Download General description of the Universe - School of Physics

The key to some of the
fundamental questions about
our Universe
Since the dawn of cilvalisation, many
philosophers have asked questions about the
fundamental nature and intrinsic properties of
our Universe. This talk will explain, in layman
terms, how the work of physicists sine the past
millennium have unveiled the keys to answers to
some of the these questions.
By Yoon Tiem Leong, 19 June 2005 at Penang Caring Society Complex
First public talk in the public lecture series jointly organised by School of
Physics, USM and PACE, in conjunction with the World Year of Physics 2005
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Plan of the talk
• General description of the Universe
• The general features of Science
• The two important branch of physics theory
governing our Universe
• Questioning the nature of matter and the
Universe:
– What are matter made of?
– Is the Universe finite in space?
– Does the Universe has a beginning or does it
existed since infinite in time?
– If it has a beginning, how and why did it get
created?
– Is our Universe unique?
• Conclusions
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General description of the
Universe
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Hierarchy of sizes of things
• Covering sizes from 10-19 m – 1036 m
• Scientific equipment extend the limit beyond our
naked eye far beyond those ancient Greeks
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A plethora of diversified physical
phenomena
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Definition of Universe
• Everything is inside
the Universe
• Equivalently: nothing
can exist outside the
Universe
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Two aspects of the Universe
• Physical – space, time, matter, energy and
interactions
• Non-physical –Consciousness, spirituality
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Hence science is not
omniscient
• Restricted to only the physical aspect of
the Universe
• It is not supposed to be able to answer
questions outside its scope
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The general features of
Physics
• Physics only treats physical phenomena that are
physically accessible in the Physical Universe
• Simply means phenomena that are measurable
• All physical phenomena are assumed to be
governed by some fundamental laws which are
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formulated in terms of physics theory or theorems
Fundamental Physical laws are
UNIVERSAL
• Invariant (unchanged) in time
and space
• Valid to all observers
• Repeatable
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Features of Physics theories
• Constructed by human mind to describe the
fundamental physical laws
• Physics theory must be testable, and be tested
by experiments to check for validity
• Logically self-consistent and preserve causality
• Use mathematics as a tool
• Precise and not ambiguous
• Must be FALSIFIABLE (at least in principle)
• It is approximate truth
• Has a range of validity
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Comparison with philosophy and
ancient science
• philosophy is highly
contemplative, thinkingintensive, intuitive
• not empirical (bad for ancient
science)
• “bath tub science”
• Tell us why but not how
• Science tell us how but not why
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Two fundamental theories that
governs the Physical Universe
• Quantum mechanics (microscopic world)
• General theory of relativity (cosmological
world)
– Classical Physics (the ordinary world) are
special cases of QM and GR
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GR and QM are two mutually
exclusive theories
• Irony: They can’t be reconciled with each
other into a quantum theory of gravity
• All right at most scenarios because
quantum effects and GR effects don’t
usually arise simultaneously
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Planck scale physics
• Planck scale = 10-34 cm or
10-44 s or smaller
• Planck scale is the limit of
validity of known physics
• Happen during first creation
of Universe and in Black
Hole
• Both quantum and GR effect
arises in these scenarios
• need quantum gravity which
still not found
• All known physics
temporarily breakdown
• Relevant to answer how
Universe is created
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The Grand Play in the physical
Universe
• Our Universe is an
existence that is
made up of:
• Space
• matter and energy
interact according to a
set of physical laws
• time is running at the
background
• Witnessed by
conscious observers
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Simile of the stage performance
•
•
•
•
Actors = matters and energies
Music = flow of time
The stage = space
Languages spoken= fundamental
interactions
• Plot of story line = universal
physical laws
• Audience = conscious observers
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Fundamental questions
• Is matter made of fundamental
building blocks?
