# Modern physics

Modern physics is an effort to understand the underlying processes of the interactions of matter utilizing the tools of science & engineering. In general, the term is used to refer to any branch of physics either developed in the early 20th century and onwards, or branches greatly influenced by early 20th century physics

Modern Physics can be considered consisting of Classical physics, The Standard Model of physics and Theoretical physics including Quantum physics, Relativity and more.

Low velocities and every day distances are usually considered in the realm of classical physics.

The Standard Model of physics is based on laboratory observations from laboratories like CERN and other laboratories and does not include a theory for gravitation such as relativity or other purely theoretical or mathematical physics.

Modern physics, however, today also involves theoretical and extreme conditions represented by quantum effects and relativity typically involving distances comparable to atoms (roughly 10−9 m), while relativistic effects typically involve velocities comparable to the speed of light (roughly 3×108 m/s). In general, quantum and relativistic effects are believed to exist across all scales, although these effects can be very small in everyday life.

In a literal sense, the term modern physics, means up-to-date physics. In this sense, a significant portion of so-called classical physics is modern. However, since roughly 1890, new discoveries have caused significant paradigm shifts: the advent of quantum mechanics (QM) and theoretical physics such as Einsteinian relativity (ER). Physics that incorporates elements of either QM or ER (or both) is said to be modern physics. It is in this latter sense that the term is generally used.

Modern physics is often encountered when dealing with extreme conditions. Quantum mechanical effects tend to appear when dealing with "lows" (low temperatures, small distances), while relativistic effects tend to appear when dealing with "highs" (high velocities, large distances), the "middles" being classical behaviour. For example, when analysing the behaviour of a gas at room temperature, most phenomena will involve the (classical) Maxwell–Boltzmann distribution. However near absolute zero, the Maxwell–Boltzmann distribution fails to account for the observed behaviour of the gas, and the (modern) Fermi–Dirac or Bose–Einstein distributions have to be used instead.

German physicists Albert Einstein, founder of the theory of relativity, and Max Planck, founder of quantum theory, respectively

Very often, it is possible to find – or "retrieve" – the classical behaviour from the modern description by analysing the modern description at low speeds and large distances (by taking a limit, or by making an approximation). When doing so, the result is called the classical limit.

## Hallmarks

These are generally considered to be the topics regarded as the "core" of the foundation of modern physics: