In the rich, velvety darkness of prehistoric night, humans no doubt gazed up at the starry sky in awe at its sublime beauty and mystery. Simple human nature led them to wonder why such gorgeous lights appeared above, and moved as they did. As cultures developed, complex mythological systems were created in an imaginative effort to explain the existence and movements of those heavenly bodies. Burgeoning civilizations created the need for accurate time keeping. Ancient people turned to the sky to fill that need. Gradually, science began to come into the picture. Imagination and fables gave way to investigation and facts, bringing ever more marvelous wonders, and new mystery.
When Galileo Galilei first turned a primitive telescope to the sky in 1609 he saw things no human had ever seen before, like the four largest moons of Jupiter. Modern astronomers have developed new types of telescopes that detect all sorts of electromagnetic waves (Electromagnetic Wave: An electric and magnetic disturbance that travels through space like a wave. What we experience as light is an electromagnetic wave. Electromagnetic waves therefore travel at the Speed (Speed: For a wave, the speed of a particular point (such as its crest).) of Light (Speed of Light: A constant of Nature. This speed is precisely 299,792,458 meters per second, or roughly 670,616,629 miles per hour. One of the most unusual discoveries of science has been the fact that all Observers measure light as moving at exactly this speed, even if those observers are moving relative to each other. This fact is one of the basic ingredients in Einstein's Special Theory of Relativity (Special Theory of Relativity: Einstein's version of the laws of physics, when there is no gravity. The two fundamental concepts in the foundation of this theory are equality of observers, and the constancy of the speed of light. The first of these means that the laws of physics must be the same, no matter how quickly an observer is moving. The second means that everyone measures the exact same speed of light. This theory is useful whenever the effects of gravity can be ignored, but objects are moving at nearly the speed of light. It has been successfully tested many times in particle accelerators, and orbiting spacecraft. For objects moving much more slowly than light, Special Relativity (Special Theory of Relativity: Einstein's version of the laws of physics, when there is no gravity. The two fundamental concepts in the foundation of this theory are equality of observers, and the constancy of the speed of light. The first of these means that the laws of physics must be the same, no matter how quickly an observer is moving. The second means that everyone measures the exact same speed of light. This theory is useful whenever the effects of gravity can be ignored, but objects are moving at nearly the speed of light. It has been successfully tested many times in particle accelerators, and orbiting spacecraft. For objects moving much more slowly than light, Special Relativity becomes very nearly the same as Newton's theory, which is much easier to use. ) becomes very nearly the same as Newton's theory, which is much easier to use. ).). Other types of electromagnetic wave range from Radio Waves and Microwaves, through to X-Rays (X-Ray: A type of light — or electromagnetic wave — which is invisible to the naked eye. X-Rays are much more energetic than the light we see. They can penetrate skin very easily, for example. In the doctor's or dentist's office, X-Rays are detected on a photographic plate, allowing us to see inside the body. Like all other forms of electromagnetic radiation, X-Rays travel at roughly 300,000,000 meters per second (186,000 miles per second). ) and Gamma Rays. ) — gamma rays, X-Rays, ultraviolet, infrared, microwaves, and radio, as well as visible light. They've even developed instruments that allow them to watch as other types of particles — such as cosmic rays and neutrinos (Neutrino: A type of particle which has no charge and an extremely small mass. It is a Fermion, and is extremely difficult to stop or to detect. Nonetheless, they are produced in large numbers. The Sun, for example, sends 30 million neutrinos through every square inch of the Earth every single second. They are so hard to stop, however, that if a neutrino were sent through a solid light year of lead, it would still have a 50:50 chance of flying right through without stopping. ) — stream toward us from the most distant reaches of the cosmos.
Using these techniques, astronomers have discovered that our Universe is 80 billion trillion miles across, with hundreds of billions of galaxies, and hundreds of billions of stars like our own Sun in each of those galaxies. Before modern astronomy, the height of human knowledge of the Universe claimed that the Earth was flat, and the Sun carried across the nearby shell of the sky on a golden chariot. Now, we know the breathtaking extent of the Cosmos, and have a far more sophisticated understanding of its astounding processes.
The development of astronomy has led an expansion of human knowledge reaching out, ever farther from our home. Yet this growth in our understanding is limited by our tools. The limits are familiar to us. Light cannot be used to see through objects. Although certain “colors” can penetrate objects better than others — like X-Rays through our bodies — there is always a limit. Light can always be absorbed, which means that certain things will always be hidden to us if we only use light. Some of the most interesting events in the Universe lie hidden behind an impenetrable veil of dust and other scattered light. In fact, for the first million years after the Big Bang (Big Bang: An astrophysical theory of the beginning of the Universe. It suggests that the Universe began in a very tiny region of space, and exploded outward. Astrophysicists believe that this occurred roughly 14 billion years ago. Other astrophysical theories for the beginning of the Universe — like the Braneworld theory — exist, though none is as thoroughly studied and supported by the data as the Big Bang model. Scientists have no idea what came before the Big Bang.), all of the matter in the Universe was so hot it glowed, and light could barely travel anywhere. If astronomers want to see the Universe much before this time, they can't use any type of telescope used before.
Gravitational-wave detectors fit the bill nicely. Unlike light, gravitational waves (Gravitational Wave: A gravitational disturbance that travels through space like a wave. This type of wave is analogous to an Electromagnetic Wave. Gravitational waves are given off by most movements of anything with mass. Usually, however, they are quite difficult to detect. Physicists are currently working hard to directly detect gravitational waves. Experiments like LIGO and LISA are designed for this purpose. ) are not stopped by dust — or even stars and planets. In fact, when two neutron (Neutron: One of the particles in an atomic nucleus. These particles have no electric charge, but they hold together the protons (positive particles in a nucleus), and account for roughly half of the particles in the nucleus. Neutrons are fermions, and are believed to form the majority of the matter in a neutron star.) stars (Neutron Star: A type of star which is very old, having cooled off and stopped nuclear fusion reactions. When gravity pulls the star down on itself, the electrons and protons are squeezed together, leaving just neutrons. The star is then supported against gravity by "neutron degeneracy pressure" (no two neutrons can be in the same place at the same time). These are produced when a star is too heavy to be a white dwarf (White Dwarf: A type of star which is very old, having cooled off and stopped nuclear fusion reactions. A white dwarf is supported by "electron degeneracy pressure" (no two electrons can be in the same place at the same time). These are produced when a star is not heavy enough to turn into a Neutron Star or a Black Hole. )})|white dwarves}), but not heavy enough to turn into a Black Hole. ) collide, a standard telescope would only see what happens on the surfaces of the stars or above. A gravitational-wave detector, on the other hand, would be able to peer into the very center of the collision — where the most mysterious events are happening. Of course, detecting gravitational waves is enormously challenging, and will require an extraordinary triumph of science and engineering. Fortunately, that triumph is at hand.