Modern Physics

The 13 branches of classical and modern physics

Between the branches of classical and modern physics , we can highlight acoustics, optics or mechanics in the most primitive field, and cosmology, quantum mechanics or relativity in those of more recent application.

Classical physics describes the theories developed before 1900 and modern physics the events that occurred after 1900. Classical physics deals with matter and energy, on a macroscale, without delving into the more complex quantum studies, subjects of modern physics.

Branches of classical physics

1- Acoustics

The ear is the biological instrument par excellence for receiving certain wave vibrations and interpreting them as sound.

Acoustics, which deals with the study of sound (mechanical waves in gases, liquids and solids), is related to the production, control, transmission, reception and effects of sound.

Acoustic technology includes music, the study of geological, atmospheric and underwater phenomena.

Psychoacoustics studies the physical effects of sound on biological systems, present since Pythagoras first heard the sounds of vibrating strings and hammers that hit anvils in the sixth century BC. C. But the most impressive development in medicine is ultrasound technology.

2- Electricity and magnetism

Electricity and magnetism come from a single electromagnetic force. Electromagnetism is a branch of physical science that describes the interactions between electricity and magnetism.

A magnetic field is created by a moving electric current, and a magnetic field can induce the movement of charges (electric current). The rules of electromagnetism also explain geomagnetic and electromagnetic phenomena, describing how charged particles of atoms interact.

In the past, electromagnetism was experimented on based on the effects of rays and electromagnetic radiation as the effect of light.

Magnetism has been used as a fundamental tool for compass-guided navigation.

The phenomenon of electrical charges at rest was detected by the ancient Romans, who observed the way in which a comb rubbed attracted particles. In the context of positive and negative charges, like charges repel and others attract.

3- Mechanics

It is related to the behavior of physical bodies, when they are subjected to forces or displacements, and to the bodies’ subsequent effects on their environment.

In early modernism, scientists Jayam, Galileo, Kepler, and Newton laid the foundations for what is now known as classical mechanics.

This sub-discipline deals with the movement of forces on objects and particles that are at rest or moving at speeds significantly slower than that of light. Mechanics describe the nature of bodies.

The term body includes particles, projectiles, spaceships, stars, parts of machines, parts of solids, parts of fluids (gases and liquids). Particles are bodies with little internal structure, treated as mathematical points in classical mechanics.

Rigid bodies have size and shape, but maintain a near-particle simplicity and can be semi-rigid (elastic, fluid).

4- Fluid mechanics

Fluid mechanics describes the flow of liquids and gases. Fluid dynamics is the branch from which subdisciplines such as aerodynamics (study of air and other gases in motion) and hydrodynamics (study of liquids in motion) emerge.

Fluid dynamics is widely applied: for calculating forces and moments in aircraft, determining the mass of oil fluid through pipelines, in addition to forecasting weather patterns, compressing nebulae in interstellar space, and modeling weapon fission nuclear weapons.

This branch provides a systematic framework that encompasses empirical and semi-empirical laws derived from flow measurement and used to solve practical problems.

The solution to a fluid dynamics problem involves calculating fluid properties such as flow velocity, pressure, density and temperature, and functions of space and time.

5- Optics

Optics deals with the properties and phenomena of visible and invisible light and vision. Study the behavior and properties of light, including its interactions with matter, and create appropriate instruments.

Describe the behavior of visible, ultraviolet and infrared light. Since light is an electromagnetic wave, other forms of electromagnetic radiation, such as X-rays, microwaves, and radio waves, have similar properties.

This branch is relevant to many related disciplines such as astronomy, engineering, photography and medicine (ophthalmology and optometry). Its practical applications are found in a variety of technologies and everyday objects, including mirrors, lenses, telescopes, microscopes, lasers and optical fibers.

6- Thermodynamics

A branch of physics that studies the effects of work, heat, and energy on a system. It was born in the 19th century with the appearance of the steam engine. It only deals with the observation and response on a large scale of an observable and measurable system.

