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  2. Entropy as an arrow of time - Wikipedia

    en.wikipedia.org/wiki/Entropy_as_an_arrow_of_time

    Therefore, the thermodynamic entropy, which is proportional to the marginal entropy, must also increase with time [8] (note that "not too long" in this context is relative to the time needed, in a classical version of the system, for it to pass through all its possible microstates—a time that can be roughly estimated as , where is the time ...

  3. Time in physics - Wikipedia

    en.wikipedia.org/wiki/Time_in_physics

    In the International System of Units (SI), the unit of time is the second (symbol: s). It has been defined since 1967 as "the duration of 9 192 631 770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the caesium 133 atom", and is an SI base unit. [12]

  4. Fluctuation theorem - Wikipedia

    en.wikipedia.org/wiki/Fluctuation_theorem

    Roughly, the fluctuation theorem relates to the probability distribution of the time-averaged irreversible entropy production, denoted ¯.The theorem states that, in systems away from equilibrium over a finite time t, the ratio between the probability that ¯ takes on a value A and the probability that it takes the opposite value, −A, will be exponential in At.

  5. Thermodynamic limit - Wikipedia

    en.wikipedia.org/wiki/Thermodynamic_limit

    The thermodynamic limit is essentially a consequence of the central limit theorem of probability theory. The internal energy of a gas of N molecules is the sum of order N contributions, each of which is approximately independent, and so the central limit theorem predicts that the ratio of the size of the fluctuations to the mean is of order 1/N 1/2.

  6. Lorentz factor - Wikipedia

    en.wikipedia.org/wiki/Lorentz_factor

    The Lorentz factor γ is defined as [3] = = = = =, where: . v is the relative velocity between inertial reference frames,; c is the speed of light in vacuum,; β is the ratio of v to c,; t is coordinate time,

  7. Time constant - Wikipedia

    en.wikipedia.org/wiki/Time_constant

    In an increasing system, the time constant is the time for the system's step response to reach 1 − 1 / e ≈ 63.2% of its final (asymptotic) value (say from a step increase). In radioactive decay the time constant is related to the decay constant (λ), and it represents both the mean lifetime of a decaying system (such as an atom) before it ...

  8. List of common physics notations - Wikipedia

    en.wikipedia.org/wiki/List_of_common_physics...

    time: second (s) four-velocity: meter per second (m/s) potential energy: joule (J) internal energy: joule (J) relativistic mass: kilogram (kg) energy density: joule per cubic meter (J/m 3) specific energy: joule per kilogram (J/kg) voltage also called electric potential difference volt (V)

  9. List of limits - Wikipedia

    en.wikipedia.org/wiki/List_of_limits

    This is a list of limits for common functions such as elementary functions. In this article, the terms a, b and c are constants with respect to x.