave dualism will no longer surprise us. Quantum physics tells us that light behaves like a wave but is made up of photons. But the miracles are just beginning.

Let's put a gun in front of a plate with two slots, which will emit not light, but electrons. Let's start shooting electrons. What will we see on the screen behind the plate?

After all, electrons are particles, which means that the flow of electrons, passing through two slits, should leave only two stripes on the screen, two traces opposite the slits. Have you imagined pebbles flying through two slots and hitting the screen?

But what do we really see? All the same interference pattern. What is the conclusion: electrons propagate in waves. So electrons are waves. But after all it is an elementary particle. Again corpuscular-wave dualism in physics.

But we can assume that at a deeper level, an electron is a particle, and when these particles come together, they begin to behave like waves. For example, a sea wave is a wave, but it is made up of water droplets, and on a smaller level, molecules, and then atoms. Okay, the logic is solid.

Then let's shoot from a gun not with a stream of electrons, but let's release electrons separately, after a certain period of time. As if we were passing through the cracks not a sea wave, but spitting individual drops from a children's water gun.

It is quite logical that in this case different drops of water would fall into different slots. On the screen behind the plate, one could see not an interference pattern from the wave, but two distinct impact fringes opposite each slit. We will see the same thing if we throw small stones, they, flying through two cracks, would leave a trace, like a shadow from two holes. Let's now shoot individual electrons to see these two stripes on the screen from electron impacts. They released one, waited, the second, waited, and so on. Quantum physicists have been able to do such an experiment.

But horror. Instead of these two fringes, the same interference alternations of several fringes are obtained. How so? This can happen if an electron flies through two slits at the same time, but behind the plate, like a wave, it collides with itself and interferes. But this cannot be, because a particle cannot be in two places at the same time. It either flies through the first slot or through the second.

This is where the truly fantastic things of quantum physics begin.

Superposition in quantum physics

With a deeper analysis, scientists find out that any elementary quantum particle or the same light (photon) can actually be in several places at the same time. And these are not miracles, but the real facts of the microcosm. This is what quantum physics says. That is why, when shooting a separate particle from a cannon, we see the result of interference. Behind the plate, the electron collides with itself and creates an interference pattern.

Ordinary objects of the macrocosm are always in one place, have one state. For example, you are now sitting on a chair, weigh, say, 50 kg, have a pulse rate of 60 beats per minute. Of course, these indications will change, but they will change after some time. After all, you cannot be at home and at work at the same time, weighing 50 and 100 kg. All this is understandable, this is common sense.

In the physics of the microcosm, everything is different.

Quantum mechanics claims, and this has already been confirmed experimentally, that any elementary particle can be simultaneously not only at several points in space, but also have several states at the same time, such as spin.

All this does not fit into the head, undermines the usual idea of the world, the old laws of physics, turns thinking, one can safely say it drives you crazy.

This is how we come to understand the term "superposition" in quantum mechanics.

Superposition means that an object of the microcosm can simultaneously be in different points of space, and also have several states at the same time. And this is normal for elementary particles. Such is the law of the microworld, no matter how strange and fantastic it may seem.

You are surprised, but these are only flowers, the most inexplicable miracles, mysteries and paradoxes of quantum physics are yet to come.

Wave function collapse in physics in simple terms

Then the scientists decided to find out and see more precisely whether the electron actually passes through both slits. All of a sudden it goes through one slit and then somehow separates and creates an interference pattern as it passes through. Well, you never know. That is, you need to put some device near the slit, which would accurately record the passage of an electron through it. No sooner said than done. Of course, this is difficult to implement, you need not a device, but something else to see the passage of an electron. But scientists have done it.

But in the end, the result stunned everyone.

As soon as we start looking through which slit an electron passes through, it begins to behave not like a wave, not like a strange substance that is located at different points in space at the same time, but like an ordinary particle. That is, it begins to show the specific properties of a quantum: it is located only in one place, it passes through one slot, it has one spin value. What appears on the screen is not an interference pattern, but a simple trace opposite the slit.

