The first few nanoseconds Big Bang 2
The early Universe was nothing like it is today. It was extremely small and hot. It would have fitted into the size of an atom, making the whole Universe more dense than an atomic nucleus. There certainly was not any ordinary matter. Instead it was full of exotic particles like quarks, leptons and gauge bosons. They made up what we call the primordial soup.

The temperature of this soup was nearly ten thousand million million degrees (1016oC). Its particles were smashing into each other with enormous energy.

Evolution of particles since the Big Bang
Early growth
The density of the soup meant that there was an enormous gravity trying to hold it together. However, the particles were moving so fast that even this immense force could not hold them in such a small space. So this soup lasted about 1 nanosecond – a thousand millionth of a second - which is about the time it is taking the light from this screen to reach your eyes. Then the Universe began to expand – as it has been doing for the last 14 billion years.
A cooling place to be
As the Universe expanded, it cooled. This was because the particles lost kinetic energy as they worked against the restraining gravity. This cooling allowed new particles to form without being smashed apart in high-energy collisions.
A small baby
When it was ten thousand millionths of a second old, the temperature of the soup had fallen to a million million degrees (1012 oC). By now, protons and neutrons were beginning to form. All the while these particles were colliding and producing new particles and anti-particles in the same way that particle accelerators do today.
What are protons and neutrons made of?
M2
The story so far
The Universe expanded rapidly and cooled
As it cooled the bigger quarks could bind together
They joined into protons and neutrons after about ten nanoseconds
Question S2

a) The atomic mass of hydrogen is 1 g/mol. There are 6 x 1023 atoms in a mole. What is the mass of one atom of hydrogen?

b) The nucleus is about 10-15 m across. Assume it is a cube. What is its volume?

c) Assume all the atom's mass is in the nucleus. What is the density of the nucleus? How does this compare with the density of normal matter?

The story so far
  • The Universe came into being with the Big Bang
  • The first particles were quarks and leptons
  • There was no normal matter in the early Universe