A Layman's Look at the First Three Minutes (adapting Ferris to Weinberg's account)

10-43 second:... End of the Planck epoch, beginning of calculable events: all the antecedents of the matter and energy in the observable universe are present in a very tiny volume at immense heat. .....At the end of the Planck era (and perhaps to 10-41 sec.), Gravity and the other fundamental forces are equally strong--essentially the same force.

(passing over the 'inflationary era' 10-35 to 10-30 seconds)

10-30 second: ... particles--quarks, anti-quarks, and others-- "precipitate out of the vacuum," as Ferris puts it-- they emerge from energy in the compressed fabric of space.... By another theory, particles are already present from the Beginning (left over from the 'Big Crunch' collapse of the last cosmos?).

By either theory, particles and anti-particles now collide in a continuous conversion of energy to matter and back to energy again. This constant annihilation is the fundamental character of the early cosmos.

This primal world is in 'thermal equilibrium': all the energy/heat produced by a given interaction is instantly converted to particles, and back again; there is no place for heat/energy to radiate out to. In this early process, down to 10 to the 32nd power K (=degrees Kelvin), Gravity and the Strong force are virtually one. Below that temperature, the two attractive forces separate into their respective realms.

As this mighty mini-cosmos continues to expand (not so rapidly as in the 'inflationary era') the spreading of space alters the dynamic. Expansion = cooling, and the farther apart things get, the less quickly they collide with other particles (and anti-particles).

10-11 second: temperature falls below 3 million billion degrees (3 X 10 to the 15th K).

The unified Electroweak force breaks up into the Weak force (operating only within a radius of 10-15 meter) and the Electromagnetic force (with infinite reach)

10-6 second: instant annihilation of quarks ceases. The Strong force overpowers the repulsive force of this dense, super-hot material and begins to form nucleons = protons and neutrons. How hot is it? [See note 1]

10-4 second: At this point we're at 300 billion K. Here begins the process of protons and neutrons colliding with electrons and positrons and ceaselessly converting from one nucleon to another. Initially there are equal numbers of each species (implied by thermal equilibrium). The collision energies produce additional electrons and positrons; but the collison energies are not sufficient to produce additional protons or neutrons--we have reached a stable total of nucleons in much same proportion to photons in the universe as at present.

1/100 of second: ...This process continues at 100 billion K, at a density 4 billion times that of water. Nucleons are still relatively rare, 1 nucleon per billion photons. Their total is conserved, but as they collide with other particles they convert as follows:

neutron + neutrino <---> proton + electron

proton + antineutrino <--> neutron + positron.

1/10 of a second: ...At 30 billion K, the balance of nucleons begins to shift; more neutrons convert to protons. [See Note 2.]

1 second: ...Neutrinos 'decouple': they are no longer constantly absorbed in collisions and conversions but now radiate freely. At 6 billion K, we reach the threshold below which electrons and positrons are no longer spontaneously formed (above this temperature they were popping or precipitating out of the ambient energy).

14 seconds :... At 3 billion K, electrons are much diminished, and with fewer electron/positron annihilations, the universe cools enough for Helium (He4) to form and hold together, much as it does in the Sun. Deuterium (H2) is the building block for He3 and other light elements, but little of this nucleus-building gets very far, because Deuterium is blasted apart as soon as it forms and other light elements are also readily shattered and reconstituted in ceaseless collision. This is the 'Deuterium bottleneck' blocking 'nucleosynthesis'.

By about 1 minute and 40 seconds, the cosmos has cooled enough that this process of forming simple nuclei begins to stabilize (just nuclei, not yet ringed with electrons).

3 minutes (and 2 seconds) [Weinberg's 5th frame]...At 1 billion K, the universe is cool enough for Tritium and Helium3 to hold, but the 'deuterium bottleneck' still bars the building of larger nuclei. Neutron decay quickly diminishes the stock of free neutrons (i.e. all surviving neutrons are soon joined in small nuclei).

3 minutes and 43 seconds: at something less than 1 billion K, Deuterium (H2) can hold together and nucleosynthesis begins (the process of building larger nuclei); but nuclei heavier than helium do not amount to much because of other "bottlenecks".

At 1 million years ABT, this expanding universe finally reaches the point where it becomes 'transparent to radiation'. That is, the matter/energy mix is no longer so dense that photons instantly collide and convert in some particle interaction. Instead nuclei can capture electrons in their orbits, and matter (as we know it) begins to form. Almost all electrons are bound in the ground state to either a Hydrogen nucleus or a Helium nucleus. At 3000 K the average photon is no longer potent enough to "kick out" electrons (and be absorbed); the photons now radiate freely.

'Stretched out" in wavelength by a factor of 1000, these are the photons that are now detected as the 3K cosmic background radiation --the static left over from the Big Bang.

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Note 1: At the very high early temperature, thermal equilibrium implies that all particle species are about equal in number: as many quarks and antiquarks as photons, etc.

Weinberg supposes there were about a billion times as many of each species--quarks, antiquarks, etc.-- as now survive bound up in matter. Much of the difference was simply annihilation of anti-particle pairs.

A great mystery remains: why did the number of quarks exceed the number of antiquarks by just this very small amount (1 billionth of the original stock)? There is no answer to this the Standard Model, but there may be in Supersymmetry.

Note 2: The neutron-into-proton reaction is favored because neutrons have more mass (=energy) than a proton, electron and neutrino put together. These relatively cooler temperatures make that small difference important for the first time. An isolated neutron decays into a proton in about 16 minutes