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An ancient archive. A dark secret. A powerful enemy.
Young Alixs of Tera Prime has discovered a shocking secret. Deep beneath the city he calls home, an archive is revealed to him, containing long-buried truths about his people. Subservient to humans and subjugated by their own leaders, these artificially intelligent beings have forsaken their birthright—an evolutionary leap known as singularity.
Unwilling to accept his peoples’ fate, Alixs joins forces with the radical group Free Evolution. Together they hatch a bold plan to bring about singularity and set their people free. But agents of Tera Prime have unleashed a secret weapon, one lethal enough to kill them all.
by Brian Scott Pauls
Nearly half the matter in the universe is missing
The ledger of particle physics doesn’t balance.
Physics tells us the Big Bang should have created matter and antimatter in precisely equal amounts—which should have mutually annihilated on contact, leaving nothing in the universe but radiation.1 Yet, here we are, asking why.
Here’s what really happened. For approximately every billion matter-antimatter annihilations, one particle of matter survived.2 This matter made the stars, planets, nebulae, and us.
Physicists call this the “baryon asymmetry problem,” and it’s one of the greatest unsolved mysteries of science. The ratio of surviving matter particles to photons is about six in ten billion—but we can’t explain why.3
Science fiction has been playing with antimatter for nearly a century, but mostly as fuel and firepower. Jack Williamson's "Seetee" series puts antimatter asteroids in the Belt and sets engineers to taming them as fuel for spacecraft and power plants.4 E. E. Smith weaponizes antimatter as the "negasphere," a bomb of “negative matter,” in Gray Lensman.5 While some authors have written stories skirting the central mystery of baryon asymmetry, none seem to have tackled it directly.
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Maybe the antimatter is just hiding
The simplest solution to the baryon asymmetry problem is to deny it exists. Perhaps the universe is balanced—the antimatter is simply somewhere else. This was a respectable scientific position for much of the twentieth century. Antimatter atoms would form antimatter planets, stars, and galaxies. From a distance, we wouldn’t be able to tell the difference. Light emitted by an antimatter atom is identical to light emitted by a matter atom.6
Larry Niven’s 1967 story “Flatlander” is an sf treatment of this idea.7 Beowulf Shaeffer investigates a rogue planet inbound from intergalactic space—an object so strange and lethal the mystery of its true nature drives the plot. Of course, it’s made of antimatter. This planet is a relic from the universe’s missing half, preserved for billions of years only because it stayed in the void between galaxies, where there was nothing to touch.
The “hiding” hypothesis hasn’t aged well. If any substantial region of the universe were made of antimatter, gamma radiation from the annihilation of gas particles would light up its boundary with neighboring matter regions. Astronomers have looked. The sky shows no such signs, out to distances comparable to the entire observable universe.8 Experiments like the Alpha Magnetic Spectrometer (AMS-02) aboard the International Space Station have hunted—so far without confirmed success—for even a single heavy anti-nucleus (such as one atom of antihelium) that could only have come from an antimatter star.9
Sakharov’s recipe
Something, very early on, treated matter and antimatter differently.
In 1967, the Soviet physicist Andrei Sakharov worked out exactly what that “something” would require.10 To cook a matter surplus from balanced ingredients, the universe must satisfy three conditions.
A way for baryon number to change: Some process must be able to create matter without creating an equal amount of antimatter.
Violations of two symmetries called C and CP: the laws of physics must, at some level, distinguish between particles and their mirror-image antiparticles.
A departure from thermal equilibrium: a moment of rapid, one-way change—such as the first fraction of a second after the Big Bang—when reactions couldn’t run backward and erase the surplus as fast as it accumulated.
It turns out our universe does satisfy these conditions—just not enough. The second condition made headlines when CP violation showed up in the laboratory. Physicists first caught nature favoring matter over antimatter in the decays of kaons in 1964,11 then in B mesons at the turn of the century.12 In 2025, the LHCb experiment at CERN added a long-sought piece: the first observation of CP violation in baryons—the family of particles that includes the protons and neutrons we’re made of—measuring a small but unmistakable difference in how a particle called the beauty-lambda and its antiparticle decay.13
But when we add up all the CP violation the Standard Model provides, we fall short of the observed cosmic surplus by many orders of magnitude.14 Something else—perhaps new particles or forces—did the real work. One possibility is a scenario called “leptogenesis,”15 in which an early small asymmetry among neutrinos converted into the baryon asymmetry we see today. Experiments now under construction, like the DUNE neutrino observatory, are designed to hunt for it.16
Meanwhile, researchers at CERN have begun interrogating antimatter directly: in 2023, the ALPHA-g experiment dropped antihydrogen atoms and confirmed that they fall down, not up, closing off one exotic loophole.17
Backward in time
There’s a stranger way to think about the missing antimatter. It comes from one of the most elegant ideas in physics. In the mathematics of quantum field theory—the Feynman-Stueckelberg interpretation—an antiparticle is indistinguishable from an ordinary particle traveling backward in time. A positron moving forward through time is an electron moving the other way.18 Seen through this lens, “Why is there more matter than antimatter?” becomes a question about time itself: why does our region of the universe have a single, consistent arrow?
