I found this cool site http://htwins.net/scale2/scale2.swf?bordercolor=white and it educated me as to the existence of the Eridanus Supervoid. I estimate that all the humans who ever lived to be around 106,500,000,000 from information gathered at http://www.prb.org/articles/2002/howmanypeoplehaveeverlivedonearth.aspx). Imagine each human was equally spaced inside a cube inside this supervoid. The cube would be approximately 4x10^24 meters in length width, and height. The closest distance from one human to the next would be about 59.382 billion meters away. If you stood 30 Billion adults end to end, you would have a line of humans reaching from you to your nearest neighbor. You could fit Alderbaran between you and your nearest neighbor. That is a giant red star, by the way.