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Einstein, String Theory,
and the Future
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Relativity in a Nutshell
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60 mph
30 mph
90 mph
vnew = vold + vtrain
Common Sense Physics
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vlight
30 mph
vlight
vnew = voldvnew =
vold + vtrain_____________1 + vold vtrain /vlight2
Weird Physics
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Classical Physics (1687)
Special Relativity (1905)
fast
Quantum Mechanics (1905)
small
General Relativity (1915)
heavy
Quantum Field Theory (1940s)
String Theory ?
?
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What is String Theory?
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Standard Model of Particle Physics:
The Modern Theory of Matter
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Elementary Particles and Interactions
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In String Theory, Particles are Strings
String Combinations
Particle Interactions
Different Vibrations
Different Particles
up
quark
down
quarkelectron
String theory realizes Einsteins dream of a unified theory
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Is String Theory Right ?
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Is String Theory Testable?
It depends.
Is it falsifiable?No not yet, anyway.
Does it predict anything that could haveobservable consequences?
Yes string theory extra dimensions!
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Extra Dimensions
(x, y, z, t) + w, v,? Science fiction?
No a major topic in science today:
What is our world made of?
How does gravity work?
How did this happen?
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Isaac Newton
1687: Space and time are the static stage
on which physical processes act
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Albert Einsten
1915: Spacetime is an active player:
curves, expands, shrinks,
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Edwin Hubble
1929: The universe is expanding
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The Big Bang
The universe does not
expand into space space
itself expands
Extrapolating back, spacewas small the Big Bang
Other dimensions could exist but still be small. String theoryrequires 6 extra dimensions.
How can we test this possibility?
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Dark Matter
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Extra Dimensional Matter
However, particles can move in theextra directions.
From our viewpoint, we will see this asnew particles with masses
m ~ 0, 1/R, 2/R, 3/R, 4/R,
Each known particle has an infinitetower of copies.
Extra dimensions many new particles what good are these?
mass 1/R
2/R
3/R
4/R
0
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Standard Model of Cosmology
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A lotof dark matter isrequired to hold
galaxies together
It cannot all be made ofknown particles
It must be some new
form of matter maybea sign of extra
dimensions!
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Dark Matter Detection
DD
MM
CDMS in the Soudan mine
mile underground in Minnesota
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Dark Matter at Colliders
Large Hadron Collider at CERN, Geneva
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Strong Gravity and Black Holes
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Gravity
Gravity is the least understood force.
Many deep problems, but one obvious one:
Gravity is extraordinarily
weak. It is important in
everyday life only
because it is always
attractive.
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More quantitatively, for separation distance r ,
For two protons,
Fgravity ~ 10-36 FEM
Very likely, we are missing something important.
Why is gravity so weak?
Maybe it isnt
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Extra Dimensions
Suppose our world is only a slice of the whole universe
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Strong Gravity
In this case, gravity may be strong but
appear weak only because its strength is
diluted by extra dimensions.
Fgravity ~ 1/r2+n for small lengths, where n is the
number of extra dimensions. Can this betrue?
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1
Feng,Science
(2003)
10-60
10-40
10-20
Yes!
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If two particles passclose enough withenough energy, theywill form a tiny black
hole.
Black Holes
For 3 spatial dimensions, gravity is too weak for
this to happen. But with extra dimensions, gravitybecomes strong, micro black holes can be created
in particle collisions!
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Micro Black Holes
Where can we
find them?
What will they
look like?
S. Harris
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Black Holes
But quantum
mechanically, blackholes Hawking radiate:black holes emit light!
Classically, light and
other particles do not
escape: black holes
are black.
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Black Hole Evaporation
Normal black holes:Mass: MBH ~ Msun
Size: kilometer
Temperature: 0.01 K
Lifetime: ~ forever
Micro black holes:
Mass: MBH ~ 1000 Mproton
Size: 10-18 mTemperature: 1016 K
Lifetime: 10-27 s
They explode!
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Black Holes at Colliders
Large Hadron Collider at CERN, Geneva
p p
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Black Holes from Cosmic Rays
The Auger Observatory in Argentina
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COLLISION COURSE CREATES MICROSCOPIC BLACK
HOLES, 16 January 2002:
Dozens of tiny black holes may be forming right over
our heads A new observatory might start spotting
signs of the tiny terrors, say physicists Feng and
Shapere Theyre harmless and pose no threat tohumans.
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Summary
A century later, Einsteins remarkable papers stillare the foundation of physics, and we are stilltrying to realize his dream of a unified theory.
String theory is our best attempt so far.
Diverse experimental searches are underway.
Will they be successful?
It's tough to make predictions, especially aboutthe future. Yogi Berra