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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.