Lecture 32: Life in the Universe

Don't Panic

Sections

Introduction

The idea of LIFE off the Earth goes back to many mythologies and theologies: e.g., the sky gods of ancient Greece and the saved spirits of Dante's Paradiso (e.g., those on the Moon [

Da-377

[Dante was being allegorical: I don't think he really believed the lowest class of the saved were on the Moon.]

Perhaps, the earliest science fiction story depicting aliens was Johannes Kepler's (1571--1630) Somnium in which the hero visits the Moon and among other things describes astronomy from the point of view of the lunar inhabitants, the Subvolvans (near-side beings) and Prevolvans (far-side beings) (Ca-351--353; Ko-420--425).

The hypothesis of aliens continued from about that time to the present.

In the late 19th century, the falsely-detected MARTIAN CANALS convinced some people, notably PERCIVAL LOWELL, the founder of the Lowell Observatory in Flagstaff, Arizona that there was an intelligent civilization on Mars (e.g., IAWL: Mars: the Red Planet).

FAVORABLE OPPOSITION

MARTIAN CANALS

Ka-293

Actually, in calling them canali in Italian Schiaparelli was NOT implying that they were artificial: his meaning was probably closer to the English channels (Se-477--478).

But canals they became in popular conception and some became convinced they were constructions of intelligent beings: the MARTIANS.

../../astro/mars/historic/percival_lowell.gif

Lowell a member of the famous Massachusetts Lowell family was one of the last great astronomer magnates. He was an enthusiastic promoter of the Martian canal theory and did many observations from his own Lowell Observatory in Flagstaff, Arizona.

He drew many maps of Mars detailing the canals that he thought he could make out. In reality, they were almost entirely optical illusions caused by the eye trying to make out shapes out of variations in color at the verge of visibility.

Only one ``canal'' feature, a giant canyon he named Agathodaemon turned to be real: now called VALLES MARINERIS after the Mariner probe that really discovered it (No-578).

Lowell did believe that the canals were artificial and a product of intelligent Martians.

Credit: late-19/early-20th century photographer; download site: Eric Hutton's site Mars by Percival Lowell, 1895.

Mars

This image is one of Lowell's less elaborate drawings. The canals are not real, of course.

The dark regions may be real. Lowell certainly could make out real dark regions on Mars as did earlier observers going back to Huygens in the 17th century. But without more information I can't identify Lowell's dark regions with anything I can see on a modern map. I suppose I could look up what features Lowell was trying to represent.

Credit: Percival Lowell; download site: Eric Hutton's site Mars by Percival Lowell, 1895.

H. G. Wells in The War of the Worlds portrayed the Martians as faceless invaders. When you did meet up with them, they turned out to be giant octopuses: idea that seemed more novel in the 19th century than after Amazing Stories, etc. See John Walker's Fourmilab web The War of the Worlds.

In fact, many/most??? astronomers never believed in the MARTIAN CANALS: they were quite aware that the eye at the limit of visibility could play tricks.

The Mariner probes of the 1960s gave the first close up views of Mars and showed a barren, low-pressure atmosphere, cratered world (No-578). At first sight sterile---but there might have been LIFE there once and even possibly subsurface today (e.g., IAWL: Mars: the Red Planet).

But let us concentrate on alien intelligent life which were are NOT likely to find in our solar system.

Technologically Advanced Civilizations and the Drake Equation

``Don't you ever wonder where everybody is?''

---Enrico Fermi (1901--1954), at lunch, probably summer of 1950 at Los Alamos (Jones, E. M. 1985, Physics Today, 38, no. 8, 11).

There are several recollection of the Fermi question, and the one above is the longest one. Apocryphally, the Fermi question is often given as the more emphatic ``Where are they?''

Fermi was one of the 20th century's great physicists. The team leader for development of the first nuclear reactor: it was built under the stands of the University of Chicago's football stadium in 1942???.

UFO STORIES

The instructor spoken ex cathedra on that.

Fermi may in back-of-the-envelope style have anticipated the Drake equation, but witnesses are uncertain (Jones, E. M. 1985, Physics Today, 38, no. 8, 11).

The Drake equation, formulated by Frank Drake (circa 1960???), is a formula for estimating the number of technologically advanced civilizations (TACS) in the Milky Way or, if one wishes, in broader domains.

It can be described as a way of analyzing our ignorance.

Various versions can be given, but a typical version for the Milky Way alone is


      N=RL , where N is the number of TACS,

             R is their mean birth rate,
       
             and L is their mean lifetime.

