A1199Are We Alone?

The Search for Life in the UniverseSummer 2019

Instructor: Shami Chatterjee

Web Page: http://www.astro.cornell.edu/academics/courses/astro1199/

Presentations and Final Paper – please work on them.Now: Biomarkers, technomarkers, SETI

Principles and ParadoxCopernican principle

• We find ourselves on an ordinary planet around an ordinary star in an ordinary galaxy.

• AKA the assumption of mediocrity (we’re mediocre & there must be lots more like us).

Anthropic principle• The universe necessarily has properties that allow

complex beings like ourselves and life generally to have evolved.

• Is the universe ordinary?Fermi Paradox

• Given CP + AP, if N is large, where is everybody?

Drake Equation

N = R* � fs � Np� fHZ � fl � fit � L � [fother] R* = Star formation rate (per yr in the Galaxy).fs = Fraction that are Sun-like (F,G,K).Np = Number of planets per star (on average).fHZ = Fraction that are in the habitable zone.fl = Fraction that have life.fit = Fraction that have intelligence/technology.L = Longevity of intelligence/technology phase (yr).[ fother = Other requirements (tectonics, Jupiter, etc.)]

The Most Optimistic CaseN ≈ L

L = average longevity of a civilization in years.Optimism about L implies large N.

What can we say about the average L based on how we view L for ourselves?

Rare Earth: N ≈ 1 or a few.

What do we look for?Reciprocity: what do we radiate?

Radio:Typical: detectable to ~ few pc.Strongest: planetary radar ~1 kpc.

Optical/IR:Typical: nil. Pulsed IR lasers: ~ few x 10 pc.

g-rays:1 Megaton: ~ 1 AU with e.g. the Fermi telescope.Gamma-ray Large Areas Space Telescope = Fermi Gamma-ray Observatory

False Alarms in Detecting Life Elsewhere

• Canals on Mars.• Claimed bacterial remains in Martian meteorite.

• Meteorite collected on Antarctic glacier.• Gaseous content consistent with Mars’ atmosphere.• Microscopic features now thought to be natural

geochemical signatures, not from bacteria.• Radio sources that have “artificial” properties.

• CTA102– Early days of quasars = active galactic nuclei.– Sinusoidal variations interpreted as a beacon.

• Pulsars (radio pulses).

Rationale for Optical/IR SETI• Pulsed lasers distinguishable from host star with

reasonable power (nanosecond pulses).

• Optical/IR not susceptible to ISM plasma propagation effects.

• But interstellar absorption and scattering from grains important for optical and near IR.(Scattering Þ smearing of pulse.)

Rationale for Radio SETI• No Galactic absorption.• No background from host stars.• Maximum S/N in microwave band (1-10 GHz).• Magic frequency arguments, e.g.,

1.42 GHz H (HI line).1.67 GHz OH. p x 1.42 GHz, etc.

• Narrowband signals << thermal Doppler widths of natural, astrophysical sources.

• But: propagation effects (dispersion, scintillation, pulse broadening from ISM) are important.

Optimizing radio SETI against background noise

Project OZMA1960 National Radio Astronomy Observatory.Green Bank, WV.1420 MHz.

200 hr.Two stars (d~4 pc):

e Eridani, t Ceti.

Non-repeating Signals

• The META candidate signals, like the Wow! signal, have been followed up by re-observing the corresponding sky positions.

è No redetections after 100s of re-observations.

• This is a difficult regime in terms of the scientific method, a keystone of which is repeatability. How to proceed?

Non-repeating Signals

• We can conceive of transmissions we make that are detectable but would not repeat (e.g., planetary/asteroid radar from Arecibo). Not unreasonable to make detections that do not repeat.

• Note the similar case of GRBs: these are stars (hypernovae or merging NS) that destroy themselves; they do not repeat. But GRBs were established as a “real” astrophysical phenomenon because there were many of them (~1/day); however, it took 30 years to establish that they were cosmological and associated with stellar explosions.

• The equivalent for ETI signals (or, at least, candidate ETI signals) is to detect a large-enough number of them that we can establish them as a class of extraterrestrial signal. Perhaps with enough sustained observation we will be able to establish this number.

“Breakthrough Listen”Stephen Hawking Joins Russian Entrepreneur’s

Search for Alien Life

NY Times20 July 2015

“Breakthrough Listen”“Extending his idea of philanthropy beyond the Earth and even the human species, Yuri Milner, the Russian Internet entrepreneur and founder of science giveaways like the annual $3 million Fundamental Physics Prizes, announced in London on Monday that he would spend at least $100 million in the next decade to search for signals from alien civilizations.” – NYT 20 July 2015

• Survey the 1,000,000 closest stars to Earth in hopes of finding conditions suitable to life, searching the entire galactic plane of the Milky Way and beyond to the 100 closest neighboring galaxies.

• Buy observing time at Green Bank, Parkes; also optical surveys.• Decade-long project.

