**Time** is a physical quantity representing distances in temporal, rather than spatial, dimensions, which are usually called timelines. It is considered one of the fundamental base units, along with length, mass, current, temperature, and luminous intensity.

## Units

In SI units, time is measured in seconds.

In Planck units, time is measured in Planck times, given by the ratio $ \sqrt{\frac{\hbar G}{c^5}} $.

In Stoney units, time is measured in Stoney times, given by the ratio $ \sqrt{\frac{C k_e e^2}{c^6}} $.

In atomic units, time is measured in atomic times, given by the ratio $ \frac{\hbar^3}{m_e k_e^2 e^4} $.

In quantum chromodynamics units, time is measured in quantum chromodynamics times, given by the ratio $ \frac{\hbar}{m_p c^2} $.

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