The 2021 KS Pitzer Memorial Lecture at the University of California, Berkeley, has been delivered by Ali Alavi. His lecture entitled "A Blast from the Past" describes the work of his department on using the FCIQMC technique to revive the Unitary Group Approach and Transcorrelation, both powerful formalisms of quantum chemistry which had been developed in the 1970s but largely abandoned due to enormous technical difficulties in their implementation. Ali says that the amazing advances made by his group has revitalised some old but extremely powerful ideas in quantum chemistry, and we are using them to crack some old chestnuts, including the mysteries in the electronic structure of complex biological catalysts such as Fe-S complexes. (04.2021)