For you to live, other organisms have to die.

That’s because humans, like all animals, are heterotrophs. To fuel our bodies, we must eat other living things, killing them in the process. However, most plants and algae are autotrophs. They bootstrap their biomass without the barbarism of eating others: using photosynthesis, turning sunlight, water, and carbon (pulled from the air) into energy. They may kill through competition, but they don’t need to kill to eat.

Ultimately, everything we animals eat is a product of photosynthesis. One way or another, sunlight fuels the growth of our food (or our food’s food) before it fuels us. This realization initiated a generations-long mission in humanity to, like plants, disintermediate ourselves from the messiness and immorality of food chains, farming, and carnivorism. To stop killing to live and instead become something cleaner. To get our energy more directly, less brutally.

To become stellivores, a.k.a. “Sun-eaters.”

By copying the humble autotroph, scientists are helping solve civilization’s profoundest, most perennial problem: how to consume available energy with maximal compassion and minimal externality.

That ambition is no longer purely speculative. Across the globe, scientists are using energy — ultimately derived from the Sun — to transform air, water, and other inorganic inputs into food. Savor is making butter without agriculture, instead replicating processes found near deep-sea hydrothermal vents. Startups like Solar Foods aim to make “food out of thin air,” growing edible protein by feeding microbes with electricity and carbon dioxide.

These efforts and others don’t always eliminate life from food production, but they radically simplify it — replacing farms and animals with microscopic organisms, and ecosystems with controlled environments. By copying the humble autotroph, they are helping us solve civilization’s profoundest, most perennial problem: how to consume available energy with maximal compassion and minimal externality.

To understand how we arrived at this point — and where it might lead — we have to follow a trail taking us from early alchemists’ experiments, all the way to calculations of the calories we could get from burning the oceans by atomic fusion. From early theories of digestion to the discovery of the laws of thermodynamics, this is the story of how diverse thinkers have long felt an appetite for sunlight. Along the way, it becomes possible to ask whether “sun-eating” isn’t just a human aspiration, but something intelligences elsewhere — throughout the universe — may likewise be drawn to.

From stomachs to sunlight

The first human invention was an external stomach. Stone tools predate fire, but paleoanthropologists argue that cooking is what made us, finally, fully human. Fire delegated the effort of digestion from belly to boiling pot. Our bodies could then invest the surplus energy this saved into ganglia rather than guts, into frontal lobes instead of food. Nietzsche was right when he proclaimed, “The soul is a stomach!”

However, food — even cooked food — can be troublesome. Indigestion has long plagued us, and before modern medicine and hygiene, foodborne illnesses were as widespread as their causes were misunderstood. What’s more, as far back as the Bible, you can detect a germinal sense among humans that there is something innately unethical about carnivorism. Isaiah 65:25 states that, when Christ returns, “the lion will eat straw like the ox” and “dust will be the serpent’s meat.”

While the invention of cooking more than 1 million years ago demonstrated how ingenuity could streamline the ways we metabolize the energy we need, it wasn’t until the rise of modern science that we could properly articulate this as a goal — and thus start explicitly pursuing it.

Writing in the 1500s, the Swiss alchemical physician Paracelsus saw everything, even the cosmos itself, as a process of digestion. Alimentation formed the perfect symbol for his vocation as an alchemist: the transmutation of base matter into what’s perfect and spiritual. Tellingly, he compared good digestion — eupepsia — to an inner, nutritive “sunshine.” The more purified and angelic we become — the less tangled up in everything indigestible and dirty — the more we ourselves become like sunlight. “The human body,” he wrote, is “materialized” sunlight.

As empirical science grew and confidence in divine order began to crack, people could begin to question nutrition’s natural status quo and ask whether we could reform it. 

In 1648, Paracelsus’s Flemish protégé Jan Baptist van Helmont conducted the first quantitative study in plant science. Seeking to ascertain the source of plant nutrition, he planted a willow sapling in an isolated pot, with a prerecorded amount of soil, and watered it. Though the soil’s weight barely changed, the tree gained 164 pounds. From this, van Helmont concluded that vegetables eat water alone. He didn’t know that sunlight and carbon fixed from the air also played a role.

Two decades later, in Paradise Lost, the poet John Milton imagined the eating habits of angels. He pictured them as alchemical beings who don’t need to defecate, because they gain energy straight from matter with perfect efficiency. Perhaps he inserted this tangent into his epic poem because he lived with terrible indigestion and died, potentially, of ulceration.

Meanwhile, as empirical science grew and confidence in divine order began to crack, people could begin to question nutrition’s natural status quo and ask whether we could reform it. Already in 1626, Francis Bacon, a leading proponent of the new scientific method, dreamt of gardens whose fruits were made larger, tastier, and more nutritious through scientific manipulation.

The optimism of the learned societies that sprang up in Bacon’s wake was quickly ridiculed, though. In 1726’s Gulliver’s Travels, Jonathan Swift depicted feckless scientists attempting to find a method for directly “extracting sunbeams out of cucumbers” to be sealed in “Vials.”