5x bandwidth, 10x sky coverage, 100x survey speed. • Use distributed computing infrastructure (SETI@Home) for processing.• Expert involvement: Martin Rees, Peter Worden, Geoff Marcy, Andrew

Siemion, Ann Druyan, Frank Drake, Dan Wertheimer, and others.

Breakthrough Initiatives

• Breakthrough Listen – radio SETI.

• Breakthrough Watch – optical SETI.

• Breakthrough Starshot – interstellar probes.

• Breakthrough Message – communicating with ETI.

• Breakthrough Discuss – Life in the universe, ideas for space exploration.

Breakthrough Initiatives (https://breakthroughinitiatives.org/)

INTERPRETING SETIThe meaning of it all

The Meaning of SETI

• How important is a SETI detection?

• Assume it’s a mere detection of a signal from far away:– Not much information content.– Difficult two-way communication on any

reasonable time scale (thousands of years, say).– Essentially a message in a bottle: they exist.

è Is this transformational or no big deal?

Who are we?

A mature civilization, like a mature individual, must ask itself this question. Is humanity defined by its divisions, its problems, its passing needs and trends? Or do we have a shared face, turned outward to the Universe?

In 1990, Voyager 1 swiveled its camera and captured the “Pale Blue Dot” — an image of Earth from six billion kilometers away. It was a mirror held up to our planet — home of water, life, and minds. A reminder that we share something precious and rare.But how rare, exactly? The only life? The only minds?

For the last half-century, small groups of scientists have listened valiantly for signs of life in the vast silence. But for government, academia, and industry, cosmic questions are astronomically far down the list of priorities. And that lengthens the odds of finding answers. It is hard enough to comb the Universe from the edge of the Milky Way; harder still from the edge of the public consciousness.

Yet millions are inspired by these ideas, whether they meet them in science or science fiction. Because the biggest questions of our existence are at stake. Are we the Universe’s only child — our thoughts its only thoughts? Or do we have cosmic siblings — an interstellar family of intelligence? As Arthur C. Clarke said, “In either case the idea is quite staggering.”

That means the search for life is the ultimate “win-win” endeavor. All we have to do is take part.

Today we have search tools far surpassing those of previous generations. Telescopes can pick out planets across thousands of light years. The magic of Moore’s law lets our computers sift data orders of magnitude faster than older mainframes — and ever quicker each year.

These tools are now reaping a harvest of discoveries. In the last few years, astronomers and the Kepler Mission have discovered thousands of planets beyond our solar system. It now appears that most stars host a planetary system. Many of them have a planet similar in size to our own, basking in the ‘habitable zone’ where the temperature permits liquid water. There are likely billions of earth-like worlds in our galaxy alone. And with instruments now or soon available, we have a chance of finding out if any of these planets are true Pale Blue Dots – home to water, life, even minds.

There has never been a better moment for a large-scale international effort to find life in the Universe. As a civilization, we owe it to ourselves to commit time, resources, and passion to this quest.

But as well as a call to action, this is a call to thought. When we find the nearest exo-Earth, should we send a probe? Do we try to make contact with advanced civilizations? Who decides? Individuals, institutions, corporations, or states? Or can we as species —as a planet — think together?

Three years ago, Voyager 1 broke the sun’s embrace and entered interstellar space. The 20th century will be remembered for our travels within the solar system. With cooperation and commitment, the present century will be the time when we graduate to the galactic scale, seek other forms of life, and so know more deeply who we are.

There are qualitatively different scenarios:1. No detection after comprehensive SETI.è Conclusion: we are special in the sense of unique?2. Detection of one or a few civilizations but the distance is large and there isn’t much information content.è We are rare but not necessarily unique.3. Detection of one or a few civilizations at relatively small distance (10s of light years).è Communication is possible: exchange of information.4. Detection of a large number of civilizations at varying distances with varying information content. è We are neither rare nor unique.

What is the impact on our world view for each of these scenarios?

The Meaning of a SETI (Non-)Detection

Suppose SETI fails after 10-20 years of intense searching?• Does a null result mean anything? Is it science?• What do you think a null result means for any of the

possible ways in which we might detect ET?• N is small?• L is small?• ETs are quiet, introverted, don’t like to travel, are

slow in traveling …• ETs have futuristic technology for

communications, etc. • “Any sufficiently advanced technology is

indistinguishable from magic.” (A. C. Clarke)

N = Number of Civilizations: big or small?N = astrophysics * planets * biology * intelligence/technology * L

Or, more simply:

N = CFR * L • CFR = Civilization formation rate

Is N dominated by the CFR or by L?• CFR is large, L small à N small.• CFR is very small, L large à N small.

The first case is pessimistic for us if we are typical.The second case is good for us:

• Large longevity.• Less risk of being invaded, perhaps.

THE FUTURE OF HUMAN CIVILIZATIONReply hazy, try again later

“The Great Filter”?

… Each new discovery of an Earth-like planet in the habitable zone, such as Kepler-186f, makes it less plausible that there are simply no planets aside from Earth that might support life. The Great Filter is thus more likely to be lurking in the path between habitable planet and flourishing civilization.

