The word quantum got its magical superpowers from quantum physics. But what is quantum?

Quantum realm, Quantum jumps, Quantum healing, Neophos Quantum.

It seems that both Hollywood screenplay writers, alternative practitioners and detergent producers all share a common joy for the word quantum. Are you writing a big scifi-screenplay and need to justify some random course of action? Just put quantum in front of whatever you are dealing with and suddenly it holds a mind-blowing mystique that needs no further explanation. (Cue Matthew McConaughey looking for quantum data in “Interstellar”).

Do any of these quantum-fications make any sense? And what even *is* quantum?

The word quantum got its magical superpowers from quantum physics. Quantum physics, also called quantum mechanics, describes the strange and unpredictable behavior of the smallest parts we know in the Universe. Quantum physics not only has wizard cool mathematical notation, it also has weird implications for particle physics and eventually allows us to determine what distant space objects such as the Sun and Jupiter are made of. But how? Maybe you already know that we get our information of distant objects via the light they emit, but do you also know what role quantum physics plays?

We will investigate all these questions when we go on a journey towards understanding how quantum physics works and what the word quantum means.

Before diving into the physics, let us first take a detour around music, just to sort of keep one foot inside the entertainment industry while trying to understand one of the most complicated areas of physics.

Life On Mars And Instruments On Earth

In the hit song “Life on Mars” David Bowie’s smooth voice is accompanied by the sound of a rock’n’roll guitar sending out tunes of A, C minor, C7 and F minor. The guitar is backed up by rhythms by the drums, a deep humming from a bass guitar, and characteristic keys on a piano.

I will go ahead and tell you straight away that I have never met David Bowie and I assume that neither have you. I never met his orchestra, I never went to any of his concerts and I never even owned an album of his. I only ever heard him on the radio or TV. So, how can we know which instruments are in his songs when we have never met him or his orchestra?

The answer is obvious for us. We simply listen to the song, and immediately we recognize the sounds of a guitar, a deep bass, a piano and a hammering set of drums. And we do not even have to be there live. A microphone recorded the song some fifty years ago and today we can replay the song by listening the recording, either from a CD, vinyl or cassette tape (or Spotify or Apple Music (hey there fellow kids)).

Figure 1: When instruments play they emit sound waves. We can pick up those waves using a microphone and forever store and listen to the music. Illustration: Astronomicca.

Instruments playing together make up the song that we all know, despite us not being anywhere near the musicians, i.e. the origin of the sound. We use a microphone to pick up the sound waves the song emits, and subsequently we use our ears to analyze the music and determine which instruments make up the song. We can do this as long as the emitted sound wave has a frequency above 20 Hz. This frequency is the lowest sound our human ear can hear.

It turns out that observing the Universe essentially works the same way, but instead of playing instruments and composing songs, the Universe plays atoms and composes objects. From that perspective, David Bowie’s tool is song writing while the Universe uses quantum physics.

Let us now jump headfirst into why space works like a giant music studio, and explore a bit what quantum physics is.

Quantum Jumps Are Not Actually Jumps – But They *Are* Quantum

You, me and everything around us is made up by atoms. The air we breathe is made of Oxygen atoms mixed with Nitrogen atoms. Circus balloons contain Helium atoms, and diamonds are made of Carbon atoms.

If we look a bit outside planet Earth, we know that the Sun is made mostly of Hydrogen atoms and Helium atoms. How do we know this, when we have never been there?

The answer is very similar to how we detect a song. All the atoms that make up the Sun work as tiny individual instruments.

Figure 2: When the Sun burn Hydrogen atoms in its core, it emits light waves. We can pick up those waves using a telescope and forever store and view the spectrum. Illustration: Astronomicca.

Picture the Hydrogen atom as a guitar. The Hydrogen atom emits a wave every time an electron makes a so-called quantum jump from a high energy level to a lower energy level (see illustration below). This is sometimes called a quantum jump, but it is in fact not an actual jump. The proper term is de-excitation. Vice versa, an excitation is when the energy goes from a low energy level to a higher, and in this case, it would be an absorption instead of an emission.

So, why is it not a jump? Let us look at the difference between a jump and a de-excitation.

A jump requires an object to have not only a start position and an end position, but the object also must move smoothly between these two points during the jump. An electron has only a start level and an end level. An electron does *not* exist between these two levels. In fact, the electron does not even have a locatable position. It is merely an energy package that disappears at one level and appears in another without being present anywhere in between those two levels. We will therefore go ahead and call the movement between two energy levels a transition and leave the expression “quantum jump” to those who enjoy using confusing alternative phrases for large leaps.

