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Home , Active SETI, Allen Telescope Array, Breakthrough Starshot, Galactic habitable zone, Great Filter, Mediocrity principle

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Orin Harris and Greg Anderson Department of Physics & Northeastern Illinois University

Spring 2021

c 2012-2021 G. Anderson., O. Harris Universe: Past, Present & Future – slide 1 / 95 Overview

Dating Rocks Life on How Did Life Arise? Life in the Life Around Other SETI Review

c 2012-2021 G. Anderson., O. Harris Universe: Past, Present & Future – slide 2 / 95 Dating Rocks Zircon Dating Sedimentary Grand Canyon

Life on Earth How Did Life Arise? Life in the Solar System Life Around Dating Rocks Other Stars Interstellar Travel

SETI

Review

c 2012-2021 G. Anderson., O. Harris Universe: Past, Present & Future – slide 3 / 95 Zircon Dating

Zircon, (ZrSiO4), minerals incorporate trace amounts of but reject lead.

Naturally occuring uranium: • U-238: 99.27% • U-235: 0.72% Decay chains: • 238U −→ 206Pb, τ =4.47 Gyrs. • 235U −→ 207Pb, τ = 704 Myrs. 1956, Clair Camron Patterson dated the Canyon Diablo meteorite: τ =4.55 Gyrs.

c 2012-2021 G. Anderson., O. Harris Universe: Past, Present & Future – slide 4 / 95 Dating Sedimentary Rocks

• Relative ages: Deeper layers were deposited earlier • Absolute ages: Decay of radioactive isotopes

old (deposited last)

oldest (depositedolder first)

c 2012-2021 G. Anderson., O. Harris Universe: Past, Present & Future – slide 5 / 95 Grand Canyon: Earth History from 200 million - 2 billion yrs ago. Dating Rocks

Life on Earth Earth History Timeline Late Heavy Bombardment Hadean Shark Bay Stromatolites Cyanobacteria Q: Earliest Fossils? Life on Earth O2 History Q: Life on Earth How Did Life Arise? Life in the Solar System Life Around Other Stars Interstellar Travel

SETI

Review

c 2012-2021 G. Anderson., O. Harris Universe: Past, Present & Future – slide 7 / 95 Earth History

Earth Forms (4.6 Ga) in Impact Forms (4.5 Ga) Late Heavy Bombardment Isotopic Evidence (3.8 Ga) Stromatolites (3.45 Ga)

Hadean Archean Proterozoic Phanerozoic 5 4 3 2 1 0 Billions of ago

c 2012-2021 G. Anderson., O. Harris Universe: Past, Present & Future – slide 8 / 95 Earth History

Earth Forms (4.6 Ga) Oxygen in Atmosphere Impact Forms Moon (4.5 Ga) Late Heavy Bombardment Isotopic Evidence (3.8 Ga) Stromatolites (3.45 Ga)

Hadean Archean Proterozoic Phanerozoic 5 4 3 2 1 0 Billions of years ago

Paleozoic Mesozoic Cenozoic

c OSD C P TR J K Pg N 550 450 350 250 150 50 Millions of years ago c 2012-2021 G. Anderson., O. Harris Universe: Past, Present & Future – slide 8 / 95 Timeline for Early Life on Earth

Life arose on Earth soon after the end of late heavy bombardment. • 4.6 billion years ago (Ga) - earth forms • 4.2, 4.4 Ga - evidence of oceans (detrital zircon) • 4.1–3.8 (3.85-3.82) Ga – late heavy bombardment • 3.8 Ga – Isotopic % BIF evidence from Greenland • 3.5, 2.7 Ga – Stromatolites and other fossils. • 2.3 Ga – The great oxygenation event • 2.0 Ga – of Cells with Nuclei () • 1.2 Ga – Evolution of complex multicellular organisms • 0.5 Ga –

c 2012-2021 G. Anderson., O. Harris Universe: Past, Present & Future – slide 9 / 95

Hadean Earth c Don Dixon Fossil Stromatolites Modern stromatolites: Shark’s Bay Cyanobacteria “blue-green algae”

• The fossil record for early life (Stromatolites) goes back 3.5 Gyrs (disputed) [2.7 Gyrs (undisputed). • Early created a great oxygenation event 2.4 Gyrs ago.

