The Theory of Everything: The Origin and Fate of the Universe

The most remarkable property of the universe is that it has spawned creatures able to ask questions.

We now know that our galaxy is only one of some hundred thousand million that can be seen using modern telescopes, each galaxy itself containing some hundred thousand million stars. We live in a galaxy that is about one hundred thousand light-years across and is slowly rotating; the stars in its spiral arms orbit around its center about once every hundred million years. Our sun is just an ordinary, average-sized, yellow star, near the outer edge of one of the spiral arms.

As often happens in science, discoveries are made in the pursuit of an elusive (and sometimes nonexistent) goal.

The discovery that the universe was expanding was one of the great intellectual revolutions of the twentieth century.

one has a singularity contained within a region of space-time known as a black hole.

I realized that if one reversed the direction of time in Penrose’s theorem so that the collapse became an expansion, the conditions of his theorem would still hold, provided the universe were roughly like a Friedmann model on large scales at the present time.