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  • Albert Einstein and astrophysics have often become synonymous with genius and rocket science. What comes to mind when you think of this particular branch of science? What’s your impression of Einstein’s contribution to physics over the past century or so?


Frontiers 1904 Dr. Orsola De Marco Marconi’s pioneering radio transmission and receiver designs led to the development of long-distance telecommunication and eventually the discovery of radio waves from the Milky Way. ©Marconi Corporation plc Enlarge image » In 1904 the world was full of confident physicists and excited engineers. There was a law of gravitation, which predicted with accuracy the motion of the planets and their moons. Light was understood as an electromagnetic wave, after the efforts of the brilliant Scottish physicist James Clerk Maxwell (1831-1879). In 1901, the Italian physicist Guglielmo Marconi (1874-1937) had turned the German physicist Heinrich Hertz’s (1857-1894) theoretical predictions on the propagation of electromagnetic radiation into the transmission of a signal across the Atlantic Ocean, the first form of telecommunication. Overall, science was high on governments’ agendas because of military applications, and this gave a boost to research and funding. In an address to the British Association for the Advancement of Science in 1900, the Irish physicist Joseph Larmor (1857-1942) summarized the scientific advancements of the previous 20 years. He expressed confidence that, although some pieces of the puzzle were missing, physics seemed headed in the right direction: it was only a question of time before the puzzle would be completed. Before we turn our attention to those details that were still missing in the overall picture, we should stress a general characteristic of pre-Einstein physics. Many phenomena were explained by a rule, or mathematical formula, but the reason why these phenomena worked the way they did was not clear. In many cases, it was known how something worked, but not why it worked. To give an example, gravity was described by a well-understood formula from which applications could easily be derived. But physicists of the time did not know what gravity actually was! Modern quantum theory describes light’s behavior sometimes as waves and other times as a stream of particles. ©AMNH Enlarge image »
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The Blind Men’s Universe and the Quest to Describe the Ether In 1904, our physical understanding of the world was analogous to the three blind men’s impression of the elephant: the first man touches one of the elephant’s tusks and deduces that the elephant is like a spear. The second touches the elephant’s side and concludes that the elephant is like a wall. The third touches the trunk and decides that the animal must be a bit like a snake. Of course, they all touched the same animal, but they came up with three different theories. In a similar way, many rules and equations described the world in a reasonably accurate way (just like the three blind men accurately described what they felt with their hands). However, nobody realized that many of these rules were just different expressions of the same phenomena. So, we might ask, if everyone was so satisfied with the state of things, how could a change in our vision of the world come about? As Larmor had expressed in his 1900 speech, the questions that still bothered physicists at the turn of the century appeared to be of a minor nature. Surely it was important to answer them, but it did not appear that the answer to these questions would cause many of their well-tested theories to crumble. One such question stemmed from the nature of light. Isaac Newton thought that light was a stream of particles. It later became clear that many of light’s properties indicated that light was a wave. But if light is a wave, what is waving? A sound wave needs air particles to propagate itself, which is why noises would go unheard in empty space. A water wave clearly needs water. So what is the medium that undulates in the case of a light wave? And so the idea that the universe was filled with a thin substance called the ether became very popular. The idea of the ether had been proposed by Aristotle (who certainly was not yet thinking about the propagation of light waves) as a way of filling space. (We will go into much greater depth about the concept of space in a few weeks.) Many 19th-century optical theories, theories dealing with the propagation of light, assumed that some form of the ether was present. However, people were very well aware that the theory of the ether presented substantial problems. For instance, matter had to be able to move through it with no resistance, or the ether would be detected as a drag force that slowed down planets as they moved through it. (Like when we wade into water at the seashore, our every step is made harder because of the drag of the water on our legs.) Since the planets do not appear to slow down as they move, this drag force was not detectable, and hence the ether could not possibly be interacting with matter. The ether was really an ad hoc theory. By this I mean a theory called upon when needed but ignored when there was no need for it, just like when we change the rules during a card game to suit our situation.