• Democritus’s atom
• Modern days’ atom
• We have understood very well what are
matter made using scientific methodology
• atoms = nucleus + electrons
• nucleus is a composite of nucleons
• Two types of nucleons: proton and
neutron(~10-15 m)
• neutron is electrically neutral
• proton is positively charged
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Constituent of matter
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Quarks
• protons and neutron are
made of ‘quarks’
• 6 types of quarks: ‘up’,
‘down’, ‘charm’, ‘strange’,
‘down’, ‘bottom’
• Two types of “flavour”
(+1/2,-1/2)
• Three family
• Quarks don’t exist as free
particles
• Proton and neutron are
made of uud and ddu
• Each flavour comes in three
colours
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Mesons and hadrons
• ‘hadron’ are particles made
up of three quarks
• Mesons are particles made
up by quark + anti quark
• Most hadrons and meson are
rapidly decaying into neutron,
proton, electrons
• Hadron + meson = baryon
• Neutron and proton are the
most common Baryons that
forms the nucleus in matter
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Charged leptons
• Another class of
elementary particles
distinct from quarks
• Also three family
• Electron
• Muon (106 times heavier)
• Tauon (1784 times
heavier)
• Heavy cousins to electron
• Muon and tauon are rare
and decay rapidly
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Most elementary particles are rare
from daily experience
• Neutron, proton, electrons are
familiar
• Other baryons and heavy
charged leptons are far less
common in our daily life
because they are unstable and
decays rapidly into the above
familiar light particles
• Created by cosmic rays and
particle accelerators
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Neutral leptons
• neutrinos
• Little cousins to charged leptons
• Come in three familes: electrontype, muon-type, tauo-type
neutrino
• “ghost particle”
• Neutral in electric charge
• Almost massless
• Extremely inert
• ~1012 passing through you every
seconds, unaware
• Leptons also have the +1/2, -1/2
‘flavour’ as the quarks
• Flavour ½ = charged leptons
• Flavour -1/2 = neutral leptons
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Matter particle
• Matter particle = leptons
+ quarks
• Quarks made up mesons
(q+anti q) and baryons
(3q)
• Leptons = charged (e,
mu, tau) + neutral
(neutrinos)
• Matter particles have spin
½
• They are ‘fermions’
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Interactions among the matter
particles
• 4 fundamental types
• Strong force (among
coloured quarks) - gluons
• Electromagnetic force
(among charged particle)
- photons
• Weak force – among
flavoured particles – Z,
W+, W• Gravity – among all types
of particles – graviton
• They are boson, with
integral or 0 spin
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Unification of forces
• Interactions are similar to
‘languages’ spoken in the stage
play
• Disparate interactions are thought
to be low energy manifestation of a
unified force higher up
• EM + weak = electroweak force
(accepted, Standard Model)
• Electroweak + strong = Grand
Unified Theory, GUT (in the
making, not experimentally
confirmed)
• GUT + gravity = TOE (theory of
everything) (???)
• Thought to have occurred during
the early Universe when
temperature is extremely hot
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Questions on the cosmos:
• Is the Universe finite in space?
• Does the Universe has a beginning or
does it exist since the infinite past?
• If it has a beginning, how and why did it
get created…
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Olbers paradox
• Olbers, German astronomer,
1826
• Paradox regarding ‘night sky
is dark’
• Night sky should be as bright
as the surface of the sun
according to calculation!!!
• What went wrong in the
calculation?
• Have wrongly assumed stars
(galaxies) are static in the
Universe
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The Universe is expanding !!!
• 1929 detected by Edwin
Hubble
• Predicted by GR
• Measured value of
Hubble constant tell us
the receding speed of
galaxy, age and size of
universe using GR
• Age = 13.7 billion years
old
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The Universe …
• is finite is size
• Is finite in age
• does not exist since
forever
• does not maintain a
state of eternality
• It necessarily evolves
with time
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Hot Big Bang
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Rewinding Universe
• We can trace the evolutionary history of
the Universe using physical laws
• Can trace the history as early as we can,
until the logical links break down at the
First Moment of creation
• Good thing: Can check predictions against
observations
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Primordial plasma
• Universe today is vast in
space, cool and no
collisions between particles
• But as Universe goes back
in time further, temperature
rises to millions and trillions
of degrees
• All matter would melt down
into the elementary
particles, mixed with forces
particles in hot soup called
plasma
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Particle physics and evolution of
the Universe
• Particle physics meets
cosmology in the early
universe
• Interplay between the
elementary particles
physics with cosmology
directly affect the later
evolution of the Universe
(including our FATE)
• Many predictions can be
made
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CMBR: hard core evidence to big
bang, produced at age 300,000,
3000 K
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Other confirmation: BBN
• Big bang nucleosynthesis
• tells us how Helium, deuterium
etc. are formed from the
primordial ingredient neutron
and proton around 1 - 3 mins
• Predicts the abundance of He
in present in our Universe
• has been measured to be just
the right amount as predicted
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Is our Universe unique?
•
•
•
•
•
•
•
Steps to create a universe?
Prepared spacetime by whatever means
prepare laws of physics
prepare initial conditions in terms of natural constants
prepare ‘boundary condition’ of ‘there is nothing outside the Universe’
supply the ingredient matter and energy
then says, “let’s rock’
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Does GOD has any choice?
• Evolve a universe is easy
• But not so if want to evolve one
with a conscious mind to ask the
question about the Universe
• Required extreme fine tuning and
consistency of physical laws
• Einstein asked: 'How much choice
did God have
in constructing the universe?’
• Maybe He don’t given the
extremely tight constraint
• Anthropic principle?
• Since we can’t ever access ‘the
other universe’ physically we can’t
tell scientifically if we are unique
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What caused big bang?
• Need to understand
quantum gravity and
Planckian physics to
answer this question
• Don’t know what’s the
answer at the
moment (from physics
point of view)
?
?
?
?
?
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Conclusion
• Questions asked by
philosophers are now being
provided by physics
• Amazing! Successful
application of physical laws
across so many orders of
magnitude in physical scales
to understand the Universe
• Still many fundamental
questions unanswered due
to ignorance of the Planck’s
domain
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Will we finally knows everything
and understand our Universe with
physics?
• A lost traveler moving
in a seemingly
endless desert, could
he ever know whether
he will reach an oasis
at the end of the
horizon, or will he just
find another endless
piece of desert land?
• We don’t know, but
still, we keep walking.
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