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God and Cosmology
William Golightly
The Fundamental Forces of Nature
The Laws of Nature: General
Relativity and Quantum Mechanics
• General relativity explains gravity as a
warping of space and time
• Quantum mechanics says there is an
inherent unpredictability, or fuzziness, to
nature on microscopic distance scales
• Quantum mechanics applies to both
particles and fields
How Forces Arise in Quantum
Mechanics
The Fundamental Particles of
Nature
The Expanding Universe
• Edwin Hubble studied the spectra of
galaxies and found from their redshifts that
nearly all galaxies are receding from us
• The speed of recession is roughly
proportional to distance
The Hubble Law
The Balloon Analogy
The Cosmic Microwave
Background Radiation
The Cosmic Microwave
Background Spectrum
The Creation of Matter
• In the first moments after the Big Bang, the
universe was extremely hot
• Intense heat created particle-antiparticle pairs,
which then annihilated and became photons
• A slight asymmetry in matter and antimatter
allowed about one in a billion matter particles to
survive
• As the universe cooled, protons and neutrons
were able to form from quarks
Big Bang Nucleosynthesis
The Geometry of the Universe
•
Geometry of the universe depends
on its average density
•
Closed geometry (positive
curvature) has average density
greater than critical density;
eventually collapses
•
Open geometry (negative
curvature) has average density
less than the critical density;
expands forever
•
Flat geometry (zero curvature) has
average density equal to critical
density; expands forever
Dark Energy and the Accelerating
Expansion of the Universe
• Observations of distant supernovae show that the
universe was expanding more slowly a few billion years
ago, so expansion rate is now accelerating
• The vacuum energy (dark energy) of an unknown field is
believed responsible
• Vacuum energy has a large negative pressure, creating
repulsive gravity, accelerating the expansion
• The puzzle is not that vacuum energy exists, but that it is
not far greater (perhaps 10120 times greater) than it is;
crucial to existence of life
Formation of Structure in the
Universe
• Had to be some roughness in early universe for structure
to develop and eventually lead to stars and galaxies
• Non-interacting dark matter was able to clump together
from the start; essential for life
• Visible matter (nuclei and electrons) formed a plasma
and underwent acoustic oscillations until atoms formed
380,000 years after the Big Bang
• Degree of roughness was just right for life to exist
Cosmic Microwave Background
Shows Early Roughness
Spectrum of microwave
background is a powerful tool
• Temperature fluctuation
spectrum shows harmonics
pattern (angles are smaller
toward the right)
• Details of the pattern show the
universe is flat, with 4% visible
matter, 23% dark matter, and
73% dark energy, in
agreement with other
observations
• Polarization spectrum agrees
well with theoretical predictions
Summary of Evidence for Big Bang
• Redshifts of galaxies indicates expanding universe; age
of 13.7 billion years consistent with measurements of
ages of oldest stars
• Observed abundances of elements agrees well with
predictions of Big Bang model
• Cosmic microwave background has the temperature and
frequency spectrum predicted by Big Bang, as well as
the temperature fluctuation and polarization spectrum
• Computer simulations of development of universe based
on Big Bang model yield accurate predictions
The Universe is Just Right for Life
• Quantum mechanics: Pauli exclusion principle
and characteristics of electrons allow atoms and
molecules to exist
• Slight early asymmetry of matter and antimatter
allowed permanent matter to exist
• Both visible and dark matter needed for stars to
form and life to exist
• Dark energy field is weak enough for stars and
galaxies to have formed; contrary to expectation
The Universe is Just Right for Life
• Neutron-proton mass difference
– The neutron is just slightly more massive than
the proton
– If neutron mass were slightly greater relative
to proton mass, atomic nuclei could not form
– More equal proton and neutron masses would
have caused nearly all hydrogen to fuse into
helium; stellar lifetimes greatly shortened
– Neutron mass slightly smaller than proton
mass would lead to an all-neutron universe
The Universe is Just Right for Life
• Strength of the Weak
Nuclear Force
– If much weaker,
proton/neutron ratio would
be nearly 1 during
nucleosynthesis; nearly all
hydrogen fuses to helium
– If much stronger or weaker,
ability of neutrinos to push
heavy elements away from
supernovae could be
compromised
The Universe is Just Right for Life
• Production of
Carbon in Stars
– Excited state of
carbon is at just the
right energy for 3
helium nuclei to be
able to fuse into
carbon
– Excited state of
oxygen allows both
carbon and oxygen
to exist
The Universe is Just Right for Life
• Weakening of strong force by 50% or
more would prevent heavy elements
essential to life from forming
• Gravity is 1037 times weaker than
electromagnetic force; if only 1033 times
weaker, stellar lifetimes greatly shortened
• Universe has three spatial dimensions and
one time dimension; ideal for complex but
orderly universe
The Multiverse Hypothesis
• Basic idea: Enormous number of
universes with different parameters/laws of
physics would inevitably include a
universe just right for life
• If universes all independent, creates more
problems than it solves
• Popular multiverse concept supposes all
universes originated in the same process
Cosmological Puzzles
• Horizon problem: How can widely
separated regions be at the same
temperature?