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Math as Language, Science as Poetry Dr. Charles Liu Mathematics is, in many important ways, a language like English, French, or Chinese. It has an alphabet (numbers and symbols), a grammar (mathematical rules and techniques), and sentences (equations). Why, then, do so many more people think differently about math than they do about English, French, or Chinese? Since we’re all familiar with language, let’s run a little with this metaphor. Math as language—what does this mean? To me, it means that the secrets of the universe are accessible to us all! Five-year-old children speak Russian fluently, but I do not. Does this mean that I am unintelligent compared with five-year-old Russian children? Or that I am “bad” at Russian? Or that, since my parents were no good at Russian, and since I come from a long line of non-Russian speakers, I clearly won’t ever have the “head” for Russian? Obviously not. I just have too little exposure to Russian at this point in my life. If I were to go to Russia and do nothing but speak, read, and write Russian, there's a very good chance I'd be fluent in Russian after five years. I have nothing to fear from Russian—I just need either to get used to it, or to have a good translator. If I worked at it, I’d be reading Tolstoy, Chekhov, and Pushkin before too long—and soon, I’d start to understand Russia, its people, and its culture, through the eyes of its great authors and poets. How is this process of learning about Russia different from the process of learning math, then using it to interpret science, and from that gaining insight into the nature of the universe? It’s not! If we approach mathematics with the same attitude we have toward learning a foreign language, we can think of it as an extension of our ability to learn—or as a useful skill to help us in our daily lives. The key is to realize that if we don't speak it often, we might get a phrase wrong once in a while. It's no big deal; as long as we communicate the main ideas, we'll do just fine. With the right combination of trajectory and force on the ball, the baseball star can hit a home run. ©AMNH Enlarge image »
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Humans, Math, and Science Whether you realize it or not, you use math all the time—and well. If you live in a reasonably large city and you want to get across town by noon, would you leave your home at 11:59 A.M., 11 A.M., or 6 A.M.? You use math to figure that out. If you want to buy a medium-priced house, should you plan to spend $100, $100,000 or $100,000,000? Again, math shows itself. Of course, you probably won't compute beforehand that you need to leave at precisely 11:06 A.M. to arrive precisely at noon, or that you'll spend exactly $123,692 for your house. Rather, you find an answer that “feels right” or “makes sense.” That’s the whole point of mathematical reasoning. Let’s look at another example. When a baseball star is at the plate, he observes the incoming pitch, predicts its trajectory and location of arrival, optimizes the ideal bat location, generates energy and work to swing the bat, and finally imparts the maximum force on the ball, all to make the ball travel as far and high as possible. It’s all physics, revealed through math! Every day, our lives are infused with math and science. The only trick is translating the natural language of our everyday existence into the numbers and shorthand that others expect to see. This process is exactly what science is all about—whether it’s to explain a batter hitting a ball, or a planet orbiting a star, or an atom emitting a photon. The Language of the Universe Albert Einstein truly understood the utility of math and science, perhaps more deeply than anyone else who ever lived. “How can it be,” he once wrote, “that mathematics, being after all a product of human thought independent of experience, is so admirably adapted to the objects of reality?” He answered his own question with a quote, also attributed to Galileo Galilei: “Mathematics is the language with which God has written the universe.” Hmm, that makes science the poetry of the universe! It’s an entertaining metaphor to ponder, and it reveals a deep insight. All the forces, quantities, and processes that shape our earthly lives match the forces, quantities, and processes that shape everything else in the universe, including the cosmos itself. The heavens and the Earth are one; a speck of dust is the stuff of the stars; and the tiniest components of subatomic matter may have sown the seeds of the universe. And we puny humans have a way to grasp all this wonder: math and science. Einstein saw that nature, in both its simple perfection and its nigh-infinite complexity, follows a remarkably small set of rules. And the amazing variety of phenomena we observe in the universe arises from applying those rules to particular local
