In 2005, Professor Larry Summers, President of Harvard University, stated, “The physicists in the top 25 universities in the US are probably 3.5 standard deviations above the mean IQ.” This equates to an IQ of 100 + 3.5 x 15 or 152.5. IQ is a reasonably good measure of the ability to think in abstract terms, and to see patterns and draw inferences from observations that appear random to others. These are critically important cognitive skills for anyone attempting to model nature in environments (like the microcosm) where humans have no direct experience. A strength in mathematical knowledge and skill is also a prerequisite to research in theoretical physics because all the models of nature are expressed in mathematical notation.
A person who displays an IQ below 105 on repeated tests of IQ, has little chance of achieving success as a brilliant theoretical physicist. However, this is not impossible, because human intelligence is a multi-faceted entity. Some deep thinkers do not show well on IQ tests because they do not function well under time constraints. They are not good in math olympiads, but they can solve difficult problems given enough time. Consequently, we would say that it is highly improbable, but not impossible, for a person with IQ 105 or lower to become a brilliant theoretical physicist.
