In
physical cosmologyPhysical cosmology, as a branch of astronomy, is the study of the largest-scale structures and dynamics of our universe and is concerned with fundamental questions about its formation and evolution. Cosmology involves itself with studying the motions of the celestial bodies and the first cause....
, the
Planck epoch (or
Planck era), named after
Max PlanckMax Planck was a German physicist. He is considered to be the founder of the quantum theory, and thus one of the most important physicists of the twentieth century. Planck was awarded the Nobel Prize in Physics in 1918.-Biography:Planck came from a traditional, intellectual family...
, is the earliest period of
timeTime is a component of the measuring system used to sequence events, to compare the durations of events and the intervals between them, and to quantify the motions of objects...
in the history of the
universeThe Universe comprises everything that physically exists, the entirety of space and time, all forms of matter and energy, and the physical laws and constants that govern them...
, from zero to approximately 10
−43 seconds (
Planck timeIn physics, the Planck time, , 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...
), during which
quantum effects of gravityQuantum gravity is the field of theoretical physics attempting to unify quantum mechanics with general relativity in a self-consistent manner, or more precisely, to formulate a self-consistent theory which reduces to ordinary quantum mechanics in the limit of weak gravity and which reduces to...
were significant. One could also say that it is the earliest moment in time, as the Planck time is perhaps the shortest possible interval of time, and the Planck epoch lasted only this brief instant.
In
physical cosmologyPhysical cosmology, as a branch of astronomy, is the study of the largest-scale structures and dynamics of our universe and is concerned with fundamental questions about its formation and evolution. Cosmology involves itself with studying the motions of the celestial bodies and the first cause....
, the
Planck epoch (or
Planck era), named after
Max PlanckMax Planck was a German physicist. He is considered to be the founder of the quantum theory, and thus one of the most important physicists of the twentieth century. Planck was awarded the Nobel Prize in Physics in 1918.-Biography:Planck came from a traditional, intellectual family...
, is the earliest period of
timeTime is a component of the measuring system used to sequence events, to compare the durations of events and the intervals between them, and to quantify the motions of objects...
in the history of the
universeThe Universe comprises everything that physically exists, the entirety of space and time, all forms of matter and energy, and the physical laws and constants that govern them...
, from zero to approximately 10
−43 seconds (
Planck timeIn physics, the Planck time, , 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...
), during which
quantum effects of gravityQuantum gravity is the field of theoretical physics attempting to unify quantum mechanics with general relativity in a self-consistent manner, or more precisely, to formulate a self-consistent theory which reduces to ordinary quantum mechanics in the limit of weak gravity and which reduces to...
were significant. One could also say that it is the earliest moment in time, as the Planck time is perhaps the shortest possible interval of time, and the Planck epoch lasted only this brief instant. At this point approximately 13.7 billion years ago the force of gravity is believed to have been as strong as the other fundamental forces, which hints at the possibility that all the forces were unified. Inconceivably hot and dense, the state of the universe during the Planck epoch was unstable or transitory, tending to evolve, giving rise to the familiar manifestations of the fundamental forces through a process known as
symmetry breakingSymmetry breaking in physics describes a phenomenon where small fluctuations acting on a system crossing a critical point decide a system's fate, by determining which branch of a bifurcation is taken. For an outside observer unaware of the fluctuations , the choice will appear arbitrary...
. Modern cosmology now suggests that the Planck epoch may have inaugurated a period of unification or
Grand unification epochIn physical cosmology, assuming that nature is described by a Grand unification theory, the grand unification epoch was the period in the evolution of the early universe following the Planck epoch, in which the temperature of the universe was comparable to the characteristic temperatures of grand...
, and that symmetry breaking then quickly led to the era of
cosmic inflationIn physical cosmology, cosmic inflation, cosmological inflation or just inflation is the theorized exponential expansion of the universe at the end of the grand unification epoch, 10
−36 seconds after the Big Bang, driven by a negative-pressure vacuum energy density...
, the
Inflationary epochIn physical cosmology the inflationary epoch was the period in the evolution of the early universe when, according to inflation theory, the universe underwent an extremely rapid exponential expansion...
, during which the universe greatly expanded in scale over a very short period of time.
