Origin of the Universe

Understanding Earth’s uniqueness

Planetary evolution

• Where does water come from?• Why do we have oceans?• Why do we have life as we know it?• Elemental composition• Present day configuration relative to origins• Hydrological cycle• Dissolved gases/Ocean and Atmosphere

How did the earth become habitable?

• How did Earth evolve?

• What makes it different from other planets?

Origin of the universe

• Importance of time scales

• Forces at work in the past – some changes as planet evolved

• Forces at work today

• How can we measure age of the earth

How old is Earth?

• Biblical scholars of 19th century (Bishop Ussher) – 6000 years (started at 4004 BC)

• Classical Greeks – infinite – history endlessly repeats itself

• Mayans believed earth recycled on a 3000 year time scale

• Han Chinese thought earth was recreated every 23,639,040 years

• The age we now except may change but is consistent with current theory

More recent efforts

• Lord Kelvin - 80 million years old – based on cooling of molten Earth

• Darwin - really old based on time for natural selection (biological argument)

• Hutton – really old based on uniformitarianism (processes in the past taking place at rates comparable to today) (geological argument)

Earth’s age

• Earth is about 4.5 (or 4.6) BY old

• First 700 MY Earth was a spinning cloud of gas, dust and planetoids

• These condensed and settled to solidify into a series of planets

• Since that time, geological history and evolution commenced.

Formerly “oldest life”

Oldest life?

1st Bigbang COSMIC EXPLOSION 20 BYA

2nd Bigbang SUPERNOVA

3rd Bigbang Nemesis Hypothesis (65MYA thru Walter Alvarez)

The Big Bang Theory• Currently the dominant theory• First iteration proposed by Georges Lemaître in 1927.

He observed the red shift in distant nebulas and invoked relativity.

• Hubble found experimental evidence (1929) – galaxies are moving away from us with speeds proportional to their distance.

• Theory suggested because it explains the expansion & predicts the existence of cosmic radiation (leftover photons) & nucleosynthesis

• 1964 cosmic radiation discovered (Arno Penzias & Robert Wilson who won the Nobel Prize)

Big Bang – what is it?• Collapsing cloud of interstellar dust

• Cloud dense and cold so collapses under its own self-gravity (cold gas has less internal pressure to counteract gravity)

• Once collapsed, it immediately warms up because of release of gravitational energy during collapse

• All mass and energy concentrated at a geometric point

Big Bang

• ~14 or 15 BY ago• Beginning of space and time• Expansion/cooling of universe began• Protons and neutrons form• Cooling initiated the formation of atoms – first

mostly H (the most abundant form of matter in the universe) and He (two lightest elements)

The universe• H2 and He gas are still the dominant elements in the universe

– Still about 99% of all material

• Giant gas and dust clouds form– Clouds begin to break into megaclouds– Megaclouds organized into spiral and elliptical shapes due to

rotational forces– Galaxies or nebulae are the gases and dust in the disk

• Some of the gas in these galaxies broke up into smaller clusters to form stars– Gravitational collapse of stars produces heat– Initiates fusion reactions that make other elements

The Eagle Nebula from the Hubble telescope

Interstellar clouds

Formation of galaxy and stars

• Galaxy – rotating aggregation of stars, dust, gas and debris held together by gravity

• Stars are massive spheres of incandescent gases• 100’s of billions of galaxies in the universe and 100’s

of billions of stars in the galaxies• Sun is a star• Sun plus its family of planets is our solar system• Our solar system formed about 5 BY ago

• Our galaxy is out in a spiral arm

• Our solar system orbits the galaxy’s core– (230 million year orbit at 280 km/s)

Formation of the Sun

• Clouds in interstellar space are many 1000’s of times the mass of the sun

• Clouds contract, producing smaller fragments

• Form 1 or more star – depending how fast the cloud fragment is rotating (faster yields more stars)

The disk around the star Beta Pictoris as seen from the Hubble Space Telescope) – real and false color

Stars

• Stars form in nebulae, large diffuse clouds of dust and gas.

