The word "Nature” is a very broad term. It can be used to refer to very different things. For example, a predator hunting prey is a manifestation of nature, a volcano that is erupting (or not) is part of nature, the weather cycle, the movement of tectonic plates, the bio-diversity of the planet, the mineral resources, the landforms, the constellations, the stars, etc. are the kind of stuff that comes to mind when one refers to the term “nature”.
Then there is nature that does not occur naturally.
The artificial world created by man is also part of nature. The air conditioning system in my room, the electric power supply, the device on which I am writing down this post, and the internet where I hope to share my thoughts with you, are also part of nature.
For the naturalist out there, the things made by man might not be as majestic and holy as the ones made by God. For the physicist, on the other hand, the things made by God and the things made by man are all made up of the same stuff. The predator and the keyboard are both made up of atoms, and the predator hunting the prey and the keyboard typing a letter are both manifestations of the same laws of nature. These laws of nature present a few mysteries as we dig deep into the building blocks of matter and energy. These building blocks can be conveniently referred to as quanta. We will discuss these more in a while.
Nature at the most basic “quantum” level
Nature at the level of building blocks of matter and energy is very different from how we experience it in our everyday life. In our everyday life, we experience that a ball thrown towards a wall will hit the wall and bounce back. With practice and more experience, we can predict where the ball will hit on the wall. This determinism is the hallmark of the world around us, and it vanishes as we approach nature at the most basic level.
A quantum ball thrown at a wall may or may not bounce back. It may just tunnel through the wall. Even if it does bounce back, there is absolutely no way to tell where it will hit the wall. This is a mystery of nature.
Nature seeks to hide the information at the most fundamental level.
Building blocks of matter and energy
Let us look at the examples of the quantum ball discussed above --- the building blocks of matter and energy. The building blocks of matter are atoms. They themselves are made up of sub-atomic particles. The most interesting one is the electron. The electrons in motion constitute the electric current we are all familiar with (It runs all our electrical and electronic appliances). A single electron fired towards a negatively charged plate is an example of a quantum ball hitting the wall.
The building blocks of energy (for our purpose today) are photons. These are a little hard to explain, but a working understanding is all we need to follow the argument.
Look at the light source in your room. The light coming towards you basically consists of a large number of photons. The brighter the light is, the more abundant the photons are. If you reduce the intensity of light, for example, by placing a screen in front of you, you reduce the number of photons reaching you. The things we see are because of the photons reaching our eyes--- either directly emitted or scattered by those things (there is also a part of the vision that we do not actually see and merely cook up in our brains. That is the story of another mystery).
Interactions between building blocks
The interactions between the building blocks of matter and energy are simple. An atom can absorb a photon and go into the excited energy state. It can later emit that energy and come back to its preferred ground state. This simple energy exchange is at the heart of a technique that uniquely identifies all the elements in the universe and has been efficiently used by scientists for the last 200 years.
The mystery
The mystery involved in the simple energy exchange is that nature does not allow us to know when an atom will absorb the photon. If there are a bunch of atoms, we can not know which one will absorb it. Once an atom goes into the excited state, we do not know when it will emit light to come back to the ground state. We can not know in which direction the emitted photon will go. We can not know which atom it will excite next.
The seemingly simple questions tend to be nature’s deeply guarded secrets.
Nature’s answer to all the above questions is the following: “God will play a dice, and a random output will be selected”. This randomness is the mystery of nature. Nature at the quantum level plays a dance between the atoms and the photons, and we are never allowed to know the next step. This is one of nature’s most secretly guarded mystery, and a fundamental limitation to our knowledge.
Away from this deep level, nature does not have problems with us uncovering its secrets. It has let us hear the whispers of the universe that were uttered over a billion ago. It has very recently allowed us to look at the very early light of the universe. But it has issues if we ask which photon we will see next. If you find it a bit uncomfortable, then you are not alone. This state of affairs has troubled some of our very best minds.
We remain unaware of the mystery because we seldom witness individual quantum events. We always experience such a large collection of these events happening so fast that the underlying dance and the mystery are completely masked. However, there are ways to explore and appreciate the mystery.
A thought experiment
Imagine yourself in a well-lit room with a few more people. You can all agree on everything you see in the room, including the color of the light. We take the color of light to be white to be more dramatic. Now here comes the first surprise.
There are no white photons.
The white color you see is your brain’s way of coping with an enormous number of differently colored photons. “How enormous is that number?" can be easily googled or read in another post.
Now let’s slow down things. Imagine that we reduce the intensity of light. This will lower the number of available photons, the room will become darker, and it will be difficult to distinguish colors. This is a limitation of our vision. Our eyes are not designed to see the colors in the dark. The night vision receptors in our eyes are different from the ones we use in daylight. However, we can overcome this limitation by pretending that we have people with exceptionally good vision (after all, this is a thought experiment).
If we keep on reducing the intensity of light, we will reach a point where only a few photons will be emitted by the source at a time (Single-photon sources are commercially available). At this point, it will be pitch dark, and the mystery will reveal itself.
The source will still keep on emitting photons --- one at a time, but not all those photons will reach the eyes of the people in the room. Most of the time, they will report no light. Once in a while, someone in the room will report a little light spark. Every time this happens, he will be alone to report it. No one else in the room will see it. No two people will ever report the same spark. When you see the spark, no one else in the room will be able to see it, and when someone else sees it, you won’t be able to see it. A single photon may go anywhere in the room, but it can only be seen by a single individual (one receptor in one eye only).
Moreover, the color of the spark will never be white simply because there are no white photons. Every time the light is emitted, it will have a different color may be red, green, or blue. Every time a person reports the light spark, he will report a different color. Every event now will be a different subjective experience.
If you visualize the scenario discussed above, you can appreciate the quantum dance nature is playing. Now here is something to baffle your sense of reality.
The quantum dance is going on right now in front of all of us.
The scenario discussed in the thought experiment above is the reality that is going on right now in front of all of us. The part of the light that you are seeing right now can not be seen by any other person. The other person sees the other part of the light. The only thing is that we have so much light available that all subjective experiences coalesce into one objective reality. In our experiment, if we restore the light to its normal intensity, the quantum dance will disappear, and everyone will once again start reporting “white” light.
Nature’s naked mystery
The mystery has its uses. The randomness and the indeterminism that follows may help us come up with a satisfactory explanation for free will. We might be able to settle the age-old debate regarding the emergence of life on the planet and our existence. We might come up with new philosophies in light of how nature behaves at the very fundamental level.
The random quantum dance going on in nature at the very basic level is a naked mystery. It is a mystery because nature never allows us to guess the next step, and it is naked as the dance is going on in front of all of us all the time.
Thanks for reading the post. I hope you have enjoyed it. You can read more about quantum theory (in a non-technical description) here.