             This equation can be understood simply.

                 If one just turns on the 
        Milky Way, 
                   in the first period L
                   RL TACS are born, but none die. 
               
                 After the first period L, the rate of births 
                   and deaths are equal and cancel exactly.

                 Thus, the number of TACS stays constant at RL. 

     R is can be parameterized by

     R = R_star * f_planet * n_habitable * f_life * f_intelligent * f_TAC

R_star: the birth rate of suitable stars.
If stars are too massive then their lives may be too short for life or intelligent life to evolve or their UV flux may sterilize any planets.
If the stars are too small, then the orbital region about them where liquid water can exist (if starlight is the only relevant temperature factor) may be too small for it to be likely that planets exist there. Life as we know it requires liquid water.
This region is called the HABITABLE ZONE (CM-479). Smaller stars have smaller HABITABLE ZONES.
The definition is too restrictive really since the conditions for liquid water can exist outside of the formal HABITABLE ZONE.
For example, on Jupiter's moon EUROPA liquid water probably exists below a frozen surface. The interior of EUROPA is heated by Jupiter's tidal force flexing EUROPA.
Nevertheless, we'll assume for the sake of argument that only stars with masses not too different from the Sun are likely to have habitable planets.
CM-480 suggest only FGK type stars, which have masses of order 1.6 to 0.5 solar masses (Cox-480), are suitable.
The estimated birth rate of such stars is about 1 per year in the Milky Way (CK-454).
So we take R_star=1. This number is probably order of magnitude accurate.
f_planet: fraction of suitable stars with planets.
Observations suggest planets and planet formation are common. Perhaps nearly all single stars have planets (CK-454). Double star can have planets too, but their orbit can sometimes be complex.
We estimate f_planet=1. This number is probably order of magnitude accurate.
n_habitable: number of habitable planets orbiting a suitable star with planets.
They have to be habitable enough for TACS to evolve.
There could be more than 1 habitable planet per solar system, but there are so many ways a planet could be unhabitable that many people think n_habitable could be orders of magnitude smaller than 1.
We are clueless---in more ways than one actually.
Let us set n_habitable=1. This number could an overestimate by orders of magnitude: I don't think anyone would say it was a gross underestimate.
f_life: fraction of suitable habitable planets that evolve life.
Well Earth is such a planet and it may have evolved life very early.
The first fossil evidence for life dates back 3.5 Gyr (CM-475; HI-500).
Recall that the Earth formed 4.6 Gyr ago and the heavy bombardment by early-solar system bodies only tailed off after 3.8 Gyr ago (Se-422, 446, 447).
Impactors probably disrupted life initiation and the largest ones probably caused shocks that ejected entire proto-atmospheres???.
Thus life on Earth may have started as early as it possibly could.
On the other hand, some believe the evidence for life is not strong before 2.7 Gyr ago????.
We estimate f_life=1. This may be a great overestimate, but it is plausible.
f_intelligent: the fraction of biospheres that develop life at least as intelligent as ourselves.
Multicellular life developed only about 1 Gyr ago (CM-481): maybe 2.5 Gyr after life itself developed.
Intelligence---of the human level---is almost a novelty.
Anatomically modern HUMANKIND has only been around for a relatively brief phase (i.e., since about 160,000 years for sure [Gibbons, A. 2003jun13, Science, 300, 1641]; since about 195,000 years with some probability [Fleagle, J., et al. 2005, Nature]).
The emergence of multicellular life and intelligent life may have been unlikely flukes that just turned up after long waits.
Both multicellarity and intelligence have survival advantages, but there are many survival advantages and their interplay is immensely complex and perhaps chaotic.
NATURAL SELECTION in evolution only recognizes advantages that are advantages in the local environment. An advantage that doesn't help locally is NOT selected for.
And some advantages may be rather marginal.
The great apes are rather intelligent animals, but they are NOT particularly numerous or successful: this was true even before human activities started endangering them.
Then there are DOLPHINS and porpoises. They are rather intelligent and quite successful. But I don't think they are overwhelmingly more successful than sharks which are NOT particularly intelligent.

Dolphins in the bow wave of the NOAA Ship Rude.
Rather intelligent, but they don't have hands and can't have fire.
But they do have fun.
Credit: National Oceanic and Atmospheric Administration/Department of Commerce: Image ID: anim0860, NOAA's Ark (Animals) Collection Location: Louisiana coast, Gulf of Mexico Photographer: Commander Grady Tuell, NOAA Corps.

