THE GREAT START...
At 500,000 years old the Universe contained the seeds of galaxy clusters among its filaments and voids.
At 1.3 billion years old individual galaxies had formed within crowded filaments that were rich in dust and young stars.
At 13.8 billion years old (the present) the whole universe has taken on a galaxy-supercluster structure.
THE BIG - BANG THEORY
The Universe is thought to have been born 13.8 billion years ago in a searing hot maelstrom known as the Big Bang. One strong piece of evidence for this energetic beginning comes in the form of a ubiquitous source of microwave radiation appearing across the whole sky, known as the Cosmic Microwave Background (CMB). As the Universe has stretched and expanded since the Big Bang it has also stretched the wavelength of the radiation emitted when it was very young. So what was once higher-energy, shorter-wavelength radiation now appears as lower-energy, longer-wavelength microwaves. Tiny fluctuations in the density of matter early on in the Universe acted like seeds around which matter began to clump, setting the scene for the formation of vast clusters of galaxies. The fingerprints of these "seeds" can be seen stamped as minute variations in the Cosmic Microwave Background.