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 other and they move under the influence of these forces For example: the attraction which causes an apple 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 orbit the nucleus which is composed of Protons and Neutrons

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: + up down strange charm bottom top Proton & Neutron Quarks red green 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: electron electron-neutrino muon muon-neutrino tau tau-neutrino Leptons

The idea of String Theory is that this diversity of quarks and leptons comes from 1 String HO p n e 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 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,g photons & gluons But gravity does not fit nicely into the Quantum Mechanical world. Applying Q.M. to gravitation gives infinities.

String Theory combines all forces Strong,Weak, Gravitation, Electromagnetism & all matter electrons,protons, neutrons… into one object… …a MatterForce e -, p +, nγ, 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 vibrationDifferent sound! Fundamental string Different vibrationDifferent particles! electronphotongraviton

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!