What dark matter iswhy galaxies need unseen mass
Dark matter makes up over 80% of the universe's matter, yet nobody knows what it is. The real research behind the Cosmos Era ending “What dark matter is”.
Dark matter makes up more than 80% of the matter in the universe, and galaxies really do form inside dark matter halos. It is detected only through gravity, and what it is remains unknown. The game's ending “What dark matter is” offers a fictional answer: dark matter is the civilization of the previous universe. That answer is made up. The question itself is one of the biggest unsolved mysteries in real science.
This page first explains how to unlock the ending, then follows the history of dark matter in order: the first proposal in 1933, galaxy rotation in 1970, the Bullet Cluster in 2006, and finally a large experiment in 2025 that found no signal.
How to unlock it
- Hint: Dark matter gives off no light and says nothing. Perhaps it is just waiting for someone who will listen.
- Condition: Collect all seven dark matter research cards, unlock Dark matter halos, Dwarf galaxy, Galaxy cluster and Gravitational lens, then unlock “Talking to dark matter” and witness the end of the universe.
- Reward: “Era legacy” is renamed “Hand of the Ancestors”, and the legacy exponent rises by 0.1 permanently.
This ending belongs to the Physics category. The seven research cards it needs are the papers in the history of dark matter listed below. The task of the “Talking to dark matter” node is to put all the evidence about dark matter together and listen to that string of low-energy events.
How dark matter was discovered
The story of dark matter is built from the following steps.
- First proposal (1933): Fritz Zwicky found that galaxies in the Coma Cluster moved too fast and proposed the existence of "dark matter". The idea was ignored for decades (Zwicky, Helvetica Physica Acta, 1933).
- Galaxy rotation (1970): The outer parts of the Andromeda Galaxy rotate too fast, so a large amount of unseen matter must supply the gravity. Dark matter was no longer just a guess (Rubin and Ford, The Astrophysical Journal, 1970).
- "Cold" dark matter (1984): If dark matter is "cold", meaning slow-moving, galaxies assemble from the bottom up, which matches observations (Blumenthal, Faber, Primack and Rees, Nature, 1984).
- Shape of the halos (1996): Computer simulations showed that cold dark matter halos, from dwarf galaxies to galaxy clusters, follow the same density curve. It was later named after its three authors (Navarro, Frenk and White, The Astrophysical Journal, 1996).
- The Bullet Cluster (2006): After two galaxy clusters collided, the gas stayed in the middle while the center of gravity moved to the two sides. The dark matter had been "flung out". The paper's title calls this a direct empirical proof of dark matter (Clowe et al., The Astrophysical Journal Letters, 2006).
How much of the universe is it?
The Planck satellite measured tiny fluctuations in the cosmic microwave background: ordinary matter makes up about 5% of the universe's total energy, dark matter about 27%, and the rest is dark energy. The same team also gave the most precise cosmological parameters so far: an age of about 13.8 billion years, and ordinary matter at only about 5% (Planck Collaboration, Astronomy & Astrophysics, 2020).
What is it? Nobody knows
An experiment waiting for dark matter particles with 7 tonnes of liquid xenon, about 1.5 km underground, found no signal and set the strictest limits so far. What dark matter is remains unknown (LZ Collaboration, Physical Review Letters, 2025). This is where reality and the game part ways: the game gives an "answer", and reality does not have one yet.
Game lore, not real
"Dark matter is the civilization of the previous universe" is fiction. The game uses the idea to make a bold guess about a familiar scientific question.
Related real research
Every item in the history of dark matter above is related real research. They are the foundation for the science behind this ending, not evidence that dark matter is a civilization. The last one is the most worth remembering: seven tonnes of liquid xenon found no signal, which shows that real detection of dark matter is far from over.
Want to read the originals? Search these titles
- Zwicky (1933): "Die Rotverschiebung von extragalaktischen Nebeln", roughly "The redshift of extragalactic nebulae"
- Rubin and Ford (1970): "Rotation of the Andromeda Nebula from a spectroscopic survey of emission regions"
- Blumenthal et al. (1984): "Formation of galaxies and large-scale structure with cold dark matter"
- Navarro et al. (1996): "The structure of cold dark matter halos"
- Clowe et al. (2006): "A direct empirical proof of the existence of dark matter"
- Planck Collaboration (2020): "Planck 2018 results. VI. Cosmological parameters"
- LZ Collaboration (2025): "Dark matter search results from 4.2 tonne-years of exposure of the LUX-ZEPLIN (LZ) experiment"
Real basis
Dark matter makes up a little over 80% of the universe's matter, and galaxies really did form inside dark matter halos; it is detected only through gravity, and what it is remains unknown.
Talking to dark matter: Put all the evidence about dark matter together and listen to that string of low-energy events.
Related research
These studies relate to this topic but are not direct proof of this page.
Recipe of the universe: The Planck satellite gave the most precise cosmological parameters yet: an age of about 13.8 billion years, with ordinary matter only about 5%.
Source: Planck Collaboration, Astronomy & Astrophysics 2020, "Planck 2018 results. VI. Cosmological parameters"
Invisible mass: The outskirts of the Andromeda galaxy rotate too fast, so a large amount of unseen matter must supply the gravity. Dark matter was no longer just a guess.
Source: Rubin & Ford, The Astrophysical Journal 1970, "Rotation of the Andromeda Nebula from a spectroscopic survey of emission regions"
First proposal of dark matter: Zwicky found that galaxies in the Coma Cluster moved too fast and proposed that “dark matter” exists. The idea was ignored for decades.
Source: Zwicky, Helvetica Physica Acta 1933, "Die Rotverschiebung von extragalaktischen Nebeln"
Bullet Cluster: After two galaxy clusters collided, the gas stayed in the middle while the centers of gravity ended up on either side. Dark matter had been “flung” out.
Source: Clowe et al., The Astrophysical Journal Letters 2006, "A direct empirical proof of the existence of dark matter"
Cold dark matter: If dark matter is “cold” and slow-moving, galaxies gather bottom-up step by step, which matches observations.
Source: Blumenthal, Faber, Primack & Rees, Nature 1984, "Formation of galaxies and large-scale structure with cold dark matter"
The shape of dark matter halos: Computer simulations show that cold dark matter halos, from dwarf galaxies to galaxy clusters, all follow the same density profile. The profile was later named after its three authors.
Source: Navarro, Frenk & White, The Astrophysical Journal 1996, "The structure of cold dark matter halos"
Recipe of the universe: The Planck satellite measured the tiny fluctuations in the cosmic microwave background: ordinary matter makes up about 5% of the Universe's total energy, dark matter about 27%, and the rest is dark energy.
Source: Planck Collaboration, Astronomy & Astrophysics 2020, "Planck 2018 results. VI. Cosmological parameters"
Seven tons of liquid xenon: About 1.5 km underground, 7 tonnes of liquid xenon waited for dark matter particles and saw no signal, setting the strictest limits so far. What dark matter is remains unknown.
Source: LZ Collaboration, Physical Review Letters 2025, "Dark matter search results from 4.2 tonne-years of exposure of the LUX-ZEPLIN (LZ) experiment"
Game lore (fictional)
- Dark matter being the civilizations of a previous universe is fiction.
- Node “Talking to dark matter”: collect all seven research cards on dark matter, and unlock the dark matter branches of the Tree of the Cosmos (dark matter halos, dwarf galaxies, galaxy clusters, gravitational lensing).