Transcript ASTR100 Class 01 - University of Maryland Department of

ASTR100 (Spring 2008)
Introduction to Astronomy
Cosmological Inflation
Prof. D.C. Richardson
Sections 0101-106
Inflation
What aspects of the universe were
originally unexplained
by the Big Bang theory?
Mysteries Needing Explanation
1. Where does structure come from?
2. Why is the overall distribution of
matter so uniform?
3. Why is the density of the universe so
close to the critical density?
 That is, why does the universe have such a
flat geometry?
An early episode of rapid inflation can
solve all three mysteries!
Inflation can
make structure
by stretching
tiny quantum
ripples to
enormous size.
Inflation can
make structure
by stretching
tiny quantum
ripples to
enormous size.
These ripples
in density then
become the
seeds for all
structure in the
universe.
How can microwave temperature be nearly
identical on opposite sides of the sky?
Regions now on opposite sides of the sky were close
together before inflation pushed them far apart.
Density = Critical
Density > Critical
Density < Critical
The overall
geometry of
the universe is
closely related
to total density
of matter and
energy.
Inflation of
universe flattens
overall geometry,
causing total
density of matter
plus energy to be
very close to
critical density.
How can we test the idea of
inflation?
Patterns of structure observed by WMAP tell us the
“seeds” of the universe.
Observed patterns of structure in universe agree (so
far) with what inflation should produce.
“Seeds” Inferred from CMB
 Overall geometry is flat.
 Total mass + energy has critical density.
 Total matter is ~ 26% of total.
 Ordinary matter ~ 4.4% of total.
 Dark matter is ~ 22% of total.
 Dark energy is ~ 74% of total.
 Universe is 13.7 billion years old.
In excellent agreement with observations
of present-day universe and models
involving inflation and WIMPs!
Why is the darkness of the night sky
evidence for the Big Bang?
Olbers’ Paradox
If universe were
1) infinite;
2) unchanging;
3) everywhere
the same;
then, stars would
cover the night
sky.
Olbers’ Paradox
If universe were
1) infinite;
2) unchanging;
3) everywhere
the same;
then, stars would
cover the night
sky.
The night sky
is dark because
the universe
changes with
time.
As we look out
in space, we
can look back
to a time when
there were no
stars.
The night sky
is dark because
the universe
changes with
time.
As we look out
in space, we
can look back
to a time when
there were no
stars.
Cool fact: if you tune your TV set between
channels, a few percent of the "snow" that
you see on your screen is noise caused by
the background of microwaves…
Is there life beyond the Earth?
The Drake Equation
Number of civilizations with whom we could
potentially communicate
= NHP  flife  fciv  fnow
NHP
flife
fciv
fnow
= total number of habitable planets in galaxy;
= fraction of habitable planets with life;
= fraction of life-bearing planets with
civilization at some time;
= fraction of civilizations around now.
We do not know the following values for the
Drake equation:
NHP
flife
fciv
fnow
:
:
:
:
probably billions.
??? hard to say (near 0 or near 1).
??? it took 4 billion years on Earth.
??? can civilizations survive long-term?
SETI
Looking for deliberate signals from E.T.
We’ve even sent a few signals ourselves…
Earth to globular cluster M13: Hoping we’ll hear
back in about 42,000 years!
Your computer can help! SETI @ Home:
screensaver with a purpose.
How difficult is interstellar travel?
Current Spacecraft
 Current spacecraft travel at <1/10,000 c;
100,000 years to the nearest stars.
Pioneer plaque
Voyager record
Are We Alone?
I hope not!
ASTR100 (Spring 2008)
Introduction to Astronomy
Course Review
Prof. D.C. Richardson
Sections 0101-0106
Our Cosmic Address
Our Cosmic Origins
Our Cosmic Motion
Chapter Summaries
1.
2.
3.
4.
5.
6.
7.
8.
9.
Our Place in the Universe
Discovering the Universe for Yourself
The Science of Astronomy
Making Sense of the Universe
Light: The Cosmic Messenger
Formation of Planetary Systems
Earth and the Terrestrial Worlds
Jovian Planet Systems
Asteroids, Comets, and Dwarf Planets
Chapter Summaries
10. Our Star
11. Surveying the Stars
12. Star Stuff
13. The Bizarre Stellar Graveyard
14. Our Galaxy
15. Galaxies and Cosmology
16. Dark Matter, Dark Energy, and the
Fate of the Universe
17. The Beginning of Time
18. Life in the Universe
Latest Material (Ch. 12–14)
 Star Stuff
 Star birth.
 Stellar evolution (low-mass vs. high-mass).
 Planetary nebulae, massive star supernovae.
 The Bizarre Stellar Graveyard
 White dwarfs, neutron stars, black holes.
 Novae, white dwarf supernovae, pulsars.
 Gamma ray bursts (skipped).
 Our Galaxy
 Structure, star-gas-star cycle, formation.
 Galactic center.
Latest Material (Ch. 15–17)
 Galaxies and Cosmology
 Galaxy types, distances, evolution.
 Hubble’s Law.
 Quasars and other Active Galactic Nuclei.
 Dark Matter, Dark Energy, and the Fate
of the Universe
 Dark matter: nature, evidence.
 Structure formation.
 Fate of the universe, dark energy.
 The Beginning of Time
 The Big Bang, evidence, inflation.
Final Exam
 Fri May 16, 8 am – 10 am, this room.
 Don’t be late! And DON’T miss the exam!!
 Special needs: go to Shoemaker, same time.
 Chapters 1 through 17 inclusive.
 Most weight on chapters 12–15.
 No notes, calculators, cell phones, etc.
 Worth 120 points (~22%)…
 48 × 1-2/3 for multiple choice.
 4 × 10 for short answer (night sky, planets,
stars, galaxies).
 5-pt bonus!