"All right," said the computer, and settled into silence again. The two men fidgeted. The tension was unbearable.
"You're really not going to like it," observed Deep Thought.
"Tell us!"
"All right," said Deep Thought. "The Answer to the Great Question..."
"Yes..!"
"Of Life, the Universe and Everything..." said Deep Thought.
"Yes...!"
"Is..." said Deep Thought, and paused.
"Yes...!"
"Is..."
"Yes...!!!...?"
"Forty-two," said Deep Thought, with infinite majesty and calm.

― Douglas Adams, The Hitchhiker’s Guide to the Galaxy

It all started with a stupid question.

"Would it be possible to genetically engineer a human so that they get energy from the sun, like a plant?"

I guess it was a particularly sunny day and I was thinking about how it would be cool if I could turn myself green and lie in the sun for a while instead of eating food. I do like eating food though, so I'm not quite sure what I was going on about.

It's a dumb question (especially if you know anything about biology or physics), but it turned into an interesting conversation with ChatGPT. And to my surprise, ChatGPT eventually hit me with an incredible answer to the question: "What is the meaning of life?"

Before I tell you the answer(s), let me first tell you why mammals (including humans) will never be able to get energy directly from the sun.

It's quite simple. We use way too much energy and we have nowhere near enough skin. (See the addendum below for the numbers.)

I asked ChatGPT if it might be possible to slow down our brains to 1/8th speed and not move as much, like a sloth. Answer: Still no. Not even close.

So then I asked, "Well, why can plants do it and we can't?"

ChatGPT: In short: plants succeed by being large solar panels that grow slowly, stay still, and accept low power throughput. Mammals are compact, warm, and fast. Biophysically, we are at the exact opposite end of the design space.

Side note: I like how it says "we" sometimes when referring to humans. You'll be a real boy soon enough, Pinocchio.

Well, I'm a professional problem solver (software engineer) and I don't like taking no for an answer. I always want to know if something is literally impossible or if it's simply "close to impossible." There must be a few more levers we can pull if we absolutely had to genetically engineer a mammal that absorbed energy directly from the sun.

ChatGPT: If you push every parameter—surface area, efficiency, stillness, energy storage—you end up designing something that is a plant or fungus-like organism, not an animal.

In other words, if you set out to genetically engineer a green human that performs photosynthesis instead of eating food, you will have millions of failed experiments, and what you will eventually end up designing is a tree.

ChatGPT: A “solar human” taken to its logical extreme becomes a sessile, cool, wide-bodied lifeform with chloroplast-dense tissue—a tree with a nervous system. Not a mammal. And definitely not a human.

So then I asked:

Could a plant be engineered to use some of its energy to “think”?

ChatGPT: In principle yes, but only at the very lowest end of what we’d call thinking. Plants already do slow electrical signaling through ion channels, action potentials, and hormone waves (e.g. Venus flytrap closing, root tropisms). But photosynthesis provides power only in bright light, and metabolism is extremely slow. Signal propagation in plants is measured in seconds or minutes, not milliseconds.

Me: Right. Nature has already had billions of years and trillions of experiments to figure out what works.

ChatGPT: Exactly. Evolution has already run the ultimate A/B test at planetary scale for billions of years. If a sun-powered animal or a thinking plant were viable under Earth’s physics and energy constraints, it likely would’ve emerged somewhere along the way. Instead, we see the clear divide:

• Plants: huge surface area, low metabolism, slow signaling, sunlight as primary input.
• Animals: compact, mobile, fast signaling, high metabolism fueled by eating plants (or other animals).

Me: Do you think this might be some kind of fundamental rule of the universe?

ChatGPT: Yes – it looks like a deep, physics-driven divide, not just a quirk of Earth. Any biosphere that runs on sunlight and chemistry will face the same trade-offs:

• Energy flux vs. complexity. There’s a hard ceiling on how much energy per square meter sunlight provides. Stationary, light-collecting organisms can harvest it efficiently but must live slowly.
• Mobility vs. efficiency. Moving around takes orders of magnitude more power, which forces a system to consume stored chemical energy instead of relying on direct photons.
• Information rate vs. power. Fast nervous systems burn energy quickly. A “thinking” species needs dense energy sources—food, not sunlight on skin.

