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The Bekenstein–Hawking entropy of a black hole is one-fourth the area of its event horizon in units of Planck length squared. [11]: 370 Since the 1950s, it has been conjectured that quantum fluctuations of the spacetime metric might make the familiar notion of distance inapplicable below the Planck length.
The micrometre (SI symbol: μm) is a unit of length in the metric system equal to 10 −6 metres ( 1 / 1 000 000 m = 0. 000 001 m). To help compare different orders of magnitude , this section lists some items with lengths between 10 −6 and 10 −5 m (between 1 and 10 micrometers , or μm).
The smallest meaningful increment of time is the Planck time―the time light takes to traverse the Planck distance, many decimal orders of magnitude smaller than a second. [ 1 ] The largest realized amount of time, based on known scientific data, is the age of the universe , about 13.8 billion years—the time since the Big Bang as measured in ...
Symbol Quantity Value [a] [b] Relative standard uncertainty Ref [1] speed of light in vacuum 299 792 458 ... molar Planck constant 3.990 312 712 893 4314 ...
symbol If set to yes, the value is preceded by the symbol of the constant, followed by ≈ or = depending on whether round is set. round If omitted, the value is shown along with its standard uncertainty. If set to an integer n, the value is rounded to the first n digits after the decimal point. unit
For example, the speed of light is defined as having the numerical value of 299 792 458 when expressed in the SI unit metres per second, and as having the numerical value of 1 when expressed in the natural units Planck length per Planck time. While its numerical value can be defined at will by the choice of units, the speed of light itself is a ...
The Planck time is the time that light takes to travel one Planck length. The TU (for time unit) is a unit of time defined as 1024 μs for use in engineering. The svedberg is a time unit used for sedimentation rates (usually of proteins). It is defined as 10 −13 seconds (100 fs).
Symbol Meaning SI unit of measure ... inverse length squared (1/m 2) ... Planck constant: joule second (J⋅s)