The Big Bang Big Bang 1
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The story of the Universe starts about14 thousand million years ago with the Big Bang. This was a huge explosion that brought the Universe into existence. Before the Big Bang, there were no laws of physics, no time and certainly no particles. At the very beginning, there was an immense amount of energy in the form of radiation. The fundamental particles were born out of this energy.
Evolution of particles since the Big Bang
The quarks and leptons were amongst the first particles to appear. However, this early Universe was changing quickly as it expanded and cooled. The quarks have never again existed in isolation but have remained confined within protons, neutrons and other hadrons for the last 14 billion years. Although these hadrons were formed in the first hundredth of a second, it took a further million years before there were any atoms.

Looking back
In order to recreate the conditions that particles experienced in the very early Universe, scientists build bigger and bigger particle accelerators to smash today’s particles apart. The bigger accelerators can give particles more and more energy. They then start to move at speeds close to those that they would have had in the inferno of the first billionths of a second. However, they have yet to reach the energies that particles had when quarks were free to roam the Universe.

Question S1

a) The primordial soup was extremely dense and therefore the gravity was huge. Why didn't this stop the Universe from expanding?

b) Why did the Universe cool as it expanded?

The story so far
  • The Universe is made from matter and radiation
  • The Universe is not static - it has constantly changed over its 14 billion years and is still expanding to this day
  • One billion years is equivalent to 1 thousande million years