Universe's Curvature & Two Events: Cosmic Microwave Background & Big Bang Nucleosynthesis, Study notes of Health sciences

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Curvature of the Universe and Two Important Events:^ Formation of the Cosmic Microwave Background

Big Bang Nucleosynthesis

Curvature in the 4

th^ Spatial Dimension and theRules of Geometry

-^ The geometry you know is valid when drawn on a flat surface. •^ The rules change if the surface is not flat. •^ There are three possible curvatures for the universe.

flat (Euclidean) geometry

Oddly, we are close to a Flat geometry! The Universe is expanding, so each geometry expands also.^ Flat sheets (sphere, etc.) become larger with time^ Even for flat sheets, lines get closer together as you go back in time Thought experiment:^ Spread out the galaxies today so they are uniform (gas)^ Run the universe backwards: denser at earlier times^ Dense gas is hotter (due to this compression)

Universe gets hotter as you go back in time.

Once the universe is about 3,000 K (like a surface of a red giant star) The gas becomes ionized and light is scattered easily The Universe becomes opaque!

bird poop? try cleaning the horn…

Jim Peebles & Bob Dicke: “Maybe you’ve detected the big bang”

Nobel Prize for them:^ The universe ITSELF

is^3 °^ K, everywhere you look.

detection of the

hot, primordial particle/photon

soup the Big Bang! “Big Bang” was a derogatory name given by Hoyle.. who thought this was ridiculous before it was detected.

All-Sky Map: Nearly Perfectly Uniform Tiny variations in temperature and density (

-5) eventually collapse to form galaxies, and clusters of galaxies (higher densities are the darker parts). Collapse cannot start before recombination (formation of the CMB) at 300,000 yr. Collapse must compete with expansion of universe (not everything collapses).

simulations:^ look like our “pie diagrams” of the distribution of galaxies!

REMINDER OF WHAT THEUNIVERSE REALLY LOOKS LIKE…

Suppose we found an old astronomy textbook from some ancient civilization thatlived about 7 billion years ago (about half the age of the universe). Aftertranslating the book we read the section on the cosmic microwavebackground, whose temperature this civilization measured to be: 1. About 2.7 K 2. About twice the temperature that we measure today. 3. About half of the temperature that we measure today.

Big Bang Nucleosynthesis

1 second – 3 minutes after the Big Bang Universe has the temperature of the center of a star (

7 9 – 10^ K).

Before^ 1 second: just photons (

γ), electrons, protons, and neutrons (too hot for atomic nuclei to exist!)

matter

If T > 10

12 K γ

+^ pn^

- e

- p

γ^

+n e antimatter

We get the observed ratio of H/He for a particular density in Big Bang Nuc. What do you think would happen to the H/He ratio if the density wereincreased? Think about how nucleosynthesis is affected by density. 1. The H/He ratio is unchanged. 2. You get a relative increase in the amount of He. 3. You get a relative decrease in the amount of He.