1. Stars, Planets, and Moons
N = R* fP nPM fl fi L
R* = rate at which solar-type stars form
= 1/year
fP = fraction of those stars with planets
= 0.2 – 0.9

2. The Right Temperature N = R* fP nPM fl fi L Too cold Just right
nPM = number of suitable planets and moons =
Just right
Too hot

3. Getting Life Started N = R* fP nPM fl fi L
fl = probability of getting life started
= ?? – 1
The basic building blocks of life (elements, amino acids) are common
Life started fairly quickly on Earth
But even very simple life is extremely complicated/unlikely

4. Getting Advanced Civilization
N = R* fP nPM fl fi L
fi = probability of life evolving intelligence
= ?? – 0.5
Evolution follows naturally from physical laws
Evolution naturally leads to some complexity
Intelligence is a very useful kind of complexity
Catastrophes could wipe out advanced life
Evolution may sometimes lead to dead ends

5. Keeping Civilization Alive
N = R* fP nPM fl fi L
Q. 118: Duration of Intelligent Life
L = Mean lifetime of intelligent life
= 100 – 109 years
We have the ability to destroy civilization
We are also damaging our environment
We are using up non-renewable resources
Civilizations may “mature” – some evidence
Sustainable civilizations is technically possible

6. Are We Alone? N = R* fP nPM fl fi L = 0 - billions R*= 1/yr
L = 100 – 109 yr
N = R* fP nPM fl fi L
= 0 - billions
Intelligent life could be rare
Intelligent life could be common
My opinion:
We are first in the galaxy, and possibly the visible universe
Ultimately, this is an experimental question

7. Searching Stars for Life
How can we know if intelligent life exists around other stars?
Visitors from outer space?
Fermi paradox – If they exist, why aren’t they here?
Travel to distant stars?
Search for signals from space?
Q. 119: Spreading Civilization

8. Traveling Between the Stars
How best to do it?
Best chemical rockets: 10-4c – 10-3c
Millenia to nearest star
Nuclear rockets, solar sails, ion engines
10-2c – 10-1c
Decades – centuries to nearest star
Solutions:
Unmanned missions
Generation ships – parents have children
Long life span/hibernation

9. Signals From Space Q. 120: How to Communicate
We can send/receive electromagnetic signals throughout the universe at c
The universe is a noisy place
Dust/gas/etc. blocks many wavelengths
Q. 120: How to Communicate
Some radiation can penetrate gas and dust
In radio waves, the Earth outshines the Sun

10. Signals From Space
We send accidental and intentional signals into space
We also look for signals from alien civilizations
Nothing found so far

11. End of Material for Test 4
Outline of Final:
66 questions total
39 new material
18 = 63 review questions
Mostly a bit easier (I hope)
9 = 33 questions from this semester’s exams, word for word
Not necessarily easier
Final Info Online
Final Exam
Friday May 3
2 – 4 PM
Lab Makeups:
Talk to me or TA if no opportunities left

12. Final Exam Equations c = lf P2 = a3 (M + m)P2 = a3 c = 3  108 m/s
F = ma
E = hf
P = knT
lmaxT = 2900 Km
4 H + 2e -  He + 2 neutrino + energy
L = 4d2B
v = H0d
H0 = 21 km/s/Mly