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You have probably heard many times about inexplicable secrets of quantum physics and quantum mechanics. Its laws bewitch mysticism, and even physicists admit that they do not understand them to the end. On the one hand, it is interesting 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 to know and to search for the truth, but there is not enough time for all the books. You are not alone, very many inquisitive people type in the search box: «Quantum physics for kettles, quantum mechanics for kettles, quantum physics for beginners, quantum mechanics for beginners, fundamentals of quantum physics, fundamentals of quantum mechanics, quantum physics for children, what is quantum mechanics.»
You will understand the basic concepts and paradoxes of quantum physics. You will learn :
- What is quantum physics and quantum mechanics?
- What is interference?
- What is spin and superposition?
- What is "measurement" or "collapse of wave function"?
- What is quantum entanglement (or Quantum teleportation for teapots)?
- What is the "Schroedinger Cat" mental experiment?
What is quantum physics and quantum mechanics?
Quantum mechanics is a part of quantum physics.
Why is it so difficult to understand these sciences? The answer is simple: quantum physics and quantum mechanics (part of quantum physics) study the laws of the microcosm. And these laws are absolutely different from the laws of our macro world. 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 micro-worlds: in our macro-world, if you put the ball in one of the two boxes, then one of them will be empty, and the other - the ball. But in the microcosm (if there is an atom instead of a ball), the atom can be in two boxes simultaneously. This is confirmed experimentally many times. Isn't it hard to fit it into your head? But you can't argue with the facts.
A little excursion into history. For the first time, scientists thought about the quantum world when in 1900 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 spreads continuously. The first person to take Planck's discovery seriously was the then-unknown Albert Einstein. He realized that light was not only a wave. Sometimes he behaves like a particle. Einstein received the Nobel Prize for his discovery that light is emitted in portions or quanta. The quantum of light is called photon (photon, Wikipedia).
To better understand the laws of quantum physics and mechanics (Wikipedia), it is necessary to abstract from the usual laws of classical physics in some sense. And imagine that you dived like Alice into a rabbit hole in Wonderland.
What is interference?
Interference of light is a "wave" behavior of light, when many bright and dark vertical stripes are displayed on the screen. These vertical stripes are also called interference patterns.
In our macro world, we often observe that light behaves like a wave. If you put your hand in front of a candle, there will be not a clear shadow on the wall by hand, but with blurring contours.
So, it's not that hard! It is quite clear to us now that the light has a wave nature and if we illuminate the 2 cracks with light, we will see the interference picture behind them on the screen.
What is back 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 cracks, we realized that it flies as if through two cracks simultaneously. Otherwise, how can we explain the interference picture on the screen?
But how do you imagine that the photon flies through two cracks at the same time? There are two options.
- variant: the photon as a wave (as water) "swims" through 2 cracks simultaneously
- variant: the photon, as a particle, flies simultaneously along the 2nd trajectory (not even two, but all at once)
In principle, these statements are tantamount to We have come to the "trajectory integral". This is a formulation of quantum mechanics from Richard Feynman.
By the way, it is Richard Feynman who has the well-known expression that we can confidently say that no one understands quantum mechanics
But that expression worked at the beginning of the century. But we are now smart and we know that a photon can behave like a particle and a wave. That it can fly through two cracks at the same time in some way that we don't understand. Therefore it will be easy for us to understand the following important statement of quantum mechanics:
Strictly speaking, quantum mechanics tells us that this behavior of the photon is a rule, not an exception. Any quantum particle is usually in several states or at several points in space simultaneously.
Macro-world objects can be located only in one definite place and in one definite state. But a quantum particle exists according to its own laws. And it doesn't care that we don't understand them. This is the point.
We just have to admit as an axiom that the "superposition" of a quantum object means that it can be on two or more trajectories at the same time, in two or more points simultaneously