With these cucumbers, Swift was in fact satirizing the experiments of his contemporary and fellow clergyman, Stephen Hales. In 1725, Hales had started suggesting that plants require elements from the air and perhaps also sunbeams to grow. He’d established this with careful tests, but it wasn’t until 1776 that Dutch-British botanist Jan Ingenhousz would discover photosynthesis, proving through his own meticulous experimentation that vegetation required light, water, and carbon dioxide to create their own food. 

Dreams of cleaner nutrition

Not long after this, the moral case against meat-eating began to grow. Though vegetarianism has been a permanent fixture in non-Western cultures, it largely disappeared from Europe following its Christianization in the early Middle Ages, only to return in the early 1800s. The Romantics were particularly proactive proponents. Mary Shelley lent the issue prominence with 1818’s Frankenstein, depicting the titular scientist’s monster as less reanimated corpse and more “Modern Prometheus”: a creature forged by synthetic biology to be morally and physiologically superior to humans. It informs its creator that, unlike most humans, it need not “destroy the lamb” to “glut” itself. The monster is content surviving on acorns and berries.

A breakthrough in synthetic biology came in 1828, when Friedrich Wöhler used non-living materials to create urea, a substance previously thought producible only by living organisms.

Other early foreseers of synthetic biology imagined how it could create a world wherein predation was abolished, as the Bible dimly prophesied. In 1822, the French socialist Charles Fourier pictured a bioengineered future in which “lions” and “crocodiles” have been transmogrified into herbivorous “anti-lions” and “anti-crocodiles” that might pacifistically power our railways and barges. 

Fourier’s predictions were bold, to say the least. But just six years later, in 1828, Friedrich Wöhler, a German chemist, became the first to synthesize an organic compound, urea, from inorganic reactants — in other words, he created a substance previously thought producible only by living organisms from non-living materials. Over the coming decades, chemists would begin predicting that “with a hundred years of physiological science,” humans would rewrite all “organic laws.”

Following Wöhler’s lead, renowned chemist Marcellin Berthelot would synthesize many organic compounds from inorganic substances. Since all food is organic — in the chemical sense — this made the idea that we could create food from non-living elements seem tantalizingly possible. In an 1894 interview, he proclaimed that the “epicure of the future is to dine upon artificial meat [and] artificial vegetables.” Cornfields and farms would thus disappear from Earth. “Coal will no longer be dug,” he continued, except “with the object of transforming it into bread or meat.” A year later, Berthelot pronounced nothing could “arrest” the eventual “social revolution” of artificial food. 

In 1872, the British explorer-historian William Winwood Reade envisioned a future where “our enlightened posterity will look back upon us who eat oxen and sheep just as we look back upon cannibals.”

In 1897, the theme entered sci-fi. The German philosopher Kurd Laßwitz’s voluminous Auf zwei Planeten depicted a hyper-advanced civilization of Martians who had “emancipated themselves” from animality through synthetic nutrition. They had made “themselves direct sons of the sun,” capable of conjuring “mineral-butter,” “coal-sausage,” and “test-tube-roast” via “solar energy.” They consider us carnivorous Earthlings barbarous. But, as our colonizers, they have a “civilizing” plan: to cover Earth’s surface, in one year, with sunlight-sapping factories, providing “inexhaustible” nutrient-jelly. They want to liberate humanity — transforming corpulent gourmand into airy genius — so we only digest works of the mind, not of the butcher or chef.

But back in 1872, the British explorer-historian William Winwood Reade had already forcefully made synthetic food a matter of sociocultural and ethical maturation. Foreseeing “flesh and flour” concocted from elements alone, he rhapsodized that food will be “manufactured in unlimited quantities at trifling expense” to utterly banish “starvation.” Not only this, but “our enlightened posterity will look back upon us who eat oxen and sheep just as we look back upon cannibals.”

The physics — and future — of food

Meanwhile, from the 1850s onward, the science of thermodynamics had matured, clarifying the source of all Earthly energy by specifying two fundamental laws: 

1. Energy is never created or destroyed, only transformed.
2. Through these transformations, some useful energy is always lost, never to be recouped.

Put together, this illuminated the fact that all effort draws on some reservoir that, no matter how vast, is dwindling.

It was quickly realized that the upstream reservoir of all activity at Earth’s surface, save some negligible exceptions, is the Sun. Pounding our planet with its largesse, incoming sunlight drives weather and fuels photosynthesis, thus feeding ecosystems. But, given thermodynamics also taught that this reservoir was dwindling, people started to look upon unused sunlight as wasted opportunity. This created the context wherein people could more forcefully argue that human civilization should become an autotroph.

Science writers of the 1920s predicted that “direct exploitation of solar energy” would render Earth “habitable to many billions more people than it now contains.” 

In 1886, Ludwig Boltzmann described all life as a “struggle for entropy” that becomes “available through the transition of energy from the hot Sun to the cold Earth.” By 1906, other physicists had begun lamenting the “great flood” of light radiating into “empty space,” given that only a vanishing “fraction” is intercepted by planets. They started mourning this as wealth “forever wasted.” The same could also be said of some of the lion’s share of light that does hit Earth. So, what if we could somehow eat it?

