Astro 2299 The Search for Life in the Universe

Lecture 2 Last time: Intro to course Today:

•  Drake equation (as continuing intro) •  Our universe = ΛCDM, originated in hot big bang •  Time scales, distance scales •  Important features

Instructors: Jim Cordes & Shami Chatterjee

http://www.astro.cornell.edu/academics/courses/astro2299/

1

Principles and Paradox Copernican 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?

The Drake Equation A guesstimate for how many advanced civilizations may be in the Milky Way (answers range from 1 to millions!)

N = R* x fs x Np x fHZ x fl x fi x [fother] x L

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 around a star or planet fl = fraction that have life fi = fraction that have intelligence/technology fother = other requirements (tectonics, Jupiter,etc.) L = longevity of intelligence/technology phase (yr)

The Drake Equation A guesstimate for how many advanced civilizations may be in the Milky Way (answers range from 1 to millions!)

N = R* x fs x Np x fHZ x fl x fi x [fother] x L

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 around a star or planet fl = fraction that have life fi = fraction that have intelligence/technology fother = other requirements (tectonics, Jupiter,etc.) L = longevity of intelligence/technology phase (yr)

Astronomy, astrophysics, chemistry, biology

The Drake Equation A guesstimate for how many advanced civilizations may be in the Milky Way (answers range from 1 to millions!)

N = R* x fs x Np x fHZ x fl x fi x [fother] x L

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 around a star or planet fl = fraction that have life fi = fraction that have intelligence/technology fother = other requirements (tectonics, Jupiter,etc.) L = longevity of intelligence/technology phase (yr)

Astronomy, astrophysics, chemistry, biology

Speculation (for now)

How many civilizations might be in the MW?

My view Life is likely very common in the Galaxy (and in all galaxies) Some useful numbers:

~ 100 billion Sun-like stars in the MW ~ 100 billion MW-like galaxies in the universe ~ 1/3 of stars appear to have planets à 1022 planetary systems in the universe

Bacteria are easy to form Complex, technological life likely rare but not uncommon

•  Surely Earth is not the only planet harboring “us” •  But what do the others look like? Are they noisy

enough electromagnetically/technologically to be detectable?

Astrobiology More “astro” than “bio” so far

No known life elsewhere But organic molecules are detected in meteorities, atmospheres of planets and in interstellar gas clouds We expect to find evidence of life elsewhere… soon

The ingredients for life are universal Planets appear to be the best venues for the origins of life (but nature has the ultimate say) We now know ~ 5000 exoplanets + candidates

1600: Giordano Bruno burned at the stake for speculating about multitudes of other worlds

1991: First extrasolar planets found around a neutron star (pulsar) 1995: First extrasolar planets found around an “ordinary” star

Astrobiology What will our state of knowledge be in 2030?

We will know of tens of thousands of planets We will have measured spectra of atmospheres of planets,

allowing us to identify biological processes affecting those atmospheres

We will have used powerful radio telescopes to search for technomarkers of other civilizations

How likely is it that civilizations like ours are out there?

Funding issues: the current state of science funding in the US is not good but there are significant projects in the pipeline this decade (more solar system missions, planet finding missions, James Webb Space Telescope)

Basics of Cosmology see pdf document on course web page (later today)

•  The universe was formed in a hot big bang 13.7 Gyr ago •  We live in a “ΛCDM universe”

CDM = cold dark matter Λ = cosmological constant The geometry of space is flat Evidence: distant supernovae, element abundances, cosmic microwave

background, structure of the cosmic web (distribution of galaxies)

•  Only 4% of the gravity in the universe is contributed by matter as we know it (“baryonic”) •  73% hydrogen, 25% helium, 2% trace elements (by mass)

•  A few elements were formed at ~ 3 minutes after the BB and the rest not until the universe was ≥ 0.1Gyr old

•  Most of the universe is inhospitable to life but we expect a large number of venues for life to exists

