What Is Physics?

Physics is the branch of science that studies the behavior of nonliving matter and the laws that govern the natural world.

The word physics comes from the Greek term "physis", which means nature.

Physics aims to understand how nature works by observing natural phenomena and describing them through physical quantities, mathematical models, and scientific laws.

Note. Physics investigates only part of the natural world. It does not study biological processes or chemical transformations, which belong respectively to the fields of biology and chemistry.

To study natural phenomena, physicists use the experimental method, introduced by Galileo Galilei in the 17th century. This method is based on observation, measurement, experimentation, and mathematical analysis.

The History of Physics

The history of physics is usually divided into two major phases:

• Classical Physics
  Classical physics includes the laws and principles developed between the 17th and 19th centuries to describe motion, forces, energy, heat, light, and electricity. Major examples include Newtonian mechanics, Maxwell's electromagnetism, thermodynamics, and classical optics. Classical physics is also known as non-relativistic physics because it studies phenomena occurring at speeds much lower than the speed of light.
• Modern Physics
  Modern physics emerged during the 20th century and introduced new theories that profoundly changed the classical view of nature. The two main pillars of modern physics are Einstein's theory of relativity and quantum mechanics, developed from the work of Max Planck and many other physicists. Modern physics studies phenomena occurring at extremely high speeds, very small scales, or under extreme physical conditions.

Over time, physics has undergone several major scientific paradigm shifts.

Until the 19th century, physics was largely based on the deterministic paradigm, according to which natural phenomena follow precise laws that make events predictable.

During the 20th century, the rise of quantum mechanics introduced the probabilistic paradigm, bringing uncertainty and probability into the description of physical phenomena.

Note. Another important framework in modern physics is chaos theory, which studies highly sensitive and apparently unpredictable systems known as chaotic systems.

Classical Physics

Classical physics (or Newtonian physics) studies phenomena that occur at speeds much lower than the speed of light (c) $$ v << c $$ that is $$ \frac{v}{c} << 1 $$

Here, c is the constant representing the speed of light.

$$ c \simeq 3 \cdot 10^8 \ m/s $$

This is approximately equal to 300 million meters per second, or 300 thousand kilometers per second.

Note. The mathematical symbol << means "much less than". It should not be confused with the standard less-than symbol <, which simply expresses an order relation between two numbers without indicating how large the difference is.

Under these conditions, physicists refer to the situation as a non-relativistic regime.

And so on.