• Roughness problem: What is the origin of
the unevenness in the early universe that
led to the development of structure?
• Flatness problem: Why is the universe
apparently geometrically flat? Crucial for
the existence of stars, galaxies, and life
Inflation
Alan Guth’s idea:
Intense burst of
accelerating
expansion occurred
within the first second
of universe’s
existence
Inflation
• How inflation solves these problems
– Points close together before inflation could be
very far apart after inflation; horizon problem
solved
– Quantum fluctuations during inflation would
cause microscopic variations to be stretched
out over large distances
– Universe would be flattened by enormous
expansion, leaving universe at critical density;
flatness problem solved
Why Inflation Would Flatten the
Universe’s Geometry
The Hypothesized Cause of
Inflation
• Vacuum energy of inflaton field proposed as
cause of accelerating expansion
• Field would decay, ending inflation; enormous
energy in field would be transformed into matter,
radiation, and heat
Eternal Inflation and Spontaneous
Symmetry Breaking
• Quantum fluctuations may prevent the inflaton
field from decaying in some places, where
exponential expansion continues
• If so, then once started, inflation continues
indefinitely, continually producing new pocket
universes
• Spontaneous symmetry breaking might allow
different pocket universes to have different
parameters/laws of physics
Superstring Theory
• Every particle consists of a tiny filament of vibrating
energy; different states of string correspond to different
particles
• If true, would unify particles and forces
• Requires nine spatial dimensions; six must be tiny and
curled up (“compactified”)
Inflationary Superstring Multiverse
• Universes with
different ways of
curling up extra
dimensions could
have different laws of
physics and
parameters
• Could be 10500
different possible
universes
Is Eternal Inflation True?
• Inflation has not yet been proven; verified
predictions of inflation are not unique
• Detailed observations of cosmic
microwave background (B-mode
polarization) may soon tell us whether
inflation is correct
• Even if inflation is true, we don’t know that
our theories about how it works are right
Is Superstring Theory True?
• The theory has never made a specific
prediction that has been verified by
experiment or observation
• Existing versions of the theory we can
study in any detail do not accurately
describe our universe
• Superstring theory is not so much a
theory, as a hope that a theory might
someday exist
Comment by Leonard Susskind on
String Theory
“Elegance requires that the number of defining
equations be small. Five is better than ten, and
one is better than five. On this score, one might
facetiously say that String Theory is the ultimate
epitome of elegance. With all the years that
String Theory has been studied, no one has ever
found a single defining equation! The number at
present count is zero. We know neither what the
fundamental equations of the theory are nor
even if it has any. Well then, what is the theory,
if not a collection of defining equations? We
really don’t know.”
How Solid is the Multiverse?
Comment on the multiverse by Martin Rees:
“If one does not believe in providential design, but still
thinks the fine-tuning needs some explanation, there is
another perspective – a highly speculative one, so I
should reiterate my health warning at this stage. It is the
one I much prefer, however, even though in our present
state of knowledge any such preference can be no more
than a hunch” [emphasis added].
Is the Multiverse Fine-Tuned?
Comment by Paul Steinhardt and Neil Turok:
“For all its strengths, the inflationary model rests on a
significant number of unproven assumptions. The first,
that the Big Bang was the beginning of time, immediately
forces a second. To explain how the universe became
so smooth and flat within the first second, the existence
of a powerful new element, inflationary energy, has to be
assumed. To perform its task, the inflationary energy
must have specially tuned properties. Although the
tuning is an unattractive feature, cosmologists accepted
it because inflation seemed like the only idea that had a
chance of resolving the cosmological problems of the
early universe.”
Is The Multiverse Fine-Tuned?
• Must have an inflaton field with the right
properties
• General relativity needed so that vacuum fields
can cause gravitational repulsion
• Superstring theory requires exactly nine spatial
dimensions (or ten in M-theory)
• Must be possible for some dimensions to be
compactified in a wide variety of ways
• Must be possible for the way space is
compactified to spontaneously change
• Need quantum mechanics
Conclusions
• It is extremely unlikely that an arbitrary cosmic
design would just happen to be compatible with
life, or with the generation of an enormous
number of universes with varying laws of physics
• We cannot seem to get away from the
appearance of intelligent design – we can only
push the problem back to another level
• Unless we have some a priori commitment to a
materialistic worldview, it seems clear that the
solution that is simplest and requires the least
faith is that the universe has a Creator