Transcript Extra-terrestrial Civilizations

Extra-terrestrial Civilizations
Are we alone? Contact …
• Direct contact through
traveling to the stars and their
planets
• Will be a challenge because
of the vast distances involved
and the (slow) speeds we can
travel
Are we alone? Contact …
• Radio
communication
more likely
possibility for
contact
• Electromagnetic
radiation travels at
the speed of light.
Civilizations
• Will life always develop technology?
Some societies on Earth have not
developed the means to communicate with
ETs.
• Will a society want to communicate? A
society may develop the means to search
for ET but elect not to attempt to reach
out.
Consider ...
• How many intelligent civilizations exist?
• How long on average do they last?
• How does communication proceed?
Drake Equation
• One possible way to
estimate the number,
N, of civilizations.
• N=
Ns x fs x ps x ls x lc x L
Stars in the Galaxy, Ns
• The number of stars in the Milky Way
galaxy … about 300 billion.
Suitable stars (fraction), fs
• Star must be old
enough to allow life to
develop: spectral
types F, G, K
• Star must have
enough heavy
elements to form
planets … 0.005
Suitable planets in a Solar System,
ps
• To date, extra-solar planets have been ‘hot
Jupiters’
• Planets to sustain life need to be in the
habitable zone around a star … 1.0
Fraction of planets suitable for life, ls
• Very speculative … sample of 1 only to
date (Earth)
• If a planet is suitable for life, good reason
to think life will develop
• Conservative approach suggest: Earth and
Mars could produce life … 0.5
Life develops a civilization, lc
• Again, very speculative.
• Simple life started on Earth
nearly 3.5 billion years ago.
• Extinction level events
common … for example
250 and 65 million years
ago.
Life develops a civilization, lc
• As long as some form of life
exists after an extinction
event occurs, natural
selection should continue
and life redevelops.
• Assuming life develops then
a case can be made that a
form of civilization is
inevitable … 0.33
Lifetime of a civilization, L
• Firstly, the age of our
Milky Way galaxy is 10
billion years.
• How long have we had
the ability to communicate
with ET … about 50 years.
• How many times have we
sent a communication …
not many!
• Radio telescope, Pioneer
and Voyager
Drake Equation Result
• Substituting into
N = Ns x fs x ps x ls x lc x L
• N = 300x109x0.005x1x0.5x0.33xL/10x109
= L/40
• Large numbers top and bottom tend to
cancel out.
Range of answers …
• Depending upon your optimism or
pessimism, N can vary significantly …
• From 10L (Carl Sagan,1978) to a very
optimistic 120L to a pessimistic L/10 billion
• If civilization survives for 100s or 1,000s of
years then N could be very large indeed.
Survival lifetimes
• Dinosaurs lived for 150 million years …
can we survive for longer thus increasing L
substantially?
• Some species of life have lived for over
200 million years on Earth.
• Humans are living ‘outside’ the laws of
Natural Selection … may well reduce L.
• Upper limit based upon life of a star … 10
billion years.
More than the Milky Way …
• Ours is not the only galaxy in the universe
Why communicate at all?
• Curiosity
• The urge to talk and
listen!
• The hope to learn/gain
knowledge
• The need for resources
and/or living space
• Because we can!
Why not?
• Fear (enslavement, destruction, etc)
• Inertia … happy as we are
• Economics … expensive to try and need
to deploy resources appropriately.
• Of course, contact may happen by
accident … leakage of radio and TV
signals.
How far away is a civilization?
• Even assuming optimistic values for the
Drake Equation, the closest civilization
maybe 100s of light years away!
• Average stellar separation in the outskirts
of a galaxy … 5 to 10 light years.
• Two way communication then becomes a
problem.
People or Photons?
• People have mass and that requires
enormous amounts of energy to
accelerate.
• People have needs (food, water, air, etc)
which means more mass to transport!
How much mass per person to take?
• Space ships travel very slowly
• Photons are mass-less and travel at the
speed of light!
