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Of STRINGS and PARTICLES Chiara Nappi Princeton-GranSasso program Summer 2006 Our path towards elementary constituents: does it end here? lepton e m t n e nm nt quark u d s c b t String Theory •20th century physics was all about two big theories •Einstein’s General Relativity…the theory of stars, galaxies, the universe. •Quantum mechanics…the theory of atoms and subatomic particles. •But these theories don’t work well together—when one tries to combine them, one runs into a web of contradictions. •That isn’t a satisfactory situation; physicists want a single unified theory that applies to both the large and small objects. •The one idea about how to combine quantum mechanics with general relativity is “String Theory”: String Theory Point Particle String •Like a violin string, one of these strings can vibrate in many ways: •Richness of music and unity of the elementary particles. •Out pops Quantum Gravity—like it or not. •Out pops Gauge Symmetry … •the bread and butter of standard particle physics. •And out pop Ten Dimensions of spacetime—like it or not. We need to compactify the extra dimensions (Einstein and P. Bergman (1937). Out of the geometry particles and symmetries pop out! Conclusions • A very interesting time in the history of high energy physics. If we are lucky, we are going to see the confluence of different fields. Data from cosmology and particle accelerators could help us solve many exciting common puzzles.