A journey into the small universe: great quanta!

Wouldn’t it be fascinating to be in several places at once?

In our everyday life this seems hard to imagine, and yet such effects occur on the scale of the smallest particles, the atoms and electrons. If you only look deep enough into the matter, a strange world opens up to you, which follows its own rules. The theory that describes these laws is quantum physics. This is partly so absurd that even Albert Einstein did not want to accept it. And yet quantum physics is one of the best tested physical theories to date.

A monstrous idea revolutionizes science

At the beginning of the 20th century it was believed that physics was complete. Apart from a few contradictions, all the events could be explained. But a few young scientists, who developed new ideas and were not deterred by absurdity, revolutionized physics.

Black bodies

One of these scientists was the German physicist Max Planck, who studied the radiation of a “black body”. A black body is a model for our sun or the filament of an incandescent lamp, for example. But even for such (supposedly) simple objects, the observed emission spectra could not be explained at that time. An emission spectrum describes the intensity with which different colours are emitted from an object.

Planck succeeded in developing a formula that could reproduce these spectra. But it was based on an outrageous assumption:

Energy cannot be absorbed and released continuously, but only in discrete packets – it is “quantized”.

Act of desperation

With this discovery Planck laid the foundation for quantum physics. Ironically, he himself did not initially recognize the significance of his energy quanta and called it an “act of desperation”, since he had only introduced it as a mathematical auxiliary construction.

Albert Einstein finally gave the mysterious quantum objects a physical meaning. Accordingly, the energy packets are a property of the radiated light itself: Light particles, later called “photons”, each transport a certain amount of energy.

Erratic quanta

So nature makes jumps, at least at atomic level-this idea was contrary to all previous theories. No wonder, then, that quantum physics had to face strong criticism in its early days.

But not everyone was deterred by this new view of the world. Niels Bohr took a decisive step when he used the basic ideas of quantum physics in his description of atoms, the tiny building blocks of our universe.

In Bohr’s atomic model, the negatively charged, light electrons orbit a positively charged and heavy atomic nucleus on fixed orbits. Although this model has its weaknesses and there are now better descriptions, it has been able to explain observations that classical physics had previously failed to make.

An electron is not a billiard ball

In a similar way, it happened again and again in the following decades: Phenomena that could not be classically described suddenly made sense from the perspective of quantum physics.

Quantum objects, such as atoms or electrons, behave completely differently from macroscopic objects – larger ones like our body or a ball – which are each composed of a huge number of small particles. An example: If we had detailed information about the location and speed of a billiard ball, we could in principle predict exactly where the ball would stop and whether we would score a hole. In practice, of course, no one measures this so precisely, but theoretically it would be possible-just the opposite of measuring on a quantum object.

Even if we want to determine the exact location and speed of an electron, we can never do that. The more precisely we know the place, the less precise our knowledge of the speed (and vice versa) becomes, according to Heisenberg’s uncertainty principle.

In several places at the same time

With quantum objects, one must therefore abandon the idea that particles move on firmly defined paths (this is a problem of the Bohr atomic model, by the way). An exact prediction of where an electron will be located is therefore not possible, and instead only statements about residence probabilities can be made. The electron thus exists as a kind of smeared cloud distributed over several locations. It is only through a measurement that the electron “decides” its location at random.

They like to keep a low profile: quanta!

Sounds weird? It is quite natural that such ideas initially make our hair stand on end: after all, the world as we experience it every day behaves according to the rules of classical physics.

This is because the quantum mechanical effects that occur at the microscopic level of atoms can be neglected in our macroscopic world.

By way of comparison: the size ratio of an atom to a 2-Euro coin is approximately the same as that of that coin to the size of the earth! So you look at this strange, erratic quantum world from a very, very far distance. At this distance, a staircase looks almost smooth like a street, although in reality it has very high steps.

Our everyday life is full of quantum physics

So does quantum physics play no role in our daily lives? On the contrary! Technologies such as LEDs, solar cells and lasers could only be developed because they are based on the findings of quantum physics. And further applications such as the quantum computer are already in the starting blocks.

This series will focus on the technologies behind quantum physics and the ideas behind them in detail. So stay tuned!

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