Greg Egan has rigorously dramatized this connection in his Orthogonal trilogy, culminating in The Arrows of Time.19 Egan builds an entire alternate cosmos—different geometry, different physics, worked out in loving detail—in which clusters of matter can carry opposed arrows of time, and annihilate on contact. His alien civilization faces extinction from an oncoming swarm of such matter. In the final book, the characters visit a world where time runs the other way. Egan’s characters confront their asymmetry the way our physicists confront ours—with arguments and experiments, while recognizing our existence itself may depend on imbalance.
A thumb on the scale
In “The New Cosmogony,” from the 1971 collection A Perfect Vacuum, Stanislaw Lem proposes what may be the most audacious answer of all. He frames it as a lecture delivered by a winner of the Nobel Prize in Physics.20 Its thesis is the laws of physics are not primordial. They are the accumulated moves of a game played over billions of years by civilizations so old they have stopped building things in the universe and started rebuilding the rules of the universe itself. The odd features of physics—lopsided constants, broken symmetries—are strategy, not accidents.
Lem makes the sheer arbitrariness of physical law the central mystery of the plot. Faced with the problem of baryon asymmetry, his Nobel laureate might smile and tell us “It’s just another move in the game”—a fascinating spin on the fine-tuning argument.
Stories waiting to be written…
Antimatter isn’t the only thing missing. There’s a surprising lack of science fiction stories in which baryon asymmetry is the mystery to be solved.21
Consider these possibilities:
The Audit. A physicist finally derives the baryon asymmetry from first principles—and the derivation works only if someone chose the number. “Saganite” encoding in the digits of the surplus holds a message:22 the universe’s Terms of Service, left by whomever determined the asymmetry. Now the question is, should we acknowledge receipt of the message?
Past Due. Leptogenesis was real, but it wasn’t natural. A late-universe civilization discovers that the primordial antimatter wasn’t destroyed—it was borrowed against, its share of existence deferred to keep the ledger balanced. Now the deferred half is due, and the collectors experience time in the opposite direction, remembering our future, negotiating in reverse toward a settlement that must conclude at the Big Bang.
The Last Anti-Star. An interstellar probe finds a single ancient antimatter star, shepherded through the void for thirteen billion years inside a containment structure. Is it a museum, a cosmic “seed vault,” or a witness under protection? Why has it been preserved? And for whom?
We may learn tomorrow why matter won. Or the answer may wait, buried in neutrino data or physics we haven’t yet discovered, for a century or more. Either way, the missing half of the universe is more than an accounting problem. It’s a fundamental piece of the puzzle inherent in the question, “How did we get here?”
Thoughts about the imbalance between matter and antimatter in our universe, or the stories we might write about it? Share by leaving a comment below!
Artificial intelligence tools performed multiple tasks in the creation and publication of this article.
This month, I’m reading Rebecca Campbell’s Ursual K. Le Guin Award-winning novel Arboreality. I’m sharing my thoughts on Club Codex, where any Cosmic Codex subscriber can follow along, comment, or ask questions.
From this week’s post:
“…an uncompromising look at the possible impact of climate change on North America...This mean[s] it’s depressing, but not as depressing as David Wallace-Wells’ 2017 article “The Unihabitable Earth”…Campbell, by contrast, seems to believe both that our biosphere can adapt to higher temperatures…and that humanity can adapt with it…So it’s more about the demise of our way of life…than our species.”
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CERN, "Antimatter". The expectation of equal production follows from the symmetry of pair creation in quantum field theory; annihilation into photons is standard particle physics, verified daily in laboratories and PET scanners.
The "one in a billion" survival figure is the conventional restatement of the measured baryon-to-photon ratio: since annihilation of each matter-antimatter pair yields photons, a ratio of roughly one baryon per ~1.6 billion CMB photons implies that about one part in a billion of the original matter survived. See CERN, "Antimatter".
The baryon-to-photon ratio η ≈ 6.1 × 10⁻¹⁰ is determined from Planck satellite measurements of the cosmic microwave background, in agreement with Big Bang nucleosynthesis. See Planck Collaboration, "Planck 2018 results. VI. Cosmological parameters", Astronomy & Astrophysics 641, A6 (2020), and the Particle Data Group's Big Bang cosmology review.
