Astronomy - State of the Art is a course covering the hottest topics in astronomy. In this section, the potential for life in the universe is covered, including extreme life on Earth, the Drake equation and SETI

3. Science is Seeing
Biology

4. Life has Order

5. Life uses Energy

6. (c) Response to the
environment
(a) Order
(d) Regulation
(g) Reproduction(f) Growth and
development
(b) Evolutionary
adaptation
(e) Energy
processing
Properties of Life

7. 1 The biosphere
Hierarchy
From biosphere…
…to organisms

8. Cell
8 Cells
6 Organs and organ systems
7 Tissues
10 Molecules
9 Organelles
50 µm
10 µm
1 µm
Atoms
Figure 1.3
…to cells and molecules and atoms
But the reductionist approach fails; biological systems
cannot simply be understood in terms of components.

9. • Water is special (and it
is a common molecule
throughout the universe).
• Carbon is special (and it’s
the second most abundant
element made in stars).
• With a versatile chemical toolkit, the possibilities of
information storage and biological function are almost
infinite. Alternate biologies are definitely possible! We
just have to look for them. But the question is how…?

10. Unity of Life

11. In traditional
tress of life
based on
species, we
are usually
placed at the
top. We are
special, the
natural end
point of all
evolution up
to this point.

12. Molecular Tree of Life

13. • The Modern Tree of Life
– Maps evolution via the gradual deviation of the
base pair sequences in DNA or RNA.
– Does not depend on identifying or recognizing
distinct species.
– Can track evolution back to the dawn of life but not
with good time precision.
– Places us as a minute twig on the tree of life in an
overwhelmingly microbial world.

14. Evolutionary Linkage through Cytochrome C
Organism # Deviant nuclic acids (in 110)
Human 0
Rhesus Monkey 1
Dog 13
Chicken 18
Rattlesnake 20
Tunafish 21
Moth 36
Wheat 43
Yeast 45
Next time you look
into your beer glass,
acknowledge that
there is kinship.

15. RNA
phenotype
replication
expression
The Central Dogma
…greatly simplified

16. DNA
RNA
proteins
Structure and function
of organism
replication
processing
processing

17. DNA
RNA
proteins
Structure and function
of organism
natural
selection

18. The Book of Life
Biology uses a four-letter
“alphabet” of base pairs,
coding proteins in a cell.
The delicate spiral ladder
of DNA holds information
equal to an encyclopedia.

19. The Genetic Code

20. The “Book” of DNA
Base pair 10 1 Letter
Codon 100 6 Word
Gene 10,000 1000 Sentence
Bacterium 10,000,000 1,000,000 Short book
Human 3,000,000,000 6,000,000,000 Encyclopedia
Level Atoms Bits Language analog

21. The “Tape” of DNA
Base pair 0.00000003 mm 0.03 mm Letter
Codon 0.0000001 mm 0.1 mm Word
Gene 0.05 mm 0.5 m Sentence
Chromosome 5 cm 500 m Short book
Human 2 m 20 km Encyclopedia
Level Actual Scale model Language

22. In biology,
there is
metabolic
complexity.

23. In biology,
there is
structural
complexity.

24. Extremophiles

25. Extreme Dryness

26. Extreme Cold

27. Extreme Heat

28. Extreme Radiation

29. Extreme Toxicity

30. Extreme Isolation

32. 0.1mm
Meet the amazing
tardigrade, with its
own phylum and
many species, it’s
got four pairs of
legs, a digestive
system, a single
gonad, and it can
go into a very dry
suspended state
(cryptobiosis) for
over a thousand
years, moving by
being carried on
the wind and also
in fur of animals.

33. Exobiology

34. Life on Other Worlds
Epicurus “Letter to Herodotus”
There is an infinite number of worlds, similar to ours, and an infinite number of
different worlds…One must agree that in all these worlds, without any exception,
there are animals, plants, and all the living things we observe.”
Thales Epicurus Lucian Democritus
But the primacy of Aristotle’s geocentric cosmology mostly squashed a
discussion of the plurality of worlds until the Copernican revolution.

35. Evidence that
ingredients for life
are widely available
in time and space
Evidence that
planet and moon
habitable locations
are abundant

36. Pale Blue Dot
Earth, backlit against a
gossamer ring of Saturn,
is almost certainly not a
unique host for biology.

38. What might be, but isn’t

39. Majority of the biosphere is
still unexplored.
Over 99% of microbes have
not yet been cultured.
Only remote sensing through
most of the Solar System.
A small fraction of habitable
planets/moons discovered.
A tiny fraction of SETI search
space explored.
What We Know
(and don’t…)

40. Isn’t
Is
Imaginable
Possible
WHAT IS AND ISN’T

41. Using Carbon
Using Planets
EXOBIOLOGY
Recognizable Life
Unrecognizable Life
DNA-Based

42. Origin of Life

47. • The “life in a bottle experiments of Miller and Urey in the
1950’s didn’t create life; they just showed how plausible
early Earth conditions could have led to amino acids and
other building blocks of life.
• More recent lab experiments show how vesicles or simple
cell precursors could have formed and concentrated and
amplified RNA fragments inside.
• Chemical complexity can build on itself and some form of
chemical “natural selection” may have preceded biology.

