On the right, how it would look if the Universe were contracting. No explanations are necessary for this problem. Suppose we were to compile a catalog of all the galaxies with apparent luminosity brighter than some threshold. Justify your answer in 2-3 sentences. Justify your answer in 2-3 sentences.
Astronomers have wide-ranging opinions on the existence of extraterrestrial intelligent life.
One major factor in determining whether or not our search for such life will be successful is how long civilizations can be expected to survive.