Nature

Understand quantum mechanics in five minutes

"If you can talk about quantum mechanics without dizzying, you don't understand."

This quote is from Niels Bohr, one of the founders of quantum mechanics. And the Danish physicist had a point, because quantum mechanics still gives scientists headaches 100 years after the theory was born.

Quantum mechanics is the branch of physics that deals with particles smaller than atoms. The laws of nature no longer apply to very small particles. That is why a special theory is needed to explain how everything is connected.

Quantum mechanics and the standard model

Quantum mechanics consists of a number of components, one of which is easier to understand than the other.

The standard model describes what atoms are made of and thus maps out the different particles that quantum mechanics deals with.

The majority of the standard model has now been demonstrated, but the researchers are not there yet. The standard model can explain all the known matter in the universe, from distant galaxies to the amino acids in your body. However, it has not yet been possible to incorporate gravity into the model.

All matter in the universe consists of twelve elementary particles, four force-transmitting particles and the Higgs particle:

Quarks, muons and Higgs particles

Elemental particles are the physical building blocks that make up all the atoms in the universe. There are twelve, but only four of them are still present in nature today: electrons, electron neutrinos, up-quarks and down-quarks. The others only existed immediately after the big bang in their original form, but were later reproduced in a particle accelerator.

Electron Has a negative electrical charge. It can be free in space or be bound to an atom.

Electron neutrino Has no load and only a very small mass. Is released during radioactivity.

Up quark Normal matter consists of up and down quarks and electrons. A quark never occurs individually.

Down quark Protons consist of one down quark and two up quarks, and neutrons from two down quarks and one up quark.

Muon Looks like the electron, but is about 200 times as heavy and therefore unstable.

Muon neutrino It resembles the electron neutrino, but is slightly heavier, although still extremely light.

Charm quark Has three times the mass of a proton and has a positive electrical charge.

Strange quark Has a negative electrical charge.

Tau Is approximately 3500 times as heavy as an electron and has a very short lifespan.

Tau neutrino An uncharged particle. It is very light, although it is slightly heavier than the other neutrinos.

Bottom quark Is four times as heavy as a proton. It is formed among other things by the decline of top quarks.

Top quark This is the heaviest elementary particle. It weighs almost as much as a gold atom.

The force transferring particles hold the building blocks together. They transfer the four fundamental forces of nature to the atoms:

Photon A massless light particle that transmits the electromagnetic force.

Gluon Binds quarks together to form hadrons and transmits the strong nuclear force.

W and Z boson Transmit the weak nuclear power and play a role in various forms of radioactivity.

Graviton Particle that would transfer gravity. Its existence has not yet been confirmed, but CERN researchers in Switzerland are working hard on that.

Then there is it Higgs particle. This was found in 2012 with 99.99 percent certainty. The particle gives the building blocks of the atomic mass. Quarks bind more strongly to Higgs particles, making them heavier than, for example, electrons.

Looking for the gravitational particle

Apart from gravitons, all elementary particles have been reproduced by scientists with the help of particle accelerators. The search for the mysterious particles has started again after the Large Hadron Collider from CERN has been rebuilt.

However, the researchers are convinced that it is not possible to find gravitons. That is why they are looking for twin particles that must demonstrate the existence of gravitons.

The description of the building blocks of the universe is the understandable part of quantum mechanics. Measuring the particles and describing their properties is a lot harder.

What is Schrödinger's cat?

Some properties change as soon as you start measuring them. According to Niels Bohr you can no longer assign them a position or speed, because those concepts no longer have meaning.

An example of this is the paradox of Schrödinger's cat.

Schrödinger's cat paradox. Image: Shutterstock

A cat is locked up in a steel room with an unstable atomic nucleus. A Geiger counter measures the decay of the atomic nucleus. At the first sign of decay, poison gas is released into the room, killing the cat.

Because the atomic nucleus is unstable at the start of the experiment (in principle both decayed and non-decayed), the same uncertainty applies to the cat. He finds himself in a situation where he is both dead and alive.

When the room is opened, it appears whether the cat is dead or alive. So the cat loses one of its characteristics the moment you open the space to find out how he is doing.

Based on the laws of nature that we know in our daily lives, this seems absurd. For our understanding, a cat cannot be dead and alive at the same time - it is one of them.

But that is how quantum mechanics works to a large extent, so the quote from Niels Bohr still applies:

Did you get dizzy from this lecture?

Video: If You Don't Understand Quantum Physics, Try This! (November 2019).

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