Theoretical ideas
As there presently exists no widely accepted framework for how to combine
quantum mechanicsQuantum mechanics is a set of principles describing the physical reality at the atomic level of matter and the subatomic . These descriptions include the simultaneous wave-like and particle-like behavior of both matter and radiation...
with relativistic gravity, science is not currently able to make predictions about events occurring over intervals shorter than the Planck time or distances shorter than one
Planck lengthIn physics, the Planck length, denoted ℓP, is a unit of length, equal to . It is a base unit in the system of Planck units. The Planck length can be defined from three fundamental physical constants: the speed of light in a vacuum, Planck's constant, and the gravitational constant...
, the distance light travels in one Planck time—about 1.616 × 10
−35 meters. Without an understanding of
quantum gravityQuantum gravity is the field of theoretical physics attempting to unify quantum mechanics with general relativity in a self-consistent manner, or more precisely, to formulate a self-consistent theory which reduces to ordinary quantum mechanics in the limit of weak gravity and which reduces to...
, a theory unifying quantum mechanics and relativistic gravity, the physics of the Planck epoch are unclear, and 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. If quantum effects are ignored, the universe starts from a
singularityA gravitational singularity or spacetime singularity is a location where the quantities that are used to measure the gravitational field become infinite in a way that does not depend on the coordinate system...
with an infinite density. This conclusion could change when quantum gravity is taken into account.
String theoryString theory is a developing branch of theoretical physics that combines quantum mechanics and general relativity into a quantum theory of gravity...
and
Loop quantum gravityLoop quantum gravity , also known as loop gravity and quantum geometry, is a proposed quantum theory of spacetime which attempts to reconcile the theories of quantum mechanics and general relativity...
are leading candidates for a theory of unification, which have yielded meaningful insights already, but work in
Noncommutative geometryNoncommutative geometry, or NCG, is a branch of mathematics concerned with the possible spatial interpretations of algebraic structures for which the commutative law fails, that is, for which xy does not always equal yx. For example; 3 steps of 4 units and 4 steps of 3 units length might be...
and other fields also holds promise for our understanding of the very beginning.
Experiments exploring this time
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 test hypotheses about the universe's first trillionth of a second (although the cosmic microwave background radiation observed by WMAP originated when the universe was already several hundred thousand years old). 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 SurveyorPlanck is a space observatory designed to observe the anisotropies of the cosmic microwave background over the entire sky, using high sensitivity and angular resolution. Planck was built in the Cannes Mandelieu Space Center by Thales Alenia Space and created as the third Medium-Sized Mission of...
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 acceleratorA particle accelerator is a device that uses electric fields to propel ions or charged subatomic particles to high speeds and to contain them in well-defined beams. An ordinary CRT television set is a simple form of accelerator...
s provides meaningful insight into the early universe as well. Experiments with the
Relativistic Heavy Ion ColliderThe Relativistic Heavy Ion Collider is a heavy-ion collider located at and operated by Brookhaven National Laboratory in Upton, New York...
have allowed physicists to determine that the
Quark-gluon plasmaA quark–gluon plasma is a phase of quantum chromodynamics which exists at extremely high temperature and/or density. This phase consists of free quarks and gluons, which are the basic building blocks of matter...
(an early phase of matter) behaved more like a liquid than a gas, and the
Large Hadron ColliderThe Large Hadron Collider is the world's largest and highest-energy particle accelerator intended to collide opposing particle beams of either protons at an energy of 7 TeV per particle or lead nuclei at an energy of 574 TeV per nucleus...
at
CERNThe European Organization for Nuclear Research , known as CERN , , is the world's largest particle physics laboratory, situated in the northwest suburbs of Geneva on the Franco–Swiss border, established in 1954...
will allow us to probe still earlier phases of matter, but no accelerator (current or planned) will allow us to probe the
Planck scaleIn particle physics and physical cosmology, the Planck scale is an energy scale around 1.22 × 1028 eV at which quantum effects of gravity become strong...
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.
See also
- Big bang
The Big Bang is the cosmological model of the initial conditions and subsequent development of the Universe that is supported by the most comprehensive and accurate explanations from current scientific evidence and observation...
- Planck particle
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
Quantum gravity is the field of theoretical physics attempting to unify quantum mechanics with general relativity in a self-consistent manner, or more precisely, to formulate a self-consistent theory which reduces to ordinary quantum mechanics in the limit of weak gravity and which reduces to...
- Timeline of the Big Bang
This timeline of the Big Bang describes the events according to the widely accepted scientific theory of the Big Bang, using the cosmological time parameter of comoving coordinates....
- Unified field theory
In physics, a unified field theory is a type of field theory that allows all of the fundamental forces between elementary particles to be written in terms of a single field. There is no accepted unified field theory yet, and this remains an open line of research. The term was coined by Albert...
External links