Small-scale gas interactions are described by the kinetic theory of gases. The methods complement each other and are explained in terms of thermodynamics or kinetic theory.

The laws of thermodynamics are:

  • Enthalpy law : relates the various forms of kinetic and potential energy in a system to the work that the system can perform, plus heat transfer.
  • This leads to the second law and the definition of another state variable called the law of entropy .
  • The zero law defines large-scale thermodynamic equilibrium, of temperature as opposed to the small-scale definition related to the kinetic energy of molecules.

Branches of modern physics

7- Cosmology

It is the study of the structures and dynamics of the Universe on a larger scale. Research on its origin, structure, evolution and final destination.

Cosmology, as a science, originated with the Copernican principle – celestial bodies obey physical laws identical to those of the Earth – and Newtonian mechanics, which allowed us to understand these physical laws.

Physical cosmology began in 1915 with the development of Einstein’s general theory of relativity, followed by major observational discoveries in the 1920s.

Dramatic advances in observational cosmology since the 1990s, including the cosmic microwave background, distant supernovae, and galaxy redshift surveys, have led to the development of a standard cosmological model.

This model adheres to the content of large amounts of dark matter and dark energies contained in the universe, the nature of which is not yet well defined.

8- Quantum Mechanics

A branch of physics that studies the behavior of matter and light, on the atomic and subatomic scales. Its objective is to describe and explain the properties of molecules and atoms and their components: electrons, protons, neutrons and other more esoteric particles, such as quarks and gluons.

These properties include the interactions of particles with each other and with electromagnetic radiation (light, X-rays and gamma rays).

Several scientists contributed to the establishment of three revolutionary principles that gradually gained acceptance and experimental verification between 1900 and 1930.

  • Quantified properties . Sometimes position, velocity and color can only occur in specific amounts (like clicking number by number). This contrasts with the concept of classical mechanics, which states that these properties must exist on a flat, continuous spectrum. To describe the idea that some properties click, scientists coined the verb to quantify.
  • Light particles . Scientists have refuted 200 years of experiments by postulating that light can behave like a particle and not always “like waves/waves in a lake”.
  • Matter waves . Matter can also behave like a wave. This is demonstrated by 30 years of experiments that claim that matter (such as electrons) can exist as particles.

9- Relativity

This theory encompasses two theories by Albert Einstein: special relativity, which applies to elementary particles and their interactions – describing all physical phenomena except gravity – and general relativity which explains the law of gravitation and its relationship to other forces of a. nature.

It applies to the cosmological, astrophysical and astronomical domains. Relativity transformed the tenets of physics and astronomy in the 20th century, banning 200 years of Newtonian theory.

He introduced concepts such as spacetime as a unified entity, the relativity of simultaneity, the kinematic and gravitational time dilation, and the length contraction.

In the field of physics, the science of elementary particles and their fundamental interactions improved, along with the inauguration of the nuclear age.

Cosmology and astrophysics predicted extraordinary astronomical phenomena such as neutron stars, black holes and gravitational waves.

10-Nuclear Physics

It is a field of physics that studies the atomic nucleus, its interactions with other atoms and particles, and their constituents.


Formally, it is a branch of biology, although it is closely related to physics, as it studies biology with physical principles and methods.


Formally, it is a branch of astronomy, although closely related to physics, as it studies the physics of stars, their composition, evolution and structure.


It is a branch of geography, although it is closely related to physics, as it studies the Earth with the methods and principles of physics.

Research examples from each branch

1- Acoustics: UNAM research

The acoustics laboratory of the Department of Physics of the Faculty of Sciences at UNAM conducts specialized research in the development and implementation of techniques that allow the study of acoustic phenomena.

The most common experiences include different media with different physical structures. These media can be fluid, wind tunnels or the use of a supersonic jet.

An investigation currently taking place at UNAM is the frequency spectrum of a guitar, depending on where it is played. Acoustic signals emitted by dolphins are also being studied (Forgach, 2017).

