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