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In physics, the Planck time () is the unit of time in the system of natural units known as Planck units. It is the time required for light to travel, in a vacuum, a distance of 1 Planck length.〔(【引用サイトリンク】 Big Bang models back to Planck time )〕 The unit is named after Max Planck, who was the first to propose it. The Planck time is defined as:〔(CODATA Value: Planck Time ) – The NIST Reference on Constants, Units, and Uncertainty.〕 : where: :}} is the reduced Planck constant (sometimes is used instead of in the definition〔) : = gravitational constant : = speed of light in a vacuum : is the SI unit of time, the second. The two digits between parentheses denote the standard error of the estimated value. ==Physical significance== The Planck time is the unique combination of the gravitational constant , the special-relativistic constant , and the quantum constant , to produce a constant with units of time. Because the Planck time comes from dimensional analysis, which ignores constant factors, there is no reason to believe that exactly one unit of Planck time has any special physical significance. Rather, the Planck time represents a rough time scale at which quantum gravitational effects are likely to become important. The nature of those effects, and the exact time scale at which they would occur, would need to be derived from an actual theory of quantum gravity. All scientific experiments and human experiences happen over billions of billions of Planck times, making any events happening at the Planck scale hard to detect. , the smallest time interval uncertainty in direct measurements is on the order of 12 attoseconds (1.2 × 10−17 seconds), about 2.2 × 1026 Planck times.〔 (【引用サイトリンク】 title=12 attoseconds is the world record for shortest controllable time )〕 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Planck time」の詳細全文を読む スポンサード リンク
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