The composition of our universe

One of the more difficult fundamental problems which confronts science today is that of determining the chemical composition of the matter of which our universe is made. Man, bound to the surface of his planet, can see the billions of stars which exist within the galaxy of which his sun is a member, and the billions of galaxies extending in all directions as far as his telescopes can penetrate; but he has only the light that the stars emit with which to work. He knows that a very large amount of matter is scattered throughout interstellar space; but he cannot sample it. He can see the other planets within his solar system; but he can study only the light that they reflect from the sun. He is even prevented by the thick solid crust under his feet from sampling the interior of his own planet.