AST 248, Lecture 16

AST 248, Lecture 16

James Lattimer

Department of Physics & Astronomy449 ESS Bldg.

Stony Brook University

October 21, 2018

The Search for Intelligent Life in the [email protected]

James Lattimer AST 248, Lecture 16

Can Life Be Based on Other Forces?Timescales for life based on forces of nature and 1020 reactions

Force Environment Reaction Time Evolution Time

Strong Neutron Stars 10−21 second 0.1 secondWeak ? 1000 seconds 3 · 1015 years

Gravity Galaxy 10 million years 1027 yearsElectromagnetism Planet 0.001 second 3 billion years

“ Interstellar Cloud 1000 seconds 3 · 1015 yearsI Conclusion: Chemistry is favored.

I Chemical life is easier with a struc-tural element that is able to sharemany electrons ⇒ C or elementsbelow it in the periodic table.

I Julius Scheiner in 1891 first specu-lated on the suitability of Si for life.

I Si is abundant in planetary crusts.

I Heat stabillity of Si compoundsmight allow high-temperature life.

I Si-based clays could develop simplemetabolisms (genetic takeover theory).

I Artificial life or intelligence could contain a significant silicon content.

⇒


Why is C favored over Si?

I C, Si, Ge: Versatility from ability tobind with up to 4 atoms at a time

I Ge: not very abundant in space oron planetary crusts.

I Si is 1000 times as abundant as C inplanetary crusts.

I Si-Si bonds have half the strength ofC-C bonds; are therefore fragile.

I Si-O bonds are much stronger thanSi-Si or C-O bonds and tend to short-circuit the formation of long chains of Si’s.

I Complex Si-based molecules can’t survive long in water.I Si doesn’t normally form double bonds, which limits its range of reactions.I C is mobile in the environment as CO2, but Si is immobile since SiO2 is a

solid (quartz, etc.).I Observational evidence: Ubiquity of C-based complex molecules in space

and in meteorites; there is a lack of complex Si-based molecules.I Although Si is not favored to form polymers, the strong Si-O bond

suggests that SiO units could form the backbones of polymers. SiOpolymers are called silicones and can be produced to substitute for manyorganic materials, for example, cosmetics and lubricants (Mobil One).

The Horta, Star Trek episode 26, “Devil in the Dark”


Other Possibilities

Boron – Ammonia

I Boron forms covalent bonds like carbon, but with only 3 valenceelectrons.

I No direct analogues to hydrocarbons.

I Boron bonds with nitrogen like carbon with carbon, formingcompounds similar to methane, ethane and benzene.

I These boron-based compounds are more reactive and would operateat lower temperatures where ammonia is a liquid, which couldoperate as the solvent.

I A big drawback is its scarcity: in the Earth’s crust boron has anabundance of 1 part in 100,000.


Important Properties of Solvents for Life

I AbundantI Chemically simpleI Wide temperature rangeI High heat capacity and heat of vaporizationI Good solventI Large surface tension

Interesting Properties of Water

I Self-shields against ultraviolet lightI Expands upon freezing

Liquid Total T Heat Heat of Surface Solvency♥

Range† Capacity‡ Vaporization∗ Tension♥

Water 100 1 595 1 1Ammonia 45 1.23 300 1/2 1/2

M. Alcohol 159 0.6 295 1/3 1/2† of liquid, degrees Celsius‡ cal/g/degree Celsius∗ cal/g♥ relative


Ammonia-Based LifeI In 1954, Haldane suggested the replacement of water with ammonia.I Water has ammonia analogues: CH3OH→CH3NH2.I Ammonia-based counterparts to proteins and nucleic acids exist.I Amide molecules would substitute for amino acids, and these form

polypeptides also.I Whole systems of organic and inorganic chemistry takes place

inammono instead of acqueous solutions.I Ammonia can dissolve most organics as well as or better than water,

and can dissolve many elemental metals like Na, Mg and Al, andother elements like I, S, Se and P.

I Although ammonia has a narrow liquidity range at 1 atm, it is muchlarger at higher pressures.

I Ammonia is a poorer insulator but has a higher heat of fusion andspecific heat and is also less viscous.

I In an ammonia system, water would appear to be a strong acid andquite hostile to life.

I Ammonia-based life could use Cs and Rb-chlorides to regulateelectrical potentials of cell membranes as opposed to K and Na-saltswith water-based life.

I The hydrogen bonds in ammonia are much weaker than those inwater, making it difficult to hold prebiotic molecules together.

I The surface tension of ammonia is weaker than in water.James Lattimer AST 248, Lecture 16


Plasma-Based Life?

I Another Star-Trek idea might not be so far-fetched: plasma-basedlife.

I In 2003 Romanian physicist Sanduloviciu created blobs of plasmathat could grow and replicate similarly to biological cells.

