The Black CloudA thinking interstellar cloud

If an interstellar cloud drifting toward the Sun were intelligent, what would it want? This page covers dark clouds, organic molecules and related research.

Interstellar clouds are real. Thinking interstellar clouds exist only in fiction. The "The Black Cloud" channel in the game borrows the premise of Fred Hoyle's 1957 novel The Black Cloud: a cloud of interstellar gas drifts into the Solar System and blocks the sunlight, and people later discover that the cloud is alive and very intelligent.

This page first covers the real science of interstellar clouds: how they block starlight, what molecules they hold, and how long a cloud would need to "think" a thought. Then it covers the story the game imagines, and finally lists related real research. Hoyle was a real astrophysicist, which is why this premise is worth discussing.

Dark clouds are real

Hiding the stars: Barnard 68 is about 500 light-years away and about half a light-year across. Visible light cannot get through at all, and the stars behind it cannot be seen.
Radio echo: molecules in interstellar clouds emit radio spectral lines at specific frequencies, and astronomers use them to measure a cloud's temperature and velocity.
What it wants is light: dust absorbs starlight and re-emits it as infrared radiation, so dark clouds are in fact bright in the infrared.

Organic molecules in the cloud

Sagittarius B2 is a huge molecular cloud near the center of the Milky Way. Organic molecules detected in it include ethanol, ethyl formate and branched isopropyl cyanide. The author of The Black Cloud did not make this up: interstellar clouds really do contain complex organic molecules, and several have been found in Sagittarius B2.

How fast can a cloud "think"

If a cloud really could think, it would be slow, because no signal can travel faster than light. For a thought to spread across a whole brain takes at least the time light needs to cross it. A brain the size of Earth needs only about 0.04 seconds. A cloud one astronomical unit across needs more than 8 minutes.

Magnetic field lines run through the cloud, and charged particles move along them. That is the real starting point of the game's "Magnetic nerves". For communicating with a completely alien mind, the most often cited starting point is mathematics: prime numbers, geometry, physical constants.

The life and death of a cloud

A molecular cloud usually lives only a few tens of millions of years, then collapses into stars or is blown apart. When a molecular cloud is cold and dense enough, it collapses under its own gravity. This is called the Jeans instability, and it is how stars are born. So for a thinking cloud, collapse means death.

In 1950, over lunch, Enrico Fermi asked: "Where is everybody?" The game puts that question to this cloud as well.

The idea in the game

What follows is game lore. The channel tells of astronomers noticing that the stars in one patch of sky are disappearing one by one. Something ahead is blocking the light behind it and drifting toward the Sun, and it is changing course. It is discovered in the interstellar-civilization era, once space telescopes exist. The mechanic is slow thinking: every question has to wait until it finishes "thinking" before you get an answer, and the deeper the question, the longer the wait. When it stops near the Sun, it blocks part of the sunlight, and the main civilization's "Interstellar civilization" output drops.

In the scenario, it thinks with electric currents in its magnetic fields. It says it is older than the Sun and has come to "feed", absorbing starlight to replenish its energy. It says other clouds in the galaxy are also thinking, and one sentence between them takes hundreds of years to travel. It answers the question humans have always wanted to ask: most of them are waiting, waiting for the universe to cool. The channel has two endings. It slowly retreats into interstellar space, leaving one sentence: "When the universe has cooled, we will meet again." Or it stays at the edge of the Solar System, like a thin halo. All of this is fiction.

The studies below concern Hoyle himself and organic molecules in space. They are related real science, not evidence that clouds can think.

A systematic account of how stars forge the elements of the periodic table step by step, where "we are all star dust" begins (Burbidge, Burbidge, Fowler and Hoyle, Reviews of Modern Physics, 1957).
So that stars could make enough carbon, Hoyle predicted that carbon-12 must have a special energy level, which experiment then confirmed (Hoyle, The Astrophysical Journal Supplement, 1954).
Water, methane, ammonia and hydrogen sealed in a flask and subjected to continuous electric discharge produced the amino acids that make up proteins (Miller, Science, 1953).
Amino acids of extraterrestrial origin were found in the Murchison meteorite, so the raw materials of life may be common in the universe (Kvenvolden et al., Nature, 1970).

