ORIGIN OF THE UNIVERSE P In 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 P Cosmic background radiation P Cosmological 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.

6 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 P The universe has no preferred center of expansion. P We are not the center of the universe nor is anything else. P Every observer, no matter where in the universe will see the universe expanding in the same way.

Age of the Universe P Calculations indicate an age of about 15 billion years for the age of the universe. No objects older than this have been observed. P E.G. the age of the earth is about 4.5 billion years P The oldest stars are about 10 billion years.

Dawn of civilization Time Now (15 billion years after B.B.) Beginning of “Big Crunch” ?????????

Gamma Rays Particle Anti- particle Gamma Rays Particle Anti- particle Radiation and Matter: Origin of the Universe

After about 1 microsecond P Universe was hot and dense P Radiation converted into protons and antiprotons plus quarks and anti-quarks and visa versa P Small volume, jammed with quarks and antiquarks annihilating each other by creating radiation, began to expand. P The 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 P A few quarks survived and combined to make protons and neutrons. P Without this tiny imbalance in quarks (symmetry breaking) the universe would be void of matter containing only cosmic radiation. P Space was then filled with ordinary matter and radiation and continued to expand.

Radiation and Matter: Origin of the Universe After about 5 seconds P Universe still hot enough to create light particles, electrons and anti-electrons. P Protons and electrons interact to produce neutrons P Universe continues to expand P Universe cools to a few billion degrees and the creation of matter stops.

Radiation and Matter: Origin of the Universe About 3 minutes P Expansion cools the universe to a few hundred million degrees. P Approximately 1/4 of the protons are fused into helium. P All 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 P Expansion cools the universe to about 3000 K P Atoms can now form by nuclei capturing electrons - recombination. P Before recombination, the universe behaved as a single blend of radiation and matter. P After recombination, matter and radiation acted as separate entities.

Radiation and Matter: Origin of the Universe The matter Era P Since matter and radiation are no longer locked together, radiation just expands with the universe to become the 2.7 K cosmic radiation of today. P Clouds 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 particles Light-particle era 10 sec 10 Photons make light particles Radiation era 10 sec 10 Only a few particles left in a sea of photons Matter era 10 yrs 3000 Radiation & matter decouple Now 10 yrs 3 Current picture of universe Creation 0 infinite ?

Evolution of Forces in the Big Bang Strong nuclear force Gravity Electromagnetic force Weak nuclear force 10 Sec K 10 3 K Now

19 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

Nucleosynthesis P Universe begins with “ Big Bang” - plasma of protons & neutrons. P Plasma cools & forms hydrogen nuclei P Gravity pulls hydrogen together to form stars P Collapsing hydrogen heats up (for about 10 million years) & the hydrogen becomes fused into helium, releasing energy.

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

Questions P Dark Matter - missing mass? P Open, closed or flat? P Other universes - other dimensions? P Why is the universe all ordinary matter, i.e. no antimatter? P Why 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?