It is commonly known among serious scientists and particularly among astronomists that there was a Big Bang at the beginning of the universe. One evidence for it is the fact that the universe is expanding with a steady (or decreasing, or increasing) rate.
This has been supported by the data collected by the Hubble Telescope, see Universe development, Expansion. Edwin Hubble was the very founder of the theory of the expansion of the universe (see "The Birth of Time" by John Gribbin, Weidenfeld & Nicholson, London 1999).
Before this Big Bang, all agree, matter must have been concentrated in a hugely dense and solid mass, the size of which nobody knows. Scientists conjecture by estimating density and size of the known universe. They interpret the difference between electromagnetic waves, like the colour of light, that can be measured in distant galaxies. This is the redshift. There must have been a big explosion in the beginning, as shown above.
