Modern physics is a branch of

physics Physics is the natural science that studies matter, its fundamental constituents, its motion and behavior through space and time, and the related entities of energy and force. "Physical science is that department of knowledge which ...

that developed in the early 20th century and onward or branches greatly influenced by early 20th century physics. Notable branches of modern physics include

quantum mechanics Quantum mechanics is a fundamental theory in physics that provides a description of the physical properties of nature at the scale of atoms and subatomic particles. It is the foundation of all quantum physics including quantum chemistry, ...

special relativity In physics, the special theory of relativity, or special relativity for short, is a scientific theory regarding the relationship between space and time. In Albert Einstein's original treatment, the theory is based on two postulates: # The law ...

and

general relativity General relativity, also known as the general theory of relativity and Einstein's theory of gravity, is the geometric theory of gravitation published by Albert Einstein in 1915 and is the current description of gravitation in modern physics ...

. Classical physics is typically concerned with everyday conditions: speeds are much lower than the

speed of light The speed of light in vacuum, commonly denoted , is a universal physical constant that is important in many areas of physics. The speed of light is exactly equal to ). According to the special theory of relativity, is the upper limit fo ...

, sizes are much greater than that of atoms, and energies are relatively small. Modern physics, however, is concerned with more extreme conditions, such as high velocities that are comparable to the

(special relativity), small distances comparable to the

atomic radius The atomic radius of a chemical element is a measure of the size of its atom, usually the mean or typical distance from the center of the nucleus to the outermost isolated electron. Since the boundary is not a well-defined physical entity, there ...

(

), and very high energies (relativity). In general, quantum and relativistic effects are believed to exist across all scales, although these effects may be very small at

human scale Human scale is the set of physical qualities, and quantities of information, characterizing the human body, its motor, sensory, or mental capabilities, and human social institutions. Science vs. human scale Many of the objects of scientific in ...

. While quantum mechanics is compatible with special relativity (See: Relativistic quantum mechanics), one of the unsolved problems in physics is the unification of quantum mechanics and general relativity, which the Standard Model of

particle physics Particle physics or high energy physics is the study of fundamental particles and forces that constitute matter and radiation. The fundamental particles in the universe are classified in the Standard Model as fermions (matter particles) an ...

currently cannot account for. Modern physics is an effort to understand the underlying processes of the interactions of matter using the tools of science & engineering. 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: especially the advent of

(QM) and 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 behavior. For example, when analyzing the behavior of a gas at room temperature, most phenomena will involve the (classical)

Maxwell–Boltzmann distribution In physics (in particular in statistical mechanics), the Maxwell–Boltzmann distribution, or Maxwell(ian) distribution, is a particular probability distribution named after James Clerk Maxwell and Ludwig Boltzmann. It was first defined and use ...

. However near absolute zero, the Maxwell–Boltzmann distribution fails to account for the observed behavior of the gas, and the (modern)

Fermi–Dirac Fermi–Dirac may refer to: * Fermi–Dirac statistics Fermi–Dirac statistics (F–D statistics) is a type of quantum statistics that applies to the physics of a system consisting of many non-interacting, identical particles that obey the Pa ...

or Bose–Einstein distributions have to be used instead. Very often, it is possible to find – or "retrieve" – the classical behavior from the modern description by analyzing the modern description at low speeds and large distances (by taking a

limit Limit or Limits may refer to: Arts and media * ''Limit'' (manga), a manga by Keiko Suenobu * ''Limit'' (film), a South Korean film * Limit (music), a way to characterize harmony * "Limit" (song), a 2016 single by Luna Sea * "Limits", a 2019 ...

, or by making an approximation). When doing so, the result is called the '' classical limit''. Black body

Hallmarks

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

Hallmarks

See also

References

Notes

External links