H205 Cosmic Origins

The Beginning of Time (Ch. 23)Gravity (Ch. 4) on Wednesday

EP2 Due Wednesday

APOD

Special Lecture

7:30 Tuesday, March 24Fine Arts 015Tom Hartquist

“The Chemical Heritage of Star and Planet Formation”

Olber’s ParadoxYou are lost in a very large forest

The forest is uniformly dense with trees

What do you see?

Why Is the Sky Dark?

IF:•The universe is infinite•The universe is filled with galaxies, clusters of galaxies, and superclusters•The universe is eternal and unchanging

Olbers’ Paradox

If universe were

1) infinite

2) unchanging

3) everywhere the same

Then, stars would cover the night sky everywhere

EarthRadius: 6400 kmDistance from Sun: 150,000,000 km

1 AU, 8 light minutes

Moon

Radius: ¼ Earth’s radiusDistance from Earth:

384,000 km

An Overview

TheSun

Radius: 700,000 kmDiameter: 1,400,000 km

(about 100 x the diameter of Earth)

Mass: 300,000 x mass of Earth

The Nearest

Stars

The closest star to our Sun is Proxima Centauri, about 4 light years distant.

Most of the stars we see in

the sky are within 250 light

years

Our Sector of the Galaxy

The Sun lies along one of our Galaxy’s spiral arms, known as the Orion Arm

View of theMilky Way Galaxy

Our Milky Way galaxy contains two hundred billion stars.

The Sun is about 26,000

light years from the center.

Our Milky Way Galaxy is part of a small cluster of about 3 dozen galaxies.

Virgo Superclust

er

Our Local Group of galaxies is part of a larger Supercluster of galaxy groups.

Galaxies and clusters of galaxies collect into vast streams, sheets, and walls of galaxies.

The Visible Universe On the largest scales, the universe seems to be more or less uniform

Our Goal•How did the Universe begin?•How did the Universe become what we see today?

•What does the state of the Universe today tell us about the origin of the Universe?

A Concept We Need

•Lookback Time –Astronomers can see into the past

•How?

What are the properties of the Universe?

•Size•Distribution of matter•Age

•Models of the Universe–Steady State Model–Big Bang Model

More Evidence for the Big Bang

The cosmic microwave background radiation

In 1965, two engineers at AT&T’s Bell Labs in New Jersey were puzzled by a constant “noise” in a microwave antenna they were calibrating

The cosmic microwave background – the radiation left over from the Big Bang – was detected by Penzias & Wilson in 1965

A Serendipitous Discovery and a Nobel Prize

• The noise could not be explained by terrestrial or extraterrestrial sources. It seemed to be everywhere

• Penzias and Wilson shared the 1978 Nobel Prize in physics for their discovery of the Cosmic Microwave Background (CMB) radiation

A uniform, faint signal from all over the sky

The CMB

• In 1989, NASA launched the Cosmic Background Explorer (COBE) satellite to study the spectrum of the CMB

• COBE showed that the CMB has a perfect thermal spectrum at a temperature of 2.726 K

• Cold! No natural object in the Universe can be colder than this (why not?)

Spectrum of a 2.726 K degree

blackbody

COBE data points

The existence of the CMB shows that the universe was hot and dense in the distant past

Wilkinson MICROWAVE Anisotropy

Probe

The microwave light that we detect has been stretched out as the universe has expanded, so light that was once very short wavelength is now reaching us as microwaves.

Background has perfect thermal radiation spectrum at temperature 2.73 Kelvin… COLD!

Wilkinson Microwave Anisotropy Probe

The microwave light captured in this picture is from 380,000 years after the Big Bang, over 13 billion years ago

WMAP, a later NASA mission, shows us the beginning of cosmic structure in the Universe. Structure began as tiny temperature differences from place to place. The temperature differences WMAP sees vary by only millionths of a degree.

A baby picture of the

Universe

• Imagine a temperature map of the Earth in June 1992• WMAP makes a similar map of the sky

What are we seeing in the baby picture?

The microwave radiation comes from the time when the temperature of the Universe became low enough for atoms to form (about 3000K) Matter became transparent, allowing light to travel great distances It is like seeing the bottom layer of clouds on an overcast day.

Background radiation from Big Bang has been freely streaming across universe since atoms formed at temperature ~ 3,000 K: visible/IR

What does the “baby picture” tell us?

On what angular scales do we see variations in the

CMB?

A “Power Spectrum”How strong are variations on different angular scales?

Different angular scales probe different aspects the early

Universe

• Parameters include an expansion rate, a composition, age, etc.

• Astronomers compute a complex physical model of conditions and adjust parameters to match the observed curve

A simple “Big Bang” doesn’t explain all the properties of the Universe

1)Where does structure come from?2)Why is the overall distribution of

matter so uniform?3)Why is the density of the universe so

close to the critical density?

Explaining the Origin of Structure

• The simple Big Bang model gives a Universe with no structure

• To explain why the Universe has structure, we need “inflation”

What is Inflation?• A period of

extremely rapid expansion when the Universe was very young.

