String Theory, Quantum String Theory, Quantum Mechanics and RelativityMechanics and Relativity

Dr. David BermanLecturer

Department of PhysicsQueen Mary CollegeUniversity of London

1. Theoretical Physicsthe search for unity

2. RelativityEinstein’s great theory of gravitation

3. Quantum Mechanicsthe failure of the ‘classical’

4. Unification needs String TheoryString Theory

5. More about stringsthe exciting way strings changes our view of the universe

History• Newton (1687):

Unified GravityThe 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

1mman

10-9m0.000000001mmolecule

10-10m0.0000000001matom

10-14mnucleus

10-18mquark

When do we stop?

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 –

Quite good, but we can do better!

Gravity‘Electroweak nuclear’Strong Nuclear

Michael Green John Schwarz

Unity: One Single Building Block

STRING THEORYSTRING THEORY

• String: The different ways a string can vibrate look like different particles to us.

Just like a violin string produces manydifferent 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 = spacetimeSpacetime 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?