• Cyanobacteria obtain their energy through photosynthesis, and pro- duce oxygen as a byproduct. • By releasing oxygen into the atmo- sphere, Cyanobacteria allowed for the evolution of more complex life- forms on Earth.

c 2012-2021G.Anderson.,O.Harris Universe:Past,Present&Future – slide 13 / 95 Q: Earliest Fossils?

According to fossil evidence, how far back in time did life on Earth exist? A) About 65 million years B) About 545 million years C) About 1.0 billion years D) > 2.7–3.5 billion years or more

c 2012-2021G.Anderson.,O.Harris Universe:Past,Present&Future – slide 14 / 95 Q: Earliest Fossils?

According to fossil evidence, how far back in time did life on Earth exist? A) About 65 million years B) About 545 million years C) About 1.0 billion years D)

Fossil stromatolites in Australia are 3.5 Ga.

c 2012-2021G.Anderson.,O.Harris Universe:Past,Present&Future – slide 14 / 95 History of Atmospheric Oxygen

• Before 2.3 Ga levels of atmospheric oxygen were to low to sustain aerobic life. • By 0.5–0.6 Ga, atmospheric oxygen was plentiful enough to support complex multicellular life.

c 2012-2021G.Anderson.,O.Harris Universe:Past,Present&Future – slide 15 / 95 Q: Life on Earth

You have a time machine with a dial that you can spin to send you randomly to any time in Earth’s history. If you spin the dial, travel through time, and walk out, what is most likely to happen to you? A) You’ll be eaten by . B) You’ll suffocate because you’ll be unable to breathe the air. C) You’ll be consumed by toxic bacteria. D) Nothing: you’ll probably be just fine.

c 2012-2021G.Anderson.,O.Harris Universe:Past,Present&Future – slide 16 / 95 Q: Life on Earth

You have a time machine with a dial that you can spin to send you randomly to any time in Earth’s history. If you spin the dial, travel through time, and walk out, what is most likely to happen to you? A) You’ll be eaten by dinosaurs. B) You’ll suffocate because you’ll be unable to breathe the air. C) You’ll be consumed by toxic bacteria. D) Nothing: you’ll probably be just fine.

c 2012-2021G.Anderson.,O.Harris Universe:Past,Present&Future – slide 16 / 95 Dating Rocks

Life on Earth How Did Life Arise? Origin of Life on Earth Phylogenetic tree Hydrothermal Vents How did life arise? Miller-Urey How Did Life Arise? Experiment (1953) RNA World Hypothesis pre-cells DNA DNA Strand Evolution Natural Selection Peppered Moth Q: Natural Selection? Life in the Solar System Life Around Other Stars Interstellar Travel c 2012-2021G.Anderson.,O.Harris Universe:Past,Present&Future – slide 17 / 95 Origin of Life on Earth

Last Universal Common Ancestor (LUCA): • All life on Earth shares a common ancestry. • We may never know exactly how the first organism arose, but laboratory experiments suggest plausible scenarios. Possibilities include: • tidepools • hotsprings • deep sea hydrothermal vents

c 2012-2021G.Anderson.,O.Harris Universe:Past,Present&Future – slide 18 / 95

Hydrothermal Vents

Some lines of evidence, including DNA sequencing, suggest the first life earth may have been an which lived in extremely high temperatures near deep sea hydrothermal vents.

c 2012-2021G.Anderson.,O.Harris Universe:Past,Present&Future – slide 20 / 95 How did life arise?

1. Simple organic form 2. Replicating molecules (RNA?) evolve and begin to undergo natural selection. 3. Replicating molecules become enclosed within membranes. 4. Some cells evolve modern metabolic processes. 5. Multicellular life evolves

c 2012-2021G.Anderson.,O.Harris Universe:Past,Present&Future – slide 21 / 95 Miller-Urey Experiment (1953)

Stanley Miller & Harold Urey’s U. Chicago experiment to simulate conditions on early Earth:

Ingredients for Primor- dial Soup:

• Water (H2O)

• Methane (CH4)

• Ammonia (NH3)

• (H2)

Shocked, heated cooled, ...produced Amino acids: the building blocks for protiens. Modern versions of this experiment have produced even more builing blocks for life.

c 2012-2021G.Anderson.,O.Harris Universe:Past,Present&Future – slide 22 / 95 RNA World Hypothesis

The first life on earth used RNA to store genetic information and to catalyze chemical reactions. • Discovery of Ribozymes - RNA can catalyze chemical reactions. • Formation of long RNA strands may catalyzed by clays, salty ice water

c 2012-2021G.Anderson.,O.Harris Universe:Past,Present&Future – slide 23 / 95 pre-cells

Clay minerals catalyze formation of membranes around RNA. c 2012-2021G.Anderson.,O.Harris Universe:Past,Present&Future – slide 24 / 95 Deoxyribonucleic acid (DNA)

Molecule that encodes the genetic instructions for all living cells.

