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In ], the '''Planck time''' ({{math|<var>t</var><sub>P</sub>}}) is the ] in the system of ] known as ]. A Planck time unit is the ] required for ] to travel a distance of 1 ] in a ], which is a time interval of approximately 5.39 × 10 <sup>−44</sup> s.<ref name="gsu_hbase">{{cite web | url = http://hyperphysics.phy-astr.gsu.edu/hbase/astro/planck.html | title = Big Bang models back to Planck time | publisher = ] | date = 19 June 2005}}</ref> The unit is named after ], who was the first to propose it. |
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The Planck time is defined as:<ref> – The ] Reference on Constants, Units, and Uncertainty.</ref> |
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:<math>t_\mathrm{P} \equiv \sqrt{\frac{\hbar G}{c^5}}</math> |
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where: |
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:{{math|<var>ħ</var>}} = {{frac|<var>h</var>|2<var>{{pi}}</var>}} is the ] (sometimes {{mvar|h}} is used instead of {{mvar|ħ}} in the definition<ref name="gsu_hbase" />) |
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:{{mvar|G}} = ] |
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:{{mvar|c}} = ] in ] |
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Using the known values of the constants, the approximate equivalent value in terms of the ] unit, the ], is |
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:<math> 1 \ t_\mathrm{P} \approx 5.391\,16(13) \times 10^{-44}\ \mathrm{s},</math> |
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where the two digits between parentheses denote the ] of the approximated value. |
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==History == |
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The Planck time (also known as Planck second) was first suggested by ]<ref>M. Planck. Naturlische Masseinheiten. Der Koniglich Preussischen Akademie Der Wissenschaften, p. 479, 1899</ref> in 1899. He suggested that there existed some fundamental natural units for ], ], ] and ]. Planck derived these using ] only using what he considered the most fundamental universal constants: the speed of light, the Newton gravitational constant and the Planck constant. The Planck time is considered by many physicists to be the shortest possible measurable time interval; however, this is still a matter of debate. |
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==Physical significance== |
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The Planck time is the unique combination of the ] {{mvar|G}}, the ] {{mvar|c}}, and the ] {{mvar|ħ}}, to produce a constant with dimension of ]. 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. This essentially means that while smaller units of time can exist, they are so small their effect on our existence is negligible. 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 ]. |
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The ] of the Planck time, which is ], can be interpreted as an upper bound on the frequency of a ]. This follows from the interpretation of the ] as a minimal length, and hence a lower bound on the wavelength. |
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All scientific experiments and human experiences occur over time scales that are many orders of magnitude longer than the Planck time,<ref>{{cite serial |title=]|episode=First Second of the Big Bang |network=Discovery Science |year=2014}}</ref> making any events happening at the Planck scale undetectable with current scientific knowledge. {{As of|2016|11}}, the smallest time interval uncertainty in direct measurements is on the order of 850 ] (8.50 × 10<sup>−19</sup> seconds)<ref>{{cite web|url=http://www.sciencealert.com/scientists-measure-the-smallest-fragment-of-time-ever-witness-an-electron-escaping-an-atom|title=Scientists have measured the smallest fragment of time ever|last=|first=|date=2010-05-12|website=|publisher=|accessdate=2012-04-19}}</ref> |
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==See also== |
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{{div col|colwidth=30em}} |
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* ] |
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* ] |
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* ] |
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* ] |
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* ] |
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== References== |
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{{Reflist|colwidth=30em}} |
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== External links == |
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* (up to 10<sup>−43</sup> seconds after ] of ]) (]). |
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{{Planck's natural units}} |
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{{Time measurement and standards}} |
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{{Orders of magnitude seconds}} |
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{{Time topics}} |
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{{Scientists whose names are used in physical constants}} |
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{{Portal bar|Physics|Science|Time}} |
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