Study Material

What is modern physics?

We explain what modern physics is, what it studies, its branches, the differences with classical physics and leading scientists

Modern physics considers that space and time make up a fabric and gravity is nothing more than a distortion of that fabric, caused by the presence of a mass, such as the Sun for example.

What is modern physics?

The modern physics refers to physics developed in the early twentieth century and is dedicated to the study of objects whose speed is comparable to that of light, as well as the bodies of tiny dimensions: the atom and the constituent particles .

The 19th century was crucial for thermodynamics and electricity, fueled by the Industrial Revolution . But as technology advanced, increasingly sophisticated experiments showed phenomena that scientists could not fully explain with accepted theories.

Three phenomena in particular were the keys to the emergence of the new physics: radiation emitted by very hot objects, line spectra caused by electrical discharges in gases, and the photoelectric effect.

Scientists had no satisfactory explanations for these phenomena, unless the revolutionary postulates of quantum mechanics and the dual wave-particle nature of both light and matter were accepted . This was the birth of modern physics at the dawn of the 20th century.

Accepted today by the scientific community, at the time they were controversial theories, in many ways far removed from Newtonian physics, around which all areas of classical physics revolve.

What does modern physics study?

The two main fields that modern physics studies are the theory of relativity and quantum mechanics.

The theory of relativity deals with explaining the behavior of mobiles with speeds close to that of light. For its part, quantum mechanics delves into matter and the study of its constituent particles.

The theory of relativity

The theory of relativity, proposed by Albert Einstein (1879-1955), deals with processes that take place at speeds close to that of light. The speed of light is a constant of nature whose value in vacuum is approximately equal to 300,000 km / s. Nothing moves faster than this.

However, it is wrong to think that the postulates of classical or Newtonian physics are not valid according to the new approach given by modern physics.

In contrast, the theory of relativity is a broader point of view, including Newtonian physics when speeds are much less than that of light. And most everyday objects move like this, except for the light itself.

Quantum mechanics

For its part, quantum mechanics deals with matter at the level of the particles that compose it. At such a small scale, particles show dual behavior: they are particles and waves at the same time.

Particles have mass and waves have energy, therefore, if subatomic particles are both things at the same time, it happens that mass m and energy E are equivalent, as shown by the equation:

E = mc 2

Here c represents the speed of light in a vacuum.

Furthermore, because they are wavelike in nature, the particles are not point objects whose track can be followed like that of a billiard ball. A surprising fact is that only the probability that the particle is in a certain position can be known.

Branches of modern physics

Modern physics extends into several branches, closely related, among which it is worth mentioning:


It postulates that the laws of physics are the same regardless of the reference frame used, as well as the fact that the speed of light is constant in vacuum for any observer, even if it has motion.

Quantum mechanics

It deals with the behavior of matter on an atomic scale and that of the particles that compose it, considering that energy is quantized, which means that it does not appear in arbitrary values, but in multiples of a quantity: the quantum.

Likewise, it contemplates that both light and matter exhibit a dual nature: waves and particles. Light is an electromagnetic wave, and at the same time a particle, called a photon, whose energy E is directly proportional to the frequency f:

E = h ∙ f

Where h is Planck’s constant, whose value in International System units is: 6.62607015 × 10 -34 J ∙ s

Atomic physics

It focuses on studying the properties of the atom, the essential constituent of matter, as well as the interactions that take place between them and between atoms and light.

Nuclear physics

The atom has a structure composed of a nucleus and electrons in orbitals around it. The nucleus possesses, not only almost all of the mass of the atom, but also the properties that give each element its individuality. Nuclear physics is responsible for studying their properties and interactions.

Particle physics

There is a universe of particles at the subatomic level, whose characteristics and interactions are studied by particle physics.

Particles are classified into two large groups: bosons and fermions, the former are responsible for mediating fundamental interactions, such as electromagnetic through the photon. The second group includes material particles such as the electron.


Study the origin and evolution of the universe, governed by light and the particles that make up matter.

Differences between modern physics and classical physics

Classical physics is more familiar and close, in the sense that it satisfactorily explains the macroscopic world and the behavior of objects at low speeds.

Another relevant difference is that there are magnitudes that in modern physics are quantized, such as energy and momentum, while in classical physics they take any value.

Finally, in classical physics, mass and energy are two different quantities, which modern physics links through the speed of light in the famous Einstein equation mentioned above:

E = mc 2

Scientists of modern Physics and their contributions

important scientists of modern physics
The most important scientists of modern physics, gathered at the V Solvay conference, held in Brussels in 1927

Max Planck (1858-1947)

He was the first to propose the existence of the energy quantum, as the only way to satisfactorily explain black body radiation, which is why he is considered the father of quantum theory.

Albert Einstein (1879-1955)

Einstein is the creator of the theory of relativity. His first work on the subject was published in 1905 and the second in 1916, but he was not awarded the Nobel Prize for them, but for his explanation of the photoelectric effect in which he proposed that the carrier particle of the electromagnetic interaction is the photon.

Niels Bohr (1885-1962)

He devised the first quantum atomic model, by proposing that an electron can only occupy those orbitals in which its momentum is an integer multiple of h / 2π. When the electron changes from one orbital to another, its energy also varies by quanta, equivalent to the difference in energy between the final state and the initial state.

Werner Heisenberg (1901-1976)

He is best known for the uncertainty principle that bears his name, but he also made great contributions to the mathematical formulation of quantum mechanics.

Erwin Schrodinger (1887-1961)

He devised a model of the atom based on quantum mechanics, but his most notable contribution is the wave equation that bears his name, through which it is possible to evaluate the probability that an electron is in a certain position.

Related Articles

Leave a Reply

Your email address will not be published. Required fields are marked *

Back to top button