• Condensation theory – spinning nebula starts to shrink and heat under its own gravity

• Protostar – condensed gases• At temperature of ~10 million degrees C, nuclear fusion

begins (H’s fuse to form He) which releases energy and stops shrinkage

• Star is stable once fusion reactions begin (form atoms as heavy as C and O)

Star classification – most fall along main sequence band and are “normal”Effective radiating temperature calculated using Wein’s lawBrightest bluest and most massive are O and B, early type stars (left)Dimmest, reddest and least massive are K and M, late type starsOur sun is a G2 star

Our sunin 5 by

Our suneventually

Element synthesis

• Series of fusion reactions producing elements up to Fe

• Fusion reactions convert a small amount of mass to heat– Heats up star– Increases stars density

• Combine to increase core temperature

Beginning of the end

• Star starts consuming heavier atoms increasing energy output and swelling to a “red giant”

• Nuclear fuel in core is spent

• Incinerates planet and throws off matter including heavy elements

• More massive stars get hotter and consume H at higher rates and make heavier atoms (e.g., Fe)

Our Solar System

• Our solar nebula was struck by a supernova• Caused our condensing nebula to spin• Introduced heavy atoms to seed the formation of planets• 5 BY ago, the solar nebula was 75% H, 23% He and 2%

other material• Center became protosun• Outer material became planets – smaller bodies that

orbit a star but do not shine by their own light

Chemical composition of Sun

• Our sun did not form early after the big bang• Contains elements that could only form during

death of a red giant (elements beyond Fe)• Gasses and dust from explosion of a red giant

condensed to form our sun• Same material that formed the sun also formed the

planets– Earth and terrestrial planets are also predominantly Fe,

Mg, Si, and O

Our solar system• Most of the material in the cloud that formed our sun

ended up in the sun– Chemical elements in sun similar to elements in universe

• Some material ended up in the nebular disk around the sun– Formed planets, moon, asteroids, comets

• This material was different in chemical composition– Elements that were contained in dust and ice formed planets

• Gasses not retained by sun were largely lost– Exception is some of the large, gassy outer planets

Planets• Grew by accretion – big clumps use gravitational pull to accrete condensing

matter

• Near sun, first materials to solidify had higher boiling points (metals and rocky minerals) – Mercury is mostly Fe, Ni. Inner rocky planets.

• Next Mg, Si, H2O and O2 condensed (plus some Fe and Ni). Middle planets (e.g., Earth).

• CH4 and NH3 in frigid outer zones. Outer gassy planets (Jupiter, Saturn, Uranus and Neptune).

Timeline (since big bang)

• 10-35 sec ABB (The Big Bang)– The universe is an infinitely dense, hot fireball.

• 10-6 sec ABB (1 millionth of a second)– Universe forms: Expansion slows down; universe cools and

becomes less dense– The most basic forces in nature become distinct: first gravity,

then the strong force, which holds nuclei of atoms together, followed by the weak and electromagnetic forces. By the first second, the universe is made up of fundamental particles and energy: quarks, electrons, photons, neutrinos and less familiar types. These particles smash together to form protons and neutrons.

• 3 sec ABB– Formation of basic elements– Protons and neutrons come together to form the nuclei of

simple elements: hydrogen (1 proton), helium (2 protons) and lithium (3 protons) (1, 2 and 3 in periodic table). It will take another 300,000 years for electrons to be captured into orbits around these nuclei to form stable atoms.

• 10,000 yr ABB– Radiation Era– The first major era in the history of the universe is one in

which most of the energy is in the form of radiation -- different wavelengths of light, X rays, radio waves and ultraviolet rays. This energy is the remnant of the primordial fireball, and as the universe expands, the waves of radiation are stretched and diluted until today, they make up the faint glow of microwaves which bathe the entire universe.

• 300,000 yr ABB– Matter dominates– The energy in matter and the energy in radiation are equal. As

universe expands, waves of light are stretched to lower and lower energy, while the matter travels onward largely unaffected. Neutral atoms are formed as electrons link up with hydrogen and helium nuclei. Microwave background radiation gives us a direct picture of how matter was distributed at this early time.

