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