Download Which model predicts the youngest age for the universe today?

ASTR 101
General Astronomy:
Stars & Galaxies
Three models for fate of universe
in a matter-dominated Universe
REVIEW
ANNOUNCEMENTS
MIDTERM III: Monday, May 4th
Midterm make-up: Tue, May 5th, 11am
Last Astronomy public talk, May 8th (up to 3%
Extra class credit – (see Blackboard
announcement for details)
CLOSED
Friday class: REVIEW for Midterm III (led by
TA Melissa Hoffmann)
Very important diagram
measure of
“expansion factor
of Universe”
OPEN
REVIEW
A. Recollapsing
(closed)
REVIEW
B. Critical
(flat)
NOW
Hubble constant NOW
sets how fast
universe is
expanding NOW
Clicker Question
Which model predicts the youngest
age for the universe today?
SIZE
“Average distance
between
galaxies”
FLAT
TIME
C. Coasting
(open)
Big Bang = when distance zero
Clicker Question
•  A. Recollapsing
•  Age of universe is
how far to left
curves hit
horizontal axis
(distance between
galaxies = 0)
What determines the future average
distance between galaxies?
A. The rate of expansion, with a slower expansion
rate meaning a greater average distance
B. The rate of expansion, with a faster expansion
rate meaning a greater average distance
C. Only on the density of matter in the universe.
Clicker Question
What determines the future average
distance between galaxies?
A. The rate of expansion, with a slower expansion
rate meaning a greater average distance
B. The rate of expansion, with a faster expansion
rate meaning a greater average distance
C. Only on the density of matter in the universe.
Clicker Question
Which model has the slowest future rate of
expansion?
A. Recollapsing
B. Critical
C. Coasting
Clicker Question
Which solution is realized?
Which model has the slowest future rate of
expansion?
Is there enough dark matter
to recollapse the universe?
A. Recollapsing
Baryonic matter: only a few % of critical density
B. Critical
Dark matter: only about 25% of what is needed
C. Coasting
The Universe will expand forever
… and with an unexpected twist…
A New Twist for the
Century
•  Scientists using white
dwarf supernovae to
measure distances
discovered something
quite strange
21st
Using supernovae to determine
the fate of the Universe
•  Redshifts of the
supernovae gives
their vertical
position
–  Space has
stretched since
they gave off their
light
•  Apparent
brightness gives
their horizontal
position
–  Dimmer=more
distant = high
lookback
Supernovae are not consistent even with
the expectations of a coasting universe!!!
How can the universe be
accelerating???
A force that counteracts gravity?
“Dark energy”– outweighs every other form of
mass/energy!
Truly an unknown force in all of physics
The Cosmological Constant actually exists!
Universe is accelerating?!?!
Four models for fates of universe
( Einstein s Greatest Blunder )
The Fate of the Universe
Eternal expansion:
CLOSED
– Cold, galaxies dimming
– Star formation slowing
– Everything winds up as a brown dwarf,
black dwarf, neutron star or black hole
FLAT
OPEN
ACCELERATING
Clicker Question
Clicker Question
What is meant by “dark energy”?
What is meant by “dark energy”?
A.  The energy associated with dark matter through
E=mc2
B.  An unknown form of energy that counteracts
gravity and causes the expansion of the
universe to accelerate.
C.  Any unknown force that acts like gravity
D.  Highly energetic particles that are believed to
constitute dark matter
E.  The total energy in the universe after the Big
Bang but before the first stars
A.  The energy associated with dark matter through
E=mc2
B.  An unknown form of energy that counteracts
gravity and causes the expansion of the
universe to accelerate.
C.  Any unknown force that acts like gravity
D.  Highly energetic particles that are believed to
constitute dark matter
E.  The total energy in the universe after the Big
Bang but before the first stars
At LAST: In the very Beginning…