Primordial universewhat happened right after the Big Bang
From the Planck epoch to electroweak symmetry breaking, the first instant of the universe saw inflation and reheating. Each stage and the research behind it.
On the Cosmic Calendar: The first 3 minutes of January 1From 0 s after the Big BangSee the full calendar
In its first instant, the universe went through the separation of gravity, the grand unification epoch, inflation, reheating and electroweak symmetry breaking. The pivotal step was inflation: space expanded by a factor of 10²⁶, then the inflaton field decayed and its vacuum energy turned into particles and radiation. Only then did a hot universe truly begin.
The closer we get to the start, the more we depend on theory rather than direct observation. Some of what follows has been confirmed by observation and some is still a theoretical framework, so keep that difference in mind as you read.
The first seven stages
- 10⁻⁴³ s · Planck epoch: Time and space begin to have meaning. Before this, words like "before and after" or "near and far" do not yet apply.
- 10⁻⁴³ s · Gravity separates: Gravity breaks away from the unified force and becomes an interaction of its own.
- 10⁻³⁶ s · Grand unification epoch: The strong, weak and electromagnetic forces are still one, like a single paint that has not yet been poured into three bottles.
- 10⁻³⁶ s · Cosmic inflation: Space expands by a factor of 10²⁶. What stretches is space itself, not the things in it flying off in all directions.
- 10⁻³² s · End of inflation: The inflaton field decays.
- 10⁻³² s · Reheating: Vacuum energy turns into particles and radiation. Inflation made the universe huge and cold; reheating released the stored energy, which became the source of all later matter and light.
- 10⁻¹² s · Electroweak symmetry breaking: The Higgs field gives particles mass, and different particles start to have their own "weight".
The expanding universe: from theory to observation
That the universe expands was first deduced in theory, and three papers passed the baton. Alexander Friedmann showed from general relativity that the universe could expand or contract, seven years before observational evidence (Friedmann, Zeitschrift für Physik, 1922). Georges Lemaître independently proposed that the universe is expanding and later imagined it starting from a "primeval atom", an early form of Big Bang theory (Lemaître, Annales de la Société Scientifique de Bruxelles, 1927). Observation followed: the farther a galaxy is from us, the faster it recedes, so the universe is not static (Hubble, PNAS, 1929). Hubble's paper is titled "A relation between distance and radial velocity among extra-galactic nebulae". Friedmann's paper dealt with the curvature of space, and Lemaître's with a homogeneous universe of constant mass and growing radius. Put side by side, the three papers follow the order "theory first, observation after".
Inflation: why the universe is so flat and uniform
Alan Guth proposed that the early universe expanded exponentially, which explained at a stroke why the universe is so flat and why its temperature is almost the same everywhere (Guth, Physical Review D, 1981). His paper's title, "Inflationary universe: A possible solution to the horizon and flatness problems", names the two puzzles. The first asks why distant regions have almost the same temperature; the second asks why the universe looks so flat. The original model had a flaw, though. Andrei Linde fixed the problem of how inflation could end gracefully, which made inflation theory workable (Linde, Physics Letters B, 1982).
The universe is still accelerating today
A "standard candle" is a light source of known brightness, like a row of bulbs with the same wattage: the dimmer one looks, the farther away it is. Researchers used distant supernovae as such bulbs and found that the expansion is accelerating. Dark energy entered the picture, and the work won the 2011 Nobel Prize (Riess et al., The Astronomical Journal, 1998). Another team reached the same conclusion independently: some energy in the universe is driving the acceleration (Perlmutter et al., The Astrophysical Journal, 1999). The Planck satellite gave the most precise cosmological parameters to date: an age of about 13.8 billion years, with ordinary matter making up only about 5% (Planck Collaboration, Astronomy & Astrophysics, 2020).
Where mass comes from
Peter Higgs proposed a field filling all of space that gives particles their mass, and predicted a new particle (Higgs, Physical Review Letters, 1964). The Large Hadron Collider found a new particle at about 125 GeV, confirming a prediction that had waited 48 years (ATLAS Collaboration, Physics Letters B, 2012). This matches the electroweak symmetry breaking step above: the Higgs field gives particles mass.
How the game shows it
In the game, the Primordial universe era starts at "0 s after the Big Bang" and its resource is energy. The generators are called Quantum fluctuation, Inflaton field, Vacuum decay and Reheating, named after the key ideas above.
Real basis
Planck epoch (10⁻⁴³ s): time and space begin to mean something
Gravity separates (10⁻⁴³ s): gravity splits from the unified force
Grand unification epoch (10⁻³⁶ s): the strong, weak and electromagnetic forces are still one
Cosmic inflation (10⁻³⁶ s): space expands 10²⁶-fold
End of inflation (10⁻³² s): the inflaton field decays
Reheating (10⁻³² s): vacuum energy turns into particles and radiation
Electroweak symmetry breaking (10⁻¹² s): the Higgs field gives particles mass
Related research
These studies relate to this topic but are not direct proof of this page.
The universe is expanding: Hubble found that the farther a galaxy is, the faster it recedes. The universe isn't static; it is expanding.
Source: Hubble, PNAS 1929, "A relation between distance and radial velocity among extra-galactic nebulae"
Friedmann's universe: Friedmann derived from general relativity that the universe can expand or contract, seven years before the observational evidence.
Source: Friedmann, Zeitschrift für Physik 1922, "Über die Krümmung des Raumes"
The primeval atom: Lemaître independently proposed that the universe is expanding, and later imagined it began as a “primeval atom,” the forerunner of Big Bang theory.
Source: Lemaître, Annales de la Société Scientifique de Bruxelles 1927, "Un Univers homogène de masse constante et de rayon croissant"
Inflationary universe: Guth proposed that the early universe underwent exponential expansion, explaining in one stroke why it is so flat and why temperatures are almost the same everywhere.
Source: Guth, Physical Review D 1981, "Inflationary universe: A possible solution to the horizon and flatness problems"
New inflation: Linde fixed the problem of how inflation could end gracefully, making inflation theory truly workable.
Source: Linde, Physics Letters B 1982, "A new inflationary universe scenario"
Accelerating expansion: Using distant supernovae as “standard candles,” they found the expansion of the universe is accelerating. Dark energy entered the picture, and the work won the 2011 Nobel Prize.
Source: Riess et al., The Astronomical Journal 1998, "Observational evidence from supernovae for an accelerating universe and a cosmological constant"
42 supernovae: Another team independently reached the same conclusion: some energy in the universe is driving the accelerating expansion.
Source: Perlmutter et al., The Astrophysical Journal 1999, "Measurements of Omega and Lambda from 42 high-redshift supernovae"
Recipe of the universe: The Planck satellite gave the most precise cosmological parameters yet: an age of about 13.8 billion years, with ordinary matter only about 5%.
Source: Planck Collaboration, Astronomy & Astrophysics 2020, "Planck 2018 results. VI. Cosmological parameters"
Where mass comes from: Higgs proposed a field filling space that gives particles mass, and predicted a new particle.
Source: Higgs, Physical Review Letters 1964, "Broken symmetries and the masses of gauge bosons"
Finding the Higgs particle: The Large Hadron Collider found a new particle at about 125 GeV, confirming a prediction made 48 years earlier.
Source: ATLAS Collaboration, Physics Letters B 2012, "Observation of a new particle in the search for the Standard Model Higgs boson with the ATLAS detector at the LHC"