1. How Does Gravity Work?!?! General Relativity

2. Aristotle described the effect of gravity as the natural motion of an object to return to its realm. Kepler thought that the force that caused the planets to orbit the Sun was a form of magnetism. Isaac Newton described gravity by observing the moon and a falling apple. F G = Gm 1 m 2 /d 2 Einstein explained that objects with mass warp (bend) the space around them. This warped space causes straight lines to be curved and objects that are trying to follow a straight path through warped space have their path curved. This explanation of gravity is part of Einstein’s General Theory of Relativity

3. Evidence that Supports Einstein’s Theory about How Gravity Works (General Relativity) During the day we know there are stars in the sky, we just can’t see them because the Sun is too bright. However we know where it is. During a solar eclipse, however, we can see the stars that are behind the Sun. The problem is we see the star in the wrong position!!!!!!! As the light from the star passes the Sun, it bends. This bending of light is caused by the warping of the space around the Sun. When the light reaches us we project it along a straight line, making the star appear in the wrong location. Not only does General Relativity explain why the star appears in the wrong place, but the theory predicts EXACTLY where it should appear!!!!!!!!!!!!!!!!!!!!

4. GPS (Global Positioning Satellite) also gives evidence that General Relativity is correct. When GPS was first invented, it worked pretty well for a short time. However after that it had a tendency to drift. For example: If a GPS system in your cell phone were turned on it would pin- point your location, but after a time the position it shows would be off by a small amount. The more time the system is on the farther off its coordinates of your position become. To correct for this flaw, the engineers and scientists had to design the system to account for the effects of General Relativity. Once they did this, GPS was born!!!! GPS

5. Newton VS. Einstein If the Sun were to disappear suddenly, what would happen to the Earth’s Motion? What do you think? Watch the Video Clip from “The Elegant Universe” to determine what the fight between Newton & Einstein is all about. What did Newton think? What did Einstein think?