To talk about quantum mechanics, first let’s get straight what mechanics is. Mechanics is the study of physical bodies under the influence of forces. When you throw a baseball up in the air, it goes up, but then slows and falls back down. The force from your arm sends it up, and the force from gravity brings it back.

In the example shown above, the two spheres are assumed to be very large, like planets. To figure out how planets move in relation to each other, you don’t need quantum mechanics. Newton’s mechanics (classical mechanics) will do. However, in the early 20th century, when people were trying to figure out the model of the atom, Newton’s mechanics would not work out. That’s when quantum mechanics was discovered.

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Anna asks: I feel that to be a citizen of the 21st century, I should get my head around a few more things before I die. Herewith: Would you kindly explain, in clear simple language, what quantum mechanics is?

The Clear Science staff has gotten variations of this question a few times. Quantum mechanics: what is it? We’re going to try and throw some Clear Science on it.

To understand why atoms can’t fall through each other—despite the huge amount of empty space in them—we first need to think about electrons. Remember, the nucleus has protons, which are positive. The electrons are negative and attracted to the protons, so they orbit the nucleus.

A hydrogen atom has one proton and one electron. However, remember we also said the physics for electrons were strange. Namely, they are quantum mechanical. What this means is that they are kind of everywhere around the nucleus, without being anywhere exactly. Weird, right?

What this means is they are kind of a blur, or a smear. Think of the space around the nucleus as being a cloud, all kind of negative.

Physics and size

We at Clear Science initially compared atoms to tiny solar systems. Here we see where that comparison is incorrect.

The laws of physics are slightly different depending on how big something is. The solar system and our everyday world have rules called Classical Mechanics. (And the Theory of Relativity is a part of Classical Mechanics that deals with very massive or fast things, like planets and stars.)

Atoms and the particles that comprise them are ruled by something called Quantum Mechanics.

When physicists talk about a “Theory of Everything,” they mean slightly different equations that work out at all sizes: a unification of Classical and Quantum Mechanics.