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Encyclopedia > Planck time

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. This is a discussion of a present category of science. ... Look up time in Wiktionary, the free dictionary. ... In physics, natural units are physical units of measurement defined in terms of universal physical constants in such a manner that some chosen physical constants take on the numerical value of one when expressed in terms of a particular set of natural units. ... In physics, Planck units are physical units of measurement defined exclusively in terms of the five universal physical constants shown in the table below in such a manner that all of these physical constants take on the numerical value of one when expressed in terms of these units. ... In modern physics the photon is the elementary particle responsible for electromagnetic phenomena. ... This article does not cite any references or sources. ... The Planck length, denoted by , is the unit of length approximately 1. ... â€œPlanckâ€ redirects here. ...

It is defined[1] 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
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.

## Contents

A commemoration plaque for Max Planck on his discovery of Plancks constant, in front of Humboldt University, Berlin. ... According to the law of universal gravitation, the attractive force between two bodies is proportional to the product of their masses and inversely proportional to the square of the distance between them. ... â€œLightspeedâ€ redirects here. ... Look up Vacuum in Wiktionary, the free dictionary. ... Look up second in Wiktionary, the free dictionary. ... For technical reasons, :) and some similar combinations starting with : redirect here. ... In probability and statistics, the standard deviation of a probability distribution, random variable, or population or multiset of values is a measure of the spread of its values. ...

According to the Big Bang theory nothing is known about the universe at time=0, though it is presumed that all fundamental forces coexisted and that all matter, energy, and spacetime expanded outward from an extremely hot and dense singularity. One Planck time after the event is the closest that theoretical physics can get to it, and at that time it appears that gravity separated from the other fundamental forces. According to the Big Bang theory, the universe originated in an infinitely dense and physically paradoxical singularity. ... For other uses, see Universe (disambiguation). ... A fundamental interaction is a mechanism by which particles interact with each other, and which cannot be explained by another more fundamental interaction. ... This article is about matter in physics and chemistry. ... For other uses of this term, see Spacetime (disambiguation). ... Singularity has several different meanings: mathematical singularity - a point where a mathematical function goes to infinity or is in certain other ways ill-behaved. ... Theoretical physics employs mathematical models and abstractions of physics, as opposed to experimental processes, in an attempt to understand nature. ... Gravity is a force of attraction that acts between bodies that have mass. ...

One second is about 1.855×1043 Planck times. The estimated age of the Universe in the Big Bang theory (4.3×1017 s) would be roughly 8×1060 Planck times. The average life expectancy of a human is approximately 3.9×1052 Planck times. The age of the universe, in Big Bang cosmology, refers to the time elapsed between the Big Bang and the present day. ... World map of human life expectancy, 2005 Life expectancy is a statistical measure of the average length of survival of a living thing. ...

As of 2006, the smallest unit of time that has been directly measured is on the attosecond (10−18 s) timescale, or around 1026 Planck times. [2][3] 2006 is a common year starting on Sunday of the Gregorian calendar. ... An attosecond is an SI unit of time equal to 10-18 of a second. ...

## Derivation

Ignoring a factor of π, the Planck mass is roughly the mass of a black hole with a Schwarzschild radius equal to its Compton wavelength. The radius of such a black hole would be, roughly, the Planck length. The Planck mass is the natural unit of mass, denoted by mP. It is the mass for which the Schwarzschild radius is equal to the Compton length divided by Ï€. â‰ˆ 1. ... For other uses, see Black hole (disambiguation). ... The Schwarzschild radius (sometimes inappropriately referred to as the gravitational radius[1]) is a characteristic radius associated with every mass. ... The Compton wavelength of a particle is given by , where is the Planck constant, is the particles mass and is the speed of light. ... The Planck length, denoted by , is the unit of length approximately 1. ...

The following thought experiment illuminates this fact. The task is to measure an object's position by bouncing electromagnetic radiation, namely photons, off it. The shorter the wavelength of the photons, and hence the higher their energy, the more accurate the measurement. If the photons are sufficiently energetic to make possible a measurement more precise than a Planck length, their collision with the object would, in principle, create a minuscule black hole. This black hole would "swallow" the photon and thereby make it impossible to obtain a measurement. A simple calculation using dimensional analysis suggests that this problem arises if we attempt to measure an object's position with a precision greater than one Planck length. In philosophy, physics, and other fields, a thought experiment (from the German Gedankenexperiment) is an attempt to solve a problem using the power of human imagination. ... Electromagnetic waves can be imagined as a self-propagating transverse oscillating wave of electric and magnetic fields. ... In modern physics the photon is the elementary particle responsible for electromagnetic phenomena. ... The wavelength is the distance between repeating units of a wave pattern. ... Dimensional analysis is a conceptual tool often applied in physics, chemistry, and engineering to understand physical situations involving a mix of different kinds of physical quantities. ...

This thought experiment draws on both general relativity and the Heisenberg uncertainty principle of quantum mechanics. Combined, these two theories imply that it is impossible to measure position to a precision greater than the Planck length, or duration to a precision greater than the time a photon moving at c would take to travel a Planck length. Hence in any theory of quantum gravity combining general relativity and quantum mechanics, traditional notions of space and time will break down at distances shorter than the Planck length or times shorter than the Planck time. For a less technical and generally accessible introduction to the topic, see Introduction to general relativity. ... Werner Karl Heisenberg (December 5, 1901 â€“ February 1, 1976) was a celebrated German physicist and Nobel laureate, one of the founders of quantum mechanics and acknowledged to be one of the most important physicists of the twentieth century. ... In quantum physics, the Heisenberg uncertainty principle is a mathematical property of a pair of canonical conjugate quantities - usually stated in a form of reciprocity of spans of their spectra. ... Fig. ... This article does not cite any references or sources. ...

To help compare different orders of magnitudes this page lists times between 10-44s and 10-43s. ... Named after Max Planck, in cosmology the Planck epoch (or Planck Era) is the earliest period of time in the history of the universe, from zero to 10-43 seconds (one Planck time), during which all four fundamental forces were unified and elementary particles did not yet exist. ...

## 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).
 Planck's natural units Base Planck units: Planck time  | Planck length  | Planck mass  | Planck charge  | Planck temperature Derived Planck units: Planck energy  | Planck force  | Planck power  | Planck density  | Planck angular frequency  | Planck pressure  | Planck current  | Planck voltage  | Planck impedance  | Planck momentum

Results from FactBites:

 Planck time - Wikipedia, the free encyclopedia (144 words) Eponymously termed for Max Planck, it is considered to be the smallest possible interval of time. The Planck time is the time it would take a photon travelling at the speed of light to cross a distance equal to the Planck length, and is thus considered to be a "quantum of time". Shortest time interval measured - coverage of 2004 event on BBC news.
 Planck units - Wikipedia, the free encyclopedia (2030 words) In physics, Planck units are physical units of measurement defined exclusively in terms of the five fundamental physical constants shown in the table below in such a manner that all of these fundamental constants take on the numerical value of 1 when expressed in terms of these units. Planck units are only one system of natural units among other systems, but might be considered unique in that these units are not based on properties of any prototype, object, or particle but are based only on properties of free space. With the exception of the Planck momentum and Planck impedance and the possible exception of the Planck mass, base and derived Planck units are impractical for empirical science, engineering, and everyday use, unless rescaled by many orders of magnitude.
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