Alan Harvey Guth (born February 27, 1947) is an American theoretical physicist and cosmologist. Guth has researched elementary particle theory (and how particle theory is applicable to the early universe). He is currently serving as Victor Weisskopf Professor of Physics at the Massachusetts Institute of Technology. Along with Alexei Starobinsky and Andrei Linde, he won the 2014 Kavli Prize “for pioneering the theory of cosmic inflation.”He graduated from MIT in 1968 in physics and stayed to receive a master's and a doctorate, also in physics.

As a junior particle physicist, Guth developed the idea of cosmic inflation in 1979 at Cornell and gave his first seminar on the subject in January 1980.Moving on to Stanford University Guth formally proposed the idea of cosmic inflation in 1981, the idea that the nascent universe passed through a phase of exponential expansion that was driven by a positive vacuum energy density (negative vacuum pressure). The results of the WMAP mission in 2006 made the case for cosmic inflation very compelling. Measurements by the BICEP and Keck Array telescope give support to the idea of cosmic inflation, preliminary confirmation of which was given on 17 March 2014, with the findings of the B-mode polarization signature.However, on 19 June 2014, lowered confidence in confirming the cosmic inflation findings was reported.