The Early Universe and Life in the Universe

Review for Astronomy 123 Midterm Exam 3

posted May 31, 2017, jeb

Outline

The Early Universe

Life in the Universe

The Early Universe

Major Events of the Early Universe

10^-43 seconds	GUT epoch begins, leading to inflation
10^-32 seconds	Inflation ends
10^-4 seconds to about 1 minute	Matter emerges as dominant over anti-matter
few minutes	Nucleosynthesis - fusion of neutrons and protons into light elements
50,000 years	Radiation Era ends Matter Era begins
400,000 years	Light de-couples from matter
Today	Dark energy era is underway Expansion of the universe is accelerating

The Big Bang

The early universe was radiation dominated

In the early universe, matter and anti-matter were being created equally out of the radiation

pair production

Anti-Matter
anti-matter consists of anti-particles
Each type of particles is "matched" by an anti-particle of opposite charge
for example, the anti-electron(positron) carries a positive charge

Matter and anti-matter can be created in pairs from energy (or electromagnetic radiation)
E = m c²
E = energy
m = mass
c² = speed of light squared (here just a constant of proportionality)

Anti-matter and matter can also annihilate into energy

The Early Universe

Due to very high temperature matter and anti-matter were continuously created initially

As temperature decreased, eventually even the lightest particles could not be created

Eventually, through interactions, matter came to dominate anti-matter

this occurred about a minute after the Big Bang

Evolution of the Universe

Evolution of Matter

Radiation Era (The radiation era lasted for about 50,000 years)

Planck Epoch

First 10^-43 seconds after the Big Bang

No current theory of physics (quantum gravity) exists

GUT (Grand Unified Theory) Epoch

After 10^-43 seconds, temperature fell to 10³² K

Quark Epoch

Creation of protons and neutrons continued for about 10^-4 seconds

Temperature drops below 10¹³ K, and protons and neutrons are no longer produced in pairs

Lepton Epoch

Ends when the universe is about 100 seconds old

During this epoch, the leptons (electrons, neutrinos, and other light particles) are still produced in pairs, because they are light

Ends when temperature drops below 1 billion K

Nuclear Epoch

Protons and neutrons fuse into light nuclei
nucleosynthesis

Last until the Universe is about 15 minutes old

Matter Era

Atomic Epoch

Galactic Epoch

Stellar Epoch

Vacuum-energy Era (Dark Energy Era)
Last few billion years
Universe's expansion is accelerating
Our recognition of this era is too new to be in the textbook

Formation of Atoms and Nuclei

Light nuclei were formed during the Early Universe
Notably helium and deuterium
helium = 2 protons + 2 neutrons (+2 electrons)
deuterium = 1 proton + 1 neutron (+1 electron)

Why is there so much Helium?
About one quarter of the normal mass of the universe is helium
This is only exceeded by hydrogen, which comprises about three quarters of the normal mass
Heavier elements are a much smaller fraction of the normal mass of the universe

Helium (and other light elements) was produced just after the Big Bang due to extreme temperature in the Primordial Fireball

Present abundances (like deuterium) tell us what was going on very early in the evolution of the universe
Deuterium Cosmology

The amount of deuterium reveals the density of the early universe

Implys that the density of "normal" matter in the universe is at most a few percent of the critical value

deuterium is not formed in stars in much quantity

Heavier nuclei were formed later in burning stars and supernovae explosions.

Inflation

Puzzles of the Early Universe

Why does the universe appear so flat?

not clearly open or closed

If the early universe differed slightly from critical density (flat), it would differ greatly today

Flatness Problem

How did the universe become so homogeneous and isotropic?

Horizon problem

Background radiation nearly the same in all directions

Therefore - entire universe must have been at uniform temperature near beginning

But - different regions are not in contact and never have been

Answers from Grand Unified Theory (GUTS).

