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. Correspondingly; the entire universe occupied the Planck scale domain at this time, which marked the beginning of the Big Bang. Unbelievably hot and dense, the state of the universe during the Planck epoch was unstable or transitory, tending to evolve and giving rise to the familiar manifestations of the fundamental forces through a process known as symmetry breaking. It is currently believed that the Planck epoch inaugurated the Inflationary period, or Inflationary epoch, during which the universe greatly expanded in scale over a very short period of time. Max Karl Ernst Ludwig Planck (April 23, 1858 – October 4, 1947) was a German physicist. ... Cosmology, as a branch of astrophysics, is the study of the large-scale structure of the universe and is concerned with fundamental questions about its formation and evolution. ... Two distinct views exist on the meaning of time. ... The deepest visible-light image of the cosmos, the Hubble Ultra Deep Field. ... In physics, the Planck time (tP), is the natural unit of time. ... A fundamental interaction is a mechanism by which particles interact with each other, and which cannot be explained by another more fundamental interaction. ... In particle physics, an elementary particle or fundamental particle is a particle not known to have substructure; that is, it is not made up of smaller particles. ... In physics, Planck units are physical units of measurement originally proposed by Max Planck. ... According to the Big Bang theory, the universe emerged from an extremely dense and hot state (bottom). ... Promotional picture Symmetry Breaking is a rock band from Northern New Jersey, in the United States. ... Cosmic inflation is the idea, first proposed by Alan Guth in 1981, that the nascent universe passed through a phase of exponential expansion (the inflationary epoch) that was driven by a negative pressure vacuum energy density. ... The inflationary epoch is the term used in cosmology to describe the brief time in the very early universe when, according to inflation theory, the universe was expanding exponentially. ...

Theoretical Ideas

Standard quantum mechanics says that it is meaningless to speak of durations shorter than the Planck time or distances shorter than one Planck length, the distance light travels in one Planck time—about 1.616 × 10^-35 meters. Accordingly; most physicists believe the history of the universe should be measured, not from zero, but from one Planck time. Likewise, the volume of the universe is seen to start at one Planck length in diameter rather than at zero. Thus; it is likely there never was a singularity of infinite density, even at the very beginning. But the exact manner in which the fundamental forces were unified, and how they came to be separate entities, is still poorly understood. Three of the four forces have been successfully integrated in a common framework, but gravity remains problematic. As of 2006, there is no generally accepted theory that unifies quantum mechanics and relativistic gravity. String theory and Loop quantum gravity are leading candidates for a theory of unification, which have yielded meaningful insights already, but work in Noncommutative geometry and other fields also holds promise for our understanding of the very beginning. However; there are no definitive answers yet. A future complete theory may or may not allow more to be said about the Planck epoch. Only time will tell. Fig. ... In physics, the Planck time (tP), is the natural unit of time. ... The Planck length, denoted by , is the unit of length in the system of units known as Planck units. ... 2006 is a common year starting on Sunday of the Gregorian calendar. ... Gravity is a force of attraction that acts between bodies that have mass. ... Interaction in the subatomic world: world lines of pointlike particles in the Standard Model or a world sheet swept up by closed strings in string theory String theory is a model of fundamental physics whose building blocks are one-dimensional extended objects (strings) rather than the zero-dimensional points (particles... Loop quantum gravity (LQG), also known as loop gravity and quantum geometry, is a proposed quantum theory of spacetime which attempts to reconcile the seemingly incompatible theories of quantum mechanics and general relativity. ... In mathematics, there is a close relationship between spaces, which are geometric in nature, and the numerical functions on them. ...

Experiments Exploring the Planck Epoch

Experimental data casting light on this cosmological epoch has been scant or non-existent until now, but recent results from the WMAP probe have allowed scientists to 'see' the universe's first trillionth of a second. Although this interval is still orders of magnitude longer than the Planck time, other experiments currently coming online including the IceCube neutrino detector and the Planck Surveyor probe, promise to push back our 'cosmic clock' further to reveal quite a bit more about the very first moments of our universe's history, hopefully giving us some insight into the Planck epoch itself. Of course; data from particle accelerators provides meaningful insight into the early universe, as well. Experiments with the Relativistic Heavy Ion Collider have allowed physicists to determine that the Quark-Gluon plasma (an early phase of matter) behaved more like a liquid than a gas, and the Large Hadron Collider soon to come online at CERN will allow us to probe still earlier phases of matter, but no accelerator (current or planned) will allow us to probe the Planck scale directly. However; the more we understand about how matter forms, the more precisely we will be able to interpret what we learn from astrophysical data, and from other sources. Artist depiction of the WMAP satellite at the L2 point The Wilkinson Microwave Anisotropy Probe (WMAP) is a NASA satellite whose mission is to survey the sky to measure the temperature of the radiant heat left over from the Big Bang. ... The IceCube Neutrino Detector is a neutrino telescope currently under construction at the South Pole. ... WMAP image, unrelated to Planck The Planck Surveyor is the third Medium-Sized Mission (M3) of ESAs Horizon 2000 Scientific Programme. ... A 1960s single stage 2MeV linear Van de Graaff accelerator, here opened for maintenance A particle accelerator is a device that uses electric and/or magnetic fields to propel electrically charged particles to high speeds. ... The Relativistic Heavy Ion Collider at Brookhaven National Laboratory. ... The Large Hadron Collider (LHC) is a particle accelerator and collider located at CERN, near Geneva, Switzerland ( ). Currently under construction, the LHC is scheduled to start operation in November 2007, when it will become the worlds largest and highest energy particle accelerator. ... CERN logo The European Organization for Nuclear Research (French: Organisation Européenne pour la Recherche Nucléaire), commonly known as CERN, is the worlds largest particle physics laboratory, situated just west of Geneva on the border between France and Switzerland. ... In physics, Planck units are physical units of measurement originally proposed by Max Planck. ...

See also

• Big bang
• Planck scale
• Planck particle
• Quantum gravity
• Timeline of cosmology
• Unified field theory

According to the Big Bang theory, the universe emerged from an extremely dense and hot state (bottom). ... In physics, Planck units are physical units of measurement originally proposed by Max Planck. ... A Planck particle is a hypothetical subatomic particle, defined as a tiny black hole whose Compton wavelength is the same as its Schwarzschild radius. ... Quantum gravity is the field of theoretical physics attempting to unify the theory of quantum mechanics, which describes three of the fundamental forces of nature, with general relativity, the theory of the fourth fundamental force: gravity. ... The timeline of cosmology lists the sequence of cosmological theories and discoveries in chronological order. ... In physics, unified field theory is an attempt to unify all the fundamental forces and the interactions between elementary particles into a single theoretical framework. ...

External Links

• The Planck Era from U of Tennessee Astrophysics pages
• The Planck Era from U of Oregon Cosmology pages
• The Planck Era by Sten Odenwald from Astronomy Cafe
• The Planck Era - definition from U of Ottawa's Astromomy Knowledge Base