Figure 3: Unlike what many atom-illustrations convey, electrons do in fact not have a certain location. Instead, they each operate at a certain energy level, and only one electron can occupy one energy level at a time. Their locations are probabilistic, which means that there is some probability to find them in a certain place. But we can not know where. Illustration: Astronomicca.

Let us elaborate a bit on the nature of electrons as energy packages. Each state of the electron requires a specific energy, which means that when the electron transitions to an inner orbital (i.e. a lower energy state) then this difference in energy will be emitted as a wave of light. An atom emitting such a wave works much the same way as a guitar emitting a certain characteristic sound wave when it is played. When an electron makes a transition in an atom, we call the emitted light waves: photons.

The Lower Limit Of Waves

The human ear is unable to detect sound waves below a frequency of 20 Hz. This does not mean that sound waves do not exist below this limit, it just means that we cannot hear them. Sound waves do indeed exist below 20 Hz. Studies have found that elephants can hear sound waves around 15 Hz, and some animals probably even lower.

Light waves emitted by the de-excitation of electrons in atoms are limited by quantum physics, and this is a significant difference from sound waves. The lowest frequency a Hydrogen atom can emit is when an electron transitions from the 4th orbital to the 3rd. This has nothing to do with what we can detect. Instead, it is the lowest frequency that quantum physics *allows* a Hydrogen atom to emit – at least in our Universe. Who knows which laws govern other universes.

The electrons’ specific transitions in a Hydrogen atom create a unique pattern, which we call an emission spectrum. We measure an emission spectrum using a telescope to detect the signals much the same way we put up a microphone to detect the sound waves from an instrument. That way we have forever saved the waves emitted by atoms in for instance the Sun, and in some fifty years we can take out that spectrum and enjoy it without having to be anywhere near the Sun – like storing a recording of David Bowie’s music and listen to it without having to be anywhere near his orchestra.

Figure 4: The emission spectrum of Hydrogen. These lines are called the Balmer series and are the transitions from energy levels higher than 2 de-exciting down to 2. From Wiki Commons.

The emission spectrum of Hydrogen is different from that of Helium, because Helium is made up by more particles. Hence electrons in different atoms make different transitions that lead to different emission spectra. By observing the emission spectrum of for instance the Sun, we can identify the spectra of Hydrogen and Helium and from those we can conclude that Hydrogen and Helium are present in the Sun. The same goes for Jupiter, Pluto, Andromeda or any other space object.

Science also allows us to not only identify the fingerprints of specific elements in space objects far away, it also allows us to estimate the abundance with high accuracy. To understand how, we must picture a symphony orchestra with lots of string instruments instead of David Bowie’s band. Otherwise, we keep the same analogy with instruments being atoms.

Picture a symphony orchestra with 1 string instrument and 1 drum. They would take up roughly half of the sound space each. You would in other words hear each of them to an equal amount. But if you instead of 1 string instrument add 100, then the sound of violin tunes would sound way more intense compared to the drum.

Space observations work the same way. If one element, say, Hydrogen is way more abundant than, say, Helium then the emission spectrum of Hydrogen will be way more intense. This is how we estimate percentages of certain elements for instance in the Sun.

Quantum Is A Word To Describe The Package-like Behavior Of Energy

In this post we wanted to know what the word ‘quantum’ means. Quantum is the term used to describe how the energy of the electrons comes in packages. The energy does not smoothly move from one energy level to another, it simply vanishes from one level and occurs in another.

The energy is emitted (and absorbed but we left that part out to keep this somewhat short) in small packages called photons, and each photon has a well-defined energy. The energy of the emitted photon cannot just be anything. It can only have a certain value that is allowed by quantum physics. This is how our Universe works, and if you ask “Why?” you will get no answer. This is simply how it is.

There is much more to quantum physics than what is described here, but one very important characteristics of quantum physics is the package-like behavior of energy transmitted inside an atom. So, as you now know, it has little to do with detergent or the Marvel universe, and maybe it is even a bit less mysterious by now.

Another very important aspect of quantum physics is the non-deterministic nature of when some atoms chose to emit photons or even electron, neutrons and protons. But let us leave that for now and deal with that in part 2.

Credit, Sun spectrum: Pixabay, Wikimedia, Teresa Gonzalez.