Seriously, it is not that complicated

It was more than a 100 year ago that Max Planck introduced the notion of the quantization of radiation from a black body. The full-blown formulation of quantum mechanics is almost a hundred years old (the 5th Solvay conference more or less represents that achievement). Over the years since then, many ideas have been introduced about quantum physics in the struggle to understand it. Once new ideas have been introduced, nobody can ever remove them again regardless of how misleading they may be. Nevertheless, among these ideas, we can find enough information to form a picture representing an adequate understanding of quantum physics.

It would be very arrogant to claim that this understanding is unassailable or even complete. (I still have some issues with fermions.) Therefore, I simply call it my current understanding. It is a minimalist understanding in that it discards the unnecessary conceptual baggage (thus following Occam’s razor). Yet, it provides an ontology (although not one that guarantees everybody’s satisfaction).

I’ve written about many aspects of this understanding. So, where possible, I’ll thus link to those discussions. Where additional discussions may be necessary, I’ll postpone those discussions for later. Here then follows a breakdown of my current understanding of quantum physics.

Firstly, fundamental particles are not particles in the traditional sense. They are not “dimensionless points traveling on world lines.” Instead, they are better represented by wave functions or fields (or partites). Interactions among these fundamental fields (using the term “fields” instead of “particles” to avoid confusion) are dimensionless events in spacetime.

As a consequence, there is no particle-wave duality. Fields propagate as waves and produce the interference as, for example, seen in the double-slit experiment. Whenever these fundamental fields are observed as discrete entities, it is not a particle in the traditional sense that is being observed, but rather the localized interaction of the field with the device that is used for the observation.

Secondly, interactions are the key that leads to the quantum nature of the physical world. What Max Planck discovered was that interactions among fundamental fields are quantized. These fields exchange energy and momentum in quantized lumps. This concept was also reiterated in Einstein’s understanding of the photo-electric effect. Many of the idiosyncratic concepts of quantum physics follow as consequences of the principle of quantized interactions.

The Heisenberg Uncertainty Principle is not a fundamental principle. It is a consequence of the quantization relations associated with interactions. These relations convert conjugate variables into Fourier variables, which already represent the uncertainty principle. As a result, the conjugate variables inherit their uncertainty relationship from Fourier theory. It becomes more prevalent in quantum physics, due to the restrictions that the quantization of interactions imposes on the information that can be obtained from the observation of a single “particle.”

Planck’s constant only plays a physical role at interactions. Once these interactions are done, the presence of Planck’s constant the expressions of the fields have no significance. It can be removed through simple field redefinitions that have no effect on the physical representations of these fields. As a result, the significance that is attached to Planck’s constant in scenarios that are not related to interactions are generally misleading if not completely wrong.

Thirdly, another key concept is the principle of superposition. The interactions among fundamental fields are combined as a superposition of all possibilities. In other words, they are integrated over all points in spacetime and produce all possible allowed outcomes. As a consequence, after the interactions, the resulting fields can exist in a linear combination of correlated combinations. This situation leads to the concept of entanglement.

Since a single “particle” only allows a single observation, the different measurement results that can be obtained from the different elements in a superposition are associated with probabilities that must add up to one. The coefficients of the superposition therefore form a complex set of probability amplitudes. The conservation of probability therefore naturally leads to a unitary evolution of the state of the single particle in terms of such a superposition. This unitarity naturally generalizes to systems of multiple particles. It naturally leads to a kind of many-worlds interpretation.

It seems to me that all aspects of quantum physics (with the exception of fermions) follow from these three “principles.” At least, apart from the question of fermions, I am not aware of anything that is missing.

Just delete “vacuum fluctuations”

How do you build a tower? One layer of bricks at a time. But before you lay down the next layer of bricks, you need to make sure the current layer of bricks has been laid down properly. Otherwise, the whole thing may be tumbling down.

The same is true in physics. Before, you base your ideas on previous ideas, you need to check that those previous ideas are correct. Otherwise, you would be misleading yourself and others, and the new theories may not be able to make successful predictions.

Physics is a science, which means that we should only trust previous ideas after they have been tested through comparison with physical observations. Unfortunately, there are some ideas that cannot be checked so easily. Obviously, one should then be very careful when you base new ideas on such unchecked ideas. Some people blame the current lack of progress in fundamental physics on this problem. They say we need to go back and check if we have not made a mistake somewhere. I think I know where this problem is.

Over the centuries of physics research, many tools have been developed to aid the formulation of theories. These tools include things like differential calculus in terms of which equations of motion can be formulated, and Hamiltonians and Lagrangians, to name a few.

Now, I see that some people claim that most of these tools won’t work for the formulation of a fundamental theory that includes gravity with quantum theory. It is stated that a minimum measurement uncertainty, imposed by the Planck scale, would render the formulation of equations of motion and Lagrangians at this scale impossible. Why is that? Well, it is claimed that the uncertainty at such small distance scales is large enough to allow tiny black holes to pop in and out of existence, creating havoc with spacetime at such small scales. This argument is the reason why people consider the Planck scale as a fundamental scale beneath which our traditional notions of physics and spacetime break down.

But why does uncertainty lead to black holes popping in and out of existence? It comes from an unchecked idea based on the Heisenberg uncertainty principle, which claims that it allows particles to pop in and out of existence, and such particles can have larger energies when the time for their existence is short enough. This hypothetical process is generally referred to as “vacuum fluctuations.” However, there does not exist any conclusive experimental confirmation of the process of vacuum fluctuations. Therefore, any idea based on vacuum fluctuations is an idea based on an unchecked idea.

