18-year-old Ewin Tang has proven that classical computers can solve the “recommendation problem” nearly as fast as quantum computers. The result eliminates one of the best examples of quantum speedup. quantamagazine 
Tang's paper : A quantum-inspired classical algorithm for recommendation systems.
"Our main result is an algorithm that samples high-weight entries from a low-rank approximation of the input matrix in time independent of m and n, given natural sampling assumptions on that input matrix. As a consequence, we show that Kerenidis and Prakash’s quantum machine learning (QML) algorithm, one of the strongest candidates for provably exponential speedups in QML, does not in fact give an exponential speedup over classical algorithms."
Another point proven here. Great advisors challenge and inspire students to rethink the status quo.