The universe started from very hot and dense fire ball also known as YLEM that explodes. Bringing torrents of gases containing proton, neutron, and electron to immerse in the vast ocean of radiation. After the explosion, the ylem cooled and contract giving birth to the universe.
The universe that exist today is a product of continuous expansion and contraction. The expansion still continues and the distance between galaxies continue to increase.
In the 1920’s, Edwin Hubble discovered that galaxies were moving away from us when he observed the red shift in light wavelengths emitted by galaxies. This is known as Hubble’s law which states that the further away a galaxy is, the greater it’s red shift and the faster it is moving away from us. This led to the calculation of the point where the Big Bang started.
Today with the Hubble Space Telescope scientists have observed that most of the galaxies are moving away from us and this means that our universe must be moving outwards and expanding.
This theory proposes that the Universe is the same everywhere and for all time, both in the past and in the future. But calculations suggest that the universe is still expanding, so in order to maintain this constant state, matter must constantly be created out of nothing.
A steady-state universe has no beginning or end in time; and from any point within it the view on the grand scale--i.e., the average density and arrangement of galaxies--is the same
Cepheid variable – pulsating star whose brightness & temperature vary accd’g to regular pattern. As it expands it becomes cooler and dimmer and when it contracts, it becomes hotter & brighter. The brightness may last for a week.