Lecture 11 - ETs Flashcards
What is the rare Earth hypothesis?
Simple life might be common, but advanced life like on Earth is extremely rare
What are the 5 arguments in favour of the rare Earth?
1) Galactic HZ: Earth-like planets can form in certain parts of the galaxy but life can die if too close or far form star.
2) Plate tectonics: Enables CO2 cycle which ensures climate stability
3) Jupiter: Deflects and swallows comets and planetoids which would’ve hit Earth
4) Water: The amount if just right on Earth
5) Big Moon: Stabilizes rotation axis tilt and keeps Earth’s climate stable
What is Drake’s equation?
Estimated the number of currently living civilizations actively communicating in the Galaxy.
N = R * fp * ne * fl * fi * fc * L
What is the modified Drake equation?
N = Nhp * flife * fciv * fnow
N: # of civilizations in Galaxy rn doing interstellar communication
Nhp: # of habitable planets in Galaxy
flife: Fraction of habitable planets that develop life
fciv: Fraction of planets with life that produce intelligent life
fnow: Fraction of communicating civs currently in existence from total that have ever existed
(Time a communicating civ exists) / (age of Galaxy)
How many planets are estimated to be in the Galaxy?
How old is the Galaxy?
1) 400 billion (Gyr)
2) 10 Gyr
What is convergent evolution?
Leads to identical products of evolution despite species not being closely related
How does the encephalization quotient (EQ) show that civilization might be inevitable?
EQ measures the growth of the brain w/ evolution. It’s not synonymous but EQ has been positively correlated with intellgence
Describe Tesla’s and Marconi’s attempts at communication with ETs.
N. Tesla: Tried to send electric power by induction of low-freq radio waves using a 60 m tower. Received strange signals instead.
G. Marconi: Sent radio signals between England and Canada but received unexplained signals.
How could the signals received by Tesla and Marconi be explained?
Thunderstorm whistlers reflected by Earth’s ionosphere.
Wavelengths were too long to penetrate so they would just bounce back to us.
Will ETs be able to detect these signals from us? Military radar AM radio FM radio TV signal
Military radar: No - it’s not continuous and often switch freqs
AM radio: No - Gets reflected by ionosphere
FM radio: No - Too broad bandwidth
TV signal: Yes - Bandwidth wife but carrier frequency is very narrow and strong. Sent horizontally to maximize energy concentration
What is a better radio window for interstellar communication than TV signals?
21 cm hydrogen spectral emission line
What are the types of expected signals to be detected from ETs?
1) Local communications leaking from civs (like TVs)
2) Communication between already established colonies
3) Intentional beacon signals to notify presence in Galaxy
What are the 3 types of special beacon signals?
1) Our TV signals are intercepted, modified and sent back by nearby civs (Theory by Carl Sagan)
2) Strong, narrow-band, repeating or changing (between 2 freq) signal
3) Unusual, coded signal that doesn’t fit nature
Where is it possible that ETs could have placed monitoring devices around us?
Lagrangian points in the Earth-Moon system or Sun-Earth system
What are the 3 types of civilizations?
I) Utilizing fully resources of their planet
II) Utilizing fully resources of their star
III) Utilizing fully resources of their galaxy
We are sub-I!
What could Type II civilizations build to capture wasted radiation from their star?
Dyson sphere
A huge sphere covering the planet and star to store energy. We would only be able to see it glowing in IR light
After the flying saucer/UFO mania started in 1940, what caused the sightings to go down?
End of the Cold War
Most sightings were actually military activity during war periods
What kind of clouds were often mistaken as UFOs?
Lenticular clouds
Disappears when it condenses
Are the signs in the desert made by ETs?
No - Made by Nazca Indian tribes 2000 years ago
Mainly made to attract gods
Which spacecraft are now being used for interstellar travel?
What batteries do they use?
Voyager 1 & 2
Radioisotope thermoelectric generators (RTGs)
What are the 2 main problems with interstellar travel?
1) Velocity cannot exceed speed of light (300,000 km/s)
2) The energy required for distant travel will be colossal
How do rockets use Newton’s 3rd law?
Fuel pushes backward, causing rocket to move forward
By repeating several times with several stages, rocket could be pushed more but at 1/2 of previous fuel and payload
What are the 3 other (stronger) ways interstellar travel can be achieved?
1) Nuclear rockets
Uses fission of heavy elements to energy
Or fusion of hydrogen to helium to make energy (H-bombs)
2) Antimatter propulsion
3) Solar sails
But only close to sun because 1/d^2
What is Einstein’s theory of relativity?
As an object travels closer to the speed of light…
- Its length becomes shorter in direction of movement
- Its mass becomes greater
- Time measured aboard object proceeds more slowly (time dilation)
What is a way for interstellar travel to occur without the problem of the speed of light?
What are the 5 arguments against this?
Wormholes (Shortcut through space)
But…
- No observational evidence
- Can’t control where they are
- Can’t control where they go
- Don’t know how to enlarge them to get spacecraft through
- Theory says they most likely will immediately collapse
What are Von Neuman machines?
Self-replicating robots for exploration
If civs live long, they might colonize other planets. Before they consider moving, these robots would explore for them
What is the Fermi paradox?
If we are not special in any way
And we are developing civilization
-> We have every reason to believe that there are more civs out there!
But intelligent life could have arisen up to ~5 Gyr aho
And w/ colonization speeds of 150 km/s (our limit), it would take only 160 Myr to colonize the whole galaxy
-> So where is everybody?
What are the 2 possibilities of the Fermi paradox?
1) We’re alone
- We’ are 1st occurrence of life that has become aware and is exploring beyond home planet
2) Civs are common but
- Interstellar travel impossible
- Civs might choose not to colonize or contact us
- Civs are short-lived
