Physics developed since 1901
Modern physics
is a branch of
physics
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
,
special relativity
and
general relativity
.
Classical physics
is typically concerned with everyday conditions: speeds are much lower than the
speed of light
, 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
speed of light
(special relativity), small distances comparable to the
atomic radius
(
quantum mechanics
), 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
. 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
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.
[1]
However, since roughly 1890, new discoveries have caused significant
paradigm shifts
:
[1]
especially the advent of
quantum mechanics
(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.
[1]
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
. However, near
absolute zero
, the Maxwell?Boltzmann distribution fails to account for the observed behavior of the gas, and the (modern)
Fermi?Dirac
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
, or by making an
approximation
). When doing so, the result is called the
classical limit
.
Hallmarks
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These are generally considered to be the topics regarded as the "core" of the foundation of modern physics:
See also
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References
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Notes
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External links
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