Class events: week 15

1
Class events week 15

• This weeks goals Great Silence (aka Fermi
  Paradox)
• What is the Great Silence?- Possible
  resolutions to the Great Silence

2
An important take-home message

• If nothing else
• I hope you leave today understanding why you
  should never again utter the phrase, There may
  be aliens in the galaxy, but I think they just
  havent gotten here yet.
• This terribly flawed perspective reveals a basic
  lack of understanding of our galaxys size, age,
  and history.

3
Timescales of space exploration

• How long will it take for a spacefaring
  civilization to explore the galaxy?
• Consider a colonization model where the exploring
  species travels to a new planet, resides there
  long enough to resupply, and then continues on
  its way.
• This move-rest-move approach results in an
  overall average speed of exploration that would
  be the same as if the explorers travelled the
  same distance, at a slower velocity.
• Move-rest-move
• Continuous motion at a slower speed
• Obviously, an expanding civilization would not
  explore the galaxy with only a single
  spaceshipit would create more as it went. This
  is called the coral model of exploration.

4
Timescales of space exploration

• Consider two colonization models.
• In the slow model, spaceships move slowly
  (0.01c), perhaps as generational arks, which then
  reside for a long time (5000 years) before moving
  on.
• In the fast model, the spaceships are very speedy
  (0.1 c), and only reside for 150 years before
  moving on.
• Slow Fast
• Travel speed 0.01 c 0.1 c
• Travel time 500 y 50 y (Stars are about 5 LY
  apart.)
• Rest on a planet 5000 y 150 y
• Resulting velocities and timescales
• ?Vexplore 0.0009 c 0.025 c
• ? Texplore 9.2107 y 3.3106 y
• While these times may seem very long, compared to
  the age of the galaxy (1010 years) they are
  exceedingly short
• Texplore / Agegalaxy 1/110 1/3000

5
Galactic differential rotation
Our galaxy rotates differentially, so stars slide
past each other with time. In effect, even the
inhabitants of a stationary solar system explore
different star systems, as its neighbors change
over time. Because of galactic
differential rotation, it will take a sub-light
civilization only about 0.5-50 million years to
completely explore the galaxy, instead of 3.3-92
million years. The new time ratio to explore the
galaxy is as small as 1/20,000.
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Timescales of space exploration

• Von Neumann Probes
• Self replicating machines that would have simple
  programming
• Find new planets, find raw materials, replicate
  new machines.
• Once the probes are ready, they move on. And they
  do this fast

7
Exploration by von Neumann Probes

• Exploration by von Neumann probes is hugely
  effective
• No need for bulky life-support ? smaller crafts
• Faster rebuilds, less time between generations
• Can make far more crafts with limited resources
• Easier to accelerate to high speed.
• No need for delicate accelerations, when 30g
  would do!

8
Exploration by von Neumann Probes

• Recall our biological exploration wave through
  the galaxy
• Robot probes, by any calculation, would explore
  the galaxy about ten times faster, exceeding even
  the rate of a fast biological exploration, 0.5
  million yearsor about 1/20,000th of the galaxys
  age.
• Robot exploration, even if it started much later
  than biological exploration, would expand in a
  wave that would quickly overtake the biological
  exploration wave.

9
They are out there, but they havent gotten here
yet

• Recall that star formation has been occurring in
  our galaxy for about 10 billion years, making
  stars (and presumably planets) just like ours for
  all that time.
• If there is just one other civilization in our
  galaxy, it might have formed at any time during
  those 10 billion years. Indeed, it would be
  preposterous to expect that its age is within 0.5
  million years, 5 million years, or even 50
  million years of our own.
• 0.5 million years (fast robot probes, fastest
  biological exploration)
• 5 million years (slow robot probes)
• 50 million years (slow biological exploration)
• 
  
  
• 
  10 billion years

10
They are out there, but they havent gotten here
yet

• 0.5 million years (fast robot probes, fastest
  biological exploration)
• 5 million years (slow robot probes)
• 50 million years (slow biological exploration)
• 
  
  10 billion years
• Instead, it would be vastly more likely that if
  even one other civilization EVER occurred in our
  galaxy, it would have had billions of years to
  explore the entire galaxy, before we even gelled
  from the primordial soup.
• Saying they havent gotten here yet, in the case
  of a 0.5 million year exploration time, would
  have the same likelihood as spending one day per
  year in a rental cabin, just to find that someone
  elsethe only other renter all yeararrives
  within 26 minutes of your arrival.
• If there is more than one other civilization in
  the galaxy, the situation is even less likely
  that they havent gotten here yet.