49. Evolution

51. When a tall tree grows from a tiny seed where does the mass
come from: (a) it was in the seed, (b) soil, (c) water, or (d) air?
Life’s Great Innovation

52. 6H2O + 6CO2 → C6H12O6 + 6O2
Photosynthesis

53. 6H2O + 6CO2 → C6H12O6 + 6O2
water + carbon dioxide + light → glucose + oxygen
Plants take in water and carbon dioxide and
rearrange the molecules into organic material
(hydrocarbons) like cellulose, respiring oxygen.
In mass units: 10 + 22 → 16 + 16
(water) (air) (plant) (air)
Plants are 2/3 water but 90% of the water is
transpired, so only 1 unit from water and 6
from air—carbon gets snatched from the air!

56. A 200 meter object that
hit in northern Arizona
35,000 years ago left a
kilometer-wide crater.
A 100 meter object that
hit Siberia in 1908, and
was luckily far from any
population center. The
30 meter object that hit
Chelyabinsk in 2013 did
not cause deaths either.

57. A world-wide layer rich
in iridium, found most
often in extraterrestrial
material, covered Earth
65 million years ago.
Clinching evidence for an
impact as the cause of the
mass extinction came with
the discovery of an impact
crater of the right age just
off the coast of Mexico.

58. Evolution is contingent. There are so many branching
points and random influences to evolution that another
set of experiments might give very different outcomes.

59. Plants
Fungi
Animals

60. Evolution of all animals in terms of DNA

62. Science is Seeing
Intelligence

63. Termite mounds are
engineering marvels,
higher than our best
skyscrapers, scaled to
organism size. In their
construction five temp
control mechanisms.

64. Social insects have
complex behavior,
specialized function
and communication
by chemical means.
Intelligent function is
distributed within the
colony or hive, rather
that individuals. How
might this evolve?

65. Alex the parrot was
talkative and playful,
coming up with the
concept of zero.
Rats are ticklish and
curious, personality
traits are seen, they
can anticipate sex,
and reflect on their
thinking processes
(meta-cognition).

66. Are we “off the chart” smart?

67. No natural enemies
Large brains
Complex language
Social animals
Mate for life
Bombs, Internet, Cars
ORCAS HUMANS

×
×







68. After four billion years of life on
Earth, homo sapiens emerged to
dominate the planet and venture
into space. Was this just a fluke or
did something like this happen on
distant planets, maybe long ago?

69. Apes
A recent surge in evolution
vaulted us to the top of the
tree in terms of brain size.

71. Weird Life

72. A Bit Weird:
Fairly Weird:
Mostly Weird:
Totally Weird:
Prokaryotes, eukaryotes,
but different cell types
Novel symbiosis, gene and
organism swapping
Non-cellular, networks as
opposed to containers
Planet-scale architecture,
geo-engineering

73. High Level Architecture
Not limited by mutation & selection;
Evo-Devo toolkit: genes, organisms

74. A Bit Weird:
Fairly Weird:
Mostly Weird:
Totally Weird:
Different amino acids, or bases
for nucleic acids
Not DNA-RNA-Proteins
(the “Central Dogma”)
Non-carbon, non-water
(silicate, ethane/methane)
High density biochemistry,
molecule-scale organisms

75. Bacterial Communities
Evolution timescale is very rapid;
information density ~ 1012 bits/cm3

76. Companionship

77. Technology
Intelligence
Technology
Multi-celled
Multi-celled: Networked, diverse biological function
Intelligence: High level processing, consciousness
Technology: Control of environment, space travel
Thresholds in Evolution

78. 0 4 8 Gyr
10
20
30
ly
+108
more
Earth
?
?
?

79. Green = stars with
planets
Blue = stars with
Earths
The couple of
hundred solar
systems found
so far, nearby,
under 30 light
years, mostly.

80. A billion habitable worlds in our galaxy, and 100 billion galaxies…

81. There are likely to be ~108 Earth-like planets in the
Milky Way, 1018 in the Universe, and there’s been 8
billion years for life to evolve before Earth formed.