I They lacked inherited material, hence were not alive, but thesespheres may offer an explanation of how life began.

I Similar to a Miller-Urey experiment, the researchers created electricdischarges that caused plasmas to form, specifically argon plasmas.

I Electric sparks spontaneously createdspheres (like bubbles forming in water).Each sphere had a boundary made of twocharged layers that trapped gas atoms.

I The spheres grew and divided, albeitrandomly.

I Even if they aren’t alive, they could havebeen forerunners of protein microspheresor coacervates.

Source: The Internet Encyclopedia of Science

The Companion, Star Trek


Notes Concerning Alien LifeformsI On Earth, life either adapted to “extreme” environments, or it originated

in “extreme” environments. Can intelligence evolve in extremeenvironments, or are benign conditions (land/water/air, needed fortoolmaking, astronomy, language) necessary?

I Will alien senses be profoundly different from our own (light, sound, smell,electric (e.g., octupi)...)?

I Is mathematics a universal language?

32 + 42 = 52, 102 + 112 + 122 = 132 + 142, e−i = −πI Diverse rates and directions of evolution, and extinction of majority of

species, show there is no goal-directed route of evolution from originationto intelligence.

I Total system of life has demonstrated an uncanny progression towardcomplexity and sophistication, even if individual lineages don’t.

I Small changes can produce dramatic outcomes, similar to catastrophes inthe mathematical sense.

I If humans became extinct, humans would not reappear; odds of findinghuman-like aliens nil.

I Yet convergent evolution does occur, representing common solutions toproblems or environments. Examples: wings of bats and birds (their lastcommon ancestor did not have wings); dorsal fins of dolphins, salmon andicthyosaurs; camera eyes of squids, mammals and box jellies; the lysozymeenzyme in monkeys and cows (permits gut fermentation); high frequencyhearing in bats, whales and dolphins; opposing thumbs in opposums andprimates. Source: The Science of Aliens by Pickover


I Other examples: prehensile tails in chameleons, sea horses,binturongs, kinkajous, anteaters, phalangers and monkeys; penguinsand auks.

I Will convergent evolution generally lead to bilateral symmetry, asopposed to, say, radial symmetry (jellyfish, octupi, starfish)? Whydo humans have exterior bilateral symmetry, but not internalsymmetry (heart, liver, stomach, etc.)? Tube-like digestive systemsviolate bilateral symmetry.

Source: The Science of Aliens

by Pickover

Common Octopus


I Nervous system (or analogy) seems essential to promote informationcapacity beyond chemical limitations of DNA. Brain develops near primarysense organs, and is given protection.

I Will evolution and interaction among individuals lead to a “hive-like”group mind, where the aggregate intelligence vastly exceeds the sum ofthe individual intelligences (ants, bees, termites, the Borg)?

I Octupi as an example of strange evolution. Its brain encircles itsesophagus, and food sometimes gets stuck in it. It has pigment-bearingcells that can change its skin color, pattern and texture (prelude toshapeshifters?). It lacks a skeleton, so isvery shape versatile. The Mimic Octopus,not discovered until 1998, has theuncanny ability to mimic several othersea creatures, including sea snakes,lionfish, flatfish, brittle stars, giant crabs,sea shells, stingrays, jellyfish, seaanemones, and mantis shrimp.

I Evolution in response to different gravity,air pressure, planetary surface chemistry,radioactivity, solar spectrum, planetaryrotation, length of year...

I Alien sex – read the book!Wonder Octopus

Source: The Science of Aliens by Pickover


Shape-Shifting (Mimic) Octopus


Artificial LifeI The philosophy of artifical life has two positions:

I Strong artificial life position: “Life is a process which can beabstracted away from any particular medium” – John von Neumann

I Weak artificial life position: Denies the possibility of creating a livingsystem outside of chemistry. Rather, life processes can be mimicedto understand the underlying mechanics.

I Techniques are mainly:I Cellular automata – consist of a regular grid of cells in any number

of dimensions. Each cell is in a finite number of states determinedfrom its neighborhood by a set of rules, and updates in time arecontrolled by another particular set of rules (like a Boolean network).

I Neural networks – mathematical models of biological neural systems.These rely on parallel processing as well as implicit instructions basedon pattern recognition of sensory inputs from external sources.

I Arificial life has taken a bottom-up approach as opposed to the top-downapproach of genetic modification (i.e., stripping) of microorganisms.

I Artificial life has had a controversial history, ranging from claims of beingfact-free science (John Maynard Smith) to the discovery of tools that haveled to breakthroughs in computational science, art, music and games.

I Artificial intelligence has had a similiarly controversial history, but has ledto advances like search engines, investing and banking tools, and robotics.

Source: Wikipedia


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AST 248, Lecture 16