Dr Sanjaye Ramgoolam

In collaboration with

J. Bedford and C. Papageorgakis

STRING THEORY arises from attempts to answer:

1) What is the world made of?

2) How & Why does the world change in time?

Answers:

1) MATTER!

E.g. Cars, Houses, Buildings, Planets…

All matter has Mass

2) Forms of matter exert Forces on each otherand they move under the influence of these forces

For example: the attraction which causes anapple to fall off a tree.

So far:

2 Questions

2 Answers

MATTER ; FORCE

Matter comes in millions of different forms:

Apples, Oranges…Cars - Hondas BMWs...Garden Hoses, Grass, Trees...Earth, Sun, Moon…Galaxies, Planets, Stars...

All this diversity in fact comes from only a few hundred atoms:

Hydrogen, Oxygen, Nitrogen...

• Each atom has a definite mass.• Each atom has an approximate size of about:

• By going from the large to the tiny, we reduce the diversity of millions to around a hundred!

• Things simplify further if we look deeper into the atom:

+Protons:

Neutrons:

-Electrons:

Electrons orbitthe nucleus whichis composed ofProtons andNeutrons

• The few hundred atoms reduce to only a handful of fundamental objects

• Our Millions of Matter objects have been reduced to just 3 - Great!

Unfortunately, the story starts to get more complicated:

+

updown

strangecharm

bottomtop

Proton&

Neutron

Quarks

redgreen

blue

Colours

•

•

•

• There are 3 ‘generations’ of these quarks & each quark can have one of 3 different ‘colours’

• Likewise there are 3 ‘generations’ of electron-like objects called leptons:

electronelectron-neutrino

muonmuon-neutrino

tautau-neutrino

Leptons

The idea of String Theory is that thisdiversity of quarks and leptons comesfrom 1 String

H O

pne

u d s c t b e

1 String

What about Forces?

“Hammer Force”

“Fuel Force”

“Astronomical Force”

All this diversity of forces comes from:

Gravity&

Electromagnetism (& its 2 cousins)

The Electric Force:

• Rub a pen against your sleeve & pick up pieces of paper.

• Rubbing - Separation of charge.

Matter contains positive & negative charges:

++

--

+ -

Repulsion

Repulsion

Attraction

On a grander scale:

Lightning is caused by the

Electric Force

The connection between

Light & Charge runs deep:

Particle physics teaches

us that “electrons

repel because of the

exchange of particles of

light called photons”

Exchange

Repulsive force

Particle physics reduces

both Matter & Force

to one kind of Entity

i.e. particles.

Matter

Forces

electrons

protons

photons

gravitons

Force of Gravity

The Physics of particles is

governed by

“Quantum Mechanics”

-Which brings about a Radical

Change in our concepts of

space.

E.g. Cannot say electron is

here and going nowhere.

Every position is assigned a

number telling us how likely

the electron is to be

at that point. x

Quantum mechanical

analogue of particle is here:

The particle has maximum

chances of being here

and

electrons in

definite orbits

is replaced by

of finding

electron

High chance

Small chance

Deep inside proton:

In addition to Electricity/Magnetism

we need to know about

Strong & Weak force.

The mediators of strong

forces are gluons.

Quantum theory & particle physics

do a great job of reducing diversity

of matter & Electromagnetism,

S & W forces to a few particles!

Forces

E.M. Strong Weak

γ,gphotons

& gluons

But gravity does not fit nicely

into the Quantum Mechanical world.

Applying Q.M. to gravitation gives infinities.

String Theory combines

all forcesStrong,Weak,

Gravitation,

Electromagnetism

& all matter

electrons,protons,neutrons…

into one object…

…a

Matter Force

e-, p+, n γ, gluon, graviton

How does a string accomplish this?

•All particles have energy.

In classical physics:

I. ; also Rest energy

II. Photons have frequency

(related to colour of light)

Planck’s constant

•Strings can vibrate in different ways

For example:

Guitar string

Different vibration Different sound!

•Fundamental string

Different vibration Different particles!

electron photon graviton

•In ordinary circumstances, we can understand

the world by applying different forces

according to the problem at hand.

•A unified Theory of matter & forces is not just pretty - it is necessary for us to understand:

1. Physics of the Early Universe

2. Black Holes

•Universe is expanding

•Every galaxy is facing away from every other

E.g.

Going back in time,

• All matter was crunched up in a very energetic state within a short distance.

• Under these conditions all forces were equally important.

• Hence String Theory becomes necessary for us to understand what happened at after the Big Bang.

•And it makes a startling prediction:

The world contains…

…Extra Dimensions!