Planck time

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Orders of
magnitude (time)
in E notation

Planck time
1 E-25 s
1 E-24 s
1 E-21 s
1 E-18 s
1 E-17 s
1 E-16 s
1 E-15 s
1 E-14 s
1 E-13 s
1 E-12 s
1 E-11 s
1 E-10 s
1 E-9 s
1 E-8 s
1 E-7 s
1 E-6 s
1 E-5 s
1 E-4 s
1 E-3 s
1 E-2 s
1 E-1 s

1 E0 s
1 E1 s
1 E2 s
1 E3 s
1 E4 s
1 E5 s
1 E6 s
1 E7 s
1 E8 s
1 E9 s
1 E10 s
1 E11 s
1 E12 s
1 E13 s
1 E14 s
1 E15 s
1 E16 s
1 E17 s
1 E18 s
1 E19 s and more
↓/↓

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 it would take a photon travelling at the speed of light in a vacuum to cross a distance equal to the Planck length.[1] The unit is named after Max Planck.

It is defined as

t_P = \sqrt{\frac{\hbar G}{c^5}} \approx 5.39121(40) \times 10^{-44} \mbox{ s}

where:

\hbar = h / 2 \pi is the reduced Planck constant (sometimes h is used instead of \hbar in the definition [1])
G is the gravitational constant
c is the speed of light in a vacuum
tP is in seconds.
The two digits between the parentheses denote the uncertainty in the last two digits of the value.

[edit] Physical significance

The Planck time is simply the time it takes a beam of light to travel a Planck length. See the corresponding section for that unit for details. As of 2006, the smallest unit of time that has been directly measured is on the attosecond (10−18 s) time scale, or around 1026 Planck times.[2][3] There is also speculation that a Planck time after the Big Bang, that statements can be made about the universe displaying properties equal to some of the other Planck units. (Some hypothesise that gravity must have separated first due to its homogeneity to the others. Some propose that the strong nuclear force is the most likely candidate due to its strength.)[4]

One Planck time should be the smallest measurable unit of time, according to quantum mechanics. But, according to news reports, analyses of Hubble Space Telescope Deep Field images in 2003 brought up a discrepancy. Images should have been blurry at very far distances, but the news articles stated that they weren't, challenging the theory that Planck time is indeed the smallest measurable unit of time in the universe.[4][5][6]

[edit] References

  1. ^ a b Big Bang models back to Planck time. Georgia State University (19 June 2005).
  2. ^ Shortest time interval measured. BBC News (25 February 2004).
  3. ^ Fastest view of molecular motion. BBC News (4 March 2006).
  4. ^ a b Hubble Pictures Too Crisp, Challenging Theories of Time and Space. Space.com (2003-04-02). Retrieved on 2008-05-30.
  5. ^ 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:10.1086/374350. 
  6. ^ Ng, Y. Jack; Christiansen, W. A.; van Dam H. (2003-07-10). "Probing Planck-Scale Physics with Extragalactic Sources?". The Astrophysical Journal Letters 591: L87–L89. The American Astronomical Society. doi:10.1086/377121. 
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Planck's natural units
Base Planck units
Derived Planck units