![]() ![]() Mass and energy both cause space to be curved. But they also apply to large situations of curved spacetime like the universe itself. As we'll see, a close to a black hole is one example. This only applies the Einsteinian theory in general relativity in situations where the gravity is very strong. Far away, the theory of Newton would apply. Objects with lots of mass and energy will curve space and distort time nearby. Mass-energy tells spacetime how to curve while curved spacetime tells mass-energy how to move. The Einsteinian concept is quite different. The Newtonian concept is that mass tells gravity how much force to exert and the force tells the mass how to move. They are part of a four-dimensional construct called spacetime. Space and time are interchangeable and one can be changed into the other in different situations in the real universe. He links them formally with the equation E equals mc squared. But to Einstein, mass and energy are interchangeable. Space and time are very different things. To Newton, mass and energy are very different things. Making this comparison throws into sharp relief just how dramatic and revolutionary general relativity was. These two very great scientists had completely different ways of thinking about the nature of gravity in space. Let's compare the worldviews of Einstein and Newton regarding space and time. What came before the Big Bang? Is there anything outside our universe? What is reality? We'll finish by looking at the role of life in the universe and ask whether the earth is the only place with biology on it. At the end, will ask questions that don't necessarily have answers. ![]() Finally, we will discuss how modern cosmology has shown us that we live in an ancient universe (14 billion years old), in one galaxy in a universe of hundreds of billions of galaxies. We will then learn about the revolutions in physics in the early 20th century that redefined our ideas of space and time, mass and energy. We'll then examine the revolutions of Copernicus, Galileo, and Newton that redefined our place in the universe. We will start with prehistoric cultures who kept accurate calendars and move through the time of the Greek philosophers who laid down the rudiments of logic and mathematics and the modern scientific method. We'll look at how humans learned to ask questions about the universe, and even before the invention of modern instruments like the telescope, learned some amazing things about their place in nature. Observations combined with the spectacularly successful inflationary theory make it likely that the universe actually is infinite, and not just for practical purposes.This is an introductory level course about the history and philosophy of astronomy, the oldest science. This lower bound implies that the cosmos is at least about 300 billion light-years across, which is a lot larger than how far we can (in principle) observe - which is about 50 billion light-years. Observations tell us the maximum curvature allowed, which corresponds to the smallest size the universe can be. There is a small chance that the universe is finite if cosmic geometry is slightly positively curved. (In fact, cosmic geometry is most likely exactly flat, since this is precisely what inflationary theory predicts.) Measurements made over the past decade indicate that the universe is very nearly flat. The spots appear bigger in positively curved space and smaller in negatively curved space. In particular, the sizes of the hot and cold spots in the cosmic microwave background left over from the early universe are sensitive to the geometry of the universe. The universe is finite if it is positively curved and infinite if it is negatively curved or flat.įortunately, cosmology experiments can measure cosmic geometry. ![]() In three spatial dimensions, however, they are a bit harder to visualize, but even in 3-D, angles in a triangle sum to 180° in a flat case, less than 180° in the open case, and more than 180° in the closed case. In two dimensions, you can represent these geometries by a sheet of paper, the surface of a saddle, and the surface of a ball, respectively. The geometry could be flat, open (meaning negatively curved), or closed (meaning positively curved). The universe’s geometry determines whether the cosmos is spatially finite or infinite. ![]()
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