Current spaceship technology
• Spacecraft travel at
speeds much less than
100,000 km per hour
• At this speed, travel to
the nearest star would
take 46,500 years!
Photons
• Sending a signal has its own energy
challenges
• Signal strength drops off as the square of
distance.
Photons …
• Thus for any given signal strength,
sending it say one million times further
requires (one million)2 times as much
energy … that is, one trillion.
• This is technically possible (bigger
transmitters, shorter messages, etc) but is
not cheap. It is cheaper than sending
people in spacecraft though.
Space Travel
• (12) Humans have
gone to the Moon
• Machines have
traveled in our Solar
System out to Neptune
and en route as we
speak to Pluto
• As a species we have
the urge to explore and
colonize.
Challenges to travel to the stars
• Distances involved are enormous and will
take us time to traverse
• The energy requirements are equally
immense and very difficult to satisfy (even
if we are willing to pay the price).
Power for the trip
• Chemical combustion is our current form of
energy in rockets … very inefficient.
• Solar power works well near stars but is also
inefficient
• Nuclear power for both on-board power (to live,
etc) as well as thrust is possible with our
technology.
• Matter and anti-matter … more efficient certainly
but also beyond our means at present.
Exotic power
• Interstellar Ramjets …
• Ion propulsion …
prototypes already
tested.
• Warp drive …
dilithiunm crystals
anyone?
Time Dilation
• As you travel faster, your own clock (in your frame
of reference) slows down from an outside
perspective.
• Traveling at a
significant fraction of
the speed of light
means you
experience a
smaller passage of
time compared to an
Earth based
observer
Relativity
• T = T0 / Sqrt (1 –v2/c2)
• where T0 is the time elapsed in the
moving frame of reference
• where T is the time elapsed in the
stationary frame of reference
• where v is the speed you are moving
relative to the stationary observer.
A solution? Perhaps traveling at
high speed will allow people to
survive interstellar treks.
Time dilation example
• You and your friend synchronize your
watches.
• You remain on Earth and your friend ‘flies
off’ at 99% the speed of light.
• Your friend returns when 1 hour of time
has elapsed according to their watch.
• You have waited approximately 7 hours for
your friend to have returned!
One more danger ..
• At higher speeds for our spacecraft, the
particles in the ISM are now moving at
enormous velocities relative to you.
• If your spaceship is moving at 99% the
speed of light, the kinetic energy of a
particle in the ISM will seem like a very
energetic bullet and could do serious
damage to the spacecraft … shields
anyone?!
Automated Messengers
• Instead of people in
spaceships, send
automated messengers.
• Pioneer and Voyager
spacecraft already carry
messages from Humanity
Von Neuman machines
• Build an automated robotic spacecraft and
send it to a distant star/planet.
• When there, let it mine resources and
replicate itself, sending copies of itself to
other stars/planets.
• In short order, such robots could be
everywhere!
• So where are they? … the Fermi Paradox
(later)
Radio contact: A test?
• If civilizations are common, then why have
we not yet ‘heard’ them?
• To find the signals from ET may involve
solving technology not yet known to us.
• Is the search for contact a test in itself …
are we worth talking to?
Consider …
• You can see a cell phone but cannot ‘hear’
what it hears.
• Electromagnetic signals pass through your
body all the time and you cannot detect
them.
• Thus the human body is limited to what
information it can process as is the cell
phone.
Direct or Accidental signals
• Realizing that signals from ET may well be
very weak, where should we look? … what
frequency?
• We may be lucky and detect signals not
beamed at us … eavesdrop on ‘Star Trek’,
‘Friends’ ,etc.
• What type of signal should we look for?
• What direction/star (planet) should we
listen to?
Where to look
• Closer civilizations if they are sending
signals will presumably have the strongest
signals and be easier to detect.
• Signal strength drops off as the square of
distance.
Type of Stars
• As discussed, stars like our Sun first targets.