Double helix composed of the nucleotides. Nu- cleotide = nucleobase + deoxyribose sugar + phosphate group. Nucleobases:

• Guanine (G): C5H5N5O

• Adenine (A): C5H5N5

• Thymine (T): C5H6N2O2

• Cytosine (C): C4H5N3O

c 2012-2021G.Anderson.,O.Harris Universe:Past,Present&Future – slide 25 / 95

Evolution

Evolution: The change in the inherited characteristics of biological populations over successive generations.”

• All life on earth has decended a common ancestor. • The fossil record shows evolution has occurred through time. • ’s theory of natural selection tells us how this evolution occurs. • This theory was supported by the discovery of DNA: our genetic information is stored in DNA, evolution proceeds through mutations.

c 2012-2021G.Anderson.,O.Harris Universe:Past,Present&Future – slide 27 / 95 Natural Selection

Charles Darwin (1809–1882), The Origin of Species (1859). Natural Selection: • Variations exists within all populations of organisms. • More offspring are produced than can possibly survive. • Individuals with certain traits are more likely to reproduce. • Over time the population evolves.

c 2012-2021G.Anderson.,O.Harris Universe:Past,Present&Future – slide 28 / 95 Evolution of the Peppered Moth

Peppered Moth (Biston betularia): Studied for 200 years. Two morphs: typica (light) vs carbonaria (dark). In the UK, over time mostly light −→ mostly dark −→ mostly light. c 2012-2021G.Anderson.,O.Harris Universe:Past,Present&Future – slide 29 / 95 Q: Natural Selection?

Which of the following best describes natural selection? A) It is the idea that organisms with genetic traits that improve their ability to reproduce are more likely to pass those traits on to future generations. B) It is the idea that the strong survive and the weak die off. C) It is a guess made by scientists about how life develops, but it has no hard evidence to support it. D) It is the idea that organisms naturally increase in complexity and with time. c 2012-2021G.Anderson.,O.Harris Universe:Past,Present&Future – slide 30 / 95 Q: Natural Selection?

Which of the following best describes natural selection? A) It is the idea that organisms with genetic traits that improve their ability to reproduce are more likely to pass those traits on to future generations. B) It is the idea that the strong survive and the weak die off. C) It is a guess made by scientists about how life develops, but it has no hard evidence to support it. D) It is the idea that organisms naturally increase in c 2012-2021G.Anderson.,O.Harriscomplexity and intelligence with Universe:Past,Present&F time. uture – slide 30 / 95 Dating Rocks

Life on Earth How Did Life Arise? Life in the Solar System Necessities ? Martian Water History Life in the Solar System Water on Mars Flows Mars Spirit Life on Jovian ? Life on Europa? & Callisto Titan Titan Lakes Cassini: Methane Lakes on Titan Cassini: Geologic diversity c 2012-2021G.Anderson.,O.Harris Universe:Past,Present&Future – slide 31 / 95 Summary Necessities for Life

• Energy source – sunlight, chemical reactions, & other internal heat • A liquid medium – water, ...methane? • Essential elements/nutrients – C, H, O, N, P, ...

c 2012-2021G.Anderson.,O.Harris Universe:Past,Present&Future – slide 32 / 95 NASA: Mars Life on Mars?

