1 The Origin, Evolution, and Fate of the Universe
2 Announcements n Homework # 8 is available as of this morning in OWL. Due date for is Friday Dec 9th n Exam # 3 will take place on Tuesday, December 6 th ; n Quiz # 7 will take place Thursday, December 8th.
3 Reading Assignments n Units 75, 76, 79, 80, 81, 82
4 Summary of what we know q The Universe is 13.7 billion years old, and 4200 Mpc in radius q It is mostly (96%) filled with dark (non-baryonic) matter and energy q It is expanding, following the Hubble Law: v = Ho D (Ho = 73 km/s/mpc) q As we look into its farthest reaches, we are looking back in time (the Universe is a `time machine!)
6 A Consequence of the Hubble Law n More distant galaxies have higher `recession velocities (they `run away from us faster): v = H o D n Their light shifts to redder wavelengths (Doppler shift) n Distant galaxies are REDDER (emit light at longer wavelengths) than nearby galaxies
7 The Universe as a time machine n The speed of light is finite: 300,000 km/s n It takes time for light to move through space n E.g. it takes 8 min to come from Sun, and ~230,000 years to come from Andromeda n When light reaches us, it shows us how those sources were at the time it left them n Hence: the further we see in space, the further back we see in time n Distant galaxies are YOUNGER!
8 No Dark Energy, no Supernova evolution
10 Does the universe have an edge? Universe has no edge and no center!
11 A model universe: two dimensional Space is expanding with time! v No edge to space, and no center. v The distances between galaxies increase. v The velocity with which galaxies escape from each other increases.
12 Olbers Paradox n If you walk through a forest, you only see trees to the farthest distance n If the Universe is infinite, every direction you look, you should meet a star or a galaxy. n Thus, the night sky should glow like a star, and should be as hot as the surface of a star! Why is this not happening?
13 Olbers Paradox - 2 n Because, even if the Universe is infinite in space, n It is not infinite in time: the Universe had a beginning time! n It started about 13.7 billion years ago! When you `peek at the Universe, you are looking `through the surface of the balloon, back in time.
14 n Because the Universe is expanding today, it had to start from a more compressed (smaller) region. If you could revert time, the galaxies would come all together!
15 n There was a point in time and space when everything was compressed to a `point, with enormous temperatures (T > K)!
16 The Big Bang: The Origin of the Universe It started as a `hot expansion that created space and time
17 The Big Bang was not really an explosion. It is that the universe was born expanding. This expansion happens everywhere in the same way Every observer sees the same thing There is no center
18 The big bang takes place everywhere! The big bang is still going on! Space and time were created with the big bang and are still changing!
19 The Universe and Its Evolution: Step by Step
21 At the Very Beginning u In the `primordial soup temperatures are enormous; u All four forces are `unified into one; u Matter/antimatter and energy are in constant interaction (think of the interior of a star, but many billions times hotter), i.e., matter and antimatter change into energy and viceversa, continuously; u Particles are very elementary: quarks and electrons (and their antimatter counterparts) are just all there is As the Universe expands, it cools down
23 The Particle Era n n n s < t <.001 s The four fundamental forces (gravity, strong, weak, and electromagnetic) are separated! Particles (both matter and antimatter) are created and destroyed with equal efficiency. n At the end of this time, when the Universe cooled to K, it is no longer hot enough to spontaneously produce protons and antiprotons. n Because of a slight imbalance (Symmetry Breaking), for every one billion antiprotons, there were 1 billion +1 protons. - All antiprotons annihilated with protons to produce photons (1 billion photons for each proton in our Universe).
25 The Era of Nucleosynthesis n s < t < 3 minutes n During this time, hydrogen (the protons left over from the Particle Era) is fused into helium and a small amount of deuterium and lithium (behaves like the interior of a star). n It is a robust prediction of the Era of Nucleosynthesis that 75% of the Universe be left over as hydrogen and the other 25% be helium (plus trace amounts of deuterium and lithium) n At the end of this time, the Universe was too cool for any more fusion.
27 The Era of Nuclei n 3 minutes < t < 300,000 years n This is the simplest the Universe has ever been and will ever be. n All that exists during this time is ionized hydrogen and helium as well as lots of photons. n The Universe during this time (and all earlier times) is opaque (think of the surface of a star, matter and light interact constantly). n n At the end of this time, however, the Universe is too cold to be opaque: Light separates from matter (Cosmic Microwave Background)
29 The Era of Atoms and Galaxies n 300,000 years < t < 13.7 billion years n Universe is no longer hot enough to keep matter ionized. n Structure formed and here we are.
30 Observational Evidence for this `Funny Story Besides the observational evidence for the expanding and evolving universe, we have the confirmation of the two key big-bang predictions: 1. The abundances of light elements in the Universe. We really do measure that about 25% of the Universe is helium, about 75% is hydrogen, and we even get the deuterium and lithium right! 2. The Cosmic Microwave Background radiation (blackbody radiation from the era of nuclei)
31 The Cosmic Microwave Background Radiation (the fossil radiation from the Big Bang) Arno Penzias and Robert Wilson (1966) The isotropic and homogeneous radiation that was set free at the beginning of the Era of Atoms, when the Universe becomes transparent.
32 Evidence for the Big Bang n Expansion of the Universe n Origin of the cosmic background radiation n Nucleosynthesis of the light elements
33 Galaxy and Structure Formation or how we go from the Era of Atoms to the Era of Humans
34 Vocabulary n in astronomy, the term structure refers to anything that s gravitationally held together. n Planets, Stars, Galaxies, clusters of galaxies, etc. are all `structures
35 Survey Question Which of the following objects would not be considered structure by astronomers? a) constellation b) planet c) star d) galaxy e) cluster of galaxies
36 Hierarchy of Structures Galaxy
37 Galaxy Cluster Hierarchy of Structures
38 The Local Supercluster of Galaxies Hierarchy of Structures
39 How did the Universe evolve from a sea of atoms to the organized structures we observe today?
41 Was the Big Bang Homogeneous? The light from the CMB has the same temperature everywhere and in every direction. However, it also shows tiny fluctuations: these grew to form galaxies and clusters today. We see the `seeds of today s galaxies and clusters!
42 The Universe as viewed in the Microwave by the WMAP satellite This small anisotropy (~ 1/10 6 ) in the CMB, emitted 300,000 years after the Big Bang, represents the small fluctuation in the matter distribution which provides the seed for the structure formation in the universe.
43 Formation of the Large-Scale Structure Due to gravity, acting on Dark Matter, which then attracts regular matter
45 The Same Picture but made with Galaxies (these are the Clusters)
46 How did we go from the clusters of dark matter to the galaxies of baryonic matter?
50 Collapse of baryonic gas clouds provided the initial seeds for the galaxies. Galaxies grew subsequently by `merging, i.e., by accreting other galaxies
51 Galaxies interactions and mergers have been a strong evolutionary mechanism (Movie)
52 Galaxies like to cluster: eg. M81 group
53 What will happen to the Universe? q It depends entirely on how much total gravitational `pull it has: q This depends on the total content of mass and energy q A high content of matter and energy will cause the Universe to `stop its expansion in the future (far away), reverse the expansion into a contraction, and produce the Big Crunch q A low (or `critical ) content of matter and energy will cause the Universe to expand forever q Current data suggest we are accelerating q The Universe will end up as a cold, dim expanse.
54 This ends our trip through the Universe