Classical physics, explore its branches and what it is

Many times we have heard the terms quantum physics, classical physics, Newtonian physics or statistical physics. But what do these terms really mean? Today we are going to learn what classical physics really is and what areas of science are included in it.

We will see each of its branches one by one and we will give examples of its application in our daily lives.

Classical physics can be considered all physics that is not quantum. Therefore, kinematics, dynamics, classical thermodynamics, classical electrodynamics, optics or fluid mechanics would be part of the classical theory of physics.

Furthermore, within the category of classical physics we also incorporate special relativity and general relativity since they are part of classical field theories.

Therefore, quantum mechanics, relativistic quantum mechanics, quantum statistical mechanics or quantum field theory are branches of physics that are not included within what we know as classical physics or mechanics.

With it we can explain most of the phenomena of our universe and more specifically of our planet. In addition, it allows us to calculate everything necessary to create our technology. For example, we use classical mechanics to make rockets or airplanes fly. Also to float boats or to calculate the forces that a building has to withstand.

In this article we will talk about the branches of classical physics and the differences with modern physics. However, we recommend reading our article on quantum mechanics since it is an exciting world, full of mysteries and with many interesting applications in our society.

Physicists today consider classical physics to be all branches of physics that do not use quantum mechanics to make their predictions. Special relativity, thermodynamics, fluid mechanics or kinematics are examples of this type of physics.

Classical physics includes many very different branches of study. We will give a small explanation of some of it. It is important to note that branches are just a way to divide knowledge. In reality, everything is part of the same fundamental laws.

In classical mechanics we include everything related to Newton's laws. All the laws of dynamics and kinematics are included in this field of physical sciences. Therefore, we can define it as that area that studies the movement of bodies and their evolution over time.

After Newton's laws, reformulations of classical mechanics emerged that allowed many physical problems to be simplified.

Some of these reformulations are Lagrangian mechanics where the trajectory of a body is studied by finding the trajectory that minimizes the action, or what is the same, using the famous principle of minimum action.

Another type of reformulation of classical mechanics is Hamiltonian mechanics. In many cases the Hamiltonian reformulation is more useful than the Lagrangian since its equations are first order and the equations derived from the Lagrangrian formulation are second order, being more difficult to solve.

Classical mechanics is a very interesting field of physical sciences since the Lagrangian or Hamiltonian are concepts that extend to quantum theories.

For example, the Schrödinger equation is formulated from the Hamiltonian operator, which is analogous to classical Hamiltonian mechanics.

The Lagrangian is also used in quantum field theory to define the energy of a certain quantum field and all the gauge symmetries associated with it.

Classical electrodynamics is the part of electromagnetism that studies the evolution over time of physical systems related to electrical and magnetic phenomena.

These systems are studied using mathematical tools called fields. Therefore, the object of study of this branch of science is electric fields and magnetic fields.

At each point in the field a vector is associated that represents the strength of the electric/magnetic field.

The behavior of classical fields is defined by Maxwell's famous laws.

Later, classical electrodynamics was quantized to explain in deep detail the interactions of charged particles such as electrons. Simplifying, quantum electrodynamics says that the different electromagnetic interactions are due to an exchange of bosons, which in this case are photons.

Therefore, the typical repulsions and attractions between charges occur due to the exchange of virtual photons. In another publication we will go into more detail about quantum field theory and more specifically into quantum electrodynamics. It's an exciting area of ​​physics!

It is important to differentiate classical electrodynamics from quantum electrodynamics. In the classical variant we use classical fields to describe the systems. In quantum electrodynamics driven by Feynman we use quantization rules to transform the classical field into a quantum one.

Thermodynamics is the part of physics that studies heat, temperature and work in relation to energy, radiation and properties of matter.

There are different branches of thermodynamics. We have chemical thermodynamics, which studies the energies that take place in a chemical reaction, and statistical thermodynamics, which studies thermodynamics from a microscopic point of view. That is, any macroscopic property is a consequence of an average of what occurs microscopically.

For example, the temperature of a system is given by an average of the kinetic energy of the molecules contained in said system.

