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Ch 17--Fate of the Universe. What do you think?. What is the universe? Did the universe have a beginning? Will the universe last forever?. Cosmology. Cosmology--the study of the origin, structure, and evolution of the universe

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ch 17 fate of the universe
Ch 17--Fate of the Universe

ASTR103, GMU, Dr. Correll

what do you think
What do you think?
  • What is the universe?
  • Did the universe have a beginning?
  • Will the universe last forever?

ASTR103, GMU, Dr. Correll

cosmology
Cosmology
  • Cosmology--the study of the origin, structure, and evolution of the universe
  • Scientific underpinnings began in 1915 with Einstein’s General Theory of Relativity
    • The universe is spacetime
    • GR allows for a dynamic, evolving spacetime, hence a dynamic, evolving universe is possible
  • Prevailing view was that the universe is static and unchanging--steady state universe
  • Hubble’s survey of galaxies revealed the universe to be expanding--the big bang!

ASTR103, GMU, Dr. Correll

the big bang
The Big Bang
  • The Hubble constant gives us an estimate of the age of the universe
    • imagine running the expansion of the universe backwards--assuming a constant recession velocity, how long does it take to reach the “big crunch?”

Time = separation distance = 1/H0

recession velocity

= 1 / 75 km/s/Mpc = 13 billion years

    • General relativity corrects this to be closer to 9 billion years

ASTR103, GMU, Dr. Correll

big bang a simple model
Big Bang--a Simple Model
  • The expanding universe that resulted from the big bang is most accurately thought of in simple terms as a baking loaf of raison bread
    • the bread dough expands (spacetime)
    • the raisons do not, they stay the same size but move further apart from each other (matter and galaxies)

ASTR103, GMU, Dr. Correll

big bang a better simple model
Big Bang--a Better, Simple Model
  • The expanding universe that resulted from the big bang is most accurately thought of in simple terms as the surface of an expanding balloon
    • the surface of the balloon expands (spacetime)
    • galaxies on the surface of the balloon are still best thought of as raisons attached (matter and galaxies)
    • the surface of the balloon has no edges!

ASTR103, GMU, Dr. Correll

history of the universe
History of the Universe
  • In the big bang theory, the earliest moments of after its creation, the universe was a ultra-dense, ultra-hot, yet infinitesimally small place
  • Important events in the history of the universe

Time Temp Phenomena

10-43 s 1032 K Quantum gravity

10-2 s 1013 K Particle/photon interchange,

formation of light elements

106 yrs 1000 K Atoms form, radiation/matter decouple

1010 yrs 3 K Now--galaxies, stars, life

>1032 yrs All matter erodes away?!

ASTR103, GMU, Dr. Correll

unified forces
Unified Forces

ASTR103, GMU, Dr. Correll

early matter and antimatter
Early Matter and Antimatter
  • During the first second of the universe, matter, antimatter, and radiation were in equilibrium

ASTR103, GMU, Dr. Correll

early matter and antimatter10
Early Matter and Antimatter
  • After the first second, as the universe cooled, radiation no longer spontaneously creates matter antimatter pairs--matter and antimatter annihilate each other
    • but, there seems to have been an excess of matter vice antimatter!
    • Results from a strange property of, once again, quantum mechanics--”right-handedness is not strictly preserved”

ASTR103, GMU, Dr. Correll

nucleosynthesis
Nucleosynthesis
  • As the universe continued to cool, hydrogen could undergo nuclear reactions forming helium and lithium--nucleosynthesis
  • After the first three minutes, hydrogen, helium, and lithium rations were established

ASTR103, GMU, Dr. Correll

radiation matter decouple
Radiation/Matter Decouple
  • For the first 300,000 years, radiation too intense to allow electrons to be captured by nuclei
  • at about 300,000 years, temperature became cool enough for electron and protons to combine forming hydrogen atoms
  • the radiation field decoupled from matter and evolved separately

ASTR103, GMU, Dr. Correll

cosmic microwave background
Cosmic Microwave Background
  • The radiation field cools as the universe expands leaving a fossil remnant of the big bang
    • predicted by Alpher, Gamow and Bette in 1948
    • discovered by Penzias and Wilson in 1965
    • Measured by COBE satellite in 1990-

ASTR103, GMU, Dr. Correll

how big is the universe
How Big is the Universe?
  • We can see back in time to the edge of the observable universe
  • Distant regions in the universe look the same, this isotropy and homogeneity indicate the universe was once all in causal contact, even though it now isn’t
  • The inflationary universe solves this conundrum

ASTR103, GMU, Dr. Correll

acausal isotropy
Acausal Isotropy

ASTR103, GMU, Dr. Correll

inflationary universe
Inflationary Universe

ASTR103, GMU, Dr. Correll

formation of galaxies
Formation of Galaxies
  • Galaxy formation began in the first billion years of the universe
  • Elliptical galaxies form stars at a faster rate, possibly preventing the collapse of the proto-galactic cloud into a disk
  • Slower star formation rate allows disk to form leading to spiral galaxies

ASTR103, GMU, Dr. Correll

fate of the universe
Fate of the Universe
  • Will the expansion continue forever (the “big chill”), or will the universe eventually contract into a “big crunch”
  • GR allows for three scenarios
    • Unbound (expands without limit
    • Bound (will eventually collapse)
    • marginally bound (expands forever, but with a limit)

ASTR103, GMU, Dr. Correll

is the universe flat or curved
Is the Universe Flat or Curved
  • Bound
    • spherical geometry
  • Marginally bound
    • flat
  • Open
    • Hyperbolic

ASTR103, GMU, Dr. Correll

observational data
Observational Data
  • Data not yet conclusive, but universe is very nearly flat!
  • Recent data from supernovae observations indicate expansion may be speeding up! Verdict still out.

ASTR103, GMU, Dr. Correll

what do you think21
What do you think?
  • What is the universe?
    • It’s all matter, energy, and spacetime
  • Did the universe have a beginning?
    • Yes, probably occurred between 12-18 billion years ago in an event called the “big bang”
  • Will the universe last forever?
    • Current observations support the belief that it will last forever

ASTR103, GMU, Dr. Correll

questions for thought
Questions for Thought
  • Describe the history of the universe, explaining why the big bang theory is the prevailing accepted theory, and describing observational evidence which supports this theory.

(probably a mandatory question)

ASTR103, GMU, Dr. Correll

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