27. Exploring the Early Universe

1. 27. Exploring the Early Universe • Rapid inflation of the early Universe • Mass & energy formed during inflation • Most matter & antimatter annihilated each other • Neutrinos & helium are primordial fireball relics • Galaxies formed from early density variations • Grand Unified Theories unite all physical forces • Cosmic strings & other oddities may be relics • Grand Unified Theories suggest 11 dimensions

2. Rapid Inflation of the Early Universe • Two fundamental problems • The isotropy problem • The cosmic microwave background is uniform to 1:10,000 • Opposite sides are much too far apart for this to occur • The flatness problem • What could have made r0 = rc to 50 decimal places? • This is necessary to produce a flat Universe • Too little mass would have ended up with no galaxies • Too much mass would have ended up with a Big Crunch • One possible cause • Rapid inflation very shortly after the Big Bang

3. Possible Causes of Cosmic Inflation • One possible solution to the problem of isotropy • A very early & very brief period of inflation • Lasted only ~ 10–24 seconds • Universe expanded by a factor of ~ 1050 • During this time interval, the cosmological constant was huge • About 10120 times larger than Einstein envisioned • One possible solution to the problem of flatness • We see only a tiny fraction of the Universe • Our particle horizon is a sphere • This sphere enlarged so much that its surface looks flat • Similar to one acre of land on the Earth’s spherical surface

4. The Isotropy Problem

5. Inflation & the Observable Universe

6. Inflation Solves Flatness Problem

7. Mass & Energy Formed During Inflation • Matter at two scales • Super -atomic scale Everyday experience • Location & momentum can be precisely known • Accuracy depends on measuring instruments • Sub -atomic scale High-energy physics • Location & momentum cannot be precisely known • Accuracy depends on fundamental nature of matter • Quantum mechanics • Fundamental nature of matter at the smallest scale • Heisenberg uncertainty principle for location & momentum • EMR is needed to measure location & momentum of an electron • Either location or momentum will be changed by the observation • Heisenberg uncertainty principle for energy & time • Special relativity asserts that E = m . c2 • Heisenberg uncertainty principle for mass & time Dm .Dt = h / (2 .p. c2)

8. Some Aspects of Quantum Mechanics • Ambiguity of mass & time • Uncertainty regarding mass over very short times • “Empty space” might contain no mass • “Empty space” might contain abundant mass • Virtual pairs of particles spontaneously appear • The more massive they are, the less time they exist • Property of particle symmetry • Two particles are always produced • One particle has + charge & the other – charge • The overall electrical charge of the Universe does not change • Supporting observational evidence • Lamb & Retherford detect H spectral irregularities • Disturbing effects of virtual particles on H orbital electrons • Extremely small shift in spectral line positions

9. Virtual Pairs Can Become Real Pairs • Observational evidence • Two highly energetic gamma rays collide • Photon pairs disappear • Particle & antiparticle pairs appear • Combined photon energy >m . c2 • More energy produces more massive particles • Accepted interpretation of that evidence • Photon collisions convert virtual pairs into real pairs • Particle accelerators are used to study this phenomenon • Annihilation occurs when particles recombine • Photon pairs appear • Particle & antiparticle pairs disappear • Relevance to cosmology • Processes active during the inflationary period

10. Virtual Pairs Can Appear & Disappear

11. Annihilation in the Primordial Fireball • Mass & energy formed as part of the Big Bang • The mass was in the form of matter & antimatter • Temperature & pressure were both extremely high • Collisions were frequent & energetic • A condition of thermal equilibrium existed • Mass-to-energy & energy-to-mass processes in balance • The primordial fireball cooled quickly • By t = 10–4 sec, all protons & neutrons formed • Annihilation decreased the Universe’s mass content • Resulting energy contributed to the primordial fireball • By t = 10 0 sec, all electrons & positrons formed • Annihilation decreases the Universe’s mass content • The resulting energy contributed to the primordial fireball

12. A Truly Remarkable Dilemma • The symmetry problem • Annihilation left an excess of matter over antimatter • Perfect symmetry would produce only energy • Any remaining antimatter would annihilate matter • Gamma rays would be the result • Gamma rays observed from some parts of the Universe • Number & energy are both inconsistent with annihilation • Symmetry-breaking somehow occurred • The (proton + neutron) to photon ratio is ~ 1:109 • The “odds” were a highly unfavorable one billion to one!

