Cosmos: Origin and Fate of the Universe

“The cosmos is all that is or ever was or ever will be,” Carl Sagan once said. In the most alluring of combinations, the field of cosmology brings what we know about the universe together in poetic terms — understanding the origin and fate of it all. In this special package of stories, the editors of Astronomy present a walk-through of cosmology, up-to-the-minute and packed with facts, that details the state of the union on our cosmological knowledge. You’ll read about the nature of galaxies, the basic building blocks of the cosmos, and how they contain vast stores of stars, gas, and dust. Our own Milky Way, of which the Sun is but one star, contains some 400 billion suns spread over its diameter of at least 100,000 light-years. We…

ON THE EVENING of Oct. 4, 1923, near Los Angeles, a young astronomer got into his car and began a motorized trek up to Mount Wilson. There, he arrived at the observatory that housed the 100-inch Hooker Telescope, at the time the largest telescope in the world. Edwin Hubble was a fourth-year astronomer at Mount Wilson; he enjoyed using the Hooker Telescope because he was interested in, among other things, studying spiral “nebulae.” These mysterious gas clouds were scattered across the sky, and no one understood their nature. In the early days of the 1920s, Hubble had assigned himself the task of figuring them out. He pointed the great telescope toward his favorite object: the nebula in Andromeda, M31. This spiral-shaped cloud is faintly visible to the naked eye under…

HOW MANY GALAXIES EXIST IN THE UNIVERSE? No one knows, but for a generation, astronomers have believed 100 billion was the answer. Now, we’ve discovered the number is likely much higher. It’s a perplexing puzzle to take on, because the universe is so large and has evolved so much over its 13.8-billion-year history. For many of us, it’s a problem that at first may seem as difficult as counting all the grains of sand on all the beaches on our planet. Like many others before and since, when I was growing up near the coast of Florida, I would often sit on the beach and admire the vast amount of sand before me. I would naturally ask myself, “How many grains of sand are there on this beach?” The number…

ON FEBRUARY 11, 2016, two teams of scientists announced the first observation of gravitational waves, a phenomenon that Albert Einstein’s general theory of relativity had predicted a century earlier. The Laser Interferometer Gravitational-wave Observatory (LIGO) and Virgo collaborations had caught ripples in space-time itself: the wake of two black holes that collided and merged more than a billion light-years away. It was a triumph for general relativity. But to physicists, it wasn’t an end; it was a beginning. Black holes — objects so dense that not even light can escape — proved Einstein right. Now, scientists want to use them to stretch relativity to its limits, and perhaps even break it. “It’s not that we think relativity’s wrong,” says Andrea Ghez, a professor of physics and astronomy at the University…

A series of powerful observations has made it clear that our universe has expanded for billions of years, emerging from the hot, dense state we call the Big Bang. Over the past several decades, new types of precise measurements have allowed scientists to scrutinize and refine this account, letting them reconstruct the history of our universe in ever greater detail. When we compare the results from different kinds of measurements — the expansion rate of the universe, the temperature patterns in the light released when the first atoms formed, the abundances of various chemical elements, and the distribution of galaxies and other large-scale structures — we find stunning agreement. Each of these lines of evidence supports the conclusion that our universe expanded and evolved in just the way that the…

Do geologists dream of a final theory? Most people would say that plate tectonics already serves as geology’s overarching idea. The discovery of plate tectonics 50 years ago was one of the great scientific achievements of the 20th century, but is the theory complete? I think not. Plate tectonics describes Earth’s present geology in terms of the geometry and interactions of its surface plates. Geologists can extrapolate plate motions both back in time and into the future, but they cannot yet derive the behavior and history of plate tectonics from first principles. Although scientists can interpret the history through the lens of what they see today, an important question remains: Why did geologic events — such as hot-spot volcanism, the breakup of continents, fluctuations in seafloor spreading, tectonic episodes, and…