• In the Milky Way galaxy, stars with similar
spectral types (F, G, K) constitutes 10% or more
of all stars (30 billion or more).
• Double, multiple, very luminous (and thus short
lived) stars not suitable targets.
• Specialization regarding how many planets
contain technologically advanced civilizations.
What frequency to choose?
• Recall our discussion about
electromagnetic radiation and the
multitude of frequencies associated with it.
Wavelength and Frequency
• Because of its
electric and
magnetic properties,
light is also called
electromagnetic
radiation
• Visible light falls in
the 400 to 700 nm
range
• Stars, galaxies and
other objects emit
light in all
wavelengths
Familiar Frequencies
• AM dial … radio stations tuned in with
frequencies 500 – 1500 KHz
• FM dial … radio stations tuned in with
frequencies 88 – 110 MHZ
• TV channels with frequencies 70 – 1,000
MHZ
ET listens to … CBC?
• How to decide what frequency ET will
listen to?
• Is there a galactic, common hailing
frequency?
• We assume that a civilization
technologically advanced enough to
send/receive radio signals will know the
language of science.
Considerations
• Economical to send a radio photon than
say, a (visible) light photon. If we are
sending to many stars, cost needs to be
controlled (low).
• The selected frequency must be able to
traverse significant distances without
interference or loss.
Arecebo
Observatory
Problems during transmission
• Photons of energy at the wrong frequency
will be absorbed … you cannot see
through a brick wall but your phone can
pick up a signal through the same wall.
• Long wavelength radiation can travel
further with less absorption … best for
sending/receiving signals
Natural background
• The galaxy is quote noisy … stars would wash
out a visible light signal (even if it could travel a
long way through the dust).
• The cosmic background radiation is an
echo/hiss left over from the Big Bang (high
frequency cutoff).
• Charged particles (mostly electrons) spiral
around the magnetic field lines producing
synchrotron radiation (low frequency cutoff).
The water hole
• In between the upper and lower cut-offs in
frequency is a relatively radio quiet area
near where the hydrogen atom ‘flips’ giving
a unique signal at 1420 MHZ or 21.1 cm
(wavelength).
The spin-flip transition in hydrogen
emits 21-cm radio waves
The water hole … continued
• Near by is a
similar
transmission from
the OH
radical(1612,
1665, 1667, 1720
MHz).
• Thus the Water
Hole is a likely
spot to search for
a signal from ET.
Doppler Effect: the wavelength is
affected by the
relative motion between the source and
the observer
The question of Bandwidth
• The spread of frequencies examined
during a search for ET.
• A broad bandwidth (like for TV) has coned
the term ‘channel’.
• A bandwidth of as small as 1 Hz increases
the chances of detecting an artificial
signal.
• A 1 Hz bandwidth requires LOTS of
searching in a given frequency range.
Signal characteristics
• Narrow band can have more power
• Narrow can be dispersed by the Interstellar
Medium (ISM).
• Broad band carries more information.
• AM bandwidth: 10KHz
• FM Bandwidth: 200 KHz
• TV bandwidth: 6 MHz
• For all, half the power of signal confined to 1 Hz!
Common Transmissions from
Earth
Frequency
Range
Source
CB radios
(MHZ)
Fraction of
Effective
Time
Carrier,
Number of Transmitters Maximum Power Bandwidth
Transmitters
Emit
Radiated (watts)
(hertz)
2-7
10,000,000
1/100
5
2
20-500
100,000
1/10
20
1
1000-10,000
100,000
1/10010,000 to 1,000,000
1,000,000
Defenser Radarsa
400
2
1/10
10,000,000,000
1,000
FM radio stations
88-108
10,000
1
4,000
0.1
TV sound
40-850
2000
1
500,000
0.1
Professional mobile
radios
Weather, marine, & air
radars
Can we conclude ET from these
signals?
• TV signals may well vary their frequencies
periodically as a result of Earth’s rotation
(on its axis) and revolution (around the
Sun) … Doppler shifts.