Real basis

Hiding the stars: Barnard 68 is about 500 light-years away and about half a light-year across. Visible light cannot get through, and all the stars behind it are hidden.
Radio echo: Molecules in interstellar clouds emit radio lines at specific frequencies, and astronomers use them to measure a cloud's temperature and speed.
Shared numbers: The most often mentioned starting point for communicating with a completely alien intelligence is mathematics: primes, geometry, physical constants.
Organic molecules in the cloud: Sagittarius B2 is a giant molecular cloud near the center of the Milky Way, where organic molecules such as ethanol, ethyl formate and branched isopropyl cyanide have been detected.
Magnetic nerves: Magnetic field lines run through interstellar clouds, and charged particles move along them.
Light-speed thought: For a thought to spread across a whole brain takes at least the time light needs to cross it. A brain the size of Earth needs only about 0.04 seconds; a cloud one astronomical unit across needs over 8 minutes.
Its age: Molecular clouds usually last only a few tens of millions of years, then collapse into stars or get blown away.
What it wants is light: Dust absorbs starlight and re-emits it as infrared, so dark clouds are actually bright in infrared.
Stars are its death: When a molecular cloud is cold and dense enough, it collapses under its own gravity; this is called Jeans instability. This is how stars are born.
Where are they?: Fermi asked over lunch in 1950: “Where is everybody?”
The Black Cloud (Fred Hoyle, 1957), the science: Hoyle was a real astrophysicist. Interstellar clouds do contain complex organic molecules; several kinds have been found in Sagittarius B2.

Related research

These studies relate to this topic but are not direct proof of this page.

B²FH: This hundred-page paper explained, step by step, how stars forge the elements of the periodic table. We are all stardust, and this is where that idea starts.
Source: Burbidge, Burbidge, Fowler & Hoyle, Reviews of Modern Physics 1957, "Synthesis of the elements in stars"
Hoyle's prediction: For stars to make enough carbon, Hoyle predicted that carbon-12 must have a special energy level, which experiments then confirmed.
Source: Hoyle, The Astrophysical Journal Supplement 1954, "On nuclear reactions occurring in very hot stars. I. The synthesis of elements from carbon to nickel"
The Miller–Urey experiment: A graduate student sealed water, methane, ammonia and hydrogen in a flask and kept sparking it, and got the amino acids that make up proteins.
Source: Miller, Science 1953, "A production of amino acids under possible primitive earth conditions"
Amino acids in space: Amino acids of non-terrestrial origin were found in the Murchison meteorite. The raw materials of life may be common in the universe.
Source: Kvenvolden et al., Nature 1970, "Evidence for extraterrestrial amino-acids and hydrocarbons in the Murchison meteorite"

Game lore (fictional)

Node “Magnetic nerves”: It thinks with electric currents in magnetic fields.
Node “Its age”: It says it is older than the Sun.
Node “What it wants is light”: It came to “feed”: absorbing starlight to refill its energy.
Node “Stars are its death”: For a thinking cloud, collapse is death.
Node “Its kind”: It says there are other thinking clouds in the Milky Way, and a single sentence between them takes hundreds of years.
Node “An answer”: It answered a question humans have always wanted to ask.
Node “Where are they?”: Its answer: most of them are waiting, waiting for the universe to cool.
Node “Departure”: It slowly drifted away, and the stars behind it lit up again one by one.
Channel ending “Farewell”: It slowly retreats into interstellar space, and the stars behind it light up again one by one. It leaves one last sentence: when the universe cools, we will meet again.
Channel ending “Stay”: It stays at the edge of the solar system, like a thin halo. Every question humans ask takes several minutes to be answered, but no one minds the wait.
Summary of the novel The Black Cloud: A cloud of interstellar gas drifts into the solar system and blocks the sunlight. Astronomers later find that the cloud is alive, and very intelligent.

See it in the game