Continuing searches for evidence of past/present life on Mars use both telescopes and missions that have landed on Mars. • Mars had abundant liquid water in the distant past. • Mars still has subsurface water ice – perhaps near sources of volcanic heat. Life near the surface today is unlikely due to cold and extreme radiation.

c 2012-2021G.Anderson.,O.Harris Universe:Past,Present&Future – slide 34 / 95

NASA/JPL: Water on Mars Warm Season Flows

NASA/JPL: Warm Season Flows, Salty Liquid Brine?

c 2012-2021G.Anderson.,O.Harris Universe:Past,Present&Future – slide 37 / 95 Warm Season Flows

NASA/JPL: Warm Season Flows, Salty Liquid Brine?

c 2012-2021G.Anderson.,O.Harris Universe:Past,Present&Future – slide 37 / 95 Warm Season Flows

NASA/JPL: Warm Season Flows, Salty Liquid Brine?

c 2012-2021G.Anderson.,O.Harris Universe:Past,Present&Future – slide 37 / 95 Warm Season Flows

NASA/JPL: Warm Season Flows, Salty Liquid Brine?

c 2012-2021G.Anderson.,O.Harris Universe:Past,Present&Future – slide 37 / 95 Warm Season Flows

NASA/JPL: Warm Season Flows, Salty Liquid Brine?

c 2012-2021G.Anderson.,O.Harris Universe:Past,Present&Future – slide 37 / 95 Warm Season Flows

NASA/JPL: Warm Season Flows, Salty Liquid Brine?

c 2012-2021G.Anderson.,O.Harris Universe:Past,Present&Future – slide 37 / 95 NASA’s Spirit & Opportunity Rovers: mineral evidence of past liquid water on Mars. Life on Jovian Moons?

Could there be life on Europa or other Jovian moons? Jupiter alone has three potential homes for life.

Ganymede Callisto Io Europa

c 2012-2021G.Anderson.,O.Harris Universe:Past,Present&Future – slide 39 / 95 Europa Life on Europa?

• Surface mostly solid water ice. • Hypothesis: ocean of liquid water below the surface • Good place to look for life: liquid water + energy from tidal heat- ing.

c 2012-2021G.Anderson.,O.Harris Universe:Past,Present&Future – slide 41 / 95 Ganymede & Callisto

Evidence for subsurface oceans on Ganymede, Callisto, but less tidal heating energy available. Did life find a way?

c 2012-2021G.Anderson.,O.Harris Universe:Past,Present&Future – slide 42 / 95 Saturn’s Enceladus Titan Titan Titan: Liquid hydrocarbons. Titan: Liquid hydrocarbons.

Summary: Life in the Solar System

• Could there be life on Mars? - Evidence for liquid water in past suggests that life was once possible on Mars. • Could there be life on Europa or other Jovian moons? - Jovian moons are cold, but some show evidence for subsurface water and other liquids.

c 2012-2021G.Anderson.,O.Harris Universe:Past,Present&Future – slide 49 / 95 Q: Life in the Solar System?

After Mars, the next most likely candidates for life in the solar system are A) The of the Jovian . B) The large moons of the Jovian planets. C) The largest asteroids. D) in the Kuiper-belt.

c 2012-2021G.Anderson.,O.Harris Universe:Past,Present&Future – slide 50 / 95 Dating Rocks

Life on Earth How Did Life Arise? Life in the Solar System Life Around Other Stars Anthropic Life Around Other Stars Principles Suitable Systems NASA Kepler Kepler Candidates TESS Habitable Identification Steps Planetary Temperatures Circumstellar Habitable Zones Circumstellar Habitable Zones c 2012-2021G.Anderson.,O.Harris Universe:Past,Present&Future – slide 51 / 95 HEC Mediocrity Principle

Mediocrity principle: ∼ (): are not privileged observers of the universe. – Hermann Bondi (1948) • We should assume ourselves to be typical in any class that we belong to, unless there is some evidence to the contrary (Garriga and Vilenkin 2008). • Vilenkin 2011 Whitrow Lecture

c 2012-2021G.Anderson.,O.Harris Universe:Past,Present&Future – slide 52 / 95 Anthropic Principles

• : Even if intelligent life only occurs on only one planet in a trillion, those are the planets that observers will find themselves on. Thus, our location in the universe is necessarily privileged. • Survivor bias: logical errors made by focusing on civilizaton/life/planets that made it past some selection process and overlooking those that did not.

c 2012-2021G.Anderson.,O.Harris Universe:Past,Present&Future – slide 53 / 95 Galactic Habitable Zone

c 2012-2021G.Anderson.,O.Harris Universe:Past,Present&Future – slide 54 / 95 Suitable Star Systems

