Elaboration on the RPG Definition

Instead of snakes and ladders, we'll put in hidden doors and secret passages. Don't roll a die to see how far you move; you can move as far as you want. Move down the corridor to the intersection. You can turn right, or left, or go straight ahead, or go back the way you came. Or, as long as you're here, you can look for a hidden door. If you find one, it will open into another stretch of corridor. That corridor might take you straight to the exit or lead you into a blind alley. The only way t...

 Origins of the Big Bang Theory and Evidence For It

That the universe is expanding was news to Einstein. But the possibility that the galaxies are moving away from each other had been proposed a few years before Hubble's papers on theoretical grounds arising from Einstein's own equations. In 1922, Russian physicist and mathematician Alexander Friedmann investigated what would happen in a model universe based upon two assumptions that greatly simplified the mathematics: that the universe looks identical in every direction, and that it looks tha...