Alan Guth proposed a period of rapid early expansion as a physical explanation of the horizon problem and flatness problem. His 1981 model used a high-energy state whose nearly constant energy density could drive accelerated expansion before ordinary hot Big Bang evolution.
The causal argument is that a region initially small enough to equilibrate can expand to encompass the subsequently observable region. Rapid expansion also suppresses the relative importance of spatial curvature. Ending that stage and obtaining a sufficiently uniform hot state is a separate dynamical requirement; solving the motivating geometric problems does not by itself supply a successful exit.[ref]
Inflationary universe: A possible solution to the horizon and flatness problems by Alan H. Guth. Abstract and concluding discussion: initial-condition problems, inflationary mechanism and completion of the phase transition
Portrait of Alan Guth
. Betsy Devine (Betsythedevine); Trinity College, Cambridge, 19 December 2007; existing crop from her Flickr photograph 2123046495. CC BY-SA 3.0, via Wikimedia Commons. Source.
Alan Guth is an American theoretical physicist and cosmologist best known for proposing the theory of cosmic inflation. This theory suggests that the universe underwent an exponential expansion during the first few moments after the Big Bang, which helps explain several observed phenomena in cosmology, such as the uniformity of the cosmic microwave background radiation and the large-scale structure of the universe.
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