Constraints: • Old enough to allow time for evolution (rules out high-mass stars - 1%) • Stable orbits (might rule out binary/multiple star systems - 50%) • Exclude red dwarfs? () • Size of habitable zone: region in which a planet of the right size could have liquid water on its surface. Billions of stars in the seem at least to offer the possibility of habitable worlds.

c 2012-2021G.Anderson.,O.Harris Universe:Past,Present&Future – slide 55 / 95

TESS

Transiting Survey Satellite (TESS) • Launched April 18, 2018. • Two- survey of over 200,000 stars. • As of Aug 2020: identified 1835 candidate exoplanets, analysis ongoing

c 2012-2021G.Anderson.,O.Harris Universe:Past,Present&Future – slide 58 / 95 Habitable Exoplanets

• A potentially habitable exoplanet is an extra-solar planet that might support life. e.g. liquid water. – It does not necessarily have life. • Operational definition: a planet with the right size and orbit to support liquid surface water. • Habitable Exoplanets Catalog

c 2012-2021G.Anderson.,O.Harris Universe:Past,Present&Future – slide 59 / 95 Identification Steps

Steps for Identifying Potentialy Habitable Worlds

1. Physical indicators: orbital distance, size, temperature, ... 2. Chemical indicators: liquid water, dioxide, ... 3. Biological indicators: proxies for life – oxygen, methane, ...

c 2012-2021G.Anderson.,O.Harris Universe:Past,Present&Future – slide 60 / 95 Planetary Temperatures

800 b b Blackbody 700 b With Albedo b Observed 600

500 b b 400 100◦ C b “Goldilocks zone” (liquid water at 1atm) b 300 b ◦ b 0 C

Temperature (K) b b 200 b

b b b 100 b b b b 0 ' ♀ ♁ ♂ X Y Z [ Me V E M J S U N

c 2012-2021G.Anderson.,O.Harris Universe:Past,Present&Future – slide 61 / 95 Circumstellar Habitable Zones

M e rc ur y

Venus Earth

Mars Solar System

c 2012-2021G.Anderson.,O.Harris Universe:Past,Present&Future – slide 62 / 95 Circumstellar Habitable Zones

c 2012-2021G.Anderson.,O.Harris Universe:Past,Present&Future – slide 63 / 95 HEC

c 2012-2021G.Anderson.,O.Harris Universe:Past,Present&Future – slide 64 / 95 (0 ≤ ESI ≤ 1)

Not Earth Like Mars Earth Kepler-438b

0 0.2 0.4 0.6 0.8 1.0 KOI-433.02 m

n x − x wi/n ESI = 1 − i io  xi + xio  Yi=1

Property Referencevalue xio weight wi Radius r⊕ 0.57 Density ρ⊕ 1.07 Escape velocity v⊕ 0.70 Surface Temp 288 K 5.58

There is not a scientific concensus advocating use of the ESI.

c 2012-2021G.Anderson.,O.Harris Universe:Past,Present&Future – slide 65 / 95

Kepler-186f

The first known Earth-size exoplanet to lie within a habitable zone. star Kepler-186. d = 490 ly. c 2012-2021G.Anderson.,O.Harris Universe:Past,Present&Future – slide 67 / 95

Dating Rocks

Life on Earth How Did Life Arise? Life in the Solar System Life Around Other Stars Interstellar Travel Voyager’s Interstellar Travel Golden Record Pioneer Voyager Distant Spacecraft Daedalus Starshot

SETI

Review

c 2012-2021G.Anderson.,O.Harris Universe:Past,Present&Future – slide 70 / 95 Voyager’s Golden Record

Distant Spacecraft

NASA Launch Distance Current Probe Date in2014 Speed Pioneer 10 1972 112 AU 12 km/s Pioneer 11 1973 91 AU 11 km/s Voyager 1 1977 130 AU 17 km/s Voyager 2 1977 107 AU 15 km/s v = 17km/s ≈ 5.6 × 10−5c At the speed of Voyager 1 At v =0.1c • 1 light year ∼ 20, 000 years. • one light year ∼ 10 years. • α Cen ∼ 100, 000 years. • nearest stars ∼ decades. • ↔ Milky Way ∼ 2 Gyrs. • ↔ Milky Way ∼ 1 Myrs.

