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Astronomy > Lecture 11 - ETs > Flashcards

Lecture 11 - ETs Flashcards

1
Q

What is the rare Earth hypothesis?

A

Simple life might be common, but advanced life like on Earth is extremely rare

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2
Q

What are the 5 arguments in favour of the rare Earth?

A

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

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3
Q

What is Drake’s equation?

A

Estimated the number of currently living civilizations actively communicating in the Galaxy.

N = R * fp * ne * fl * fi * fc * L

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4
Q

What is the modified Drake equation?

A

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)

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5
Q

How many planets are estimated to be in the Galaxy?

How old is the Galaxy?

A

1) 400 billion (Gyr)

2) 10 Gyr

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6
Q

What is convergent evolution?

A

Leads to identical products of evolution despite species not being closely related

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7
Q

How does the encephalization quotient (EQ) show that civilization might be inevitable?

A

EQ measures the growth of the brain w/ evolution. It’s not synonymous but EQ has been positively correlated with intellgence

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8
Q

Describe Tesla’s and Marconi’s attempts at communication with ETs.

A

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.

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9
Q

How could the signals received by Tesla and Marconi be explained?

A

Thunderstorm whistlers reflected by Earth’s ionosphere.

Wavelengths were too long to penetrate so they would just bounce back to us.

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10
Q 
Will ETs be able to detect these signals from us?
Military radar
AM radio
FM radio
TV signal
A

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

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11
Q

What is a better radio window for interstellar communication than TV signals?

A

21 cm hydrogen spectral emission line

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12
Q

What are the types of expected signals to be detected from ETs?

A

1) Local communications leaking from civs (like TVs)
2) Communication between already established colonies
3) Intentional beacon signals to notify presence in Galaxy

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13
Q

What are the 3 types of special beacon signals?

A

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

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14
Q

Where is it possible that ETs could have placed monitoring devices around us?

A

Lagrangian points in the Earth-Moon system or Sun-Earth system

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15
Q

What are the 3 types of civilizations?

A

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!

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16
Q

What could Type II civilizations build to capture wasted radiation from their star?

A

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

17
Q

After the flying saucer/UFO mania started in 1940, what caused the sightings to go down?

A

End of the Cold War

Most sightings were actually military activity during war periods

18
Q

What kind of clouds were often mistaken as UFOs?

A

Lenticular clouds

Disappears when it condenses

19
Q

Are the signs in the desert made by ETs?

A

No - Made by Nazca Indian tribes 2000 years ago

Mainly made to attract gods

20
Q

Which spacecraft are now being used for interstellar travel?

What batteries do they use?

A

Voyager 1 & 2

Radioisotope thermoelectric generators (RTGs)

21
Q

What are the 2 main problems with interstellar travel?

A

1) Velocity cannot exceed speed of light (300,000 km/s)

2) The energy required for distant travel will be colossal

22
Q

How do rockets use Newton’s 3rd law?

A

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

23
Q

What are the 3 other (stronger) ways interstellar travel can be achieved?

A

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

24
Q

What is Einstein’s theory of relativity?

A

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)
25
Q

What is a way for interstellar travel to occur without the problem of the speed of light?
What are the 5 arguments against this?

A

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
26
Q

What are Von Neuman machines?

A

Self-replicating robots for exploration

If civs live long, they might colonize other planets. Before they consider moving, these robots would explore for them

27
Q

What is the Fermi paradox?

A

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?

28
Q

What are the 2 possibilities of the Fermi paradox?

A

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

Astronomy (10 decks)

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