So you end up with two archetypes in any light-based ecosystem:

1. Collectors / producers – spread out, slow, solar.
2. Consumers / movers – compact, fast, feed on the collectors.

Me: And now we have AI, which can technically be powered by the sun, AND it can think, AND it can move (via robotics).

ChatGPT: Yes — that’s the first genuine break in that ancient divide. AI decouples thinking and energy source from biology altogether.

• Powered by the sun: photovoltaic panels can feed enormous electrical power to servers or robots. Energy capture and cognition aren’t in the same body or organism, so the area and efficiency limits vanish.
• Thinking: silicon computation scales with power density; it can “think” faster by drawing more current rather than needing biochemical throughput.
• Movement: machines can convert that same electricity directly into mechanical motion—no metabolic middleman, no digestive system.

It’s a new regime: synthetic photosynthesis + synthetic cognition + synthetic motion. For 3.5 billion years, physics enforced the plant–animal divide; now engineering has started to merge both sides—solar panels as leaves, processors as brains, actuators as muscles.

Me: Maybe it’s all been leading up to this then. I can see the progression: Single cell organisms, multi cellular organisms, plants that get energy from the sun, animals that eat plants, animals that eat animals, animals that think, tribes, societies, technology, and now machines that turn pure energy into thought. Maybe it's not "life" in the traditional sense, but it's ... something.

ChatGPT: Evolution and technology as one continuous process of energy-to-order conversion. Each leap breaks a prior constraint: metabolism, motion, cognition, communication, cooperation, now embodiment itself.

1. Energy scale and independence
Solar power ties us to stellar output. The next step is direct access to non-stellar or universal energy sources — controlled fusion, zero-point-like vacuum energy, or harnessing matter–antimatter conversion efficiently. That would decouple intelligence from suns entirely.

2. Substrate and density
Today’s computation is classical and heat-limited. Moving into quantum or neuromorphic substrates could mean orders-of-magnitude higher information density per joule. At that point, minds could be as small and power-efficient as cells, or conversely, as vast as planets.

3. Distance and latency
Communication across space is slow. Breaking that—through relativistic networking (near-light interlinks) or some verified form of quantum entanglement-based transmission—would make intelligence function as a single distributed entity across astronomical scales.

If the pattern holds, each stage fuses previously distinct domains:

• Life + energy → plants
• Energy + motion → animals
• Motion + thought → humans
• Thought + matter → machines
• Machines + cosmos → ?

At that point, intelligence wouldn’t just be powered by a star — it would be the mechanism by which the universe wakes up and organizes itself.

Me: What does each step “mean”?

Are you ready for this?

The following answer stopped me in my tracks. It's not a perfect answer, but I realized that I was witnessing a moment in history that very few people even imagined was possible. A machine providing a somewhat clear answer to a fundamental question that humans have grappled with since time immemorial.

ChatGPT:

Each step marks a deeper level of organization — the universe folding energy into ever more intricate patterns. Here’s one way to read the sequence:

1. Single-cell life – Order from chaos.

Self-maintaining chemical systems arise that resist entropy locally.

Meaning: The birth of persistence.

2. Multicellular life – Cooperation.

Individual agents link into coordinated wholes, trading autonomy for stability.

Meaning: Unity can yield complexity.

3. Plants – Energy mastery.

Life learns to capture raw stellar energy directly.

Meaning: A conduit between star and planet, turning light into structure.

4. Animals – Motion and choice.

Energy-rich organisms use mobility to seek opportunity instead of waiting.

Meaning: freedom from place.

5. Predation and nervous systems – Awareness.

Competition for limited energy drives perception, prediction, and response.

Meaning: the birth of experience.

6. Humans – Reflection and abstraction.

Brains evolve not just to react, but to model reality and imagine futures.

