The Big Bang

1. The Big Bang Primordial explosion creating our universe – all matter and space, “beginning” of time. Hot and dense conditions => like a “fireball” Specific prediction for initial amounts of hydrogen and helium Source of Cosmic Microwave Background Radiation 2006 Nobel Prize in Physics

2. Primordial Nucleosynthesis • Creation of base level of Helium (~25%) in the • early universe via Hydrogen fusion • What conditions allowed this to occur, and why • did it eventually stop?

3. Primordial Nucleosynthesis • Creation of base level of helium (~25%) in the • early universe. Supports big bang model! • Stopped because temperature and density became • too low for fusion to continue

4. The Formation Of Atoms • Early universe hotter and opaque to radiation • Universe expanded and cooled • Electrons & nuclei combined => neutral atoms • Epoch of Decoupling • Universe becomes transparent to EM radiation.

5. The Epoch of Decoupling

6. The Horizon Problem • Cosmic Microwave Background • Radiation (CMBR) • - Leftover from Big Bang • Blackbody spectrum • Cooled by expansion of universe • More energy than all stars and galaxies • that ever existed! • CMBR is uniform across entire sky • Why is this a problem?

7. The Horizon Problem • Cosmic Microwave Background • Radiation (CMBR) • - Leftover from Big Bang • Blackbody spectrum • Cooled by expansion of universe • More energy than all stars and galaxies • that ever existed! • CMBR is uniform across sky • No reason why CMBR should look • the same in regions A and B. • Each lies outside the other’s • communication horizon

8. The Flatness Problem • The cosmic density appears to be • fairly close to the critical value • In terms of space-time curvature, • the universe is remarkably close to • being flat • Why is this a problem?

9. The Flatness Problem • The cosmic density appears to be • fairly close to the critical value • In terms of space-time curvature, • the universe is remarkably close to • being flat • No obvious reason why our universe • should have exactly the critical density!

10. The Theory of Inflation • A short period of unchecked • expansion • The universe swelled in size by a factor of about 1050 in only 10-32 seconds! • Solves both horizon and flatness problems! How?

11. Inflation and the Flatness Problem • Solved by taking a curved surface and expanding it enormously in size. • Example: As balloon expands, curvature becomes less pronounced on small scales • Earth looks flat to us. • The universe appears close to being flat because of inflation.

12. Inflation and the Horizon Problem Initially, regions A and B could communicate Inflation => expand at speeds much greater than that of light => no time for density and temperature fluctuations to form Possible Mechanisms Cosmological constant? Inflaton – repulsive particle that decayed almost immediately?

13. Variable Speed of Light (VSL) Theories Much larger 'ultimate speed limit' in early universe Solves horizon problem Speed of light must have decreased to current value Noether's theorem: Time-evolving laws of physics => mass-energy not conserved VSL predicts mass-energy is destroyed in closed and created in open universe => flat universe becomes an attractor! Same argument also explains why universe is homogeneous Feature of universe not explained by inflation

14. Extraterrestrial Life (as We Know It) • “Life as we know it”is generally taken to mean • carbon-based life that originated in a liquid-water • environment. • Requirements?

15. Extraterrestrial Life (as We Know It) • “Life as we know it”is generally taken to mean • carbon-based life that originated in a liquid-water • environment. • Requirements? • Liquid water, protection from radiation, temperate climate • What are some important characteristics of living organisms?

16. Characteristics of a Living Organism Reacting to environmental stimuli Taking in nourishment and growth/healing Reproducing and passing on characteristics Genetic changes (mutations/evolution)

17. Extraterrestrial Life Assumptions of mediocrity Life on Earth depends on just a few basic molecules. Elements are common to all stars. Laws of physics the same everywhere => life fairly common in the cosmos.

18. The Miller-Urey experiment attempts to recreate the chemical conditions of the primitive Earth in the lab, and synthesize building blocks of life.

19. Review Question The point in time when the temperature of the universe first dropped low enough to allow atoms to form is called the epoch of ______. A) inflation B) expansion C) contraction D) decoupling

20. Review Question The properties of the cosmic background radiation imply that in the past the universe was ___ and ___. A) transparent, cooler B) transparent, hotter C) opaque, cooler D) opaque, hotter

21. Review Question Which of the following is NOT a characteristic of “life as we know it?” A) the capacity to heal and grow B) reproduction without mutation C) carbon-based chemistry D) responsiveness to external stimuli

22. ET Life in the Solar System? Besides the Earth, which bodies in our solar system are most likely to harbor life?

23. The Moon and Mercury lack liquid water, protective atmospheres, and magnetic fields.

24. Venus has far too much • atmosphere.

25. Planet most likely to harbor life • Mars, but still • No Liquid water • Atmosphere is thin • Lack of magnetism and ozone layer • Jovian moons Titan and • Europa also good candidates

26. The Drake Equation average number of habitable planets within those planetary systems rate at which new stars are formed (avg. over galactic lifetime) number of technological, intelligent civilizations in the Milky Way fraction of stars having planetary systems x x = fraction of those habitable planets on which life arises fraction of those life-bearing planets on which intelligence evolves fraction of those planets with intelligent life that develop technological society average lifetime of a technological civilization x x x x Each term is less certain than the preceding one! Only in last twenty years have we addressed the second term. Only in the last five years have we addressed the third term.

27. Contact? How might we go about trying to determine whether or not technologically advanced civilizations exist in our galaxy?

28. SETI • Search for ExtraTerrestrial Intelligence • - Listens for radio signals from alien worlds • Clear window on the cosmos? • - Electromagnetic spectrum, as viewed from Earth, • is a noisy place • Microwave Window - in radio part of EM spectrum • - Photons travel relatively unhindered through the interstellar • medium, at the speed of light • - Natural noise is at a minimum

29. The Water Hole The Water Hole Barney Oliver dubbed the spectral region between H and OH the Cosmic Water-Hole. "Where shall we meet our neighbors?" he asked. "At the water-hole, where species have always gathered."

30. The Fermi Paradox • More stars than sand grains (~ 1022 vs. 1018) • Most conservative estimates (1stthree terms in Drake) • In Milky Way • 100 billion stars • 5 billion Sun-like stars • 1 billion Earth-like planets • Assuming 1% (or 1% survival rate in humanity’s • lifetime) => 100,000 intelligent civilizations • So, where is everybody? • Link to Fermi Paradox Article