astronomy - state of the art - life in the universe
DESCRIPTION
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 SETITRANSCRIPT
Science is Seeing
Biology
Life has Order
Life uses Energy
(c) Response to the environment
(a) Order
(d) Regulation
(g) Reproduction (f) Growth and development
(b) Evolutionary adaptation
(e) Energy processing
Properties of Life
1 The biosphere
Hierarchy From biosphere…
…to organisms
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.
• 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…?
Unity of Life
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.
Molecular Tree of Life
• 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.
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.
RNA
phenotype
replication
expression
The Central Dogma
…greatly simplified
DNA
RNA
proteins
Structure and function
of organism
replication
processing
processing
DNA
RNA
proteins
Structure and function
of organism
natural
selection
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.
The Genetic Code
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
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
In biology, there is metabolic complexity.
In biology, there is structural complexity.
Extremophiles
Extreme Dryness
Extreme Cold
Extreme Heat
Extreme Radiation
Extreme Toxicity
Extreme Isolation
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.
Exobiology
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.
Evidence that ingredients for life
are widely available in time and space
Evidence that planet and moon
habitable locations are abundant
Pale Blue Dot
Earth, backlit against a gossamer ring of Saturn, is almost certainly not a unique host for biology.
What might be, but isn’t
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…)
Isn’t
Is
Imaginable
Possible
WHAT IS AND ISN’T
Using Carbon
Using Planets
EXOBIOLOGY
Recognizable Life
Unrecognizable Life
DNA-Based
Origin of Life
• 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.
Evolution
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
6H2O + 6CO2 → C6H12O6 + 6O2
Photosynthesis
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!
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.
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.
Evolution is contingent. There are so many branching points and random influences to evolution that another set of experiments might give very different outcomes.
Pollard 3 Plants animals fungi
Plants Fungi
Animals
Evolution of all animals in terms of DNA
Science is Seeing
Intelligence
Termite mounds are engineering marvels, higher than our best skyscrapers, scaled to organism size. In their construction five temp control mechanisms.
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?
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).
Are we “off the chart” smart?
No natural enemies
Large brains
Complex language
Social animals
Mate for life
Bombs, Internet, Cars
ORCAS HUMANS
× ×
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?
Apes
A recent surge in evolution vaulted us to the top of the tree in terms of brain size.
Weird Life
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
High Level Architecture Not limited by mutation & selection; Evo-Devo toolkit: genes, organisms
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
Bacterial Communities Evolution timescale is very rapid; information density ~ 1012 bits/cm3
Companionship
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
0 4 8 Gyr
10
20
30 ly
+108 more
Earth
?
?
?
Green = stars with planets
Blue = stars with Earths
The couple of hundred solar systems found so far, nearby, under 30 light years, mostly.
A billion habitable worlds in our galaxy, and 100 billion galaxies…
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.
Drake Equation
DRAKE EQUATION
Stars in MW
Stars in Universe
With Sentience
With Earths
With Life
DRAKE EQUATION
Stars in MW
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.
Towards a New Framework D
ura
tio
n (
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 ?
Communication
0 1 2 3 410
12
14
16
18
20
0 1 2 3 4
10
12
14
16
18
20
300nm
500nm
700nm
log
10P
(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
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
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.
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.
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.
They don’t exist
They are very rare
They are unrecognizable
They are inscrutable
They don’t care
They created us
Responses to Fermi
Life as Computation
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
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)
• 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
• 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.
“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
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
??
????
??????
Simulation
?
IS TO
AS IS TO
Gaming Analogy
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.
• 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
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.
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)
10,000 processors working for a year
Around 2050 Quantum computers should continue
the exponential trend of Moore’s law
TECHNOLOGICAL MATURITY?
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
Simulation Argument: Conclusion
‘My life is real’
High probability
Low probability
‘SH is true’
High probability
Low probability
Probability assignments (not to scale)
Another Copernican Shift
virtual
real
sum total of conscious lives
?
IS TO
AS IS TO
Evolution Analogy
• 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