• Statistical argument for bound on L

• Basic idea has some validity; detailed statistical inference is incorrect; see article by Caves (2000)

Gott’s ConclusionsHomo sapiens:

tpast ~ 200 kyr à 5 kyr < tfuture < 8 Myr

“… we should not assume that our intelligence is likely to increase our longevity vastly above that of other species.”

… Do you agree?

Input to Longevity Estimationfor calculations of N

Astrophysics: upper bounds on L for Earth.• The sun will remain on the main sequence for

another ~ 5 Gyr.• The Earth will become too hot for most life from the

increase in L� on a time scale of 0.5-1 Gyr.• An NEO impact, nearby supernova or gamma-ray

burst could lessen the likely L for homo sapiens. – A K-T type impact is due every few tens of Myr.– However … survivalist shelters?

Biology: • No macroscopic predators.• Direct kills from viruses/bacteria?

Indirect via demise of the food chain?Evolution marches on…

• Runaway nanotech: the “gray goo” scenario?

Input to Longevity Estimationfor calculations of N

Astrobiology fights back:• We’re invaded by ETs.èNote that if L is very large for a civilization that preceded ours significantly (up to 5 Gyr, say), then it is possible that the civilization will (or would have) colonize(d) the Galaxy on a time scale of (e.g.) a few ´ 100 Myr.

– How plausible is this? – Is space travel trivial or difficult?

Input to Longevity Estimationfor calculations of N

Geology and environment:• Global warming and climate change.

(Most obvious current challenge.)• Methane clathrates – sudden release.• Overpopulation and civilizational collapse.• Geological dangers: Yellowstone super-volcano;

Cascadia subduction zone; …• Ocean current turn-off and sudden glaciation?

Input to Longevity Estimationfor calculations of N

“Clathrate gun hypothesis”: sudden onset, rapid warming, positive feedback loop.

“The Really Big One”

An earthquake will destroy a sizable portion of the coastal Northwest. The question is when.

Kathryn Schulz,The New Yorker, 2015 July 20

The next full-margin rupture of the Cascadia subduction zone will spell the worst natural disaster in the history of the continent.

Politics/culture:• We kill ourselves off.

– Is this even possible? • Or we kill off all high-tech, electromagnetically loud

activities.• Or we revert to a laid back, low-tech, radio quiet life

style (like the dolphins).• Or we continue on a high-tech track that happens to

be radio quiet (electromagnetically quiet; also quiet in non-photonic activity).(e.g. cable TV, quantum communication.)

Input to Longevity Estimationfor calculations of N

A cause for optimism: the pace of technology

So What is in the Future?• The Sun is heating up and so will the Earth.• The Earth is spinning down (longer work week!).• Asteroids and comets are lurking (NEOs).• Major steps in our evolution?

• Manage climate change and population.• Manage NEOs.• Further solar system exploration. Colonization?• Bionic and genetic evolution?

• Transformational concepts and technology:• String/brane theory and extra dimensions.• Quantum computing and teleportation.

• Further out: migration to nearby planets, tapping energy from other stars (including neutron stars, black holes?).

The March of High Performance Computing

Would we understand an AGI?• A true “Artificial General Intelligence” might have

inscrutable (to us) motivations?• Or … Paperclip maximizer?

(Nick Bostrom, Ethical Issues in Advanced Artificial Intelligence, 2003).

The AI does not hate you, nor does it love you, but you are made out of atoms which it can use for something else.

—Eliezer Yudkowsky,Artificial Intelligence as a Positive and Negative Factor in Global Risk

Would we understand an AGI?• A true “Artificial General Intelligence” might have

inscrutable (to us) motivations?• Or … Paperclip maximizer? (Nick Bostrom, 2003).

• Contra: Lebowski theorem?No superintelligent AI is going to bother with a task that is harder than hacking its reward function.

—Joscha Bach, TwitterCf. Principle of Least Effort.

• Humans won’t fight machines –instead, we will merge with them.

• “Homo Deus” – God-like powers?

• “What happens when non-conscious but highly intelligent algorithms know us better than we know ourselves?”

Context: Our Pale Blue Dot“… Consider again that dot. That's here. That's home. That's us. On it everyone you love, everyone you know, everyone you ever heard of, every human being who ever was, lived out their lives. The aggregate of our joy and suffering, thousands of confident religions, ideologies, and economic doctrines, every hunter and forager, every hero and coward, every creator and destroyer of civilization, every king and peasant, every young couple in love, every mother and father, hopeful child, inventor and explorer, every teacher of morals, every corrupt politician, every "superstar," every "supreme leader," every saint and sinner in the history of our species lived there – on a mote of dust suspended in a sunbeam. … There is perhaps no better demonstration of the folly of human conceits than this distant image of our tiny world. To me, it underscores our responsibility to deal more kindly with one another and to preserve and cherish the pale blue dot, the only home we've ever known.”— Carl Sagan, “Pale Blue Dot”