Material: Topics 1-8, all material. In this review sheet, I cover material discussed since the last exam. See the first 2 review sheets for the material discussed previously.

Cosmological Constant and Vacuum Energy

• What are Virtual Pairs? What is the Lamb shift? State Heisenberg's Uncertainty Principle in terms of energy, time, and Planck's constant.
• Explain how virtual pairs may serve as the explanation for dark energy. In what sense do virtual pairs represent negative pressure (What does this mean anyway, what is negative pressure, what is normal pressure)? What is an interesting consequence of negative pressure in the context of gravity?
• What is the Cosmological Constant Problem? How bad is the Cosmological Constant Problem expressed in terms of Omega? What are the solutions (if any) for the Cosmologoical Constant Problem?

• What is the Drake Equation? How well-determined is the solution to the Drake Equation? What parts of the Drake Equation can be determined from astrophysical observation? What is likely to be the most well-determined term in the Drake Equation? What is the Habitable Zone? What determines the size of the Habitable Zone? Roughly how many extra-Solar planets have been discovered since 1995? Which parts of the Drake Equation will be difficult to determine from observation? How many extraterrestrial civilizations are there in our Galaxy based on the Drake Equation? give your assumptions (assumed values for the individual terms)? Why are the results so uncertain? What is Kepler?
• What is the Fermi Paradox? (Give the gist of the Fermi Paradox in your own words.) How solid are the implications forced upon us by the Fermi Paradox? How likely is galactic exploration? How long would it take us to travel to our nearest neighbors in space? Are we trying to travel to other stellar systems? Are such trips feasible? What are von Neumann machines? How long would it take for a civilization, if it was so inclined, to explore the Galaxy?
• Describe the Arecibo message to M13? How was it sent and how was it to be interpreted? What are the problems in formulating our attempts to communicate with extraterrestrials? Do we want to communicate with extraterrestrials? Do you think the Voyager plaques (and the earlier Pioneer plaques) are useful? Why or why not.
• What is time dilation? What is the Twin Paradox? How could utilizing the effects of time dilation aid in our exploration of the Galaxy?