82. Drake Equation

86. DRAKE EQUATION
Stars in MW
Stars in Universe

87. With Sentience
With Earths
With Life
DRAKE EQUATION
Stars in MW

88. The Drake Equation
The number N of intelligent communicative civilizations in our galaxy
can be estimated by the Drake equation (note the huge uncertainties!)
where
•R is the yearly rate at which stars form in the galaxy (1 yr-1)
•fp is the fraction of stars that possesses worlds (~0.5)
•n is the number of worlds with environment suitable for life (~4)
•fl is the fraction of worlds on which life actually develops (~0.5)
•fi is fraction of these worlds in which life gets intelligence (10-6-1)
•fc is fraction of intelligent life forms that develops culture capable
of interstellar communication (10-3-0.1)
•L is time that this culture devotes to communication (103-106 yr)
This deductive framework embeds some increasingly well-determined
numbers and some factors that are indeterminate. The elements in the
formalism are probably not independent, so it has limited utility.
N = R · fp · n · fe · fi · fc · L
Product ~1
(~determined)
Product 10-6-105
(indeterminate)
Thomas Wright (1750):
170,000,000 habitable
worlds in the galaxy.

89. Towards a New FrameworkDuration(y)
Habitability
1010
109
108
107
106
0 1
P (A | B) = n (AB) / n (B)
P (A | B) is probability of A, given B
n (AB) is # times both A and B occur
n (B) is # times B occurs
In general, P (A | B) ≠ P (B | A)
Bayes Theorem: P (B | A} = P (A | B) x P (B) / P (A)
Probability density f (A | θ), may be normal θ = (μ,σ2), or not
H = f (C,E,S | θ)
Chemistry is f (metallicity, world dist)
Energy is f (“solar” L, world M)
Stability is f (stellar ρ, world ε, debris)
Minimal (microbial) life
Maximal (intelligent) life
Number of “Living” Worlds
In galaxy: 108 In universe: 1016
(and, conservatively, with technology)
In galaxy: 102 ? In universe: 1010 ?

90. Communication

94. 0 1 2 3 4
10
12
14
16
18
20
0 1 2 3 4
10
12
14
16
18
20
300nm
500nm
700nm
log10P(W)
log10D(pc)
Optical SETI
MAGIC parameters:
Pulsed laser, 1ns, 20 kJ
Pulsed level power ~1011 W
230 m2 reflector area
Photon count, weak excess
↑ closest star Galactic ↑ Center

95. Soon, all PW pulsed lasers and
all Arecibos emitting, detected
out to 1kpc (spanning 108 stars)
So far, the search has met with
50 years of silence. But search
capacity increases exponentially

96. The Fermi Question
As originally phrased by Erico Fermi, it seems a
reasonable proposition that:
• Our civilization and technology is very young; life
forms with much more advanced technology could
have remarkable capabilities.
• A modest extrapolation of current technology
allows us mine asteroids or moons, and create
probes that could create replicas of themselves and
propagate through the galaxy.
• There are many likely sites for complex life, and
plenty of time for technology to develop, billions of
years before Earth formed.

97. They’ve Already Visited
Curiously, UFO sightings dominate in
rich Western countries, in July and in
August, and during geopolitical crisis
and activity in the US space program.

98. A Major Problem:
Science literacy is
low, around 10%,
and pop culture is
awash in all kinds
of pseudoscience,
magical thinking,
superstition, and
supernatural or
irrational belief
systems.

99. They don’t exist
They are very rare
They are unrecognizable
They are inscrutable
They don’t care
They created us
Responses to Fermi

100. Life as Computation

101. Origin of Life
Today
Would we be
surprised if life
beyond Earth: Doesn’t
exist
Has the
same
basis as
our life
Doesn’t
use DNA
Need not
use carbon
Could exist
without stars
Is unrecognizably
different from us
Doesn’t
use cells

102. Artificial Life
• Theoretical biology (exploring possible or potential biologies)
• Artificial, not unreal (new ways to meet the definition of life)
• Bottom up, not top down (generating complexity from simple parts)
• Synthesis, not analysis (the outcomes are not prescribed a priori)
• Leverages emergence (attributes like symbiosis are emergent)
• Role of computation (computation could be analog or literal)
Despite the fact that all known life is based on one form of
organic chemistry, it is worth asking whether or not known
mechanisms are the only ways to create life and intelligence.
This emerging and interdisciplinary field is characterized by:
A-life research (and its cousin, AI) have several agendas:
1. Modeling to gain a deeper understanding of biological (thought) processes
2. Simulation to understand the possible forms of biology (brain function)
3. Exploration of pure computation as a basis for life (intelligence)

105. • Randomness, with predictable macroscopic behavior.
• Solutions to differential equations (e.g. EM, QM)
• Transcendental and prime numbers.
• Turing machines (universal computers).
• Axiom systems beyond traditional mathematics.
• All of this is still true if: there is no grid, no fixed geometry
(networks), more than 2D, constraints instead of rules.
Repeated application
of simple rules leads to
patterns, randomness,
complexity. Cellular
automata generate:
© Scott Camazine
More than a Game

106. • Complexity increases dramatically with recursion/feedback.
• DNA base pair sequence is mostly random.
• Random mutation is unlikely to produce optimal organisms.
• Easy to misinterpret evolution or complexity (skins,shells).
• Simple programs readily lead to complexity (genetic
algorithms).
Computation and Evolution
Biological evolution is just one example of a wide
range of computationally equivalent possibilities
(none of these are at all deterministic)
Biology may even just be a stage in our evolution – witness
current and future merger of human/machines/computers.