• 300 MY ABB– Birth of stars and galaxies.– Gravity amplifies slight irregularities in the density of the

primordial gas. Even as the universe continues to expand rapidly, pockets of gas become more and more dense. Stars ignite within these pockets, and groups of stars become the earliest galaxies. (Still perhaps 12 to 15 billion years before the present).

• 5 BY ago Birth of the Sun– The sun forms within a cloud of gas in a spiral arm of the Milky Way Galaxy.

A vast disk of gas and debris that swirls around this new star gives birth to planets, moons, and asteroids . Earth is the third planet out.

– The image on the left, from the Hubble Space Telescope, shows a newborn star in the Orion Nebula surrounded by a disk of dust and gas that may one day collapse into planets, moons and asteroids.

• 3.8 BY ago Earliest Life– The Earth has cooled and an atmosphere develops. Microscopic living

cells, neither plants nor animals, begin to evolve and flourish in earth's many volcanic environments.

• 700 MY ago Primitive Animals appear– These are mostly flatworms, jellyfish and algae. By 570 million years

before the present, large numbers of creatures with hard shells suddenly appear.

• 200 MY ago Mammals appear– The first mammals evolved from a class of reptiles that evolved

mammalian traits, such as a segmented jaw and a series of bones that make up the inner ear.

• 65 MY ago Dinosaurs become extinct– An asteroid or comet slams into the northern part of the Yucatan Peninsula

in Mexico. This world-wide cataclysm brings to an end the long age of the dinosaurs, and allows mammals to diversify and expand their ranges.

• 600,000 yr ago Homo sapiens evolve– Our earliest ancestors evolve in Africa from a line of creatures that

descended from apes.

• 170,000 yr ago Supernova 1987a explodes– A star explodes in a dwarf galaxy known as the Large Magellanic

Cloud that lies just beyond the Milky Way. The star, known in modern times as Sanduleak 69-202, is a blue supergiant 25 times more massive than our Sun. Such explosions distribute all the common elements such as Oxygen, Carbon, Nitrogen, Calcium and Iron into interstellar space where they enrich clouds of Hydrogen and Helium that are about to form new stars. They also create the heavier elements (such as gold, silver, lead, and uranium) and distribute these as well. Their remnants generate the cosmic rays which lead to mutation and evolution in living cells. These supernovae, then, are key to the evolution of the Universe and to life itself.

• 1054 Crab Supernova appears– A new star in the constellation Taurus outshines Venus. Chinese,

Japanese, and Native American observers record the appearance of a supernova. It is not, however, recorded in Europe, most likely as a consequence of lack of study of nature during the Dark Ages. The remnants of this explosion are visible today as the Crab Nebula. Within the nebula, astronomers have found a pulsar, the ultra-dense remains of a star that blew up.

• 1609 Galileo builds first telescope– Five years after the appearance of the great supernova of 1604, Galileo

builds his first telescope. He sees the moons of Jupiter, Saturn's rings, the phases of Venus, and the stars in the Milky Way.

• 1665 Newton describes gravity» At the age of 23, young Isaac Newton realizes that gravitational

force accounts for falling bodies on earth as well as the motion of the moon and the planets in orbit. This is a revolutionary step in the history of thought, as it extends the influence of earthly behavior to the realm of the heavens. One set of laws, discovered and tested on our planet, will be seen to govern the entire universe.

• 1905 Einstein’s Theory of RelativityRelativity recognizes the speed of

light as the absolute speed limit in the universe and, as such, unites the previously separate concepts of space and time into a unified spacetime. Eleven years later, his General Theory of Relativity replaces Newton's model of gravity with one in which the gravitational force is interpreted as the response of bodies to distortions in spacetime which matter itself creates. Predictions of black holes and an expanding Universe are immediate consequences of this revolutionary theory which remains unchallenged today as our description of the cosmos.