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Two observations in conflict

• 1) If aliens exist in our galaxy then they should
  have reached the Earth long, long ago.
• 2) Daily public experience tells us that we are
  not surrounded by a constant barrage of aliens.
• WHERE ARE THEY?? This is the Fermi paradox.
• WHY CANT WE HEAR THEM?? This is the Great
  Silence.

12
Systems in equilibrium

• In general, science proceeds on the assumption of
  near-equilibrium. This assumption is valid
  because changes to systems usually transpire
  slowly
• stars evolve, but slowly
• mountains grow or erode, but slowly
• trees grow larger over time, but very slowly.
• Of course, many systems can move rapidly from one
  state to a dramatically different state. But such
  systems spend very little time in the actual
  transition process.
• In other words, dramatic things CAN happen, but
  the time between dramatic events is large
• stars explode, but very rarely
• earthquakes happen, but between long spaces of
  time
• trees fall over, but rarely.
• The lesson from this is that it is almost always
  very safe to assume that a system is in a
  slowly-changing stage, and that it is not in a
  stage of rapid transition.

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Equilibrium and the Copernican Principle

• Recall the Copernican Principle We cannot
  assume we are at a special place in our Universe.
  
• We are not at
• the center of the Earths surface (for
  flat-Earthers)
• the center of the solar system
• the center of our galaxy
• the center of the Universe.
• Nor can we assume that we are in a special
  moment, such as a transitional time. Such
  transitional times are rare and short-lived.
• Reflect this is really a restatement of the
  Copernican Principle.
• Avoiding the assumption of a special time or
  place is called the Copernican Principle. (In
  cosmology The Cosmological Principle.)
• It is foolish to assume we are at a special time
  in our galaxys history.

14
Equilibrium and galactic evolution

• Assuming we survive into the future, we (or our
  von Neumann probes) will explore the galaxy
  during the next 0.5-50 million years.
• If we are alone in the galaxy, we are about to
  transform it from an unexplored one, to a fully
  explored one.
• This would be a huge, dramatic transition for our
  galaxy, implying that the galaxy is in a vast
  state of disequilibrium.
• This is a huge violation of the Copernican
  Principle.

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In case you lost focus for a moment
The Milky Way Galaxy is ancient (10 billion
years), but in contrast, the time needed to
explore it is but a few million years. Other life
forms in the galaxy should have explored it by
now. (Thinking that they evolved simultaneously
as us would require an incredibly improbable
coincidence.) But we dont see them, nor have we
detected them! WHY NOT??? (Fermi Paradox/Great
Silence). How can we resolve the Fermi
Paradox/Great Silence??? If other life forms
simply dont exist, we are in the unique position
of being the first galactic explorers. We would
be about to change the galaxy forever. But that
would be a massive violation of the Copernican
Principle! How can we avoid violating the
Copernican Principle?
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14 Other space-faring civilizations do not exist

• Rare Earth Hypothesis
• Other civilizations never formed in the first
  place!
• Perhaps developing civilizations need
• Water to allow life to form
• Dry land to force technology
• Plate tectonics to regulate CO2 and avoid a
  catastrophic greenhouse effect
• A magnetic field to prevent atmospheric
  stripping
• A large satellite to stabilize the planets
  axis
• An absence of hot Jupiters inward spiraling
  giants are devastating
• A cold Jupiter to remove comets from the inner
  solar system.
• BUT
• Is this argument simply rooted in carbon
  chauvinism?
• This hypothesis violates the Cosmological
  Principle by saying we are unique, and does not
  address the fact that our galaxy is about to
  change character because of our own exploration.

