In physical cosmology, the Planck epoch
or Planck era is the earliest period of
time in the history of the universe,
from zero to approximately 10−43
seconds. It is believed that, due to the
extraordinarily small scale of the
universe at that time, quantum effects
of gravity dominated physical
interactions. During this period,
approximately 13.79 billion years ago,
gravitation is believed to have been as
strong as the other fundamental forces,
and all the forces may have been
unified. Inconceivably hot and dense,
the state of the universe during the
Planck epoch was unstable. As it
expanded and cooled, the familiar
manifestations of the fundamental forces
arose through a process known as
symmetry breaking.
Modern cosmology now suggests that the
Planck epoch may have inaugurated a
period of unification, known as the
grand unification epoch, and that
symmetry breaking then quickly led to
the era of cosmic inflation, the
Inflationary epoch, 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 mechanics 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 length, the distance
light travels in one Planck time—about
1.616 × 10−35 meters. Without an
understanding of quantum gravity, 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
singularity with an infinite density.
This conclusion could change when
quantum gravity is taken into account.
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.
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 this interval is still orders
of magnitude longer than the Planck
time, other experiments currently coming
online including 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. 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 behaved more like a
liquid than a gas, and the Large Hadron
Collider at CERN will probe still
earlier phases of matter, but no
accelerator will be capable of probing
the Planck scale directly.
See also
Big Bang
Chronology of the universe
Planck particle
Planck scale
Quantum gravity
Unified field theory
Footnotes
References
A Brief History of the Universe. 
The Planck Epoch. 
Genesis I: The Planck Epoch. 
Evolution of the Universe through the
Planck Epoch. 
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 Plank Epoch by professor James
Schombert 39O
The Planck Era - definition from U of
Ottawa's Astronomy Knowledge Base
