Cosmology (Chapter 14) NASA

Student Learning Objectives Describe the Big Bang theory Analyze possible fates of our universe

What is cosmology?  Cosmology is the study of how the universe has and is evolving.  How "big" is the Universe, does it have an "end"?  What is its large-scale structure?  How old is the Universe, how long will it continue?

Age of Observable Universe  Oldest objects indicate Billion years  Expansion rate (Hubble Law) indicates 13.8 Billion years

How did the universe begin?  Central to every theory in modern cosmology is the observation that the universe is expanding. Big Bang Theory Start of space & time Universe began to exist Beginning of expansion

Practice 1)How big is the entire universe? 2)Where is the starting point for the Big Bang? 3)What would be a better name for the Big Bang Theory?

Timeline Big Bang Event Energy becomes Matter H  He Galaxies & Globular Clusters Form Space Expansion & Cooling Second Generation Stars Born EXPANSIONEXPANSION

Second Stage Timeline Early galaxies merged Superclusters formed filaments Giant voids appeared

 Space itself is still expanding, however, localized gravity wells are maintained. (Galaxy clusters)  Structure throughout the universe is uniform. (Looks the same in every direction) Cosmological Principle

Cosmic Background Radiation  Microwave radiation is present throughout the universe.  Space has a temperature. T = 3 Kelvin Cosmological Redshift As the universe expanded, photon wavelengths were stretched into microwaves. long = low E = low T

The anisotropies of the Cosmic Microwave Background (CMB) as observed by Planck Showing tiny temperature fluctuations ESA

Practice 1)Why is the cosmic microwave background important in cosmology? 2)Are microwaves relatively high or low energy electromagnetic radiation? 3)What does anisotropic mean?

What are the possible fates for our universe?  The battle between matter (gravity) and energy (momentum) will determine the fate of our universe. More GPE  Rebound More KE  Expand forever

Practice 1)If the universe expands forever, what will eventually happen to all stars? 2)If our universe has more GPE, does matter or energy “win”? Would this be considered an open or closed universe? 3)If there is more GPE than KE, what would you expect to happen after the rebound?

Critical Density  The critical density of the universe will determine the ultimate fate of the universe. Mass per energy → Fate D = m V

Density of Matter in Universe Fate Less than Critical Density Expand Forever Greater than Critical Density Collapse & Rebound

Dark Matter & Dark Energy  If we know the total density of all matter, we know the fate of our universe. Dark Matter  If our universe is expanding at an accelerated rate, and it is, there must be something working against Dark matter. Dark Energy

"NASA results confirm that dark energy (represented by purple grid) is a smooth, uniform force that now dominates over the effects of gravity (green grid).” NASA/JPL-Caltech May 2011

Dark Energy & Our Universe  Dark energy must be accelerating expansion.  It is indicated that the universe is mostly energy. 68%+ Dark Energy 27% Dark Matter 5% “Normal” Matter

What is dark energy?  Einstein postulated that empty space can possess its own energy. Anti-Gravity Force  Property of space itself  Grows as space grows  Accelerates expansion Albert Einstein was the first person to recognize that empty space is not nothing.

 A 2 nd theory states that an energy fluid or field fills all of space. Quintessence  Effects all of space  Increasing exponentially  Accelerates expansion “Big Rip” Quintessence may be accelerating the universe to a speed that could break the nuclear forces in atoms, ending the universe in 20,000 million years.

“Chill” “Crunch” “Rip”

Current Findings  The density of all matter in universe is equal to critical density.  Dark energy plays a significant role in the evolution of our universe, and it is “winning”.

The Fate  The universe will expand forever.  Expansion will continue at an exponentially accelerated rate, "Big Rip“.

Questions to Ponder 1)If the universe is expanding and is expanding at an accelerated rate, how can we know the distance light has traveled? How can we know the age of the universe? How old is the universe really? 2)What lies beyond our “observable” universe? telescope-our-inferred-universe/