Listening in the Dark
The search for extraterrestrial intelligence
“Two possibilities exist: either we are alone in the
Universe or we are not. Both are equally terrifying.”
—Arthur C. Clarke
Why search for life?
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To prove whether life is unique
To answer scientific questions about the nature of life
We may be able to learn from other intelligent life
To discover whether we are alone
How do we search?
Methods for finding life:
How do we search?
Methods for finding life:
● Listen for “noise
pollution”
● Search for intentional
communication
● Look for modification of
the Universe
● Send a message
A feeble light in a vast sea
→ Radio waves are a form of light. Thus, they propagate at the speed of
light, but also get weaker the farther they travel.
Distance
traveled
Starting
brightness
Time
traveled
Speed of light
(299,792,458 m/s)
Observed
brightness
Distance
traveled
A feeble light in a vast sea
→ In 1936, a TV broadcast of Adolf Hitler opening the Berlin Olympics
became the first radio signal to leave the Earth.
In 1937, that signal was 1 lightyear from Earth.
In 2016, that signal is 80 lightyears from Earth, but it is 6,400 times
weaker than in 1937.
SETI today
→ The Allen Telescope Array is engaged in a search for radio signals of
extraterrestrial intelligence.
So far, it has found nothing.
A cosmic telegram
→ A laser generates a beam of highly-focused light. Lasers require
relatively little energy to be extremely bright in a single direction. Lasers
are monochromatic, which means they contain light of only one color.
Pros
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A strong signal would be easier to
detect
Would give exact source of message
Message more likely to be
unambiguous
Cons
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ET would have to be directly
contacting us
We’d need to know which color to
look for
Go big or go home
→ A Dyson sphere is a hypothetical structure that encompasses much or
all of a star in order to harvest its energy. It’s theorized that it may be
common for advanced species to construct them.
Pros
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Megastructures give a strong
indication of the advanced nature of
a species
Cons
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Structures built with our current
understanding of materials would
block only a little of the star’s light
The signal of a megastructure is
easily confused with a natural
process
A glimmer in the dark
→ A key human innovation was the development of artificial light. If
other species have also developed it, light may still be visible from the
nightside of a planet.
Pros
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Would give us information about the
behavior of an extraterrestrial
species
Cons
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Artificial light is likely extraordinarily
dim in comparison to the star
The light may not be in the visible
spectrum
A message for the stars
→ In 1977, NASA launched the Voyager 1 and Voyager 2 spacecraft.
Their mission was to explore the outer Solar System for the first time.
They also carried a message.
Each message was designed to last for a billion years.
Small group discussion
You are sending a message to intelligent life in the Universe. You may
only include images and sounds.
What do you send?
Contents of the Golden Record
“To the makers of music – all worlds, all times”
Sounds
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Greetings in 55 languages
Sounds from nature
○ Wind, birds, volcanos, a train, a
kiss
90 minutes of world music
○ Mozart, Chuck Berry, others
An hour-long recording of brain
waves
Images (116)
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The visited planets
Structure of DNA
Human anatomy
Snowflakes
Jane Goodall and chimps
Supermarket
Taj Mahal
Sunset
“This record represents our hope and our determination and our goodwill
in a vast and awesome universe.”
– Jimmy Carter
The universal language
→ The principles of mathematics are believed to be constant across the
Universe. They may offer a connection between species.
How would we know?
→ Explicit contact from another lifeform would require the expression of
knowledge unique to intelligent life.
Fibonacci sequence
→ The Fibonacci sequence is the sequence of numbers generated by
starting with 0 and 1 and adding pairs from there.
0, 1, 1, 2, 3, 5, 8, 13, 21, 34, 55, 89, 144, ...
The golden ratio
→ The golden ratio Φ is a number found throughout mathematics and
nature.
Two numbers are said to be in the golden ratio if:
Φ = 1.6180339887…
Pi
→ The ratio of the circumference of a circle to its diameter is called π
π = 3.14159265358979323846264338327950288419716939937510...
The Kardashev scale
→ The Kardashev scale is a hypothetical classification system for how
advanced an intelligent species is.
Type 1: The species is capable of harnessing all their host star’s energy
that strikes their planet.
Type 2: The species is capable of harnessing all of their host star’s
energy
Type 3: The species is capable of harnessing the energy of all the stars in
their galaxy