For the past half a century, high energy physics has enjoyed the uninterrupted success of discoveries, signified by the recent discovery of the Higgs boson at the CERN Large Hadron Collider (LHC). Our understanding of the microscopic world has been deepened to a scale as short as 10-9 nm. Yet there are still many outstanding questions to be answered. In this lecture, I will first review the historical discoveries in the past half a century, and then contemplate on the profound questions that still puzzle high energy physics world, especially those associated with the Higgs physics, including the nature of the electroweak phase transition, stability of the electroweak scale, the possible connection with dark matter, and the potential impact on the early universe cosmology. We argue that the collective efforts of future high energy physics programs, in particular the future colliders, hold great promise to uncover the laws of nature to a deeper level.

Tao Han received his PhD from the University of Wisconsin in 1990. He was a Research Associate at Fermilab and a National SSC Fellow until 1993. He joined UC Davis as an Assistant Professor in 1993 and was promoted to Associate Professor II in 1997. In 1998, he returned to UW Madison, was promoted to Full Professor in 2001, and served as co-director for the "Phenomenology Institute" from 2006. In 2011, he relocated to the University of Pittsburgh and presently serves as the founding director of the Pittsburgh Particle Physics, Astrophysics and Cosmology Center (PITT PACC). He was named Distinguished Professor of High Energy Physics in 2014. Han's research has focused on new physics at colliders, phenomenological formulation of theoretical models. He contributed to Higgs physics at hadron colliders, initiating the concepts of "central-jet vetoing", "forward-jet tagging", "cluster transverse mass" etc. He contributed to the formulation for R-parity violating interactions in SUSY, and the Lagrangian field-theoretic description for Kaluza-Klein states in large extra dimensions. He proposed to test neutrino mass generation mechanisms at colliders and other experiments. He has also worked on dark matter studies connecting collider signals with direct and indirect searches. Han was elected a Fellow of APS in 2003 and a Fermilab Frontier Fellow in 2004. He is an elected general member of Aspen Center for Physics and CTEQ. Hewas a KIAS Scholar in Korea. Han served as a HEPAP member in 2013-2015, on the "Committee of Visitors" panels for the NSF and DOE, on national lab reviews, and on international review panels for KEK and Durham University's IPPP. He served on the advisory boards for TASI, KITP/KITS-China, NCTS-Taiwan, on the DPF Sakurai Prize and Nomination Committees, on the editorial boards for Physical Review D, European Physics Letters, and Chinese Physics C. Han has been the organizing chair for the "Phenomenology Symposia" (Pheno conference) for the past 20 years, and a hosting organizer for the CTEQ Summer School. He is now Vice Chair of APS Division of Particles and Fields, Chair for the APS April Meeting, and Vice Chair for Gordon Research Conference in Hong Kong.