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.
A century ago this year, a young Swiss physicist who had already revolutionized physics developed a radical new understanding of gravity. In 1915, Albert Einstein published his general theory of relativity, which described gravity as a fundamental property of space-time. He came up with a set of equations that relate the curvature of space-time to the energy and momentum of the matter and radiation that are present in a particular region.