• 1929 Hubble discovers universe is expanding– Edwin Hubble discovers that the universe is expanding. The astronomer Edwin

Hubble uses the new 100-inch telescope on Mt. Wilson in Southern California to discover that the farther away a galaxy is, the more its light is shifted to the red. And the redder a galaxy's light, the faster it is moving away from us. By describing this "Doppler shift," Hubble proves that the universe is not static, but is expanding in all directions. He also discovers that galaxies are much further away than anyone had thought.

• 1960 Quasars discovered– Allan Sandage and Thomas Matthews find sources of intense radio energy,

calling them Quasi Stellar Radio Sources. Four years later, Maarten Schmidt would discover that these sources lie at the edge of the visible universe. In recent years, astronomers have realized that they are gigantic black holes at the centers of young galaxies into which matter is heated to high temperatures and glows brightly as it rushes in.

• 1964 Microwave radiation discovered– Scientists at the Bell Telephone Laboratories discovered microwave

radiation that bathes the earth from all directions in space. This radiation is the afterglow of the Big Bang.

• 1967 Discovery of Pulsars– A graduate student, Jocelyn Bell, and her professor, Anthony

Hewish, discover intense pulsating sources of radio energy, known as pulsars. Pulsars were the first known examples of neutron stars, extremely dense objects that form in the wake of some supernovae. The crab pulsar, is the remnant of the bright supernova recorded by Native Americans and cultures around the world in the year 1054 A.D.

• 1987 Light from supernova 1987 reaches Earth– The light from this supernova reaches earth, 170,000 years

after is parent star exploded. Underground sensors in the United States and Japan first detect a wave of subatomic particles known as neutrinos from the explosion. Astronomers rush to telescopes in the southern hemisphere to study the progress of the explosion and perfect models describing the violent deaths of large stars.

• 1990 Hubble launched– The twelve-ton telescope, equipped with a 94-inch mirror, is

sent into orbit by astronauts aboard the space shuttle Discovery. Within two months, a flaw in its mirror is discovered, placing in jeopardy the largest investment ever in astronomy.

• 1990 Big Bang confirmed– Astronomers use the new Cosmic Background Explorer

satellite (COBE) to take a detailed spectrum of the microwave background radiation. These studies showed that the radiation is in nearly perfect agreement with the Big Bang theory. Two years later, scientists used the same instrument to discover minute variations in the background radiation: the earliest known evidence of structure in the universe.

• 1993 Hubble optics repaired– Hubble's greatest legacy so far: detailed images of galaxies

near the limits of the visible universe.

Future• 100 Trillion– Astronomers assume that the universe will gradually wither

away, provided it keeps on expanding and does not recollapse under the pull of its own gravity. During the Stelliferous Era, from 10,000 years to 100 trillion years after the Big Bang, most of the energy generated by the universe is in the form of stars burning hydrogen and other elements in their cores.

• 1037 yrs– Most of the mass that we can currently see in the universe is

locked up in degenerate stars, those that have blown up and collapsed into black holes and neutron stars, or have withered into white dwarfs. Energy in this era is generated through proton decay and particle annihilation.

• 1038 to 10100 The Black Hole Era– After the epoch of proton decay, the only stellar-like objects

remaining are black holes of widely disparate masses, which are actively evaporating during this era.

• 10100 Dark Era Begins– At this late time, protons have decayed and black holes have

evaporated.Only the waste products from these processes remain: mostly photons of colossal wavelength, neutrinos, electrons, and positrons. For all intents and purposes, the universe as we know it has dissipated.

From: PBS Online (http://www.pbs.org/deepspace/timeline/)

Doppler shifting

• Wavelengths emitted by objects moving away are shifted to lower frequency (towards reds)

• Wavelengths emitted by objects moving towards us are shifted to higher frequency.

• Example of sound – pitch of fire engine is higher as truck moves towards you and lower as it moves away)

• For galaxies outside our group, the redshift is known as hubble expansion (after Edwin Hubble who discovered this phenomenon in 1929).