Transcript Document

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:
Proton
&
Neutron
Quarks
Colours
up
down
red
green
+
strange
charm
•
•
•
bottom
top
blue
• 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
The idea of String Theory is that this
diversity of quarks and leptons comes
from 1 String
H
O
e
p
n
udsctb
1 String
e
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.
electrons
Matter
protons
photons
Forces
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
High chance
of finding
Small chance
electron
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
Matter
e-, p+, n
Force
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
electron
photon
Different particles!
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
E.g. •Universe is expanding
•Every galaxy is facing away from
every other
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!