1. From Force & Matter to Strings Dr Sanjaye Ramgoolam
In collaboration with
J. Bedford and C. Papageorgakis

2. 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

3. 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.

4. So far:
2 Questions
2 Answers
MATTER ; FORCE

5. 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:

6. Electrons orbit the nucleus which is composed of Protons and Neutrons
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

7. Unfortunately, the story starts to get more complicated:
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:
Proton
&
Neutron
Quarks
Colours
red up
down
strange
charm
bottom
top
green +
blue

8. Leptons electron electron-neutrino muon muon-neutrino tau tau-neutrino
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:
Leptons
electron
electron-neutrino
muon
muon-neutrino
tau
tau-neutrino

9. The idea of String Theory is that this
diversity of quarks and leptons comes
from 1 String H O e p n
e  
u d s c t b
1 String

10. All this diversity of forces comes from: Gravity &
What about Forces?
“Hammer Force”
“Fuel Force”
“Astronomical Force”
All this diversity of forces comes from:
Gravity
&
Electromagnetism (& its 2 cousins)

11. 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 + -

12. On a grander scale:
Lightning is caused by the
Electric Force

13. 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

14. Particle physics reduces
both Matter & Force
to one kind of Entity
i.e. particles.
electrons
Matter
protons
photons
Forces
gravitons
Force of Gravity

15. 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

16. analogue of particle is here:
Quantum mechanical
analogue of particle is here:
The particle has maximum
chances of being here
and
electrons in
definite orbits
is replaced by
High chance
of finding
electron
Small chance

17. 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!

18. Forces
E.M. Strong Weak
photons
& gluons
γ,g
But gravity does not fit nicely
into the Quantum Mechanical world.
Applying Q.M. to gravitation gives infinities.

19. String! String Theory combines all forces & all matter
Strong,Weak,
Gravitation,
Electromagnetism
& all matter
electrons,protons,neutrons…
into one object… …a
String!
Matter
Force
e-, p+, n
γ, gluon, graviton

20. 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

21. Strings can vibrate in different ways
For example:
Guitar string
Different vibration
Different sound!
Fundamental string
Different vibration
Different particles!
electron
photon
graviton

22. E.g. 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:
Physics of the Early Universe
Black Holes
E.g.
Universe is expanding
Every galaxy is facing away from every other

23. 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.

24. And it makes a startling prediction:
The world contains…
…Extra Dimensions!