Another branch is classical thermodynamics which studies the exchange of heat and energy in systems near equilibrium. Also study the different thermodynamic cycles that exist, such as the Carnot cycle.

In short, this field tries to understand how energy is transferred and lost in all types of physical systems that we can find.

Some people separate classical physics from general relativity. However, the majority of physicists in the world consider it part of classical physics since its mathematical formulation requires classical field definitions.

General relativity is described by Einstein's field equations. These mathematical expressions relate how space-time is deformed by matter and how the behavior of matter is conditioned by the curvature of space-time.

This theory defines the force of gravity as a consequence of the curvature of space-time.

To define how the space-time fabric curves at each point we need to use two very powerful mathematical tools: differential geometry and tensor algebra.

Since we are talking about curvatures we can no longer use the functional analysis that we learn in school. Since this deals with problems defined on Euclidean vector spaces, that is, on a plane geometry. It is for this reason that we have to use the power of differential geometry that generalizes the vector calculus of Euclidean spaces into special topological spaces called manifolds.

In future publications we will discuss general relativity in more depth and detail so that you can understand once and for all what it is about and how Einstein formulated the field equations.

Modern physics is usually described as those post-Newtonian laws and theories. The physics we know today began with Newton's book Principia Mathematica where Newton's famous laws were explained, along with the law of universal gravitation.

Therefore, all relativistic and quantum theories are part of modern physics. However, there is no radical difference between these two concepts since there is an intersection. For example, Einstein's general relativity is considered modern physics, but at the same time, it is also considered a classical theory of physics since it is not based on quantum principles.

The only part of physics that falls within the concept of modern and non-classical physics is quantum mechanics. This was formulated at the beginning of the 20th century, therefore, since it was proposed after Newton, we consider it to be modern. But it is not classical, since as we have defined in previous sections we say that a theory is classical if it is not quantum.

Classical Physics, with its fundamental principles and established laws, has promoted countless applications in various fields of science, technology and engineering. From the design of structures to the operation of electronic devices, Classical Physics provides the conceptual framework necessary to understand and develop a wide range of technologies and practical applications.

One of the most prominent areas where Classical Physics finds application is in civil and mechanical engineering. The principles of Newtonian mechanics, such as the law of gravity and the laws of motion, are fundamental to designing safe and efficient structures, from bridges and buildings to vehicles and industrial machinery.

The application of Classical Physics in engineering includes the analysis of forces, stresses, deformations and fluids, as well as the optimization of designs to resist static and dynamic loads. Civil and mechanical engineers use concepts such as statics, dynamics, strength of materials, and classical thermodynamics to create structures and machines that are safe, reliable, and efficient.

Classical Physics also underlies the operation of electronic devices and telecommunications systems. The principles of classical electromagnetism, formulated by Faraday and Maxwell, are essential to understanding how electricity and magnetism interact and propagate through space.

In electronics, the application of Classical Physics includes the design and manufacture of electrical and electronic circuits, semiconductor devices, transistors, diodes, amplifiers and microchips. In telecommunications, classical electromagnetic theory is applied in the design of antennas, signal transmission and reception systems, communication networks and wireless technologies.

Classical Physics also plays an important role in medicine and medical diagnosis. Imaging techniques such as radiography, computed tomography (CT), and magnetic resonance imaging (MRI) apply the principles of the physics of electromagnetic waves and the interaction of radiation with matter to produce detailed images of the inside of the body. human.

Additionally, the application of Classical Physics in medicine includes the design and manufacture of medical devices such as physical therapy equipment, surgical instruments, monitoring systems and diagnostic equipment, all of which rely on the principles of mechanics, electricity and magnetism for its operation.

The exploration of outer space and the study of the universe also benefit from the application of Classical Physics. The principles of celestial mechanics, based on Kepler's laws and Newton's law of universal gravitation, allow astronomers to predict and model the motion of planets, stars, and galaxies over time.

In space exploration, Classical Physics is used to design and calculate the trajectories of space probes, launch vehicles and artificial satellites, as well as to understand astrophysical phenomena such as supernovae, black holes and galaxy formation.