13. Virtual Pair Production & Annihilation

14. Collision of Relativistic Gold Atoms

15. Neutrinos & Helium Are Fireball Relics • Neutron decay • Free neutrons are unstable Radioactive • Half-life of ~ 630 seconds • Daughter products: 1 proton + 1 electron + 1 antineutrino • By t = 2 sec, neutron decay had commenced • Number of neutrons in the Universe decreased radically • Nucleosynthesis • The deuterium bottleneck prevented He formation • Gamma rays too energetic for the synthesis process • By t = 3 minutes, the Universe cooled even more • Gamma rays too weak to prohibit the synthesis process • Helium quickly formed • The proton to neutron ratio stabilized a ~ 6:1 • By t = 15 minutes, too cool for nucleosynthesis • Only H, He, Li & Be were present in appreciable numbers

16. Nucleosynthesis in the Early Universe

17. Galaxies Formed from Density Variations • Recombination ~ 300,000 years after Big Bang • The Universe was cool enough for neutral H • Photon interactions became very rare • Matter decoupled from radiation • The Universe thus became transparent • The neutral H was very uniformly distributed • Very small density variations did exist • The characteristics of density variations • Gravity & pressure oppose each other • Thegravityincrease tends to contract the gas cloud • The pressure increase tends to expand the gas cloud • Gravity & pressure balance at some point • James Jeans 1902 • Density fluctuations larger than the Jeans length grow • Density fluctuations smaller than the Jeans length dissipate

18. Globular Clusters & Jeans Length • Conditions at recombination • T = 3,000 K rm = 10–15 g . m3 • Conditions in globular clusters • Typical mass of ~ 5 . 105 MSun • Typical diameter of ~ 100 ly • Identical to the Jeans length for typical globular clusters • Observations of globular clusters • They contain the oldest known stars • They may have been among the first structures formed • Complicated by the discovery of dark matter • Known only by its gravitational effects

19. Microwave Background Variations

20. The Growth of Density Fluctuations

21. Globular Clusters ~ Jeans Length

22. Cold & Hot Dark Matter • The fundamental problem • The nature of dark matter is unknown • Many models have been suggested • Computer models • Cold dark matter High mass particles, low speed • Galaxies form from the bottom up • Initial small clumps of matter coalesce into larger clumps • Hot dark matter Low mass particles, high speed • Galaxies form from the top down • Initial large clumps of matter break apart into smaller clumps

23. Cold Dark Matter Simulation

24. Grand Unified Theories • Four basic forces • Gravity Weakest of all • Only attractive • Electromagnetism Second strongest • Both attractive & repulsive • Strong Strongest of all • Only attractive • Weak Second weakest • Only attractive • Thought to be identical at very high energies • Weak & electromagnetic join > 10 2 GeV • Easily achieved in particle accelerators • W / E & strong join > 1014 GeV • W / E / S & gravity join > 1019 GeV

25. 7 x 10–3 Table 29-1: The Four Forces

26. The Unification of the Four Forces

27. http://physics.angelo.edu/~msonntag/physics1301/forces.jpg Unification of Forces: Another View

28. The Early History of the Universe

29. Cosmic Strings & Other Oddities • Vacuum & symmetry • Asymmetric true vacuum Truly empty space • Visualize pencils standing on their points • The pencils do not point in any direction in XY plane • Symmetric false vacuum More energy • Visualize pencils fallen on their sides • The pencils do point in some direction in XY plane • The possibility of cosmic strings • Clusters of fallen pencils keep some pencils upright • Symmetry remains intact at that location • This is analogous to cosmic strings • One possibility for dark matter

30. Symmetry Breaking & Cosmic Strings

31. Distribution of ~ 400,000 Galaxies

32. A Universe With 11 Dimensions? • Hidden dimensions of space • Einstein joined space & time into spacetime 1905 • Four dimensions • Theodor Kaluza proposed a fifth dimension 1919 • Gravity & electromagnetism both warp spacetime • Fifth dimension is curled up too tightly to be observed • Oskar Klein 1926 • Make Kaluza spacetime compatible w/quantum mechanics • Foundations of Kaluza-Klein theory • Edward Witten • All four forces best explained by 11 dimensions • Ten dimensions of space & one dimension of time • The seven extra dimensions are curled up very tightly • This suggests the existence of very massive particles • These have not yet been observed

33. Spatial Dimensions Too Small To See

34. Cosmic inflation The isotropy & flatness problems Can be solved by cosmic inflation Lasted ~ 1–24 sec Universe grew by 1050 Cosmological constant was huge The role of quantum mechanics Heisenberg uncertainty principle Location-energy & mass-time Virtual pairs of particles Can become real due to gamma-rays Extremely hot Universe Production & annihilation equal Cooling Universe Production & annihilation unequal Nucleosynthesis of H, He, Li & Be Slight excess of matter over antimatter One extra particle per billion Density variations & galaxy formation Extremely delicate mass balance The Jeans length Variations must be quite large Globular clusters formed very early Grand Unified Theories (GUTs) All four natural forces are united Extremely high energies Cosmic strings Remnants of primordial symmetry Extremely massive May help explain dark matter An 11-dimensional Universe Best explains four unified forces Extra 7 dimensions are tightly wound Too small to be directly observed Important Concepts