Transcript 10 to 10 - Otterbein University

Final Exam
• Comprehensive
– Most questions from Ch. 15-18, some from Ch. 4-14,
few from Ch. E-3
• Multiple choice
• Please study:
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Midterm exams (available on homepage)
Homework
Activities
Textbook
Powerpoint slides
Assumption: Cosmological Principle
• The Cosmological Principle:
on very large scales (1000
Mpc and up) the universe is
homogeneous and isotropic
• Reasonably well-supported
by observation
• Means the universe has no
edge and no center – the
ultimate Copernican
principle!
What General Relativity tells us
• The more mass there is in the universe, the
more “braking” of expansion there is
• So the game is:
Mass
vs.
Expansion
And we can even calculate who wins!
The Fate of the Universe –
determined by a single number!
• Critical density is the density required to just barely
stop the expansion
• We’ll use 0 = actual density/critical density:
– 0 = 1 means it’s a tie
– 0 > 1 means the universe will recollapse (Big Crunch)
 Mass wins!
– 0 < 1 means gravity not strong enough to halt the
expansion  Expansion wins!
• And the number is:
0 < 1 (probably…)
The “size” of the Universe –
depends on time!
Expansion
wins!
It’s a tie!
Mass wins!
Time
The Shape of the Universe
• In the basic scenario there is a simple relation between the
density and the shape of space-time:
Density Curvature 2-D example
Universe
Time & Space
0>1
positive
sphere
closed, bound
0=1
zero (flat)
plane
open, marginal
infinite
0<1
negative
saddle
open, unbound
infinite
finite
Back to: Expansion of the Universe
•
•
•
•
Either it grows forever
Or it comes to a standstill
Or it falls back and collapses (“Big crunch”)
In any case: Expansion slows down!
Surprise of the year 1998
(Birthday of Dark Energy):
All wrong! It accelerates!
Enter: The Cosmological Constant
• Usually denoted 0, it represents a uniform
pressure which either helps or retards the
expansion (depending on its sign)
• Physical origin of 0
is unclear
• Einstein’s biggest
blunder – or not !
• Appears to be small
but not quite zero!
• Particle Physics’
biggest failure
Triple evidence for Dark Energy
• Supernova data
• Large scale structure
of the cosmos
• Microwave
background
Microwave Background:
Signal from the Big Bang
• Heat from the Big Bang should still be around,
although red-shifted by the subsequent expansion
• Predicted to be a blackbody spectrum with a
characteristic temperature of 2.725 Kelvin by
George Gamow (1948)
 Cosmic Microwave Background
Radiation (CMB)
Discovery of Cosmic Microwave
Background Radiation (CMB)
• Penzias and Wilson
(1964)
• Tried to “debug” their
horn antenna
• Couldn’t get rid of
“background noise”
 Signal from Big Bang
• Very, very isotropic (1
part in 100,000)
CMB: Here’s how it looks like!
Peak as expected from 3 Kelvin warm object
Shape as
expected
from black
body
Latest Results: PLANCK
• Measure fluctuations in microwave background
• Expect typical size of fluctuation of ½ degree if universe
is flat
• Result:
Universe is flat !
Experiment and Theory
Expect
“accoustic
peak” at l=200
 There it is!
Supernova Data
• Type Ia Supernovae are
standard candles
• Can calculate distance
from brightness
• Can measure redshift
• General relativity gives us distance as a
function of redshift for a given universe
Supernovae are further away than
expected for any decelerating (“standard”)
universe
Pie in the Sky: Content of the
Universe
5%
23%
1
2
3
72%
Dark Energy
Dark Matter
SM Matter
We know almost everything about almost nothing!
Properties of Dark Energy
• Should be able to explain acceleration of
cosmic expansion  acts like a negative
pressure
• Must not mess up structure formation or
nucleosynthesis
• Does not dilute as the universe expands 
will be different % of content of universe as
time goes by
Threefold
Evidence
Three independent
measurements
agree:
•Universe is flat
•28 % Matter
•72 % dark energy
History of the Universe: Hot & small  cold & big
before 10-43 s
10-43 s
10-43 to 10-35 s
10-35 s
10-35 s to 10-10 s
10-10 s
10-10 to 10-4 s
10-4 s
T=1032 K
T=1028 K
T=1015 K
T=1013 K
10-4 to 500,000 years
180 s (3 minutes)
T=109 K
500,000 years
T=3,000 K
500,000 years to present
?????? (“Planck Era”)
gravity splits from other forces
Grand Unification era
Strong force splits from others. Epoch
of inflation?
“Electroweak era”
Electromagnetic force splits from others
“Quark era”
Quarks combine to form protons and
neutrons
Radiation era
Protons and neutrons combine to
form nuclei (mainly Helium, deuterium)
Nuclei and electrons combine to
form atoms – Decoupling
Matter era
Life in the Universe: Cosmic
Evolution
Miller-Urey Experiment
• build complex
biochemical
molecules from
simple chemicals plus
electric discharges
• Simulates early Earth
conditions:
– lightning
– primordial oceans
 Successful
experiment!
Is Life on Earth…
• A miracle?
• An accident?
• More-or-less inevitable given the laws of
physics and chemistry, and suitable conditions?
• Principle of Mediocrity: There’s nothing special
about the astronomical, geological, physical and
chemical circumstances on Earth; most likely
nothing special about biology either
What is Life?
• Common features:
– reacts to environment
– metabolism (draws energy from environment)
– reproduction
• Life on Earth
– Based on complex chemistry of carbon
– Fundamental building blocks are amino acids
• Small compounds containing C, O, H, N, S
– It seems unlikely that life can be based on
significantly different chemistry
Green Bank (or Drake) Equation
• Estimated number of technological civilizations present in
the Milky Way galaxy is given by
the average rate of star formation (R*)
 fraction of stars having planetary systems (fP)
 average number of planets within the habitable zone for
various types of star and star system (NP)
 fraction of habitable planets that develop life (fL)
 fr. of life-bearing planets on which intelligence appears (fI)
 fraction of intelligent life forms that develop technology (fT)
 average lifetime of a technological civilization (T)
• Could be 100 to 1 billion (?)
Pessimistic Example
• Estimated number of technological civilizations
present in the Milky Way galaxy:
N = (R*=10/year)
 (fP=10%)
 (NP=1)
 (fL=10%)
 (fI=10%)
 (fT= 10%)
 (T=1000 years)
= 10  0.1  1  0.1  0.1  0.1  1000
= 1 (one civilization in the Milky Way  us!)
Optimistic Example
• Estimated number of technological civilizations
present in the Milky Way galaxy:
N = (R*=20/year)
 (fP=50%)
 (NP=4)
 (fL=20%)
 (fI=50%)
 (fT= 50%)
 (T=100,000 years)
= 20  0.5  4  0.2 
= 200,000
0.5 
0.5 
100,000
Illustration of Drake Equation
Our Messages to the Aliens
• Golden plate
with essential
info on
humans
• On board
Pioneer 10
space probe
• Started in the
70’s
• past solar
system
In 1974 sent radio
signal from Arecibo
to globular cluster
M13 (300,000 stars,
21,000ly away)
Brighter than the Sun
“The signal, transmitted
at 2380 megahertz with a
duration of 169 seconds,
delivered an effective
power of 3 trillion watts,
the strongest man-made
signal ever sent.”
Our EM Message to the
Aliens