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Planck epoch: the first 10⁻⁴³ second
1970· Cosmic event
Open questionNobody knows the answer.
The earliest nameable era, from the start (if there was one) to about 10⁻⁴³ second, when even gravity should have obeyed quantum rules.
See it on the Science map →How it works
Run the expansion backward with known physics and, by about 10⁻⁴³ second, the temperature reaches roughly 10³² degrees. There, quantum jitter is strong enough to shake spacetime itself, so 'before', 'after' and 'distance' may lose their usual meaning. No tested theory works there. The epoch is less an observed era than the wall where current physics stops. If inflation happened, it came after or instead of this stage and stretched away any trace of it.
Why it matters
It is the absolute edge of known physics. Every origin idea on this map, from tunneling out of nothing to bounces and cycles, is a guess about this boundary or what lies beyond it.
Think of it like
Like a title search that reaches the oldest recorded deed: before it, the records cannot say whether there was an earlier owner, raw land, or no parcel at all.
How we know
None directly. Its timing and temperature follow from measured constants and today's expansion rate. No signal from it is known to survive; even inflation's hoped-for gravitational waves would date from later.
Still a mystery
Did time begin here, emerge from something timeless, or continue from an earlier shrinking universe? Without a theory of quantum gravity nobody can say, and there may be no way to look.
Connections (4)
▸Planck epoch: the first 10⁻⁴³ second gives way to Grand unification epochSpeculative
The relationship
In the standard extrapolated timeline, once the universe expanded and cooled past the Planck time, gravity became an ordinary, classical force, separate from the rest. What remained, if grand unified theories are right, was a single combined force for the strong, weak and electromagnetic interactions. The handoff is the moment gravity 'froze out' of quantum chaos into the smooth spacetime that general relativity describes.
How the link was found
Pieced together in the late 1970s and 1980s as particle physicists applied grand unified theories to the hot early universe; summarized in Edward Kolb and Michael Turner's 1990 textbook The Early Universe.
Is it proven?
Not proven. Neither era has been observed, and inflation may have erased any trace. The sequence is an extrapolation of known physics plus unconfirmed unification.
Open questions and mysteries
Was gravity ever unified with the other forces? String theory says it joins them near the Planck scale; loop quantum gravity quantizes gravity alone, without unifying it. Neither has been tested.
▸Singularities: where physics breaks marks where relativity fails, in Planck epoch: the first 10⁻⁴³ secondOpen question
The relationship
Run general relativity backward and density and curvature grow without limit, reaching infinity at t = 0. But long before that, by about 10⁻⁴³ second, curvature is so extreme that quantum effects on spacetime should dominate, and relativity's predictions stop being trustworthy. So the infinite start is probably not a real event in the timeline; it lies inside the zone, the Planck epoch, where the theory has run out.
How the link was found
Hawking and Penrose's singularity theorems (1965–1970) proved relativity must break down there. John Wheeler and others argued from the 1950s that quantum effects take over near the Planck scale.
Is it proven?
That relativity alone predicts a singularity is proven mathematics. That quantum effects intervene first is a near-universal expectation, not tested.
Open questions and mysteries
Does quantum gravity remove the singularity, replacing it with a bounce, a smallest size or a rounded-off start? Does 't = 0' have any meaning at all?
▸The Planck scale: the smallest meaningful size sets the size and time of Planck epoch: the first 10⁻⁴³ secondWell supported
The relationship
The Planck units define the epoch. When the universe's age was one Planck time, light could have crossed only about one Planck length, and the temperature was near the Planck temperature, about 10³² degrees. At that scale, quantum uncertainty in spacetime's shape is as large as the shape itself. Earlier than that, no description without quantum gravity can work.
How the link was found
Max Planck defined these units in 1899, long before cosmology existed. Using them to mark the earliest universe became standard in the 1970s, as the hot Big Bang met quantum field theory.
Is it proven?
It is a calculation: run the well-tested hot-expansion history backward and the temperature reaches the Planck value at about the Planck time. But that history is checked directly only back to about one second, via the first elements, so this is a vast extrapolation.
Open questions and mysteries
Could quantum gravity matter at much lower energies? If hidden extra dimensions exist, as proposed in 1998, its true scale could be far lower and the quantum-gravity era would have lasted much longer. The LHC has seen no sign.
▸Quantum gravity: the missing link is needed to describe Planck epoch: the first 10⁻⁴³ secondOpen question
The relationship
In the Planck epoch, energy is packed so densely that gravity is as strong as quantum jitter. Spacetime cannot be treated as a fixed stage; the stage itself fluctuates. Only a theory that makes gravity quantum could describe it, including whether time had a beginning. Candidates tell different stories: loop quantum gravity suggests a bounce, string theory offers colliding branes, and Hartle and Hawking a rounded-off start.
How the link was found
Bryce DeWitt, working with John Wheeler, wrote the first equation for the quantum state of a whole universe in 1967 (the Wheeler–DeWitt equation). James Hartle and Stephen Hawking applied it to the beginning in 1983.
Is it proven?
Not proven. There is no accepted quantum gravity theory and no observation from this era. The need follows from the Planck-scale argument.
Open questions and mysteries
Can any relic of this era survive inflation to be measured? If not, the earliest moment may stay permanently beyond observation.