E proposed cosmological constant to prove the universe is stationary. Some others suggested Universe is contracting, while some others suggested Universe is exanding and for either of them cosmological constant was considered responsible. Today when this is discovered universe is expanding with acceleration, cosmological constant is again thought to be the reason. So, if universe was stationary, reason cosmological constatn. If it was expanding at constant rate, reason cosmological constant. If it was contracting, reason cosmological constant. It is expanding with increasing rate, reason cosmological constant. CC is the same thing as zero point energy, or dark energy and has its own 'mass'. It permeates the entire universe and every point in space. As the universe expands, the amount of dark energy also increases. And this leaves a question what is the origin of dark energy? When there was no space, there was no dark energy, so where does it come from?