But how is that possible. As if the electron is joking, playing with us. At first, it behaves like a wave, and then, after we decided to look at its passage through a slit, it exhibits the properties of a solid particle and passes through only one slit. But that's the way it is in the microcosm. These are the laws of quantum physics.

Scientists have seen another mysterious property of elementary particles. This is how the concepts of uncertainty and collapse of the wave function appeared in quantum physics.

When an electron flies towards the gap, it is in an indefinite state or, as we said above, in a superposition. That is, it behaves like a wave, it is located simultaneously at different points in space, it has two spin values \u200b\u200b(a spin has only two values). If we didn’t touch it, didn’t try to look at it, didn’t find out exactly where it is, if we didn’t measure the value of its spin, it would fly like a wave through two slits at the same time, which means it would create an interference pattern. Quantum physics describes its trajectory and parameters using the wave function.

After we have made the measurement (and it is possible to measure a particle of the microworld only by interacting with it, for example, by colliding another particle with it), then the wave function collapses.

That is, now the electron is exactly in one place in space, has one spin value.

One can say that an elementary particle is like a ghost, it seems to exist, but at the same time it is not in one place, and with a certain probability it can be anywhere within the description of the wave function. But as soon as we begin to contact it, it turns from a ghostly object into a real tangible substance that behaves like ordinary objects of the classical world that are familiar to us.

"This is fantastic," you say. Sure, but the wonders of quantum physics are just beginning. The most incredible is yet to come. But let's take a break from the abundance of information and return to quantum adventures another time, in another article. In the meantime, reflect on what you learned today. What can such miracles lead to? After all, they surround us, this is a property of our world, albeit at a deeper level. Do we still think we live in a boring world? But we will draw conclusions later.

I tried to talk about the basics of quantum physics briefly and clearly.

But if you don’t understand something, then watch this cartoon about quantum physics, about the experiment with two slits, everything is also told there in an understandable, simple language.

Cartoon about quantum physics:

Or you can watch this video, everything will fall into place, quantum physics is very interesting.

Video about quantum physics:

How did you not know about this before?

Modern discoveries in quantum physics are changing our familiar material world.

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, 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. Fantasy! 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.

Fantasy! 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 ?
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?

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From the Greek "fusis" comes the word "physics". It means "nature". Aristotle, who lived in the fourth century BC, first introduced this concept.

Physics became "Russian" at the suggestion of M.V. Lomonosov, when he translated the first textbook from German.

science physics

Physics is one of the main ones. Various processes, changes, that is, phenomena are constantly taking place around the world.

For example, a piece of ice in a warm place will begin to melt. And the water in the kettle boils on fire. An electric current passed through the wire will heat it up and even make it hot. Each of these processes is a phenomenon. In physics, these are mechanical, magnetic, electrical, sound, thermal and light changes that are studied by science. They are also called physical phenomena. Considering them, scientists deduce laws.

The task of science is to discover these laws and study them. Nature is studied by such sciences as biology, geography, chemistry and astronomy. They all apply physical laws.

Terms

In addition to the usual ones in physics, they also use special words called terms. These are “energy” (in physics it is a measure of different forms of interaction and movement of matter, as well as the transition from one to another), “force” (a measure of the intensity of the influence of other bodies and fields on a body) and many others. Some of them gradually entered into colloquial speech.

For example, using the word "energy" in everyday life in relation to a person, we can evaluate the consequences of his actions, but energy in physics is a measure of study in many different ways.

All bodies in physics are called physical. They have volume and shape. They consist of substances, which, in turn, are one of the types of matter - this is everything that exists in the Universe.

Experiences

Much of what people know has come from observations. To study phenomena, they are constantly observed.

Take, for example, various bodies falling to the ground. It is necessary to find out whether this phenomenon differs when falling bodies of unequal masses, different heights, and so on. Waiting and watching different bodies would be very long and not always successful. Therefore, experiments are carried out for such purposes. They differ from observations, as they are specifically implemented according to a predetermined plan and with specific goals. Usually, in the plan, some guesses are built in advance, that is, they put forward hypotheses. Thus, in the course of the experiments, they will be refuted or confirmed. After thinking and explaining the results of the experiments, conclusions are drawn. This is how scientific knowledge is obtained.

