ORIGIN OF THE UNIVERSE

PIn the beginning, God created the heaven and the earth; and the earth was without form and void; and darkness was upon the face of the deep and the spirit of God moved upon the face of the water. And God said, "Let there be light," and there was light. And God saw the light, that it was good. Genesis 1:1-3

COSMOLOGY

The study of the origin, structure, and evolution of the universe.

Clues about the Origin of the Universe

PCosmic background radiationPCosmological redshift

What is cosmic background radiation?

This is background microwave radiation that is uniform in all directions and indicates a temperature for the current universe of about 3 degrees Kelvin. This supports the Big Bang theory.

What is the cosmological redshift?

Photons from distant galaxies are all redshifted. This is a color shift in the radiation spectrum of galaxies. The further away the galaxy the greater its redshift. This redshift is caused by the expansion of the universe - further evidence for a Big Bang. All galaxies are receding from each other as a result of the Big Bang.

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• Evidence for expansion follows from the cosmological redshift

• The expanding universe is probably the result of an explosion - The Big Bang

• The microwave background radiation is further evidence for the Big Bang

• The cosmic background radiation implies a period of “inflation” after the Big Bang

Conclusions Based on Observations

What is the Center of the Universe

PThe universe has no preferred center of expansion.PWe are not the center of the universe nor is anything else. PEvery observer, no matter where in the universe will see the universe expanding in the same way.

Age of the Universe

PCalculations indicate an age of about 15 billion years for the age of the universe. No objects older than this have been observed.PE.G. the age of the earth is about 4.5 billion yearsPThe oldest stars are about 10 billion years.

Dawn of civilization

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Big Bang

Now (15 billion years after B.B.)

Beginning of “Big Crunch” ?????????

Gamma Rays

ParticleAnti-particle

Gamma Rays

ParticleAnti- particle

Radiation and Matter: Origin of the Universe

Radiation and Matter: Origin of the Universe

After about 1 microsecond

PUniverse was hot and densePRadiation converted into protons and antiprotons plus quarks and anti-quarks and visa versaPSmall volume, jammed with quarks and antiquarks annihilating each other by creating radiation, began to expand.PThe cooler radiation was no longer hot enough to create quarks and thus most quarks disappeared from the universe.

Radiation and Matter: Origin of the Universe

After about 1 microsecond

PA few quarks survived and combined to make protons and neutrons. PWithout this tiny imbalance in quarks (symmetry breaking) the universe would be void of matter containing only cosmic radiation.PSpace was then filled with ordinary matter and radiation and continued to expand.

Radiation and Matter: Origin of the Universe

After about 5 seconds

PUniverse still hot enough to create light particles, electrons and anti-electrons.PProtons and electrons interact to produce neutronsPUniverse continues to expandPUniverse cools to a few billion degrees and the creation of matter stops.

Radiation and Matter: Origin of the Universe

About 3 minutes

PExpansion cools the universe to a few hundred million degrees.PApproximately 1/4 of the protons are fused into helium.PAll of space is now permeated by helium and hydrogen (about 71% H and 27 % He).

Radiation and Matter: Origin of the Universe

About a million years

PExpansion cools the universe to about 3000 KPAtoms can now form by nuclei capturing electrons - recombination. PBefore recombination, the universe behaved as a single blend of radiation and matter.PAfter recombination, matter and radiation acted as separate entities.

Radiation and Matter: Origin of the UniverseThe matter Era

PSince matter and radiation are no longer locked together, radiation just expands with the universe to become the 2.7 K cosmic radiation of today.PClouds of matter condense out to form clumps of matter, galaxies, etc. Formation of galaxies needs dark matter?

Sequence of Events in the Big Bang

Event Time Temperature (K) Result

Heavy-particle era 10 sec 10 Photons make massive

particlesLight-particle era 10 sec 10 Photons make light

particlesRadiation era 10 sec 10 Only a few particles left

in a sea of photonsMatter era 10 yrs 3000 Radiation & matter

decoupleNow 10 yrs 3 Current picture of

universe

Creation 0 infinite ?-44

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Evolution of Forces in the Big Bang

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• Is the universe “open” or “closed”• Open means that it will expand forever• Closed means that sometime it will stop

expanding and will begin to contract - the Big Crunch.

• Third possibility is a “flat” universe. This universe just stops expanding at some point and remains at that size.

Summary of Big Bang

Summary of Big BangNucleosynthesis

PUniverse begins with “Big Bang” - plasma of protons & neutrons.PPlasma cools & forms hydrogen nucleiPGravity pulls hydrogen together to form starsPCollapsing hydrogen heats up (for about 10 million years) & the hydrogen becomes fused into helium, releasing energy.

Summary of Big BangNucleosynthesis

PEventually, the star materials fuse into nuclei around iron, releasing energy, and the star uses up its energy.PThe larger of these dying stars explode into supernovae.PThe explosions release lots of neutrons which fuse with medium weight nuclei makeing heavier elements.PThis spreads as dust into the universe eventually forming planets in some cases.

Questions

PDark Matter - missing mass?POpen, closed or flat?POther universes - other dimensions?PWhy is the universe all ordinary matter, i.e. no antimatter?PWhy is the cosmic background radiation so smooth?

Review Questions:

Why do astronomers believe the universe is expanding?

What is cosmic background radiation and what is its origin?

How was helium formed from hydrogen in the early universe?

What is the approximate age of the universe?

What is dark matter?

What is meant by the big bang and the big crunch?

What is meant by an open and closed universe?