Extra-terrestrial Civilizations - PowerPoint PPT Presentation

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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 ….

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Extra-terrestrial Civilizations

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Extra-terrestrial Civilizations

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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

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Are we alone? Contact …

  • Radio communication more likely possibility for contact

  • Electromagnetic radiation travels at the speed of light.

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  • 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.

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Consider ...

  • How many intelligent civilizations exist?

  • How long on average do they last?

  • How does communication proceed?

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Drake Equation

  • One possible way to estimate the number, N, of civilizations.

  • N =

    Ns x fs x ps x ls x lc x L

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Stars in the Galaxy, Ns

  • The number of stars in the Milky Way galaxy … about 300 billion.

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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

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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

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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

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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.

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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

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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

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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.

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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.

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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.

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More than the Milky Way …

  • Ours is not the only galaxy in the universe

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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!

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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.

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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.

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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!

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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!

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  • Sending a signal has its own energy challenges

  • Signal strength drops off as the square of distance.

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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.

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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.

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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).

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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.

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Exotic power

  • Interstellar Ramjets …

  • Ion propulsion … prototypes already tested.

  • Warp drive … dilithiunm crystals anyone?

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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

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  • 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.

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A solution? Perhaps traveling at high speed will allow people to survive interstellar treks.

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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!

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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?!

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Automated Messengers

  • Instead of people in spaceships, send automated messengers.

  • Pioneer and Voyager spacecraft already carry messages from Humanity

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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)

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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?

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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.

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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?

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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.

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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.

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What frequency to choose?

  • Recall our discussion about electromagnetic radiation and the multitude of frequencies associated with it.

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Wavelength and Frequency

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  • 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

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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

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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.

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  • 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.

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Arecebo Observatory

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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

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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).

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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).

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The spin-flip transition in hydrogen emits 21-cm radio waves

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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.

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Doppler Effect: the wavelength is affected by therelative motion between the source and the observer

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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.

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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!

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Common Transmissions from Earth

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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.

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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

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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.

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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

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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.

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SETI Searches to-date

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The Wow! Signal

  • August 15 1977

  • Ohio State University Radio Observatory (Big Ear)

  • 72 seconds in length and VERY strong

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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)

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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

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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.

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The Flag of Earth

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The Fermi Paradox

“So where is everyone?”

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Enrico Fermi1901-1954

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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).

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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.)

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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.

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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!

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The contradiction

  • Colonization should have occurred

  • No evidence of such rampant colonization

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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.

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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.




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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!

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December ….

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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

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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.

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  • 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).

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Human Population

  • Humanity is experiencing an exponentially growing population which is, arguably, unsustainable.

  • Approximately 100 million people born annually.

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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.

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Other solutions to the Fermi Paradox: Solution #2

  • Civilizations common but have not colonized the galaxy.




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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.

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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.

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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.

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