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14 Other space-faring civilizations do not exist

• Self Destruction Hypothesis
• All civilizations destroy themselves before
  reaching space
• Nuclear disaster?
• Ecological disaster?
• Technological singularity?
• BUT
• Could these mechanisms really have a 100 kill
  rate?

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24 Critical barriers to communication exist

• Unattractive Earth Hypothesis
• Aliens are widespread, but either the Earth is
  difficult to reach, or it might not fit the
  notion of a habitability for alien species.
• Are nearby black holes necessary for space travel
  by spectacular technologies?
• The Sun is leaving a spiral armis this
  inconvenient for space travel?
• Are all other alien civilizations associated with
  K-M dwarf stars?
• BUT.
• Von Neumann probes could reach inconvenient
  planets with little delay.
• It is non-Copernican to expect our civilization
  is unique in being the only one orbiting a G star.

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24 Critical barriers to communication exist

• Overwhelming Technology Hypothesis
• Communication with aliens would be easy, if we
  knew how to look.
• Exotic communication (neutrino modulation), etc.
• Are we misinterpreting obvious beacons such as
  pulsars, etc?
• Communication is out there, but it is mostly
  carefully masked to be energy-efficient.
• While islanders in a Southeast Asian stone-age
  culture might communicate with each other via
  drum beats, they would be unaware that the air
  was also filled with radio broadcasts.
• BUT
• Wouldnt aliens be able to dumb down their
  communications to talk to us?

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24 Critical barriers to communication exist

• Government Conspiracy Hypothesis
• Aliens are, or have been, in communication with
  us, but our government is not letting the truth
  out. The hypothesis includes
• In 1947, aliens crashed in Roswell, NM.
  (Operation Mogul is a cover-up.) President
  Truman started the Majestic 12 secret
  committee of scientists. The FBIT denies this.
• Area 51 is a high-security Air Force installation
  in Nevada (130 km NW of Las Vegas). Its contents
  are secret, but may contain alien aircraft and
  bodies.
• In the 1970s, cattle were found in 15 states,
  surgically and mysteriously mutilated. Even an
  investigation by the FBI came up with questions
  about the cause. Aliens might need to experiment
  on cattle.
• The cover-up is international in scope.
• BUT
• Conspiracy theories are, in general, largely
  impractical because of the huge financial and
  celebrity gains associated with revealing them.

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34 Aliens choose to observe us quietly

• Sneaky UFO Hypothesis
• UFO-proponents argue that aliens have gone
  through all their efforts and energy
  expenditures to visit us secretlyand then
  accidentally reveal themselves!?
• Rice 1 If aliens wanted to sneak around,
• why dont they just turn off their lights?
• A those are their engines, not just their
  in-flight lights!
• Rice 2 If those are their engines lights, then
  why not use a craft that is a little more
  sneaky? After all, they knew they were coming
  here to sneak around!
• A They are so powerful, they dont need to sneak
  around, after allwe cant threaten them.
• Rice 3 Then why sneak, and in particular, sneak
  so poorly?

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34 Aliens choose to observe us quietly

• Even though UFO reports are generally lame, we
  cannot discount the possibility that we are being
  observed.
• Immaturity HypothesisWe must reach maturity
  before the aliens make themselves known.
• Prime DirectiveRoddenberry, 1966-1969
• Codex GalacticaNewman Sagan, 1981.
• Zoo HypothesisWe are oddities worth watching for
  obscure reasons.
• Quarantine HypothesisSomething is wrong with us?
  Is it our aggressive nature?

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34 Aliens choose to observe us quietly

• Have astronomers spotted mystery spacecraft?
• We have filled our sky with countless bits of
  space debris. Nearly all the pieces of debris are
  in orbit around the Earth.
• What about secret military spacecraft?
• The military is interested in bombing
• humans, not in creating space probes
• to explore the solar system. We can
• expect that secret military debris
• would only be orbiting the Earth, and
• not the Earth-Moon system.
• There is no supportable reason to
• envision that the military would
• create weaponry that would escape
• the Earth-Moon gravity, to enter
• orbit around the Sun.

