Prices of a stock will move throughout the day. Investors generally buy a stock they feel is undervalued, and sell a stock they feel is overvalued. For instance, if the price of AAPL is $600 dollars, it means the cost to purchase one share of Apple is $600 dollars.
Einstein quickly realized (or had known all along) that his new theory of gravity was really a theory of the cosmos. In 1917, he wrote a famous paper applying general relativity to the universe as a whole. Today that paper stands as the foundation for modern cosmology.
Albert Einstein's theory of relativity is actually two separate theories: his special theory of relativity, postulated in the 1905 paper, The Electrodynamics of Moving Bodies and his theory of general relativity, an expansion of the earlier theory, published as The Foundation of the General Theory of Relativity in 1916.