EVOLUTION OF UNIVERSE World scientist James Pebbles won the 2019 Nobel Prize in Physics for his contributions to the theory of the origin and evolution of our universe. In this article, he describes the ideas he co-authored with Scientific American in 1994. At a particular moment about 15 billion years ago, all the matter and energy we could see, concentrated in a region smaller than a penny, began to expand and cool at an astonishingly fast rate. The forces of nature assumed their current properties until the temperature of the Sun's core dropped 100 million times, and the elementary particles, known as quarks, were moving freely in the ocean of energy. When the universe expanded 1.0 times, the size of the solar system was filled with everything we could count on. At that time the free quark was trapped in neutrons and protons. As the universe grew by another factor of 1.0, protons and neutrons came together to form the nucleus, which contains most o
HOW OLD IS THIS WORLD In contrast, the universe seems to be about 13.8 billion years old. Scientists reached that number by measuring the age of the oldest stars and the speed of expansion of the universe. They also measured the details by observing Doppler changes in light from galaxies, almost all of which are moving away from us and from each other. The farther away the galaxies are, the faster they are traveling. Gravity is expected to slow down the galaxies from each other, but instead they are increasing rapidly and scientists do not know why. In the distant future, galaxies will be so far away that their light will not be visible from the earth.