classical physics vs quantum

Classical Physics vs Quantum Physics- The major Difference


What is the difference between classical physics and quantum physics?

Physics that studies and explains the phenomena that occur in the domain of atoms, their nuclei, and elementary particles are called quantum; and the basic mathematical theory that explains the movements and relationships in this field is called quantum mechanics. However, it should not be thought that quantum physics does not correspond to the macroscopic world. In fact, all physics is quantum; and its laws as we know them today, constitute our MOST GENERAL laws of nature. Watch video on “The Secrets of Quantum Physics” on Amazon Prime-

In the macroscopic world, the laws of nature that have been discovered are the so-called laws of classical physics. These deal with those aspects of nature for which the question of what is the ultimate constitution of matter, is not something that matters immediately. When we apply classical physics laws to macroscopic systems, we try to describe only certain global features of the system’s behavior. The finer details of system behavior are ignored. Watch video “Secrets of Quantum Physics”-

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In this sense, the laws of classical physics are approximate laws of nature, and we must consider them as limit forms of the laws of quantum physics, more fundamental and much more comprehensive. Classical physics theories are phenomenological theories. Within a certain small physics domain, a phenomenological theory aims to discover and summarise experimental evidence. In the field of physics, it is not meant to explain everything. If it is a good phenomenological theory, it will describe any aspect within that limited domain very precisely. In reality, all physical theory is phenomenological (it deals with the phenomena or events or facts that occur). 

Drawbacks of Classical Physics Theory

As we say, the classical physics theories do not have universal validity, although they are very good phenomenological theories, they do not say everything about macroscopic bodies. For example, we cannot explain why densities are?, what they are?, why the elastic constants of materials have the values they have?, why a bar breaks when we subject it to a tension beyond a certain limit?, why copper melts at 1083ÂșC?, why sodium vapor emits yellow light?, why the sun shines?, why the uranium nucleus disintegrates spontaneously?, why silver conducts electricity?, why sulfur does not conduct electricity? etc.

What came before the Big bang?

One could go on with many examples from everyday life or that have a certain impact on many things of this everyday life, about which classical physics has little or nothing to tell us. Man has always been and continues to be interested in knowing or explaining where he came from and how everything works? and that is why he investigates seeking to know if there is a general theory of matter.

Today we do not have a detailed theory for everything that happens in our world, however, and especially in the 20th century, much progress has been made, for example, now understanding very well the facts of chemistry and the properties of macroscopic matter. In these domains of physics, it is possible today to answer questions that could not be resolved within the classical physics theory. 

Particle Physics

We can say today that the standard model of particle physics, which is based on the rules of quantum mechanics, tells us how the world is built from certain fundamental blocks, which are held together by the exchange of energy in particle. Still, we do not believe that said standard model is the definitive one since the human being through his intelligence continues in the search.

Is there something innate or genetic embedded in man’s nature that leads him to this quest? Is it a call or a message left by someone? Is it the likeness of a creator God that we have incorporated? It is very likely that no one is interested in this to spend more than a fraction of their time, but we cannot say that what the duration of the said fraction.

When the physicist Max Planck studied the radiation of the black body, which is an incandescent body, he concluded that the energy was absorbed and emitted in quanta of energy proportional to the frequency of the light that is radiated. The constant of this proportionality is a number, very, very small, of the order of 10 -34, that is 0.000000000000000000000000000000001. It is good now to try to have a certain sensitivity to realize how far our daily experiences are from what we call the quantum world. 

Supersymmetric standard model

If there were a sugar cube of this dimension in cm, we would need several trillion (exactly 10^ 34) of these objects to cover the distance of 1 cm. Let’s see what this is in our reality. If we were to take the same amount of sugar cubes (10^ 34 ) and put them side by side, they would cover a distance of 1 billion light-years. 

The quantum world operates on a much smaller scale than the relationship between the size of a sugar cube and that of the entire observable universe.

Let us pause for a moment in the dimension of an atom. If we accept as a model that of a nucleus and an external “cloud” of electrons, the dimension of the nucleus is 10^-13 cm and that of the entire atom, that is, with the electron cloud is 10^ -8 cm; To perceive the relationship, if the the nucleus was 1 cm, the cloud of the most external electrons, and it would be at a distance of 10 5 cm, which is 1 km.


So the quantum world is the world of the smallest parts that make up matter, the microworld, the world of subatomic particles. The first subatomic particle to be the electron was only discovered in 1897. Particle physicists have developed models to understand what things are made of and how different parts interact with each other.

Based on the quantum mechanics laws, the standard model of particle physics shows us how the universe is composed of tiny blocks of quarks and leptons that are kept together by the exchange of particles called gluons and bosons. Unfortunately, this model does not include everything; for example, it does not include the gravitational field.

The structure of theoretical physics in the 20th century was built on two major theories, the General Theory of Relativity, which describes gravity and the macro universe, and Quantum Mechanics, which describes the microworld. The unification of both in a theory that encompasses everything is what scientists in the 21st century are looking for.

Despite this search, any improved physical theory will include quantum theory. None of these theories will perhaps be able to explain the strangeness of the quantum world, for the standards used in daily life and the common sense of people. Quantum challenges common sense, or better said, it does not make sense even though it explains with unusual precision all the phenomena that occur in the world of subatomic particles.

One of the classic examples is the phenomenon of the double identity of light and all known particles. Double identity is given by the wave identity and the particle identity. JJ Thompson opened the microworld to research when he discovered the electron as a particle. Three decades later, his son George Thompson proved that the electrons were waves.

They were both right, and they both won the Nobel Prize for their research. An electron is then a particle. It is also a wave, or rather, it is neither one thing nor the other, but rather a quantum entity that responds to certain experiments behaving like a wave and to other experiments with other characteristics behaving like a particle.

The same goes for light; It can behave as a beam of particles called photons or as a set of waves of different wavelengths, depending on the circumstances. Certainly, light is both, even though it does not manifest itself clearly in our daily life, which is why we do not consider the consequences of this double identity as something clear to our common sense.

Quantum Uncertainty

All this is also related to the phenomenon of quantum uncertainty; which means that a quantum entity, for example, a moving electron does not have a set of well determined or defined properties such as we could find that a billiard ball has when rolling by the plush of a table where it has a speed and a determined position at every moment. The quantum entity, in our case the electron moving or orbiting a nucleus, or moving through a thread of electric current, cannot know precisely where it is or where it is going. 

This, that is mentioned here may seem an irrelevant phenomenon, something without importance for our daily life (who cares, what an electron does !!). But in reality, this quantum uncertainty allows a nucleus of a hydrogen molecule to join each other in a process called nuclear fusion, which is the basic source of solar energy. 

This means that neither more nor less than if this concept of quantum uncertainty did not exist, the sun would not be what it is. Therefore, we would never ask ourselves about these “trivial” and “meaningless” things because we simply would not exist.

Recommended Books

1.  Mathematics of Classical and Quantum Physics

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