(physics) The constant (Gh/2πc5)1/2 with dimensions of “time” formed from Planck's constant h, the gravitational constant G, and the speed of light c; approximately 10-43 second.
Planck time
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(′pläŋk ′tīm)
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In physics, the Planck time, (tP), 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.[1] The unit is named after Max Planck, who was the first to propose it.
The Planck time is defined as:
where:
is the reduced Planck constant (sometimes h is used instead of 
in the definition [1])- G = gravitational constant
- c = speed of light in a vacuum
- s is the SI unit of time, the second.
The two digits between parentheses denote the standard error of the estimated value.
Physical significance
According to quantum theory, 1 Planck time should be the smallest unit of time physics can reason about in a meaningful way. As of 2006, the smallest unit of time that was directly measured was on the order of 1 attosecond (10−18 s), or about 1026 Planck times.[3][4]
Analyses of Hubble Space Telescope Deep Field images in 2003 led to a debate about the physical implications of the Planck time as a physical minimum time interval. According to Lieu and Hillman,[5] speculative theories of quantum gravity "foam" where there are space-time fluctuations on the Planck scale predict that images of extremely distant objects should be blurry. However, blurring was not seen in the Hubble images, which was claimed to be problematic for such theories.[6] Other authors have disputed this, in particular Ng et al.[7], who state that the blurring effect was overestimated by Lieu and Hillman by factors of between 1015 and 1030, thus the observations are very much less effective in constraining theory: "the cumulative effects of spacetime fluctuations on the phase coherence of light [in certain theories of "foamy" spacetime] are too small to be observable."
See also
References
- ^ a b "Big Bang models back to Planck time". Georgia State University. 19 June 2005. http://hyperphysics.phy-astr.gsu.edu/hbase/astro/planck.html.
- ^ CODATA Value: Planck Time – The NIST Reference on Constants, Units, and Uncertainty.
- ^ "Shortest time interval measured". BBC News. 25 February 2004. http://news.bbc.co.uk/2/hi/science/nature/3486160.stm.
- ^ "Fastest view of molecular motion". BBC News. 4 March 2006. http://news.bbc.co.uk/1/hi/sci/tech/4766842.stm.
- ^ Lieu, Richard; Hillman, Lloyd W. (2003-03-10). "The Phase Coherence of Light from Extragalactic Sources: Direct Evidence against First-Order Planck-Scale Fluctuations in Time and Space". The Astrophysical Journal 585: L77–L80. doi:. http://www.journals.uchicago.edu/doi/pdf/10.1086/374350. Retrieved 2008-05-30.
- ^ "Hubble Pictures Too Crisp, Challenging Theories of Time and Space". Space.com. 2003-04-02. http://www.space.com/scienceastronomy/quantum_bits_030402.html. Retrieved 2008-05-30.
- ^ Ng, Y. Jack; Christiansen, W. A.; van Dam H. (2003-07-10). "Probing Planck-Scale Physics with Extragalactic Sources?". The Astrophysical Journal Letters (The American Astronomical Society) 591: L87–L89. doi:. http://www.journals.uchicago.edu/doi/abs/10.1086/377121. Retrieved 2008-05-30.
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