Inflationary Universe

Universe expanded 10⁵⁰-fold during first 10^-32 seconds
That's 100,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000 - fold

Grand Unified Theory (GUTS) predicts period of inflation
Inflation Solves Mysteries

Why is universe so flat? (flatness problem)

Expansion flattens it

Like balloon suddenly expanding becomes very flat locally

Why so homogeneous and isotropic? (horizon problem)

Universe was in contact before inflation

but not now

Fundametal Basis for Inflation

Matter interacts through four forces (see note below)

gravity

weak nuclear force

electromagnetism

strong nuclear force

Note - these four forces can be thought of as just three, since the weak nuclear and electromagnetic force have been unified into the electroweak force

Forces of Nature Relative
Strength Role .

Strong Nuclear 1 Binds Nucleus (short range)

Electromagnetic 10^-2 Binds Atoms (long range)

Weak Nuclear 10^-13 Causes Radioactivity (short range)

Gravitational 10^-40 Binds earth to Sun
Binds galaxies (long range)

GUTS - Grand Unified Theories
States that strong, electromagnetic, and weak forces are manifestations of the same force
In other words, unifies the forces

Mathematical Theory of GUTS ------> predicts Inflation

When universe cooled to point that strong force separated from electroweak force

From about 10^-43 sec. to 10^-32 sec, universe expanded in size by 10⁵⁰

Inflation Solves:

Horizon problem

Flatness problem

Structure

Dark Matter

Recall, most of the universe is dark matter (80% or more)

So fluctuations in dark matter should be more important than baryonic.

What is dark matter?
Hot Dark Matter

lightweight particles

such as neutrinos, which have very small mass

Cold Dark Matter

heavy particles

such as exotic supersymmetric particles

Model which best explains observed universe:

Cold Dark Matter

How does Dark Matter relate to microwave background?

Density fluctuations appear first in the dark matter
then create some "ripples" in visible matter- but small "ripples"

1992 - "ripples" finally observed by COBE

at a few parts in 100,000.

21st Century - First WMAP and then Planck have measured "ripples" more precisely

Showing hot spots on cosmic fireball

WMAP angular structure measurement tells us the features of the universe

More Detailed Early Structure measured by Planck

Flat universe (Ω₀ = 1)
68% dark energy
32% matter
27% dark matter
5% normal matter
therefore, more than 80% of the matter is dark matter

Life in the Universe

Our understanding of life in the universe requires we understand how life evolved in the one place we know for sure it did - on the Earth
Life on Earth emerged as the end of an evolutionary sequence:
Life appeared on Earth about 3.5 billion years ago
Carbon based

based on complex molecules (amino acids and nucleotide bases)
early Earth provided energy sources which combined basic elements into complex molecules
basic elements
ammonia (NH₃)
methane (CH₄)
carbon dioxide (CO₂ )
water (H₂O)

energy sources
natural radioactivity
lightning
volcanism
solar ultraviolet radiation
meteoritic impacts

Liquid water essential

Life Elsewhere in the Solar System?

Metereorites often contain organic molecules
Four large bodies in the solar system besides the Earth have possibilities:

Titan, Saturn's largest moon

atmosphere of methane, ammonia and nitrogen

Cassini-Huygens probe into the Titan atmosphere indicates inhospitable conditions for Earth-like life

Europa, Jupiter's moon

liquid water below the icy surface

Mars

explored by Viking -> no life

meterorites from Mars reach Earth

Enceladus, Saturn's icy white moon

Cassini found global ocean of liquid salty water beneath its crust
Jets of icy particles from ocean, laced with a brew of water and simple organic chemicals, gush out into space continuously
First signs of hydrothermal activity beyond Earth

So far, life has only been observed on Earth

Origin of Life - Can It Happen Spontaneously?

Life - as we know it - is based on complex molecules built as carbon chains

Can these molecules be created in the lab?