By 1923, science writers were stating that “direct exploitation of solar energy” would render Earth “habitable to many billions more people than it now contains.” Two years later, the Russian geochemist Vladimir Vernadsky made the idea explicit. In an essay titled “Human Autotrophy,” he nodded to humankind’s domination of the biosphere. But this domination, he noted, was also — thus far — a destructive disturbance, potentially a suicidal one. Thus, to divert course and secure our future, he suggested civilization become “an autotroph,” like those photosynthesizers “dependent only on themselves for their nutrition.”

Already in 1920, the radiochemist Frederick Soddy was imagining futures wherein, thanks to new forms of energy capture and consumption, humans would plug themselves into “something akin to an electric lamp-socket” to draw from “public mains the supply of pure physical energy required for the day’s work” — no longer would we need to rely on the “husks” of congealed energy we currently call food.

But Vernadsky’s compatriot, the rocketeer and sci-fi writer Konstantin Tsiolkovsky, had already taken this yet further. He argued that, as life once left the sea, it must also leave behind the planet, evolving to live in the void of space, feeding purely off “sunshine.” The resulting organism, he conjectured, would resemble an “animal-plant.” He imagined one of them addressing human visitors:

We are fed and developed like plants — by action of solar beams … Do you see the green appendages of our bodies looking like beautiful emerald wings? — They contain grains of chlorophyll…

Tsiolkovsky even did calculations on the organisms’ metabolism, estimating how much sunlight would equate to “10 pounds of meat” for a human. For him, in becoming photosynthetic, civilized beings would only gain in hallmarks of intelligence, like autonomy and compassion, given that a species living off starlight converts energy to work without the messy, immoral mediation of a food chain. 

The rocketeer claimed each of these organisms — floating in the void, crowding stars like phototropic cosmic foliage — would resemble a miniature biosphere, being metabolically self-sufficient. “They surround all suns, even those without planets, and use this energy in order to live and to think,” he wrote. “The energy of stars should exist for something!”

Tsiolkovsky’s vision was fanciful, more romance than science, but the theme gained concreteness in other works of fiction. For example, mycologist and novelist E.C. Large’s Sugar in the Air (1937) realistically details the industrial invention of “Sunsap,” an edible syrup synthesized from light and air. Large’s “Sunsap” perfectly presages the “Solein®” that Solar Foods has already started selling.

By the mid-19th century, synthetic food had become a futurological mainstay. In 1953, Arthur C. Clarke offhandedly remarked that — within the extraterrestrial habitats of the future, where all food is “synthetic” — any newcomers asking for “steak or chops” would become immediately “unpopular.”

Eating the Sun

As the 1900s progressed, prominent scientists increasingly took alternate sources of energy and nutrition seriously. Indeed, by the time Clarke made his prediction, a new way of harnessing the Sun’s power had been discovered. 

With the first artificial thermonuclear reactions in the early 1950s, the alchemical forces fuelling stars had been brought down to Earth. In 1963, the Soviet-American physicist Georges Gamow whimsically calculated how many calories we could liberate by using hydrogen in Earth’s seas to fuel fusion reactions. From these, we could abolish farmlands and utilize solar energy to “synthesize” food “from elements.”

The energy of stars should exist for something!

Konstantin Tsiolkovsky

This wouldn’t be as disruptive as it sounds, for fusion only requires heavy hydrogen, which can be separated from seawater by filtration and makes up ~0.01% of all oceanic hydrogen. So, Gamow crunched the numbers. Supposing that the 1.65^17 tons of heavy hydrogen in the ocean would liberate 6^29 calories through fusion, he guesstimated that this would amply meet his contemporary population’s demand of 3^17 calories annually for another 60 billion years. That’s 3 with 17 zeroes after it: a lot of calories. (Gamow famously had both a sense of humor and a thing for eyewatering numbers.)

However, three years earlier, in 1960, the English-American astrophysicist Freeman Dyson had suggested something even more efficient, albeit more disruptive. He proposed future humanity might become motivated to demolish Jupiter, requisitioning its matter to construct a swarm of solar panels enclosing our Sun, so as to capture its entire energy output. 

Dyson saw this, serenely, as a matter of expanding civilization’s “energy metabolism.” Today, the ongoing search for extraterrestrial intelligence includes scouring the skies for similar star-girdling structures, aptly named “Dyson spheres.” Because it relies on thermodynamic fundamentals — that all activity requires energy — rather than vagaries of intentional messaging, this approach has the benefit of stripping psychological assumption from the search for other minds. Contemporary researchers talk of such civilizations as “stellivores,” or superorganisms that imbibe stars. 

Perhaps, then, the aliens have already mastered what alchemists like Paracelsus intuited long ago: that the intelligent mind, like a flower, tends sunwards. Following this tendency might finally cure us not only of indigestion but also the ancient immorality of eating other organisms.