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Recombination t = 380 ky T = 4000 K
Early on, there were nuclei, electrons, and photons Lots of photons! Free electrons scatter light efficiently Universe is opaque It was so hot atoms rarely formed Any that did form were destroyed by high energy photons At t = 380,000 y, universe cooled to 4000 K Cool enough for atoms to form Universe becomes transparent – CMBR forms t = 380 ky T = 4000 K e- Planck Era Inflation GUT Electroweak p/n freezeout Nucleosynthesis Recombination First structure Today p+
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The Cosmic Microwave Background
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First Structure Forms t = 400 My T = 30 K
The universe is definitely not uniform today Dense spots, less dense spots But at t = 380,000 yr, it was nearly so We think the tiny variations in the density grew over time: More dense spots: gravity draws things together Less dense spots: become voids By 400 Myr, these density fluctuations were big enough to make globular cluster scale Planck Era Inflation GUT Electroweak p/n freezeout Nucleosynthesis Recombination First structure Today
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First Structure Forms Today
t = 400 My – 13.7 Gy T = 30 K – 2.7 K Globular cluster size clouds form First stars form Small objects merge to make small galaxies Galaxies gather to make clusters Large galaxies form from mergers Superclusters form Planck Era Inflation GUT Electroweak p/n freezeout Nucleosynthesis Recombination First structure Today
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What the Evidence Tells Us
Three different methods help us learn the order and structure of the universe: Studying White Dwarf Supernovae distances Studying how large scale structure grew Studying fluctuations in the Cosmic Microwave Background The three methods give very consistent results: m 0.30, e 0.70
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The Four Forces of Nature
Gravity Holds the Solar System together Electromagnetic Holds atoms together Strong Nuclear (Nuclear) Holds the nucleus together Weak Nuclear Radioactive decay
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proton + electron neutron + neutrino
The Weak Force The weak force can convert protons to neutrons, and vice versa proton + electron neutron + neutrino Weak force is weak (slow) today, because energies were low It is stronger at higher energies In the early universe, temperature hotter, they were faster Also, lots of electrons and neutrinos around Protons and neutrons were in equilibrium n0 p+ e- n0 p+ e-
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Proton/Neutron Freezeout
t = 1.5 s T = 1010 K At high temperatures, equal parts neutrons & protons At about 1.5 s, or 1010 K, protons, which are lighter, are favored as the temperature falls At the same time, the weak reaction slows down, “freezes out” Locked in at about seven protons for every neutron p+ Planck Era Inflation GUT Electroweak p/n freezeout Nucleosynthesis Recombination First structure Today n0 e- p+ n0 e- e- p+ e- p+ n0 e- e- p+ n0 p+ p+ e-
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Primordial Nucleosynthesis
At high temperatures, too hot for nuclei to fuse At about 200 s, 109 K, temperature is cold enough for neutrons to stick to protons Quickly thereafter, Helium nuclei are built up Universe ends up (by mass) 25% He, 75% H Small amounts of other stuff (2H, 3He, 6Li, 7Li) t = 200 s T = 109 K p+ p+ p+ p+ n0 p+ Planck Era Inflation GUT Electroweak p/n freezeout Nucleosynthesis Recombination First structure Today p+ p+ p+ p+ p+ p+ p+ n0 p+ p+ Q. 111: Helium Production is Opposite!
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Primordial Nucleosynthesis
Hydrogen and helium formed in first few minutes
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Primordial Nucleosynthesis
Fraction of isotopes depends on how much ordinary matter there is A few isotopes besides 4He 2H, 3He, 6Li, 7Li All other atoms are made in stars Comparison with observations shows atoms = 0.046 Yet another confirmation for Big Bang
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Electroweak Unification
At low energy/temperatures, electric forces are much stronger than weak forces But weak forces get stronger as energy increases At 1015 K, these forces are equal strength Theory and experiment says they are really part of a unified theory – electroweak theory Speculated but unproven: Dark matter may be created here We should be able to test this experimentally in the next couple of years at current colliders? t = 210-11 s T = 1015 K Planck Era Inflation GUT Electroweak p/n freezeout Nucleosynthesis Recombination First structure Today
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Speculation Versus Reality
t < s T > 1015 K Using current colliders, we can see effects up to a temperature of about 1015 K Above this energy, we have no experimental evidence As we work our way to earlier times/higher temperatures, we are speculating From now on, we grow increasingly uncertain of our conclusions Planck Era Inflation GUT Electroweak p/n freezeout Nucleosynthesis Recombination First structure Today Q. 112: Knowing What We Don’t Know
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Grand Unification t = 10-37 s T = 1029 K
Above 1015 K, the strong, and electromagnetic forces have different strengths Theory says they should change as we go to higher energies Likely that at high energy these forces become “unified” into a single force This is called “Grand Unification” Speculative, unproven Could be time when all ordinary matter formed t = s T = 1029 K Planck Era Inflation GUT Electroweak p/n freezeout Nucleosynthesis Recombination First structure Today
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Unsolved Problems in Cosmology
Why did the universe start so uniform? Things that are far apart look similar The horizon problem Why is so close to 1? The flatness problem What is the origin of the density fluctuations we see? Where did all the matter come from? What is the nature of the dark matter? What is the nature of the dark energy? Inflation may solve these Planck Era Inflation GUT Electroweak p/n freezeout Nucleosynthesis Recombination First structure Today Q. 113: Inflation
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Inflation The universe is currently undergoing a (very slow) exponential growth Maybe it did so earlier If the universe went through a period of rapid exponential growth, then: Places that are currently far apart started close together Solves the horizon problem A universe that is not flat becomes very flat Solves the flatness problem Small quantum fluctuations in universe grow to cause perturbations on large scales t = s T = 1029 K Planck Era Inflation GUT Electroweak p/n freezeout Nucleosynthesis Recombination First structure Today
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How Inflation Solves Flatness:
The universe started off very curved, like a small sphere As the universe grows, the curvature gets much smaller
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Graphic From WMAP
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The Cosmic Microwave Background
These fluctuations may be signatures of inflation Q. 114: Scale of Temperature Fluctuations
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