Quantities and their units

Often, studying any perform different measurements. When a body falls, for example, height, mass, speed and time are measured. All this is, that is, something that can be measured.

Measuring a value means comparing it with the same value, which is taken as a unit (the length of the table is compared with a unit of length - a meter or another). Each such value has its own units.

All countries try to use uniform units. In Russia, as in other countries, the International System of Units (SI) is used (which means "international system"). It adopts the following units:

length (characteristic of the length of lines in numerical terms) - meter;
time (flow of processes, condition of possible change) - second;
mass (this is a characteristic in physics that determines the inertial and gravitational properties of matter) - kilogram.

It is often necessary to use units that are much larger than the conventional multiples. They are called with the corresponding prefixes from the Greek: “deka”, “hekto”, “kilo” and so on.

Units that are smaller than the accepted ones are called submultiples. Prefixes from the Latin language are applied to them: “deci”, “santi”, “milli” and so on.

Measuring instruments

To conduct experiments, you need equipment. The simplest of them are the ruler, cylinder, tape measure and others. With the development of science, new devices are being improved, complicated and new devices appear: voltmeters, thermometers, stopwatches and others.

Basically, devices have a scale, that is, dashed divisions on which values \u200b\u200bare written. Before measurement, determine the division price:

take two strokes of the scale with values;
the smaller is subtracted from the larger, and the resulting number is divided by the number of divisions that are between.

For example, two strokes with the values "twenty" and "thirty", the distance between which is divided into ten spaces. In this case, the division value will be equal to one.

Accurate measurements and with an error

The measurements are more or less accurate. The allowable inaccuracy is called the margin of error. When measuring, it cannot be greater than the division value of the measuring device.

Accuracy depends on the scale interval and the correct use of the instrument. But in the end, in any measurement, only approximate values \u200b\u200bare obtained.

Theoretical and experimental physics

These are the main branches of science. It may seem that they are very far apart, especially since most people are either theorists or experimenters. However, they are constantly evolving side by side. Any problem is considered by both theorists and experimenters. The business of the former is to describe the data and derive hypotheses, while the latter test theories in practice, conducting experiments and obtaining new data. Sometimes achievements are caused only by experiments, without theories being described. In other cases, on the contrary, it is possible to obtain results that are checked later.

The quantum physics

This direction originated at the end of 1900, when a new physical fundamental constant was discovered, called the Planck constant in honor of the German physicist who discovered it, Max Planck. He solved the problem of the spectral distribution of light emitted by heated bodies, while classical general physics could not do this. Planck made a hypothesis about the quantum energy of the oscillator, which was incompatible with classical physics. Thanks to it, many physicists began to revise old concepts, change them, as a result of which quantum physics arose. This is a completely new view of the world.

and consciousness

The phenomenon of human consciousness from the point of view is not entirely new. Its foundation was laid by Jung and Pauli. But only now, with the formation of this new direction of science, the phenomenon began to be considered and studied on a larger scale.

The quantum world is many-sided and multidimensional, it has many classical faces and projections.

The two main properties within the framework of the proposed concept are superintuition (that is, obtaining information as if from nowhere) and control of subjective reality. In ordinary consciousness, a person can see only one picture of the world and is not able to consider two at once. Whereas in reality there are a huge number of them. All this together is the quantum world and light.

It is quantum physics that teaches us to see a new reality for a person (although many Eastern religions, as well as magicians, have long possessed such a technique). It is only necessary to change the human consciousness. Now a person is inseparable from the whole world, but the interests of all living things and things are taken into account.

Just then, plunging into a state where he is able to see all the alternatives, he comes to insight, which is the absolute truth.

The principle of life from the point of view of quantum physics is for a person to, among other things, contribute to a better world order.

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 "no one 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 contributions 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 such an extent that it persists in the fields of education, even if it is inappropriate.

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 the Rutherford 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 frequency range, 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 (notably 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 though 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" clustered around the nucleus of an atom. These subshell shapes resemble graphical representations of antenna patterns with onion-like 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; etc.

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 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, not 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 should 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 proved to be 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 the electrons in the 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).