What Everyone Should Know about Quantum Physics

In this article, we let you know what we believe everyone should know about quantum physics. This includes you, even if science is not your favorite topic. We start simple, with questions about what quantum physics is and were the name comes from. Then we move on to more complex topics and conclude with how quantum physics affects your life. “My life?” you may wonder. Yes, really your life.

What Is Quantum Physics – in Three Sentences?

Quantum Physics is physics that becomes specifically relevant for small particles, on the microscopic scale. For example for atoms, classical physics, that is the physics as was known before quantum physics, would provide wrong results. One problem of classical physics — its prediction of unstable atoms — is beautifully fixed by quantum physics, as we will discuss later.

Is Quantum Mechanics the Same as Quantum Physics?

Mechanics is one of many parts of physics. So logically, quantum mechanics is a part of quantum physics. Quantum electrodynamics (QED) is another part of quantum physics. You should be aware, however, that sometimes people indeed talk about quantum mechanics when they mean all of quantum physics.

What Does the “Quantum” in Quantum Physics Mean?

To quote Wikipedia, “a quantum (plural: quanta) is the minimum amount of any physical entity involved in an interaction”. So what does this mean? It is related to the fact that physical properties can be quantized. For example, states in an atom can only have very specific energy values, while the majority of energy values are not allowed. Thus, the energies are quantized. When a transition from a higher energy state to a lower energy state occurs, usually a single quantum of light is emitted which has precisely the energy that corresponds to the energy difference of the higher and lower state. By the way, one typically calls a quantum of light (or a light quantum) a photon.

Quantum physics thus deals with the physics of quanta, i.e. tiny particles that represent the smallest amount of entities one can think of. This is in contrast to classical physics, which deals with sufficiently large bodies (which themselves consist of very many quanta).

Does Quantum Physics Have to Do with Relativity at All?

The short answer is no (but see the second paragraph). Quantum physics is an extension of classical physics for particles that are so small that classical physics is no longer valid. The special theory of relativity is an extension of classical physics for particles that are so fast that classical physics is no longer valid. For particles that are big and slow (as compared to the speed of light), the two theories give the same predictions as classical physics does. Thus in most situations, classical physics is still enough to describe the movement of bodies.

You may ask, is there something like relativistic quantum mechanics? Yes there is. It’s needed when particles are small and fast at the same time. However, this topic is quite complex and still the subject of current research. Unless stated otherwise, we only consider non-relativistic quantum physics on this website.

How Does Quantum Physics Affect Me?

You may have heard that an atom consists of a nucleus (protons and neutrons) and electrons that rapidly surround the nucleus. In classical physics it is well known that accelerated charged particles (like electrons) radiate energy. Well, the electrons that move in circles feel acceleration and thus should radiate energy. But if they would lose energy, they should classically come closer and closer to the nucleus, until they collide with it. In other words, classical theory predicts that atoms are unstable. This means you would not exist and the world as we know it would not exist.

To the rescue comes quantum physics, which postulates that only very specific – quantized – energy states can exist in an atom. And suddenly atoms become stable again. Pew, lucky for us!

Do you want more from quantum mechanics than just your life? Ok, we have one more.

You may have heard that your CD and DVD readers use a laser to read of information from your disks. Did you know that the invention of lasers was only possible with the knowledge of quantum theory? One makes use of the same energy quantization in atoms we were talking about before. Interested in the details? Let us know and we may write a complete article about how lasers work.

What Do You Now Know about Quantum Physics?

You should now know why quantum physics is called quantum physics. You should also have learned that classical physics would predict that atoms are unstable. This means you would not exist. Finally, quantum physics helped to invent amazing things like lasers, which we use in our CD and DVD drives. There are certainly more things you should know about quantum physics, and we plan to extent this article over time. If you have not done yet, have a look at our article Quantum Physics Introduction for Beginners to learn more.