The First Search: Project Ozma
• Frank Drake mounted the
first SETI search
• July 1960, 85 foot radio
telescope at Green Bank in
West Virginia
• Searched at a wavelength of
21 cm.
• Tau Ceti and Epsilon Eridani
were targets
Brief History
• Philip Morrison and Guiseppe Coconni
published Searching for Interstellar
Communication
• 1960 Project Ozma (Frank Drake)
• 1961, first SETI Conference, Order of the
Dolphin and the unveiling of the Drake
Equation.
• 1972-1973 Pioneer Probe Plaques.
History continued …
• 1973: Ohio State University begins a
major SETI project at its Big Ear
Observatory in Delaware
• 1974 Drake transmission to M13
• 1977 WOW signal
• 1977 Voyager probe disks
• 1979 Planetary Society founded (Carl
Sagan et al)
• 1984: The SETI Institute is founded
1974 Message to M13
• 20
trillion watt
transmission, lasting about 3
minutes
• Message 1679 bits,
arranged 73 lines x 23
characters (prime numbers!)
•DNA, a human being, the
Solar System, etc.
SETI Searches to-date
SCIENTIFIC
Investigator
Antenna
Diameter
(meters)
Frank Drake
V. Troitskii
B. Zuckerman & P. Palmer
G. Verschuur
S. Bowyer and others
R. Dixon and others
A. Bridle & P. Feldman
Frank Drake & Carl Sagan
T. Bania & R. Rood
P. Horowitz
NASA scientists
NASA scientists
S. Bowyer and others
D. Werthimer and others
SETI Institute scientists
26
14
91
43,91
26
53
46
305
43
26
305
26,34
305
305
64,22
Frequency
Observed (MHz)
Frequency
Resolution
(kHz)
Total
Frequency
Band (MHz)
1420
100, 1800, 2500
1413-1425
1420
variable
1420
22,235
1420, 1653, 2380
8665
1400-1720
1300-2400
1700,8300-8700
424-436
1370-1470
1200-1750
0.1
0.013
4
7
2.5
30
30
1.0
0.3
0.0005
1,7,28
0.019
0.0006
0.0006
0.001
0.4
2.2
12
20
20
0.4
3
320
1100
400
10
100
550
The Wow! Signal
• August 15 1977
• Ohio State University Radio Observatory
(Big Ear)
• 72 seconds in length and VERY strong
Current major SETI efforts
• Project Phoenix uses many radio
telescopes from around the world in
targeted searches (SETI Institute:
www.seti.org).
• The Allen Telescope Array of up to 500
radio telescopes in a linked array.
• Project SEREBDIP uses radio telescopes
‘piggy back’ to listen in to 1420 MHz.
(University of California at Berkley)
Data, data everywhere …
• SERENDIP generates vast quantities of
data that need to be searched for a signal
(from ET).
• SETI@home links idle computers (like
yours) from around the world to analyze
data (setiathome.berkeley.edu
Other search techniques
• Optical SETI assumes the use of lasers in
a pulsed manner to signal existence.
• Masers are microwave equivalents to
lasers and are being investigated as a
possible signaling medium.
The Flag of Earth
The Fermi Paradox
“So where is everyone?”
Enrico Fermi
1901-1954
The Fermi Paradox
• The belief that the universe contains many
technologically advanced civilizations, combined
with our lack of observational evidence to
support that view, is inconsistent. Either this
assumption is incorrect (and technologically
advanced intelligent life is much rarer than we
believe), our current observations are
incomplete (and we simply have not detected
them yet), or our search methodologies are
flawed (we are not searching for the correct
indicators).
Logic …
• We are not special in our development (life
on Earth)
• Thus via the Drake Equation, life should
be relatively common in the Milky Way.
• Even traveling at slow speeds,
colonization should have lead to outposts
everywhere by now. (Milky Way is 10
billion years old.)
Even worse … Von
Neuman machines
• Build self replicating machines and let
them explore the galaxy.