• 10-38 to 10-36 seconds

• Regions of the Universe expanded from the size of an atomic nucleus to the size of the Solar System

Inflation can make all the structure by stretching tiny quantum ripples to enormous size

These ripples in density then become the seeds for all structures in the Universe

Testing Inflatio

nWhy is the Cosmic Microwave Background

Radiation almost perfectly isotropic?The CMB is isotropic because regions now

on opposite sides of the sky were close together before inflation pushed them far apart

Testing Inflation

Patterns of structure observed by WMAP show the “seeds” of universe

Observed patterns of structure in the Universe agree (so far) with the “seeds” that inflation would produce

WMAP’s observation of the “seeds” of structure inferred from

the CMB confirm the existence of dark energy

• Overall geometry is flat – Total mass+energy has critical

density• Ordinary matter ~ 4.4% of total• Total matter is ~ 27% of total– Dark matter is ~ 23% of total– Dark energy is ~ 73% of total

• Age of 13.7 billion years

More evidence for the Big Bang:

The Helium Fraction

The amount of helium compared to hydrogen formed as hot, primordial energy cools and forms into matter can be predicted by physical laws

The fraction of helium in the Universe can be measured with observations

The observed abundances of elements support the predictions of the Big Bang theory

In the hot early universe, protons and neutrons combined to make long-lasting helium nuclei when universe was ~ 3 minutes old

Nuclear physics shows us how to predict the amounts of hydrogen and helium that will be produced

Big Bang theory prediction: 75% H, 25% He (by mass)Matches observations of nearly primordial gases

Abundances of other light elements agree with Big Bang model having 4.4% normal matter

The abundances depend on the density of the Universe when nuclei first formed– Deuterium– Helium-4– Helium-3– Lithium-7

Conclusion:The “Big Bang”

•Expansion implies a beginning, assuming that the universe has been expanding since it came into being

•Scientists call the beginning of our universe the Big Bang. The term was coined by British astronomer Sir Fred Hoyle in the 1940s (on a BBC broadcast!)

•The Big Bang represents a hot, dense primordial state of high energy (but not an explosion)

Summary – Strong evidence supports the Big Bang Theory

• The Universe is expanding (and cooling) from an initial, dense state

• Radiation left over from the Big Bang is now detected in the form of microwaves—the cosmic microwave background—which we can observe with a radio telescope

• Observations of helium and other light elements agree with the predictions for fusion in the Big Bang theory

Coping with a misconception…

If the Universe is expanding, what it is expanding into????????

NOTHING!!!!All of space came into being at the moment of the Big Bang.

Space itself is expanding

Balloon Model

• It depends on the density of the Universe

– The critical density is 10-29 g/cm3, about one hydrogen atom per cubic meter

– About 25 times more than the observed mass of stars and gas

– But what about dark matter?• there isn’t quite enough to re-collapse the

Universe

Will the Universe Keep Expanding…Or Re-Collapse????

But the universe isn’t even slowing down….

A brief history of the

UniverseCourtesy of Fred AdamsUniversity of Michigan

The History of the Universe in 200 Words or Less

Quantum fluctuation. Inflation. Expansion. Strong nuclear interaction. Particle-antiparticle annihilation. Deuterium and helium production. Density perturbations. Recombination. Blackbody radiation. Local contraction. Cluster formation. Reionization? Violent relaxation. Virialization. Biased galaxy formation? Turbulent fragmentation. Contraction. Ionization. Compression. Opaque hydrogen. Massive star formation. Deuterium ignition. Hydrogen fusion. Hydrogen depletion. Core contraction. Envelope expansion. Helium fusion. Carbon, oxygen, and silicon fusion. Iron production. Implosion. Supernova explosion. Metals injection. Star formation. Supernova explosions. Star formation. Condensation. Planetesimal accretion. Planetary differentiation. Crust solidification. Volatile gas expulsion. Water condensation. Water dissociation. Ozone production. Ultraviolet absorption. Photosynthetic unicellular organisms. Oxidation. Mutation. Natural selection and evolution. Respiration. Cell differentiation. Sexual reproduction. Fossilization. Land exploration. Dinosaur extinction. Mammal expansion. Glaciation. Homo sapiens manifestation. Animal domestication. Food surplus production. Civilization! Innovation. Exploration. Religion. Warring nations. Empire creation and destruction. Exploration. Colonization. Taxation without representation. Revolution. Constitution. Election. Expansion. Industrialization. Rebellion. Emancipation Proclamation. Invention. Mass production. Urbanization. Immigration. World conflagration. League of Nations. Suffrage extension. Depression. World conflagration. Fission explosions. United Nations. Space exploration. Assassinations. Lunar excursions. Resignation. Computerization. World Trade Organization. Terrorism. Internet expansion. Reunification. Dissolution. World-Wide Web creation. Composition. Extrapolation?

Copyright 1996-1997 by Eric Schulman .

For Wednesday

Chapter 4 - Making SenseFinish EP2 on Wednesday