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Cosmology and the Big Bang

Ohio University - Lancaster Campus slide 1 of 34 Spring 2009 PSC 100. Cosmology and the Big Bang. Ohio University - Lancaster Campus slide 2 of 34 Spring 2009 PSC 100. Before 1900, astronomers assumed that the universe

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Cosmology and the Big Bang

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  1. Ohio University - Lancaster Campus slide 1 of 34Spring 2009 PSC 100 Cosmologyandthe Big Bang

  2. Ohio University - Lancaster Campus slide 2 of 34Spring 2009 PSC 100 Before 1900, astronomers assumed that the universe was static in size. In fact, astronomers believed that the Milky Way Galaxy WAS the entire universe. Einstein was the first mathematical cosmologist. His equations showed that the universe must collapse under the attraction of gravity.

  3. Ohio University - Lancaster Campus slide 3 of 34Spring 2009 PSC 100 Yet, the universe hadn’t collapsed. Einstein introduced a fudge factor, a sort of anti-gravity which he called the “cosmological constant” to explain the lack of collapse. Today we call it vacuum energy or dark energy.

  4. Ohio University - Lancaster Campus slide 4 of 34Spring 2009 PSC 100 Credit: http://starchild.gsfc.nasa.gov/Images/StarChild/questions/universe_expansion.gif

  5. Ohio University - Lancaster Campus slide 5 of 34Spring 2009 PSC 100 In the early 1900’s, Edwin Hubble discovered that nebulae are actually galaxies outside our Milky Way. This increased the radius of our universe by a factor of a million. Hubble also discovered that all of these galaxies are receding away from us and from each other. The universe is expanding. The fabric of space itself is stretching.

  6. Credit: www.astroex.org - ESA/ESO’s Astronomy Exercise Series

  7. Ohio University - Lancaster Campus slide 7 of 34Spring 2009 PSC 100 About the same time, George LeMaitre, a Catholic priest (!) proposes that the universe has expanded from a “primeval atom”. LeMaitre convinces Hubble and Einstein that it’s only the relentless expansion of the universe from the moment of creation. No cosmological constant is needed. The universe is “coasting”. Credit: www.amnh.org

  8. Ohio University - Lancaster Campus slide 8 of 34Spring 2009 PSC 100 In 1949, Fred Hoyle, astrophysicist and BBC radio program host, derisively coins the phrase “Big Bang”. Hoyle adamantly supports the steady-state theory. (Hoyle believes that as the universe expands, new matter is constantly being created to fill the void.)

  9. Ohio University - Lancaster Campus slide 9 of 34Spring 2009 PSC 100 Why do we even think that a Big Bang may have occurred? What evidence exists for this idea? Direct evidence: the redshift of all the galaxies indicates the expansion of the universe. Direct evidence: the cosmic microwave background radiation.

  10. In 1965, Bob Wilson & Arno Penzias, working for Bell Labs in New Jersey, discovered an annoying hiss coming from space at microwave wavelengths. Credit: burro.cwru.edu The hiss was the static from the left-over heat of the Big Bang.

  11. In 1989, the Cosmic Background Explorer was launched with the purpose of mapping the cosmic microwave background radiation. Credit: www.lbl.gov Cosmic Background Explorer or COBE www.lbl.gov George Smoot was the principal investigator.

  12. Ohio University - Lancaster Campus slide 13 of 34Spring 2009 PSC 100 • Indirect evidence for the B.B. • Baryonic matter (p+, n0, e-, and us) can be • created from energy: E = mc2 • The early universe contained only H, He, and • traces of Li and Be, as predicted by B.B. • models. The oldest (1st generation) stars • contain only these elements.

  13. Ohio University - Lancaster Campus slide 14 of 34Spring 2009 PSC 100 Problem • We have many stars, galaxies, etc. to look at in the universe. Therefore, their history is fairly easy to define. • We have only one universe, therefore its history is difficult to define. • We must make assumptions.

  14. Ohio University - Lancaster Campus slide 15 of 34Spring 2009 PSC 100 What are the assumptions? • The same physical laws that operate here and now, operate everywhere and everywhen in the universe. • (Universality of physical laws.)

  15. Ohio University - Lancaster Campus slide 16 of 34Spring 2009 PSC 100 • The universe is homogeneous. • Matter is spread evenly throughout the universe. There are clumps, but the clumps are much smaller than the universe as a whole. Credit: The Wilkinson Microwave Anisotropy Probe on www. burro.cwru.edu

  16. Ohio University - Lancaster Campus slide 17 of 34Spring 2009 PSC 100 • Space has the same properties in all directions, or, the universe is the same no matter where you look. • (The universe is isotropic.) • For example, the temp. of the background heat is the same all over the sky to 1 part in 105. The speed of light is the same everywhere.