Previously, I have explained that the Heisenberg uncertainty principle is not a fundamental principle of quantum physics, but instead comes from Fourier theory. As such the uncertainty principle represents a prohibition and not a license. It imposes restrictions on what can exist. Instead, people somehow decided that it allows things to exist in violation of other principles such as energy conservation. This is an erroneous notions with no experimental confirmation.

Hence, the vacuum does not fluctuate! There are no particles popping in and out of existence in the vacuum. There is nothing in our understanding of the physical world that has been experimentally confirmed which needs the concept of vacuum fluctuations.

Now, if we get rid of this notion of vacuum fluctuations, several issues in fundamental physics will simply disappear. For example, the black hole information paradox. A key ingredient of this paradox is the idea that black holes will evaporate due to Hawking radiation. The notion of Hawking radiation is another unchecked idea, which is based on …? You guessed it: vacuum fluctuations! So if we just get rid of this silly notion of vacuum fluctuations, the black hole information paradox will evaporate, instead of the black holes.

Why not an uncertainty principle?

It may seem strange that there are no fundamental physical principle for quantum physics that is associated with uncertainty among those that I have proposed recently. What would be the reason? Since we refer to it as the Heisenberg uncertainty principle, it should qualify as one of the fundamental principles of quantum physics, right? Well, that is just it. Although it qualifies as being a principle, it is not fundamental.

It may help to consider how these concepts developed. At first, quantum mechanics was introduced as an improvement of classical mechanics. Therefore, quantities like position and momentum played an important role.

A prime example of a system in classical mechanics is the harmonic oscillator. Think of a metal ball hanging from a spring. Being pulled down and let go, the ball will start oscillating, moving periodically up and down. This behavior is classically described in terms of a Hamiltonian that contains the position and momentum of the metal ball.

In the quantum version of this system, the momentum is replaced by the wave vector times the Planck constant. But position and the wave vector are conjugate Fourier variables. That is the origin of the uncertainty. Moreover, it also leads to non-commutation when position and momentum are represented as operators. The sum and difference of these two operators behave as lowering and raising operators for quanta of energy in the system. The one reduces the energy in discrete steps and the other increases it in discrete steps.

It was then found that quantum mechanics can also be used to improve classical field theory. But there are several differences. Oscillations in fields are not represented as displacements in position that is exchange into momentum. Instead, their oscillations manifest in terms of the field strength. So, to develop a quantum theory of fields, one would start with the lowering and raising operators, which are now called creation and annihilation operators or ladder operators. Their sum and difference produce a pair of operators that are analogues to the position and momentum operators for the harmonic oscillator. In this context, these are called quadrature operators. They portray the same qualitative behavior as the momentum and position operators. They represent conjugate Fourier variables and therefore again produce an uncertainty and non-commutation. The full development of quantum field theory is far more involved then what I described here, but I only focused on the origin of the uncertainty in this context here.

So, in summary, uncertainty emerges as an inevitable consequence of the Fourier relationship between conjugate variables. In the case of mechanical systems, these conjugate variables come about because of the quantum relationship between momentum and wave vector. In the case of fields, these conjugate variables comes from the ladder operators, leading to analogues properties as found for the formal description of the harmonic oscillator. Hence, uncertainty is not a fundamental property in quantum physics.

The origin of Heisenberg uncertainty

Demystifying quantum mechanics II

Perhaps the one thing that everyone thinks about when they hear talk about quantum mechanics is Heisenberg’s uncertainty principle. It may even sometimes be considered as the essence of quantum mechanics. Now what would you say if I tell you that the Heisenberg uncertainty principle is not a fundamental principle and that the origin of this principle is not found in quantum mechanics? The fundamental origin of this uncertainty is a purely mathematical property and the reason that quantum mechanics inherited this principle is simply a result of the Planck relationship.

Werner Heisenberg

I have discussed this issue to some extent before. However, it forms an important part of the knowledge that would help to demystify quantum mechanics. Therefore, it deserves more attention.

Before the advent of quantum mechanics, the state of a particle was considered to be completely described by its position and velocity (momentum). The dynamics of a system could then be represented by a diagram showing position and velocity of the particle as a function of time. For historical reasons, the domain of such a diagram is called phase space. For a one-dimensional system (such as a harmonic oscillator), it would give a two-dimensional graph with position on one axis and velocity on the other. The state of the system is a point on the two-dimensional plane that moves along some trajectory as a function of time. For a harmonic oscillator, this trajectory is a circle.

A mathematical property (in Fourier analysis), which may have seemed to be complete unrelated at the time, is that the width of the spectrum of a function has a lower limit that is proportional to the inverse of the width of the function. This property has nothing to do with physical reality. It is a purely logical fact that can be proven with the aid of mathematics. If the function is, for instance, interpreted as the probability distribution of the position of a particle, the width of the function would represent the uncertainty in its location.

This mathematical uncertainty property was transferred to phase space by Planck’s relation, which links the independent variable of the spectrum (the wave number) with the momentum or velocity of the particle. The implication is that one cannot represent the state of a quantum particle with a single dimensionless point on phase space in quantum mechanics. Hence, the Heisenberg uncertainty principle.

So, the uncertainty associated with Heisenberg’s principle is inevitable due to Planck’s relation. And it is founded on pure logic in terms of which mathematics is based. Planck’s relation is the only physics that enters the picture. The Heisenberg uncertainty principle is therefore not a separate principle that is independent of Planck’s relationship as far as the physics is concerned.

Now, there are a few subtleties that we can address. There are also some interesting consequences based in this understanding, but I’ll leave these for later.