Of course, there does seem to be a take-off point with intelligence.
Human intelligence together with human hands---those poor DOLPHINS---and certain key environmental factors (see below) have enabled humans to become the dominant large animal on Earth in numbers and in the use of biosphere resources.
But quite obviously this advantageous nature of intelligence is unstable.
If the local environment contains abundant nuclear weapons and the capability of irreparably damaging the biosphere, intelligence may slip over to being a disadvantage.
To pick up the thread of our argument, intelligence may be a fluke development of evolution.
There is no evidence that it strongly selected for.
But on the other hand maybe intelligence is common. Maybe it was a fluke that intelligence developed only lately and once on Earth.
So giving intelligence the benefit of the doubt, we estimate f_intelligent=1. This may be a wild overestimate.
f_TAC: the fraction of intelligent life that develops a technologically advanced civilization (TAC).
Here we define a TAC as one with radio communication since this is the most plausible way for interstellar signaling
Humans have only had a TAC since Heinrich Hertz's discovery of radio in 1887: so not much over a hundred years.
But did we inevitably have to discover radio?
No.
Recall anatomically modern humans have been around for about 160,000 years for sure (Gibbons, A. 2003jun13, Science, 300, 1641) and about 195,000 years with some probability (Fleagle, J., et al. 2005, Nature).
Almost all of that time we were just hunter-gatherers with stone-tools and fire.
Perhaps, we weren't psychologically modern for a long time. We don't know when language was invented for example.
But another factor was climatic: the ICE AGE of last 2.5 Myr including the Pleistocene (0.01--1.64 Myr before present) and Holocene (0--10000 years before present) has been ongoing---and its not over yet probably (WB-78; Cox-248,251).

Glacier Bay. Johns Hopkins Glacier calving

Credit: National Oceanic and Atmospheric Administration/Department of Commerce: Image ID: corp1862, NOAA Corps Collection; Location: Alaska Southeast; Photo Date: August 1991; Photographer: Commander John Bortniak, NOAA Corps.

Our current ICE AGE is punctuated by interglacials about every about 100,000 years (WB-76). The current interglacial stabilized about 10,000 years ago (Fa-24) and the one before that ended about 120,000 years ago (WB-78).
During the glaciations much of Eurasian and North America was under glaciers and much of the rest cold and barren.
Moreover, most of the modern human period has been subject to rapid climate variations.
The last 10,000 has been remarkably stable (WB-79).
Before 12,000 or so years ago, the conditions were not suitable for agricultural societies to develop or to become permanent.
Without the food surpluses of agriculture, it is probably impossible to develop the specializations needed for advance beyond typical hunter-gatherer technology.
Even in the stable period when agricultural societies could and did develop, prolonged cold spells and droughts have brought about collapses of civilizations and retreats to simpler economies (Fa-xiiiff).
The upshot is that humans probably only did have a reasonable chance of going beyond the hunter-gatherer stage in the last 12,000 years when, in fact, they did (Fa-xiii).
But even having a warmish steady climate is NOT sufficient for technological progress.
One also needs domesticatable plants and animals.
The Australian Aborigines have been in Australia since about 40,000 years ago at least (Dai-300), but they never got beyond being hunter-gatherers until the Europeans arrived---well invaded.
But the Aborigines really couldn't have: there are almost no native flora or fauna of Australia that are domesticatable (Dai-308--309) and the Aborigines only brought our oldest friend, the dog, with them.
The large and connected continental areas had the advantage of more domesticatable species and an easier time spreading them.

Political World Map, year 2000.
Credit: Central Intelligence Agency (CIA); download site Perry-Casta~neda Library Map Collection University of Texas Austin. Most of the maps are in the public domain and can be downloaded. There are historical maps.

Many of the circumstances that allowed technology to develop are not universal givens.
Some intelligent species may never get beyond the hunter-gatherer stage before they become extinct.
But given massive food production available from agriculture and the absence of any worldwide catastrophes (e.g., a large, planet-devastating impactor) perhaps most worlds with intelligent life (of our sort) would go on to develop into a TAC.
Physics and chemistry are the same all across our observable universe, and so technology might follow a common course.
So although it is certainly an overestimate let us set f_TAC=1. Maybe it is NOT a bad overestimate; on the other hand, it could too large by orders of magnitude.
L: mean lifetime of a TAC.
We've been technologically advanced only since 1887 by radio discovery definition.
Since circa 1950, we have the capability of extincting ourselves with nuclear weapons.
Our exploitation of the biosphere continues to do quasi-irrevocable damage. We may be able to destroy it's capacity to support us, although I don't think we will.
But it is certainly possible for TACS to destroy themselves on the time scale of 100 years after becoming a TAC.
But on the other hand, it may be possible for a TAC to become quasi-immortal.
Of course, the quasi-immortal TAC BEINGS might transform themselves into a hyper-intelligent pandimensional beings along the way---or simply reach a quasi-perpetual steady-state with no further progress.
So L could be anything from of order 100 years to of order 10 Gyrs: i.e., the order of the age of the observable universe.
Let us just leave L general then.

