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Extra-terrestrial Civilizations

Extra-terrestrial Civilizations

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Extra-terrestrial Civilizations

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  1. Extra-terrestrial Civilizations

  2. 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

  3. Are we alone? Contact … • Radio communication more likely possibility for contact • Electromagnetic radiation travels at the speed of light.

  4. 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.

  5. Consider ... • How many intelligent civilizations exist? • How long on average do they last? • How does communication proceed?

  6. Drake Equation • One possible way to estimate the number, N, of civilizations. • N = Ns x fs x ps x ls x lc x L

  7. Stars in the Galaxy, Ns • The number of stars in the Milky Way galaxy … about 300 billion.

  8. 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

  9. 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

  10. 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

  11. 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.

  12. 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

  13. 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

  14. 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.

  15. 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.

  16. 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.

  17. More than the Milky Way … • Ours is not the only galaxy in the universe

  18. 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!

  19. 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.

  20. 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.

  21. 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!

  22. 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!

  23. Photons • Sending a signal has its own energy challenges • Signal strength drops off as the square of distance.

  24. 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.

  25. 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.

  26. 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).

  27. 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.

  28. Exotic power • Interstellar Ramjets … • Ion propulsion … prototypes already tested. • Warp drive … dilithiunm crystals anyone?

  29. 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

  30. 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.

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

  32. 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!

  33. 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?!

  34. Automated Messengers • Instead of people in spaceships, send automated messengers. • Pioneer and Voyager spacecraft already carry messages from Humanity

  35. 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)

  36. 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?

  37. 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.

  38. 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?

  39. 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.

  40. 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.

  41. What frequency to choose? • Recall our discussion about electromagnetic radiation and the multitude of frequencies associated with it.

  42. Wavelength and Frequency

  43. 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

  44. 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

  45. 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.

  46. 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.

  47. Arecebo Observatory

  48. 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

  49. 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).