I was looking at the wikipedia article about cosmic inflation (you know, the first 10-32 seconds). It says that an inflation hypothesis is a neat way to explain a number of otherwise puzzling observations, but it doesn't say much about what would make inflation occur and it doesn't mention either Einstein's or Friedman's equation. Does that mean that there is no known explanation of inflation in terms of just GR? Does it need something else? If so, what?