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Physics 120 Reading Assignment #10 Due: Monday 8 AM, April 24 Name:_________________________ Please expand this word-file and insert your answers in-place below. Please feel free to discuss questions and concepts with other students from the class. This is encouraged. However, when you sit down to answer the questions in the reading assignment, you should submit your own answers. Your completed homework assignments must be uploaded to the assignments page for this class on Canvas by the specified due date and time in order to receive credit. 1-2) The inverse square law of gravity has been tested to distances of about a millimeter. Explain how the inverse square law of gravity makes sense geometrically in our three dimensional world. Describe how one extra hidden dimension and the resultant inverse cube law (not observed in our world) could make sense if the extra dimension is curled up into a small circle of radius R. Could this resolve the hierarchy problem? If so, please explain. 3) In String Theory, the physical laws in our world depend upon hidden extra dimensions. In the 1920’s Kaluza and Klein proposed that a five-dimensional spacetime with four large spacetime dimensions and a hidden extra dimension could describe the two known forces of Nature at that time. Describe the geometry they proposed and relate the parts of this complicated geometry with the known forces or information about the forces. 4-5) The authors of the “Landscape” article say that String Theory would be the ultimate failure in democracy. a) What do they mean by this? b) How do the authors revive democracy? c) In reviving democracy, the authors present a description of how our Universe might originate from a Big Bang and end up in any number of possibilities. Describe briefly our Universe could result from navigating the Landscape. 6) In the “Illusion of Gravity” article, the author states: “A quantum theory of gravity will probably provide us with an entirely new perspective of what spacetime is.” Also, “if matter obeys the laws of quantum mechanics and gravity obeys the laws of general relativity, we end up with mathematical contradictions.” Describe this conflict between quantum mechanics and gravity. 7) If there were one extra dimension, describe how one might be able to travel backward and forward in time. Likewise, with one or more extra dimensions describe how one might have parallel universes that are not able to communicate with each other. 8) a) Which topics did you find particularly complicated and had difficulty understanding? What specific questions do you have about this (these) topic(s)? b) Which topics did you find particularly interesting and would like to discuss further in class? Any specifics or questions that you wish to add on each topic?