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.
Einstein's special theory of relativity (special relativity) is all about what's relative and what's absolute about time, space, and motion. Some of Einstein's conclusions are rather surprising. They are nonetheless correct, as numerous physics experiments have shown.