Listening in the DarkThe 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?

● 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

Speed of light(299,792,458 m/s)

Time traveled

Starting brightness

Distance traveled

Observed brightness

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

Pros

● A strong signal would be easier to detect

● Would give exact source of message● Message more likely to be

unambiguous

Cons

● ET would have to be directly contacting us

● We’d need to know which color to look for

→ 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.

Go big or go home

Pros

● Megastructures give a strong indication of the advanced nature of a species

Cons

● 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 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.

A glimmer in the dark

Pros

● Would give us information about the behavior of an extraterrestrial species

Cons

● Artificial light is likely extraordinarily dim in comparison to the star

● The light may not be in the visible spectrum

→ 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.

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

Sounds

● 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)

● The visited planets● Structure of DNA● Human anatomy● Snowflakes● Jane Goodall and chimps● Supermarket● Taj Mahal● Sunset

“To the makers of music – all worlds, all times”

“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