• In this way, while colonization is not
performed, the presence of civilizations
would be felt everywhere in the galaxy.
• Probes are not encumbered by the
physical limitations of life (air, water, aging
etc.). Relatively easy to produce.
An aside …
• Von Neuman machines
might consume all the
resources in a galaxy!
(They could develop
exponentially.)
• If so, any civilization
capable of producing
these machines would
not!
The contradiction
• Colonization should have occurred
• No evidence of such rampant colonization
Solution #1
• We are the first technologically advanced
civilization capable of interstellar travel
and communication.
• If so, SETI is a waste of time … no one out
there to talk to.
• This solution sounds much like the
Geocentric Model of the Solar System …
Earth special (unique, rare) and does not
seem likely. Nothing in astronomy or
biology suggests we are special.
Cosmic Calendar
(inspired by Carl Sagan)
• Imagine the age of the universe (and thus
life on Earth) compressed to 1 calendar
year.
• January to November inclusive. Each
month is 1 billion years, each second is
390 years.
March
August
November
The power of the media
• This type of reporting stems from alack of
understanding and a lack of research into
the facts.
• Sound familiar … remember to not
necessarily take information at face value.
A report in any media is not always
accurate … be skeptical!
December ….
To note …
• The dinosaurs existed from December 25
through 30!
• The entire human history is less than 30
seconds long (~10,000 years)!
• Planets capable of harboring life in our galaxy
could have formed in July!
• Almost any assumptions you make result in a
conclusion that civilizations have had ample time
to form and develop and colonize
Comparable age and
development?
• Perhaps a more useful question to ask is
‘Are other civilizations technologically
comparable to us?’
• We have had space travel and interstellar
communication capability a short time.
How long will we keep it?
• More likely other civilizations very
advanced or very inferior technologically
speaking.
Colonization
• Like the Von Neuman machines,
interstellar colonization would result in the
relatively rapid spread of settlements
throughout the Milky Way galaxy. The
coral model.
• Note that colonization does not represent
a solution to the population explosion on a
planet (like Earth).
Human
Population
• Humanity is
experiencing an
exponentially
growing population
which is, arguably,
unsustainable.
• Approximately 100
million people born
annually.
Why colonize?
• Assuming the attitudes associated with life
on Earth are not unique, then our history is
resplendent in voyagers of exploration and
colonization
• Other civilizations may colonize to avoid
their culture becoming extinct (existing on
more than one planet).
• Perhaps colonization is spurred on by the
need to flee persecution, etc.
Other solutions to the Fermi
Paradox: Solution #2
• Civilizations common but have not
colonized the galaxy.
– TECHNICALLY TOO DIFICULT (OR TOO
EXPENSIVE IN TIME AND ENERGY)
– THE DESIRE TO COLONIZE IS NOT
COMMON (WE ARE ATYPICAL)
– DESTRUCTION OF THE CIVILIZATION
OCCURS BY THEMSELVES OR THROUGH
NATURAL CAUSES (ASTEROIDS, ETC.)
Other solutions to the Fermi
Paradox: Solution #3
• There is a galactic civilization out there
and they have chosen to keep us isolated
(Star Trek’s Prime Directive). Thus there
is no paradox!
• Sometimes called the Zoo hypothesis …
but we may still yet detect their signals
even if they choose not to communicate
with us.
• Time likely needed for SETI to succeed.
Other solutions to the Fermi
Paradox: Solution #3 cont.
• The Sentinel
hypothesis suggests
that galactic
civilizations are indeed
monitoring us, waiting
for us to reach the right
level of technology …
allowing us to join the
Galactic Club.
Too expensive?
• It often comes down to money …
• ‘It is fine to argue about the number of
civilizations that may exist. After the
argument, there is no easy substitute for a
real search out there … we owe the issue
more than mere theorizing.’ … Philip
Morrison
• Answering the Fermi Paradox will
arguable be a turning point in our history.