•  The universe will expand forever

Cosmological Context Why do we find ourselves in this universe? Initiated 13.7 Gyr ago in a hot big bang 3 + 1 dimensions Laws of physics, fundamental constants as they are 96% of the universe is filled with stuff that we don’t

understand (dark matter, dark energy) Complexity: galaxy clusters, stars, planets, life on at

least one planet

ΛCDM•  The universe began in a hot big bang

•  Atoms were formed at around 3 minutes and later in stars

•  Most of the mass in the universe is dark and it is not baryonic

•  All large structures (galaxies and larger) grew from weak changes in density that were produced in the early universe

•  Baryonic matter collected in gravitational wells produced mostly by dark matter to form galaxies, etc.

•  In order for this to work, DM had to be “cold.” Hot DM would not have formed the gravitational wells and we would not be here.

•  Data suggest that the early density fluctuations were a gaussian random field

Formation of galaxies and galaxy clusters required matter to collect in gravitational “valleys” •  Dark matter defines the

valleys •  Baryonic matter is along

for the ride •  Dark energy is involved

in the large-scale acceleration of the universe, not the local processes

“Baryonic” means made of protons, neutrons, etc. Non-baryonic matter: neutrinos, axions, etc.

Cosmological Context

As far as we know, it doesn’t have to be this way! There may be other universes with entirely different

properties We find ourselves in this one because it has the right

properties to produce us

•  Is this statement profound or obvious? •  = the “anthropic principle”

Age of homo sapiens/age of universe

•  Recent fossil jaw bone in Morocco: 300 kyr old 300 kyr / 13.7 Gyr = 2 x 10-5 = 0.002%

•  From our late arrival vantage point we can infer what happened in the universe before the first second after the big bang

•  Better than that: down to about the first 10-35 sec •  We do not know our family trees this well

•  “The elements were cooked in less time than it takes to cook a dish of duck and roast potatoes.”

•  --- George Gamov

•  (elements formed early in the big bang, that is)

"The Essential Cosmic Perspective", by Bennett et al.)

Published by AAAS

C.-A. Faucher-Gigure et al., Science 319, 52 -55 (2008)

Fig. 1. View of the expanding universe illustrating the evolving cosmic web

Detailed Timeline for the Universe

Fundamental Observations The night sky is dark (Olbers paradox; the universe must be finite in size and age) There have been no obvious visitations from extraterrestrials (microbial or klingons) The Earth and the solar system are middle aged 4.6 Gyr vs. 13.7 Gyr (U) vs. ~12 Gyr (MW) Laws of physics:

The good news: can extrapolate back to <<1 sec after Big Bang … for describing matter and radiation The bad news:

matter is only 4% of the universe the structure of the universe was largely determined by

physics that goes beyond our ability to extrapolate backwards (the action was at 10-43 sec = the Planck time)

The Milky Way

optical

The Milky Way

optical

Andromeda (M31)

Distances101•  Speed of light: c = 3 × 105 km s-1 = 3 × 1010 cm s-1 •  Light year: speed of light x 1 year

–  1 LY ≈ 1018 cm ≈ 1013 km •  Par sec = parallax arcsecond

–  1 pc ≈ 3.09 × 1018 cm ≈ 3.25 LY •  Distance to the Sun ≈ 500 light seconds (1 AU) •  Distance to Pluto ≈ 4 to 5 light hours •  Next nearest star ≈ 1.3 pc •  Distance to nearest large galaxy (Andromeda) ≈ 0.6 Mpc •  Size of Universe ≈ 4.3 Gpc (giga-parsecs)

–  (defined in terms of the Hubble constant as c / H0)

TimeScales101•  Age of universe = 13.7 Gyr

•  Age of Earth = 4.6 Gyr

•  First bacteria: now - 3.5 Gyr

•  Modern phyla (Cambrian): now - 0.55 Gy

•  Dinosaur+ extinction event: now - 65 Myr ago

•  Homo sapiens: 300 kyr

The Milky Way

optical

infrared

Messier 1 The Crab nebula