  17. Ohio University - Lancaster Campus slide 18 of 34Spring 2009 PSC 100 • The universe has no identifiable center. • All directions & points in space are equivalent. (Cosmological Principle) • As a consequence of this: the Earth does not have a privileged place in the universe.

  18. Ohio University - Lancaster Campus slide 19 of 34Spring 2009 PSC 100 Cogito…ergo mundus talis est. The Anthropic principle challenges this last assumption. “We must be prepared to take account of the fact that our location (including time) in the universe is necessarily privileged to the extent of being compatible with our existence as observers.“ Brandon Carter,1973, Krakow symposium honoring Copernicus’ 500th birthday.

  19. Ohio University - Lancaster Campus slide 20 of 34Spring 2009 PSC 100 • Two things happened in the moments • after the Big Bang: • 4 forces separated from the original • “unified force.” • Elementary particles were created.

  20. The 4 Forces… • Gravity – very weak, but operates over infinitely(?) long distances. • Electromagnetism – strong, but rapidly grows weaker with distance. • Strong force – the strongest, but only good for about 10-15 meter (the diameter of a proton). Keeps nuclei together. • Weak force – regulates radioactive (fission) decay. Operates within particles.

  21. Ohio University - Lancaster Campus slide 22 of 34Spring 2009 PSC 100 …and the Particles • Energy can be created when matter is destroyed – we see this every day in the light from the sun. • Matter can also be created from energy, when high energy photons collide. • The more massive the particle, the higher energy (hotter) the photon needs to be.

  22. Particles are always made in pairs • One matter one antimatter • Proton anti-proton • Electron positron • One of the mysteries of our universe iswhy there’s such an imbalance between the amount of matter and the amount of antimatter.

  23. Time-line of the Inflationary Universe (the Big Bang) • Supergravity era • First 10-44 seconds 1032 K • Universe is all energy, smaller than an electron. Only 1 unified force exists initially. • Gravity separates from other 3 forces. (But how can gravity exist w/o mass?) • What if matter doesn’t produce gravity, but gravity collects matter, like rain puddling in a hole?

  24. Ohio University - Lancaster Campus slide 25 of 34Spring 2009 PSC 100 • 10-35 seconds 1028 K • Universe is still all energy, still smaller than an electron, but 1000x larger than before. • Strong force separates. This will allow heavier nuclei, like He, to form later.

  25. Ohio University - Lancaster Campus slide 26 of 34Spring 2009 PSC 100 Radiation Era • Up to 10-10 seconds 1015 K • Universe expands fast (1 um) • Electromagnetic & weak forces separate. The separation of the EMforce will later allow light to shine. • Energy begins to take a recognizable form (photons).

  26. Ohio University - Lancaster Campus slide 27 of 34Spring 2009 PSC 100 Heavy Particle Era • 10-7 seconds 1014 K • Universe expands to 1 km in size (@ 30 times the speed of light!) • High energy photons collide to make quarks, then protons & antiprotons. • Some matter & antimatter annihilate each other.

  27. Ohio University - Lancaster Campus slide 28 of 34Spring 2009 PSC 100 Light Particle Era • 0.1 second 1012 K • Universe is 1,000,000 km wide andstill expanding at ~30 times “c”. • Photons collide to make electrons & positrons • Photons are too sluggish to make any more heavy particles

  28. Ohio University - Lancaster Campus slide 29 of 34Spring 2009 PSC 100 Nucleosynthesis Era • 100 seconds to 10,000 years 1010 K • Universe is 1 LY wide in about 6 days. • Protons & electrons collide to make neutrons. • Protons & neutrons begin to stick together – make nuclei of light elements (H, He, Li, Be)

  29. Ohio University - Lancaster Campus slide 30 of 34Spring 2009 PSC 100 Matter Era • 10,000 years to now • Up to present size (>150 billion LY). Today, we can only observe about 10% of the universe’s width. • Nuclei & electrons are now slow enough that entire atoms form.

  30. Ohio University - Lancaster Campus slide 31 of 34Spring 2009 PSC 100 Matter Era • Density drops low enough that universe becomes transparent afterabout the first 300,000 years. • Matter begins to clump into nebulae. • Stars form, clump to make galaxies.

  31. About 10 years ago, two University of Californiaresearch groups led by Alex Filippenko and Saul Permutter independently determined that theuniverse’s expansion is accelerating. Alex FilippenkoU.C. Berkeley Saul PerlmutterU.C. LawrenceBerkeley Lab

  32. Credit: http://starchild.gsfc.nasa.gov/Images/StarChild/questions/universe_expansion.gif

  33. What does this imply about the ultimate fate of the universe? Heat death of the universe. Entropy goes to infinity.

  34. The End

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