c 2012-2021G.Anderson.,O.Harris Universe:Past,Present&Future – slide 73 / 95 Art: Spacecraft Starshot

Breakthrough Starshot: R&D proposal for proof-of-concept light spacecraft capable of traveling to . • Light-driven nano-spacecraft • Speed 15% – 20% lightspeed. • Travel time 20–30 years • Starshot

c 2012-2021G.Anderson.,O.Harris Universe:Past,Present&Future – slide 75 / 95 Dating Rocks

Life on Earth How Did Life Arise? Life in the Solar System Life Around Other Stars Interstellar Travel Are We Alone? SETI aliens Watterson SETI Allen Array Just an Estimate EQ Fermi’s Paradox Q: Q: Galactic xkcd Possible Solutions Great c 2012-2021G.Anderson.,O.Harris Filters Universe:Past,Present&Future – slide 76 / 95 (Hard Steps)

SETI

The Search for Extraterrestrial Intelligence • Passive SETI (SETI) – the search for extraterrestrial intelligence. – Ongoing: , SERENDIP, ... • Active SETI aka METI – attempts to send messages to intelligent life. METI: Messaging to ExtraTerrestrial Intelligence. e.g., signals, physical messages: the , ....

c 2012-2021G.Anderson.,O.Harris Universe:Past,Present&Future – slide 79 / 95 Arecibo Message

FM radio broadcast from Arecibo in 1974. 73 × 23 binary digits. Beamed for three minutes towards M13, 25,000 light years away.

c 2012-2021G.Anderson.,O.Harris Universe:Past,Present&Future – slide 80 / 95 SETI: Allen Telescope Array Frank Drake Drake Equation

Number of communicating civilizations in our :

N = R∗fpnefℓfifcL

R∗ = rate of in Milky Way.

fp = fraction of stars with planets.

ne = number of planets that could support life per star with planets.

fℓ = fraction of those planets where life develops.

fi = fraction of planets with life that develop intelligent civilizations.

fc = fraction of civilizations that develop . L = length of time for which civilizations release detectable signals.

c 2012-2021G.Anderson.,O.Harris Universe:Past,Present&Future – slide 83 / 95 Just an Estimate

Estimates based on available data:

• R∗ ≈ 7/year (NASA & ESA)

• fp ≈ 1 (microlensing surveys)

• fp · ne ≈ 0.4

• fℓ ≈ 1?? (EARLY life on Earth)

• fi · fc ≪ 1 (we evolved only recently) • L & 420 years? L N ≈ 7 ∗ 0.4(fi · fc)L = 1176(fi · fc) =? 420

c 2012-2021G.Anderson.,O.Harris Universe:Past,Present&Future – slide 84 / 95 Mass vs Body Size

4 b b 10 3 b 2/ b

b b b b b b b b b b b 3 b b b (Body Mass) b 10 b b ∝ b b b b bb b b b bb b b b b

b b b b Brain Mass b b 2 b b b 10 b b b b b b b b b b b b b b b b b b b 1 b b b b b b b b 10 b b b bb b b b b b b b b b b b b b b 0 b

Brain Mass (g) 10 b b b b hominids 10−1 b H sapiens b b other 10−2 10−3 10−1 101 103 105 Body Mass (kg)

c 2012-2021G.Anderson.,O.Harris Universe:Past,Present&Future – slide 85 / 95 Enrico Fermi’s Paradox

Where are they? • Our is young. There are billions of older stars. • The size and age of the uni- verse/galaxy suggest techno- logicially advanced civiliza- tions should exist. • Colonization of the galaxy should only take tens of mil- lions of years.

c 2012-2021G.Anderson.,O.Harris Universe:Past,Present&Future – slide 86 / 95 Q: Fermi Paradox

What is the Fermi Paradox?

A) Galactic civilizations, like ours, seem forbidden by the laws of physics.

B) Interstellar travel is possible yet would take an infinite amount of time because of relativistic time-dilation.

C) We would be unable to detect an Earth-like planet even at a distance of a few light years.

D) Reasonable assumptions predict that a galactic should have already arisen in the Milky Way. Yet, we have absolutely no evidence for it.

E) The Drake equation predicts that there should be no intelligent life in the Milky Way. Yet, we exist.

c 2012-2021G.Anderson.,O.Harris Universe:Past,Present&Future – slide 87 / 95 Q: Fermi Paradox

What is the Fermi Paradox?

