We live in a universe filled with wonders. Comets hang like celestial torches before fading on their long journeys into space. The sun descends in a golden blaze on a summer evening, and countless stars spill from zenith to horizon through the dark night. At such moments, our cosmos inspires awe.

However, we rarely feel connected to the cosmos. We live at a hectic pace on a warm planet, insulated from the universe by the bright blue dome of sky. At night, when the heavens open up to us, we seldom cast more than a glance overhead. Even when we do notice the grandeur of the universe, it seems utterly separate from our lives. Planets, stars, and galaxies appear so small to our eyes that we cannot comprehend their enormous sizes, so far away that we cannot grasp the vast gulf of space between them, and so exotic that we cannot understand how they work. Our experiences on Earth seem so different from these wonders that nature surely must have followed another set of rules in creating them. Can we ever hope to divine those cosmic principles?

The answer is a resounding "Yes." A deep insight has emerged from astronomy and physics: The basic forces, quantities, and processes that govern our lives on Earth and that govern the workings of the universe are one and the same. In fact nature's laws are fewer in number, and often simpler, than the laws that human societies invent. We can study the natural laws on our planet and in our neighborhood in space, then use those laws to understand the behaviors of objects that lie forever out of reach. In so doing, we have learned that no wall separates our Earth and sky from the rest of the cosmos. We live in One Universe.

Some of those connections are easy to see. A crystal hanging in a window lights the room with bands of color on a sunny day. We use more elaborate crystals to break up light from stars and galaxies. Special instruments extract hidden details from those delicate rainbows, revealing what the objects are made of and how they move through space. Baseball fans watch the cosmos at work when they follow the arc of a home run soaring into the bleachers. The arc is a perfect illustration of the ever-present force of gravity, which pins us to the ground, keeps the Moon in orbit around Earth, and steers our Sun through our Milky Way galaxy. The Moon and the Sun also exert gravitational pulls on Earth, creating tides that we see as the twice-daily ebb and flow of the ocean. Stronger tides elsewhere in the universe turn the insides of moons to mush and stretch pairs of closely orbiting stars into egglike shapes.

Other connections come from watching things spin, a property that applies to nearly everything in space. The whirl of a gyroscope, as children know, prevents it from toppling on its side. Telescopes in space take advantage of that same principle by using three gyroscopes to keep a steady aim. On a larger scale, Earth's daily rotation on its axis stirs our atmosphere and stretches storms into spiral shapes. Other planets display similar stormy patterns, such as Jupiter's Great Red Spot.

Some of our links to the cosmos are more surprising, for they involve events too extreme to occur on Earth. For instance, the largest stars blow up in titanic blasts that seed the galaxy with heavy elements, such as iron, calcium, and silicon. These elements come only from stars; the universe has no other way to create them. They drift into clouds of gas and dust which collapse into a new generation of stars, planets, and--in our case--life. In other words, dying stars forged the elements that compose the blood in our veins, the bones in our bodies, and the chips in our computers. The stuff of stars is all around us even though the stars themselves seem so inaccessible.

Our awareness of these connections has grown as we have studied the natural world for thousands of years. The earliest natural philosophers--Plato, Aristotle, and Archimedes among them--tried to use their five senses, in combination with logic and reason, to explain the cosmos. However, their preconceptions got in the way. Earth sat unmoving at the center of the universe, they believed, and the celestial bodies moved around it in perfect patterns. These beliefs also affected their view of physical principles on Earth. For instance, Aristotle asserted that heavier objects fall faster than light objects, but he never bothered to put that claim to the test.

Our modern approach to gathering knowledge about the universe draws from traditions established by Galileo Galilei, Isaac Newton, Albert Einstein, and other great minds of the past several centuries. These physicists didn't care whether their results conformed to common-sense views about how the universe worked. Rather, they devised careful theories based on repeated experiments and mathematical analysis. Their theories strove to explain some of what was not understood, predict previously unknown phenomena, and consistently confirm their predictions by further tests. Describing nature as it was, not as the scientists supposed it to be, was at the heart of this scientific method.

In this way, for example, Newton assembled methodical descriptions of how objects move through the universe at everyday speeds. Much later, Einstein found more basic rules that explain how all objects move, even those that travel close to the speed of light. Newton's work was still correct, but it became a special part of Einstein's overall theory. This process is typical of science. Modern technology provides more penetrating insights about nature, leading to new theories that are more accurate but increasingly simpler at their cores. Rarely does a completely surprising phenomenon arise that forces us to overturn all aspects of an existing theory.

Today, we benefit from the creative use of technology to extend our vision far beyond Earth's surface and our solar system. Telescopes, spectrographs, electronic cameras, and other tools collect data every night from the farthest corners of the cosmos, revealing what our unaided eyes could never see. We also use computers to (continued)