2- Electricity and magnetism: effect of magnetic fields in biological systems

The University of the District Francisco José Caldas, promotes research on the effect of magnetic fields in biological systems. All this in order to identify all previous research carried out on the subject and provide new knowledge.

They also talk about species that depend on the configuration of this magnetic field to be oriented, such as bees, ants, salmon, whales, sharks, dolphins, butterflies, turtles, among others (Fuentes, 2004).

3- Mechanics: human body and zero gravity

For over 50 years, NASA has advanced research into the effects of zero gravity on the human body.

These investigations allowed numerous astronauts to travel safely on the Moon or live for more than a year on the International Space Station.

NASA research analyzes the mechanical effects that zero gravity has on the body, with the aim of reducing them and ensuring that astronauts can be sent to more remote places in the solar system (Strickland & Crane, 2016).

4- Fluid mechanics: Leidenfrost effect

The Leidenfrost effect is a phenomenon that occurs when a drop of fluid touches a hot surface at a temperature higher than its boiling point.

Doctoral students at the University of Liège created an experiment to understand the effects of gravity on the evaporation time of a fluid and its behavior during this process.

The surface was initially heated and tilted as needed. The water droplets used were tracked using infrared light, activating servomotors each time they moved away from the center of the surface (Research and science, 2015).

5- Optics: Ritter observations

Johann Wilhelm Ritter was a German pharmacist and scientist who conducted numerous medical and scientific experiments. Among his most notable contributions to the field of optics is the discovery of ultraviolet light.

Ritter based his research on the discovery of infrared light by William Herschel in 1800, thus determining that the existence of invisible lights was possible and conducting experiments with silver chloride and different light beams (Cool Cosmos, 2017) .

6- Thermodynamics: thermodynamic solar energy in Latin America

This research focuses on the study of alternative sources of energy and heat, such as solar energy, with the main interest being the thermodynamic projection of solar energy as a source of sustainable energy (Bernardelli, 201).

To that end, the study document is divided into five categories:

1- Solar radiation and energy distribution over the Earth’s surface.

2- Uses of solar energy.

3- Background and evolution of the uses of solar energy.

4- Installations and thermodynamic types.

5- Case studies in Brazil, Chile and Mexico.

7- Cosmology: Research on dark energy

The Dark Energy Survey or Dark Energy Survey, was a scientific study carried out in 2015, whose main objective was to measure the large-scale structure of the universe.

With this research, the spectrum was opened to numerous cosmological researches, which aim to determine the amount of dark matter present in the current universe and its distribution.

On the other hand, the results produced by DES contradict traditional theories about the cosmos, released after Planck’s space mission, financed by the European Space Agency.

This research confirmed the theory that the universe is currently made up of 26% dark matter.

Positioning maps that accurately measure the structure of 26 million distant galaxies have also been developed (Bernardo, 2017).

8- Quantum Mechanics: Information Theory and Quantum Computation

This research seeks to investigate two new areas of science, such as information and quantum computing. Both theories are fundamental to the advancement of telecommunications and information processing devices.

This study presents the current state of quantum computing, supported by the advances of the Quantum Computing Group (GQC) (López), an institution dedicated to giving lectures and generating knowledge on the subject, based on the first Turing postulates on computing.

9- Relativity: the Icarus experiment

The experimental research Icarus, carried out in the laboratory of Gran Sasso, Italy, brought peace of mind to the scientific world, verif
whether Einstein’s theory of relativity is true.

This investigation measured the speed of seven neutrinos with a beam of light granted by the European Center for Nuclear Research (CERN), concluding that neutrinos do not exceed the speed of light, as had been concluded in previous experiments by the same laboratory.

These results were the opposite of those obtained in previous experiments at CERN, which in previous years had concluded that neutrinos traveled 730 kilometers faster than light.

Apparently, the conclusion given earlier by CERN was due to a bad GPS connection at the time the experiment was carried out (El tiempo, 2012).

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