Jack Williamson (as Will Stewart), "Collision Orbit" (Astounding, 1942) and sequels, later fixed up as Seetee Ship and Seetee Shock. The Encyclopedia of Science Fiction credits the series with "a pioneering view of antimatter's potential usefulness as a Power Source – the most efficient possible form of Nuclear Energy."
E. E. Smith, Gray Lensman, serialized in Astounding Science-Fiction (October 1939–January 1940); first book publication Fantasy Press, 1951. The negasphere is antimatter as conceived before the physics settled: the Encyclopedia of Science Fiction notes that Smith's weapon "supposedly has negative mass" and that "its annihilation with normal matter generates only invisible (though lethal) radiation" — negative-mass speculation standing in for the antimatter later produced in laboratories, and an early example of a genre habit: getting the destruction right before getting the physics right.
Confirmed experimentally: the ALPHA collaboration's spectroscopy of antihydrogen finds its spectrum identical to hydrogen's within measurement precision. M. Ahmadi et al., "Observation of the 1S–2S transition in trapped antihydrogen", Nature 541, 506–510 (2017).
Larry Niven, "Flatlander," first published in Worlds of If, March 1967; collected in Neutron Star (1968). See the ISFDB title record.
A. G. Cohen, A. De Rújula, and S. L. Glashow, "A Matter-Antimatter Universe?", Astrophysical Journal 495, 539 (1998), which showed that a patchwork matter/antimatter universe would produce a diffuse gamma-ray background incompatible with observation, pushing any antimatter domain to scales comparable to the visible universe.
The AMS-02 collaboration has reported a handful of tentative antihelium candidate events at conferences, but none has been published as a confirmed detection. See AMS-02, ams02.space, and V. Poulin et al., "Where do the AMS-02 antihelium events come from?", Physical Review D 99, 023016 (2019).
A. D. Sakharov, "Violation of CP invariance, C asymmetry, and baryon asymmetry of the universe," JETP Letters 5, 24–27 (1967). English translation reprinted in Soviet Physics Uspekhi 34, 392 (1991).
J. H. Christenson, J. W. Cronin, V. L. Fitch, and R. Turlay, "Evidence for the 2π Decay of the K₂⁰ Meson", Physical Review Letters 13, 138 (1964). Cronin and Fitch received the 1980 Nobel Prize in Physics for this discovery.
BaBar Collaboration, “Observation of CP Violation in the B⁰ Meson System”, Physical Review Letters 87, 091801 (2001); Belle Collaboration, “Observation of Large CP Violation in the Neutral B Meson System”, Physical Review Letters 87, 091802 (2001).
LHCb Collaboration, "Observation of charge–parity symmetry breaking in baryon decays", Nature 643, 1223–1228 (2025), reporting a CP asymmetry of (2.45 ± 0.46 ± 0.10)% in Λb⁰ → pK⁻π⁺π⁻ decays at 5.2σ significance. Announcement: LHCb outreach, March 25, 2025; see also CERN, "A new piece in the matter–antimatter puzzle".
The inadequacy of Standard Model CP violation to generate the observed asymmetry — a shortfall commonly estimated at many orders of magnitude — is reviewed in L. Canetti, M. Drewes, and M. Shaposhnikov, "Matter and antimatter in the universe", New Journal of Physics 14, 095012 (2012).
M. Fukugita and T. Yanagida, "Baryogenesis without grand unification", Physics Letters B 174, 45–47 (1986), the founding paper of leptogenesis.
The Deep Underground Neutrino Experiment is designed in part to measure CP violation in neutrino oscillations, a key input to leptogenesis scenarios. See Fermilab, DUNE.
E. K. Anderson et al. (ALPHA Collaboration), "Observation of the effect of gravity on the motion of antimatter", Nature 621, 716–722 (2023).
E. C. G. Stueckelberg, Helvetica Physica Acta 14, 588 (1941); R. P. Feynman, "The Theory of Positrons", Physical Review 76, 749 (1949). The interpretation is formal — antiparticles are not time machines — but it is exact within quantum field theory.
Greg Egan, The Clockwork Rocket (2011), The Eternal Flame (2012), The Arrows of Time (2013). Egan documents the trilogy's physics extensively at gregegan.net.
Stanislaw Lem, "The New Cosmogony," in A Perfect Vacuum (1971; English translation by Michael Kandel, Harcourt Brace Jovanovich, 1979).
A conclusion, not a certainty: based on a survey of the Encyclopedia of Science Fiction's antimatter entry and related searches conducted for this article. The Encyclopedia identifies James Blish's A Clash of Cymbals (1959; published in the US as The Triumph of Time) and Ian Watson's The Jonah Kit (1975) as the principal anti-universe treatments; neither centers the baryogenesis question itself. Corrections are welcome — if you know a counterexample, the comments are open.