A) Galactic civilizations, like ours, seem forbidden by the laws of physics.

B) Interstellar travel is possible yet would take an infinite amount of time because of relativistic time-dilation.

C) We would be unable to detect an Earth-like planet even at a distance of a few light years.

D) Reasonable assumptions predict that a galactic civilization should have already arisen in the Milky Way. Yet, we have absolutely no evidence for it.

E) The Drake equation predicts that there should be no intelligent life in the Milky Way. Yet, we exist.

c 2012-2021G.Anderson.,O.Harris Universe:Past,Present&Future – slide 87 / 95 Q: Galactic Civilizations

If there are other civilizations at present in the Milky Way Galaxy, which statement is almost undoubtedly true?

A) They are far more technologically advanced than we are.

B) They are anatomically much like us, with two arms, two legs, two eyes, and two ears.

C) They have social structures that are completely different from our own; for example, different types of ”family” units, and so on.

D) For fun, they enjoy ”buzzing” to Earth and temporarily abducting people, showing a clear preference for people located in less-developed rural areas.

c 2012-2021G.Anderson.,O.Harris Universe:Past,Present&Future – slide 88 / 95 Q: Galactic Civilizations

If there are other civilizations at present in the Milky Way Galaxy, which statement is almost undoubtedly true?

A) They are far more technologically advanced than we are.

B) They are anatomically much like us, with two arms, two legs, two eyes, and two ears.

C) They have social structures that are completely different from our own; for example, different types of ”family” units, and so on.

D) For fun, they enjoy ”buzzing” to Earth and temporarily abducting people, showing a clear preference for people located in less-developed rural areas.

c 2012-2021G.Anderson.,O.Harris Universe:Past,Present&Future – slide 88 / 95

Possible Solutions

• N > 1:Aliens exist, there IS a galactic civilization – They are sending signals, but we don’t know how to listen. – They have no desire to communicate. – Its dangerous to communicate – The

• N ≪ 1: Hypothesis, We are alone. – Intelligent tool making life rarely evolves. – Advanced civilizations destroy themselves on short timescales. c 2012-2021G.Anderson.,O.Harris Universe:Past,Present&Future – slide 90 / 95 Great Filters (Hard Steps)

Cyanobacteria Combigenesis Civilization Biogenesis Eukaryotes Metazoans(+Superweapons)

dP dt

−5 −4 −3 −2 −1 0 1 Billions of Years (Ga)

Brandon Carter: http://arXiv.org/abs/0711.1985v1

r−1 n−r ˙ n! t (τe − t) P (r)= n (r − 1)!(n − r)!τe

c 2012-2021G.Anderson.,O.Harris Universe:Past,Present&Future – slide 91 / 95 Further Study

• Patterson’s Paper • International Commission on Stratigraphy (ICS) • Early Earth (Elements Magazine) • Exploring Origins (Boston Museum of ) • SETI, SETI at Home • The Drake Equation • Drake Equation Calculator • The Eerie Silence: Renewing Our Search for Alien Intelligence, . • Five or Six Step Evolution, B. Carter. • The

c 2012-2021G.Anderson.,O.Harris Universe:Past,Present&Future – slide 92 / 95 Dating Rocks

Life on Earth How Did Life Arise? Life in the Solar System Life Around Other Stars Interstellar Travel Review SETI

Review Review I Review II

c 2012-2021G.Anderson.,O.Harris Universe:Past,Present&Future – slide 93 / 95 Review I

• How old is the Earth? • Where might life have first evolved on Earth? • When did life appear on Earth? • How old are the oldest fossils? • When did oxygen first appear in Earth’s atmosphere? • What was the Cambrian explosion. • What is evolution? How does natural selection work.

c 2012-2021G.Anderson.,O.Harris Universe:Past,Present&Future – slide 94 / 95 Review II

• Other than Earth, where might we find life in our solar system? • Are we more likely to find life on a planet orbiting a big star or a small star? • What is an operational definition of a habitable zone? • Have we found exoplanets in habitable zones? • What is the Drake equation? • What is the Fermi paradox? • What are some solutions to the Fermi paradox.

c 2012-2021G.Anderson.,O.Harris Universe:Past,Present&Future – slide 95 / 95