Planck time

Template:Associations/Orders of magnitude (time) In physics, the Planck time (t_P), 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. 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 )

$G$ is the gravitational constant

$c$ is the speed of light in a vacuum

$t_{P}$ is in seconds.

The two digits between the parentheses denote the uncertainty in the last two digits of the value.

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. 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.)

Two planck times should be the smallest measurable time bit, according to quantum theory and sampling theorem. 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 the smallest time bit in the universe.