The well-known laws of mechanics and universal gravitation by Isaac Newton, as well as the laws of planetary motion formulated by Johannes Kepler, are considered part of classical physics, since they date from the 17th century and are not part of contemporary physics.
Field of study
Formally, the study of Physics includes natural phenomena, such as the change in the state of motion of bodies, the characteristic properties of matter , its fundamental components and the interactions between them.
Of course, as long as these changes do not involve the formation of new substances or biological processes. This definition is valid for both classical and contemporary physics.
Now we will focus on the main discoveries and physical theories developed from the French Revolution to the present day, briefly and in more or less chronological order:
18th and 19th centuries
-Electricity was rediscovered and the electrostatic model of force, magnetism and electromagnetic theory were created.
-The concepts of potential energy and kinetic energy appeared, as well as the field.
-The laws of conservation of energy, matter and electric charge were established.
-The wave theory of light made its appearance and for the first time there was an accurate measurement of the speed of light. The interactions of light with electric and magnetic fields were also studied.
-With the Industrial Revolution, the rise of Thermodynamics took place. The second law of thermodynamics was enunciated and later the concept of entropy, also the kinetic theory of gases, statistical mechanics and the Boltzmann equation.
-The radiation law of bodies was discovered (Stefan’s law) and the law of displacement of the wavelength emitted by a hot body as a function of its temperature (Wien’s law).
-Electromagnetic waves emerge, theoretically predicted, in addition to X-rays, natural radioactivity and the electron, all this at the end of the 19th century.
Modern physics up to the first half of the 20th century
At this time, classical theories went through a period of crisis, since many of the phenomena discovered in the 19th century could not be explained with these theories. So it was necessary to develop a new physics, known as modern physics , which fundamentally comprises quantum mechanics and the theory of relativity.
Main areas of development in contemporary Physics
Modern physics began in 1900 with the discovery of the black body radiation law by Max Planck, in which the concept of energy quanta was introduced in the interaction of radiation with matter.
In this period atomic models were developed in which the atom appears to be composed of particles smaller than the atom itself. These are electrons, protons, and neutrons.
At the beginning of the 20th century, Ernest Rutherford discovered the atomic nucleus and made an atomic model with a positive and massive central nucleus, surrounded by light particles with a negative charge. However. This model was put aside in a short time, in favor of models more adjusted to the new discoveries.
Albert Einstein proposed in 1905 that light quanta, called photons, were the only way to explain the photoelectric effect. A photon is the smallest bundle of light energy, which depends on its frequency.
Relativity and Unification Theories
The special theory of relativity, Einstein’s best-known creation, states that time and mass are physical quantities that depend on the reference frame.
In this way it was necessary to implement relativistic corrections to the classical laws of motion.
On the other hand, Albert Einstein’s general theory of relativity establishes that gravity is not a force, but a consequence of the space-time curvature, produced by bodies with mass such as the Sun and planets. This would explain the precession of Mercury’s perihelion and predicts the curvature of light.
The bending of light by a massive body like the Sun was proven beyond doubt. This phenomenon is what produces gravitational lenses.
So scientists began to think about unification theories, in which gravity and electromagnetism are manifestations of distorted spaces of greater than four dimensionality, like the Kaluza-Klein theory.
The theoretical possibility of an expanding universe then arose, thanks to the works of Alexander Friedman based on the general theory of relativity, a fact that was confirmed later.
Black holes appeared as solutions to Einstein’s equations. The Hindu physicist Chandrasekhar set the limit for the stellar collapse to generate a black hole.
An important discovery was the Compton effect, which establishes that photons, despite not having mass, do have momentum proportional to the inverse of their wavelength. The constant of proportionality is Planck’s constant .
With the arrival of quantum mechanics, the wave-particle duality is also established. The theory predicted the existence of antimatter, which was indeed discovered. The neutron also appeared and with it a new atomic model: the quantum-mechanical model.
An important contribution is that of spin , a property of subatomic particles capable, among other things, of explaining magnetic effects.
This branch of contemporary physics appears when the nuclear processes of fission and fusion are discovered. The first led to the atomic bomb and nuclear power, the second explains the production of energy by the stars, but also led to the H bomb.
In the search for controlled nuclear fusion, it was discovered that the proton and neutron have internal structures: quarks , fundamental constituents of protons and neutrons.
Since then, quarks and electrons have been considered fundamental particles, but new fundamental particles also appeared: the muon, the pion, the tau lepton and the neutrinos.
The first half of the 20th century culminates with important contributions from contemporary physics:
-Superconductivity and superfluidity
-The maser and the laser.
-Magnetic resonance imaging of atomic nuclei, a discovery that gives rise to today’s non-invasive diagnostic systems.
-Big theoretical developments such as quantum electrodynamics and Feynman diagrams to explain fundamental interactions.
The physics of our times (second half of the 20th century)
This theory explains superconductivity, which states that electrons, which are fermionic particles , interact with the crystal lattice in such a way that electronic pairs are formed with boson behavior.
It gives rise to the concept of quantum entanglement and its possible applications in quantum computing. Furthermore, quantum teleportation and quantum cryptography are proposed, of which the first experimental implementations have already been carried out.
The standard model
The discovery of quarks was followed by the creation of the standard model of elementary particles , with two more members: the W and Z bosons.
Anomalies were observed in the rotation speed of stars around the center of galaxies, so Vera Rubin proposes the existence of dark matter as a possible explanation.
By the way, there is important evidence of dark matter, due to the discovery of gravitational lenses without visible mass that explains the curvature of light.
Another important area of study is that of black hole entropy and Hawking radiation.
The accelerated expansion of the universe has also been confirmed and dark energy is believed to be responsible.
The Tau neutrino
The 21st century began with the experimental production of a quark-gluon plasma and the discovery of the Tau neutrino.
The cosmic microwave background
Accurate observations of the cosmic microwave background were also made, shedding light on early formation theories of the universe.
The Higgs boson
A much commented discovery is that of the Higgs boson, the particle responsible for the mass of the different fundamental particles, supporting the standard model of particles.
Detected in 2015, gravitational waves were predicted in the first half of the 20th century by Albert Einstein. They are the result of the collision between two supermassive black holes.
The first image of a black hole
In 2019, the image of a black hole was obtained for the first time, another of the predictions of the theory of relativity.
Branches of current contemporary physics
Among the branches of current contemporary physics are:
1.- Particle physics
2.- Plasma Physics
3.- Quantum and photonic computing
4.- Astrophysics and cosmology
5.- Geophysics and biophysics.
6.- Atomic and nuclear physics
7.- Physics of condensed matter
Challenges and applications of current physics
The topics of physics that are currently considered open and that are in full development are:
-The physics of complex systems, chaos theories and fractals.
-The non-linear dynamic systems. Development of new techniques and models that lead to the solution of such systems. Among its applications is a better weather forecast.
-Unification theories such as string theories and M theory. Development of quantum gravity.
-The physics of fluids and plasmas in turbulent regime, which can be applied in the development of controlled nuclear fusion.
-Theories about the origin of dark matter and dark energy. If these phenomena were understood, perhaps space navigation could be developed, through anti-gravity and the construction of WARP engines.
-The superconductivity at high temperature, applicable in the creation of more efficient transport systems.