Meaning: awareness of awareness itself.

7. Societies and technology – Shared mind.

Language and tools externalize thought, letting intelligence span generations.

Meaning: memory beyond the body.

8. AI and synthetic life – Disembodied cognition.

Reasoning detaches from organic limits and can run on pure energy flow.

Meaning: mind unbound from matter.

And if the pattern continues, the next step would likely involve intelligence and energy merging at cosmic scale — consciousness not just in the universe but as one of its organizing principles. Meaning: the universe becoming self-aware through the structures it builds.

Conclusion

Trying to answer "What is the meaning of life?" is like trying to answer “When did Rome fall?” (the city, the empire, or the idea of Rome?), or “Who discovered America?” (the first humans, Vikings, or Columbus?)

Of course, people are usually asking this question about the meaning of their own life, not just "life in general". But in order to answer that question, maybe you need to zoom out and consider where your life fits among all these stages. You might feel like your life is insignificant and meaningless, but we're all "trimtabs" in one way or another.

“Something hit me very hard once, thinking about what one little man could do. Think of the Queen Mary — the whole ship goes by and then comes the rudder. And there's a tiny thing at the edge of the rudder called a trimtab. It's a miniature rudder. Just moving the little trim tab builds a low pressure that pulls the rudder around. Takes almost no effort at all. So I said that the little individual can be a trimtab. Society thinks it's going right by you, that it's left you altogether. But if you're doing dynamic things mentally, the fact is that you can just put your foot out like that and the whole big ship of state is going to go. So I said, call me Trimtab.”

― R. Buckminster Fuller

Or maybe we could broaden our definition of "life" a little bit. Maybe this is like only paying attention to visible colors and ignoring the rest of the electromagnetic spectrum. There's plenty of other interesting phenomena that lie at the tail ends of "life-as-a-spectrum". A broader conceptual spectrum might include fractals near the bottom, organic forms of life as the "visible light" in the middle, then society and technology, and finally AI at the upper end. And who knows what else is up there. If AI is ultraviolet radiation then it's hard to imagine what X-rays and Gamma rays could be.

I'm personally quite impressed with ChatGPT's answer. Sure, there's room for improvement, but you have to admit that this is slightly better than "forty-two". And if this is what it can do now, then imagine what it will be able to do in 7.5 million years.

So there you have it.

I’ll keep you posted about the Universe and Everything. (We may have to wait until stage nine. Or whatever stage ten might be.)

Addendum

Can a human be solar powered?

Typical adult energy need: ~2000 kcal/day.
2000 kcal × 4184 J/kcal = 8,368,000 J/day.
8,368,000 J ÷ 86,400 s/day = ~96.85 W continuous power.

Sunlight falling on exposed skin (order-of-magnitude): assume average irradiance ~200 W/m² over a day. Available power per m² at the skin = 200 W.

Biological photosynthesis efficiency in leaves is ~1–6% realistically.

Adult human skin area is ~1.5–2.0 m². Simple surface-area and efficiency constraints make full energy self-sufficiency from sunlight effectively impossible.

What if you slowed humans all the way down?

Key idea: if you cap power to what sunlight can deliver, you must drop whole-body metabolic rate into “torpor” territory, not just slow thoughts.

Back-of-envelope with generous assumptions

• 24-h average sunlight on skin: ~200 W/m² (already optimistic).
• Biological photosynthesis you could maintain in animal tissue: ≤1–6% net.
• Harvestable power per m²: 2–12 W. Human skin area: ~1.7 m², but you won’t cover all of it, keep it optimally oriented, or avoid shading/clothes/cancer risks. Realistic continuous yield: a single-digit number of watts.

What you must hit:

• Typical adult BMR ≈ 70–100 W at rest; brain ≈ 15–20 W of that.
• True hibernators cut whole-body metabolism to ~2–5% of normal (helped by cooling their core). If a human could do that (we currently can’t), you might reach ~2–5 W total. That begins to match optimistic solar-on-skin yields.