 

     N = 1*1*1*1*1*1*L = L  , where  L is the mean lifetime of a TAC.
                              

              Remember most of our estimate factors could be off by
              orders of magnitude.  

              In fact, many factors may be too high by orders of magnitude.

TACS

Milky Way

So if L=100 years, there are 100 TACS.

So if L=10**6 years, there are 10**6 TACS.

How easily could we receive signals from TACS?

That depends on distance among other things.

Remember radio communication can only be at the speed of light: so the greater the distance, the longer for a signal to reach us.

Assume the Milky Way is just the disk which is a quasi-two-dimensional space.

The planar density of TACS is then n = N/(pi * r**2) , where r is the disk radius. We can also set n = 1/d**2 , where d the length of the side of a typical square in which one finds one TAC. d is also the typical NEAREST NEIGHBOR DISTANCE among TACS. Then N/(pi * r**2) = 1/d**2 and one can solve for d=sqrt(pi/L)*r, where N=L recall. The radius of the disk of the Milky Way is of order 50 klyr. So d = about 100 klyr / sqrt(L), where we estimate sqrt(pi) by 2. We can present a small table. L (yr) d (lyr) ______________________________ 100 10,000 10**4 1,000 10**6 100 but if we get this small we again have to worry about the finite thickness of the disk.

TAC

Communication is imaginable if L is high.

But maybe TACS of order 10**6 years old have no interest in us or may not want to communicate with us: they may only observe us---there is the PRIME DIRECTIVE after all.

They may hide themselves from us, protect us, experiment on us.

All of science fiction is possible.

SETI: The Search for ExtraTerrestrial Intelligence

"Watch the skies! Keep watching the skies!"

---Scottie ?? in The Thing (1951)

CK-452

He looked for radio signals from Tau Ceti (a G8V star 11.90 lyr away) and Epsilon Eridani (a K2V star 10.49 lyr away) (CK-452). These are nearby and not so unlike the Sun.

Since then there have been many searches as well as people willing to jump on any likely signal in the course of non-SETI radio astronomy.

The most famous SETI organization is the SETI Institute, a private, non-profit organization founded in 1984.

NASA got out of SETI rather definitively in 1992 (FK-689). (Or so it used to seem: maybe NASA will jump back in.)

Given that SETI is rather controversial---many think it is just nonsense---this is probably a good thing. SETI probably should be carried out and supported by enthusiasts.

The SETI Institute also sponsors astrobiology in general: unkindly called a field without a subject (HI-496): but there is a subject: we just havn't found any samples yet.

Currently, the SETI Institute has been carrying out PROJECT PHOENIX: this project is surveying about 1000 Sun-like stars within 200 lyr of Earth in millions of frequency bands.

Other SETI projects by other organizations are also underway.

One other interesting search is SERENDIP IV (Search for Extraterrestrial Emissions from Nearby Developed, Intelligent Populations) run by scientists at University of California, Berkeley (FK-689).

This project has a subsidiary project SETI@HOME in which millions of personal computer users participate.

They load a data analysis program on their computers which analyzes SERENDIP IV data and reports back to Berkeley.

Aside from its use for SETI, SETI@HOME has been an example of massively distributed computing for many other fields. Some people may think SETI@HOME is the most valuable thing ever done by SETI.

Often anomalous signals are discovered and a list of best candidates is kept. Sometimes a signal catches media attention: e.g., one from source SHGb02+14a.

But no signal has really caused terrific excitement yet.

Question:

It would profoundly alter our lives and philosophy.
Probably nothing much since the signals would probably be completely unintelligible. People might say ``well there's another alien civilization with incomprehensible emissions.''
Who knows?

I'm betting on answer 3.

Question:

Tomorrow.
Never.
Who knows?

I'm betting on answer 3.

Beware of aliens bearing grades.