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34 Aliens choose to observe us quietly

• There are a few threads of evidence consistent
  with our being watched.
• J002E3 has a strange, temporary geocentric orbit.
  It is a discarded
• Saturn V stage from Apollo 12.
• 6Q0B44E orbits the Earth-Moon system every 80
  days. From its brightness, it is a few meters
  across. Presumably artificial junk from Earth
  research.
• 1991VG has a heliocentric, near-Earth orbit,
  passing us every 16 years. It is 9-19 m across.
  In 1991, it approached within 450000 km of the
  Earth.
• Its unstable orbit argues it is a recently
  captured (lunar?) meteoroid. Glinting brightness
  variations suggest it is metallic, but its orbit
  does not match with any space missions. Steel
  (1995) notes that
• Pnatural Pspace junk Palien 100
• If both Pnatural and Pspace junk are very small,
  then Palien is close to 100!

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34 Aliens choose to observe us quietly

• The problem with all these hypotheses (of aliens
  watching us quietly) is that galactic shear would
  move us to new stellar systems in a few million
  years enforcement of a DO-NOT-CONTACT-EARTHLINGS
  rule would require cooperation at a galactic
  scale.
• In other words, if you think we are being quietly
  observed by aliens
• the fact that we have not seen them suggests
  there must be a galactic federation of allied
  planetary civilizations!
• It starts to sound like, the fact that wehave
  never seen leprechauns, proves thatthey exist
  and are magical

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44 Deadly Probes scenario

• Suppose there were bad von Neumann probes in the
  galaxy
• Created by a xenophobic race?
• Created to terraform planets, but disregarding
  the natives?
• Arising from imperfect probe replication,
  resulting in the evolution of a hostile strain?
• Arising from an unanticipated technological
  singularity?
• The new programming
• To explore strange new worlds
• To seek out new life and new civilizations
• To boldly go where no probe has gone before
• then replicate massive attack forces, and
  sterilize it all.
• In response, civilizations would tend to be quiet
  (hide) and cautious about making contact with
  other civilizations.
• Contact beacons would be hidden or nonexistent.

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44 Deadly Probes scenario

• The Deadly Probes scenario explains all the
  observations we have made so far.
• The galaxy is in equilibriumit has been fully
  explored by previous aliens, and especially
  Deadly Probes.
• We are certainly not the first race to explore
  the galaxy in compliance with the Copernican
  Principle, it has already been explored by
  aliensincluding the Deadly Probes.
• The galaxy is filled with aliensbut they are not
  communicating with us because they are hiding
  from the Deadly Probes. Hence the Fermi Paradox
  and Great Silence.
• Problems with other hypotheses (such as unlikely
  100 efficiencies for social changes) do not
  plague this scenarioit only had to happen once.
  
• The Deadly Probes scenario makes a prediction!
• The Deadly Probes Scenario will probably play out
  in our lifetimewe have contacted about 2500
  star systems within 50 LY! These star
  systemsneed not be inhabitedthey only need to
  have Deadly Probes, whichare about to descend
  upon us, and stop us in our tracks!

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A semester in review

• Astrobiology
• The building blocks of life occur throughout the
  galaxy.
• Life evolved with great speed on Earth.
• Primitive life may occur elsewhere in our solar
  system.
• Primitive life seems likely at many sites in our
  galaxy.
• It is quite possible that we are not alone.
• It is quite possible that we are the only life in
  the galaxy.
• Might we become members of a Galactic Union?
• Are we destined to be explorers of the ruins of
  prior civilizations?
• Are we fated, by probability, to destroy
  ourselves?
• Against all odds, are we the first technological
  species to develop?
• Are, even now, alien von Neumann probes such as
  6Q0B44E and 1991VG preparing to overwhelm us with
  superior numbers and technology?
• Any of those possibilities is profound.