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What is Motion? Dr. Charles Liu The Gemini North Telescope on Mauna Kea in Hawaii, with northern circumpolar star trails. The bright star trail near the center is Polaris. ©Gemini Observatory Enlarge image » One simple definition of motion is the act of going from one place to another. But when we look more closely, it doesn’t seem possible that motion could be that simple, since it expresses itself with such great complexity in the universe. At the tiniest scales, the laws of quantum mechanics describe a relentlessly restless environment, filled with velocity, spin, and vibration, in which nothing is exactly where it appears to be. At the opposite extreme, the universe itself continuously expands, as space and time grow with each passing moment, carrying us all along for the ride. Somewhere in the middle, where we conduct our daily lives, our Milky Way galaxy moves toward the Virgo Cluster, the Sun dances in its orbit around the center of the Milky Way, and Earth travels around the Sun in its own gravitationally ordained orbit, all while we contemplate the fastest way to the grocery store. Can all of these motions stem from the same basic principles? The attempt to answer that question—what makes motion happen—has driven the entire history of scientific research and almost all progress in the physical sciences for centuries. We’ll start with a little history—just enough to help us understand the thinking that led to the Laws of Motion. Up Through Galileo Why does an object start moving? Why does it stop? What makes some things move faster than others? When two things hit each other, what happens next? The early natural philosophers who pondered these questions included Plato (c. 428– 347 BC), Aristotle (384–322 BC), and Archimedes (c. 287–212 BC). They were among the pioneers of science who tried to apply logic and reason to explain the universe around us. Despite the efforts of such formidable intellect in ancient times, they didn’t make much progress. Their main obstacle was the immaturity of the scientific method; they thought about the problems a great deal, philosophically and mathematically, but they never considered conducting controlled experiments. Here’s another way to put it: they saw, but they didn’t observe.
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In 1609, Galileo used his “optic glass” in Padua, Italy, to study and sketch the moon’s phases. One of his moon phase drawings is to the left and the corresponding section of the moon is to the right. ©Library of Congress, Lick Observatory Enlarge image » The first significant scientific study of the motion of objects was finally written by Galileo Galilei (1564-1642), considered by many to be the first modern physical scientist. Published in 1638, his work was titled “Discourses and Mathematical Demonstrations Concerning Two New Sciences, with Attention to Mechanics and Local Movement.” This work laid out the foundations of the science of physics. One of the most important ideas Galileo explained in the “Discourse” is the tendency of a moving object to keep moving, at the same speed and in the same direction, until some external stimulus makes it change—a concept we call inertia. This is the basis for the original idea of Relativity, that we measure motion by comparing the relative positions of moving objects. It’s on this concept that Isaac Newton, and later Albert Einstein, grounded their theories of motion. Galileo made another huge contribution to human knowledge by being the first person to use a telescope for astronomy. By watching the motions of the Sun, Moon, and planets—including the four major moons of Jupiter, which he discovered—Galileo proved conclusively that Earth does not sit at the center of the universe, but moves in an orbit around the Sun, as was suggested by Copernicus over a century earlier. Galileo’s 1609-1610 discovery so shook the ruling religious order that he was accused of heresy by the Roman Catholic Church, and forced to recant his findings. Defiant to the end, legend asserts that after his trial, in which he was pronounced guilty of heresy, he stamped his foot on the ground and proclaimed, “Eppur si muove”—“Nevertheless, it moves.” Nicolaus Copernicus showed that the Earth and other planets orbit the Sun. His work conflicted with prevailing religious beliefs, but it provided a heliocentric view for his contemporaries Kepler, Galileo, and Newton. ©Library of Congress Enlarge image » Newton’s Laws of Motion Galileo’s pioneering studies led others toward further deciphering motion. Four decades after Galileo’s death, Englishman Sir Isaac Newton (1642-1727) wrote a short work entitled “On the Motion of Bodies,” which grew into the monumental book “The Mathematical Principles of Natural Philosophy”—known today by many as the
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What comes to my mind when I think of this particular r branch of science?
Astrophysics is the branch of astronomy that combines the principles of chemistry and
physics to determine the nature of...

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