1953 - Harold Urey and Stanley Miller

Mixed H₂O (water), CH₄ (methane), NH₃ (ammonia), CO₂ (carbon dioxide), and applied sparks

They found amino acids were formed - the basic building blocks of life

More recent experiments have produced amino acid, complex sugars, nucleotide basse, and protein-like microspheres

no DNA

Still no life

This step remains a mystery

But research continues

Possible Alternate Origin of Life on Earth

Not from the primordial soup on Earth, but from organic material produced in interstellar space that came to Earth as interplanetary dust and with meteors
Was first organic material produced in interstellar space, coming to Earth as extraterrestrial visitor?
NASA's modern version of Urey-Miller experiment, using ultraviolet radiation to simulate energy from newborn stars
Found oily, hollow droplets rich in organic molecules

Comets do carry large amounts of organic material
Small fraction of meteorites found on surface of Earth contain organic compounds
Murchison Meteorite contained large amounts of amino acids and other organic material

The extraterrestrial origin is a possibility

Drake Equation

1961 - A small group of astrophysicists (including Carl Sagan) gathered at the National Radio Astronomy Observatory, Green Bank, WV

Frank Drake presented his equation

to estimate the number of technological civilizations that presently exist in the Milky Way

N = R_f_pn_ef_ef_if_cL

R_ = rate of star formation in the Milky Way
f_p = fraction of stars with planets
n_e = # of habitable planets/star
planet in habitable zone;
system in galactic habitable zone;
cannot include binary star systems

f_e = fraction with life evolved
f_i = fraction where life develops intelligence
f_c = fraction which choose to communicate and develop advanced technology
L = lifetime of such civilizations

(Note: This original form is a little different from the textbook)

The Drake Equation is an excellent method for us to fomulate our thinking,

but it does not lead to a well defined answer, because there are many uncertainties in the factors

UFOs (Unidentified Flying Objects)

Occam's Razor

Fundamental principle in science - "the simplest explanation that satisfies all the evidence is the best".

Occam's Razor leads to the conclusion that reported UFO's are not good evidence for extraterrestrial life
Many sightings are explained by optical illusions
Many sightings turn out to be fraud
No sign that extraterrestrials want to contact authorities - like the U.S. President

The Scientific Search

We are looking for intelligent, advanced life since we assume primitive life is too difficult to detect

Analysis of difficulty for extraterrestrials to directly observe life on Earth shows how difficult this is
like "biological rust" of Earth

We assume that intelligent life wants to communicate

Communication will take time
Round trip for radio signal over 50 light years takes 100 years
Round trip for radio signal over 100 light years takes 200 years
Round trip for radio signal over 10,000 light years takes 20,000 years

Two avenues for discovery

We discover them

SETI - search for extraterrestrial intelligence

They discover us

CETI - communication with extraterrestrial intelligence

We Discover Them (SETI)

SETI - search for extraterrestrial intelligence
What should we look for?

Popular guess among scientists

- 21 cm spin-flip line of hydrogen
(1420 MHz)
hydrogen is the simplest atom
and 21 cm is a "quiet band" known as the water hole

Searches at 21 cm (1420 MHz) have failed so far
Late 1990's - Project Phoenix used sophisticated computer controls to investigate millions of channels simultaneously
Still no sign of life

They Discover Us (CETI)

CETI - communication with extraterrestrial intelligence
We have been beaming radio signals to outerspace now for about 50 years
1974 - Arecibo - Puerto Rico
message from people on earth beamed at globular cluster M13 (many stars) - distance 24,000 light years
1679 bits of information (0000001010101000000000000101......
only factors of 1679 are 23 and 73 (1679 = 23 x 73)

One motivation for this is to learn from an advanced technological civilization

Placed messages aboard space vehicles

Pioneer

Voyager

Carbon Chauvinism

Usual assumption of SETI is that life is based on carbon chemistry, like on earth
Why Not Silicon?

We don't have an existence proof - like for carbon

Life on earth is based on molecules containing millions of atoms (DNA)

Silicon

short molecules at room temperature

and we think life would not be able to function at colder temperatures

So silicon does not look like as likely a basis for life as carbon

Search for Extrasolar Planets

One element of the Drake equation is the existence of planets around stars
We can detect the wobble of a star caused by the pull of orbiting planets
This search is biased toward large planets orbiting close to a star

Also look for reduced star light due to planetary eclipse
Kepler satellite has produced the most extrasolar planets of interest in search of life
Earth-like in habitable zone

More than 2,300 planets have been confirmed
More than 600 stars with confirmed multi-planets discovered