108. “Never make predictions, especially about the future.”
Casey Stengel, Baseball Manager
(ENIAC, from 1944, weighed 30 tons, dimmed Philly when
it was running, and was a million times slower than a PC)
“I think there is a world market for maybe 5 computers”
Thomas Watson, IBM Chairman, 1943
“Computers in the future may weigh less than 1.5 tons”
Popular Mechanics Magazine, 1949
“There’s no reason anyone would want a home computer”
Ken Olsen, CEO, Digital Equipment, 1977

109. Futurology
106 105 104 103 100 10 Now 10 100 103 104 105 106
Years Ago Years Ahead
Now
Internet
Car, plane
Medicine
Agriculture
Tools
Humans
Genetics
Cyborgs
Star travel
??
????
??????

111. Simulation

113. ?
IS TO
AS IS TO
Gaming Analogy

114. The Simulation Argument
(due to Bostrom, Dainton)
In an argument based on probability theory and logic, one or more
of the following propositions must be true:
1. The chances that a species at our level of development can avoid
going extinct before technological maturity are negligibly small.
2. Almost no technologically mature civilizations are interested in
running simulations of minds like ours.
3. You are almost certainly in a simulation.

115. • Simulation Hypothesis: for every non-virtual early 21st
century human life there are many more subjectively
indistinguishable (or broadly similar) virtual lives. The
argument assumes substrate independence, or non-
carbon based computational forms of life.
REAL VIRTUAL

116. Possibility 1 is gloomy but might be true. If increasingly advanced technologies are
increasingly dangerous, we and others may destroy ourselves before we reach
maturity.
Possibility 2 requires convergence among all sufficiently advanced civilizations. This
seems implausible on the face of it.
Suppose 1 is false. Then a significant fraction of all species at our level of
development become technologically mature.
Suppose, in addition, 2 is false. Then these mature civilizations will use some
significant fraction of their resources to run computer simulations of minds like ours.
The resources required are not large.
If 1 and 2 are false, there will be an astronomically huge number of simulated minds
like ours, vastly more than the number of organic brains. By the principle of
mediocrity, you probably have a simulated mind.
If 1 and 2 are false, you must accept 3, the Simulation Hypothesis. It is not logically
coherent to reject all three propositions.
There is no reason anyone living in a simulation would be able to detect that fact,
unless the simulators permitted it.

117. 100 billion humans x 50 years/human x 3 million secs per year
x 1014 – 1017 ops per brain per second
Typical human brain:
operations per second
= 1014-1017
Ops required for 1
ancestor simulation =
1032-25
(assumption: humankind will be
superseded in a few centuries)

118. 10,000 processors
working for a year
Around
2050Quantum computers should continue
the exponential trend of Moore’s law
TECHNOLOGICAL MATURITY?

119. R
Everyone believes their own lives to be real, non-virtual…
I’m
real!
I’m
real!
I’m
real!
I’m
real!
I’m
real!
I’m
real!
I’m
real!
I’m
real!
I’m
real!
R
• Your conviction that your life is non-virtual is no
better founded than anybody else’s.
• So, if the Simulation Hypothesis is true, the odds of
your life being non-virtual are low
I’M REAL

120. Simulation Argument: Conclusion
‘My life
is real’
High probability
Low probability
‘SH is
true’
High probability
Low probability
Probability assignments (not to scale)

121. Another Copernican Shift
virtual
real
sum total of conscious lives

122. ?
IS TO
AS IS TO
Evolution Analogy

123. • Nicolai Kardashev’s classification of civilizations:
Type 0: not in complete control of planet’s energy
Chemical propulsion, solar sails
Type I: harnesses energy output of an entire planet (1011 W)
Nuclear propulsion, laser sails
Type II: harnesses entire output of their host star (1026 W)
Antimatter drives
Type III: colonizes and harnesses output of entire galaxy (1037 W)
???
• To which could be added (with implications for SETI):
Type Ib: non-electromagnetic signals with low opacity
Neutrino beams, dark matter beams
Type IIb: orchestrated stellar cataclysms (visible across universe)
Supernovae, gamma ray bursts
Type IIIb: signals from manipulation of space-time
gravity waves, baby universes
Civilizations: Speculation