Download String Theory

String Theory, Quantum
Mechanics and Relativity
Dr. David Berman
Lecturer
Department of Physics
Queen Mary College
University of London
1. Theoretical Physics
the search for unity
2. Relativity
Einstein’s great theory of gravitation
3. Quantum Mechanics
the failure of the ‘classical’
4. Unification needs String Theory
5. More about strings
the exciting way strings changes our view
of the universe
History
• Newton (1687):
Unified Gravity
The same force that pulls you is also pulling
the moon and all the planets
Unity: A single explanation for many
different things
Picasso:
“A painter should work
with as few elements
as possible.”
So should physicists!
Faraday & Maxwell (1873):
Unified Electricity, Magnetism
and motion
Dynamo; Motor; Light Bulb…
Weinberg & Salam
(1979):
Unified
Electromagnetism and
Nuclear Force
All the forces in nature appeared as
different aspects/faces of a single
force
• This is the same for matter
(the stuff we are made from)
• The building blocks were found to
be smaller and smaller
1m
man
When do we stop?
10-9m
0.000000001m
molecule
10-10m
0.0000000001m
atom
10-14m
nucleus
10-18m
quark
How many different
‘elementary’ particles
are there?
The basic building blocks known today:
• 18 Quarks – make up protons and neutrons
• 6 Leptons – things like electrons
• 3 Types of Force – Gravity
‘Electroweak nuclear’
Strong Nuclear
Quite good, but we can do better!
Michael Green
John Schwarz
Unity: One Single Building Block
STRING THEORY
• String:
The different ways a string can
vibrate look like different particles
to us.
Just like a violin string
produces many
different notes.
• How long is a piece of string?
~10-34m
Far away, the string
looks like a point…
Einstein
playing
the violin
General Relativity
Space & Time continued = spacetime
Spacetime can bend
Gravity
Quantum Mechanics
Things on ‘small’ scales fluctuate randomly
Size matters in physics!
The smaller scales you go the more random
and non-intuitive things get.
Can we unify gravity & quantum mechanics?
• Spacetime itself must now fluctuate at
small scales
• Big problem:
The smaller you go, the more it fluctuates
String Theory provides a shortest distance
i.e. String theory is pointless
10-34m
For example:
• Examine a landscape by rolling balls over
the surface.
The detail/resolution will depend on the size
of the ball. To get perfect resolution, you
need a perfectly small ball.
Other Consequences
• We live in 10 dimensions
1 dimension
2 dimensions
3 dimensions
Kaluza & Klein
• Kaluza & Klein:
The other dimensions are curled up and
too small to see.
Why 10 dimensions?
• In 10 (and only 10) dimensions is the
theory consistent.
The remarkable price for unity!
Questions
• How does geometry change when there
are no points?
• What are the effects on the physics in the
world we see from the hidden dimensions?
• Why stop at strings? What about
membranes as fundamental building
blocks?