Atoms, Radiation & Complementarity

In the last piece we introduced the idea that gravity and light are two fundamental forces of nature. In general, these forces govern the interactions of the very large. In this piece we will discuss the strong and weak nuclear forces which govern the very small. We will also use these forces to explain a principle of complementarity in physics called wave particle duality.

The strong interaction

Let us begin with the humble atom. For those who do not know, atoms are the building blocks of matter and an atomic nucleus contains two types of blocks called nuclei. The first nucleon is the proton which has a positive charge, the second is the neutron which has no net charge and the final component of a complete atom is the electron which orbits the atomic nucleus much like a planet orbits a star. One might ask: if a neutron has no charge and a proton has a positive charge, how are they held together? The answer is the strong nuclear force; whose associated particle is conveniently named the gluon and causes the neutron and proton of an atomic nucleus to adhere to one another. The strong nuclear force is so named because it is the strongest force in the universe, orders of magnitude stronger than gravity but it only acts over a very small distance; about one attometer which is about one quadrillion times smaller than the diameter of a human hair, while in theory gravity has an infinite range.

A diagram of an atom of Helium

The weak interaction

So far we have identified that the nucleus of an atom contains both protons and neutrons. Now, what if I said that protons and neutrons are made of the same substance and that a proton can become a neutron and visa versa? Well, believe it or not it's true and we call this the weak interaction and it's responsible for radioactive decay and nuclear fission. There are numerous types of radiation in the universe, in particular the conversion of a neutron into a proton or visa versa is called beta decay and occurs by the exchange of bozons, which are the associated particles of the weak field, just as the gluon is the associated particle of the strong field. But curiously, radiation can come in either the form of a particle or in the form of a wave. Alpha decay (a type of radioactive decay) involves emission of an alpha particle. Beta decay (which we have already discussed) causes the emission of an electron, which can exist as either a wave or particle and finally gamma decay, which propagates as gamma radiation in the form of a wave.

A diagram of alpha, beta & gamma decay

Wave particle duality

This leads me to a discussion about complementarity. As we have seen from radioactive decay, matter can exist as a wave or a particle. In general we describe things in terms of its wave like properties or its particle like properties for the sake of convenience and it marks an inadequacy in the English language to describe the true nature of matter. It becomes necessary to introduce a new term to the problem of the nature of matter and that term is superposition. Superposition is a term which allows us to expand on the concept that something can exist as a wave or a particle by introducing what I can only describe as a riddle: For a binary operation in A and B, if the result is not A and not B, not both and not either, then what is it? This is the riddle of superposition and underpins the limitations of our understanding of the nature of our reality. Every observable in the universe is in a state of superposition (so it is not a wave, it is not a particle, it is not both and it is not neither). An observable will only leave superposition upon observation. The only means we have as humans to make observations is to shed light on the problem, literally and figuratively. So if there is no light falling on an object you wish to observe then objects are in a superposition of states and have no duty to remain bound in any particular position. This has many counterpoints with a theory called Heisenberg's uncertainty principle, where he states that an object has either known momentum or known position but never both simultaneously. Like a footballer, when the footballer is in motion his position is unknown but his momentum is well understood because he is in motion. When he stops running his position becomes certain again, but he's stopped moving so we have no idea what his momentum is. So what does this mean for us, the noble observer? Well it means that objects in the very room you sit in are stationary only because you can observe them to be. The act of observation keeps them from entering a superposition of states. Turn off the lights and they enter superposition, meaning they no longer have any obligation to remain in a fixed position because you have no means of observing otherwise. Verification of the concept of superposition was achieved with Young's double slit experiment in 1803, however intimations of this unusual effect come even earlier than this. I would like to finish with a quote from Werner Heisenberg.

"The two mental pictures which experiments lead us to form one of particles, one of waves are both incomplete and have only the validity of analogies which are accurate only in limiting cases [...] the apparent duality arises in the limitations of our language."