Suppose that a god has created a universe with nothing in it, except for a single, solitary celestial body. For simplicity, I'll call it a planet, although it most probably technically won't be. For instance, it isn't orbiting anything, because there's nothing to orbit in this particular universe.

Would it be possible for that planet to support sustainable humanoid life?

I was also wondering what the observable effects are of a profound lack of matter in the universe. For example, would it matter for an observer on or below the surface of the planet that there is no cosmic radiation (assuming that there is, indeed, none)?

Some story-specific elements that may be taken into account when considering an answer to this question are as follows:

  • The god can engineer the planet any way he likes, but he prefers to mass produce as much as possible. For example, the Death Star from Star Wars would technically suffice as a habitable planet/moon/space station, but the sheer amount of electrical engineering involved alone would drive the god crazy. Think of it this way, if the god had to make a thousand universes similar to this one, he wouldn't choose a design that requires an inordinate amount of attention to details. Sure, he's immortal, but not immune to tedium.
  • The god may do some maintenance work every now and then. For example, it may replenish an energy source used to heat to planet. This shouldn't have to happen very often. More than once every 1000 years is too much work.
  • The humanoids that will inhabit the planet resemble humans, but they may have been redesigned in subtle ways to take into account the living conditions on the planet. For example, certain chemicals that necessarily appear in the atmosphere might not be toxic to them.

  • The god would like to add handcrafted, inhabitable tunnels and other underground structures to the planet. Bonus points for answers that support such a design. For example, if the planet is for the most part a ball of magma, then he doesn't have much to work with.


It seems mentioning the godlike entity has distracted from the real question, which is exactly as stated:

  • Would it be possible for a solitary celestial body to sustain humanoid life?

Even supposing that it were possible, I realize that the necessary conditions would not occur naturally. By including the context of the god, I wanted to make clear that this is not a problem for me. For example, if the answer to the question requires a perfectly spherical planet made out of solid plutonium, that's what you'll get to work with. However, except for the fact that it doesn't matter where to get the materials, or how to apply or shape them, I (as in, the human being behind the computer that is writing the question) am still only interested in scenario's that make sense according to our current understanding of physics. The radiation emitted by the planet made out of plutonium should still kill every organism nearly instantly, irrespective of whether or not the godlike entity has the power to magically handwave the radiation poisoning away.

I have included the additional story-specific elements, because it might provide some insight in how useful specific answers are, or how I determine the most acceptable answer. If any of the story-specific elements are confusing, feel free to ignore them.

Also note that if the god does decide to make the laws of nature different from how we model them, than the ramifications of such alterations are best discussed in another topic.

  • $\begingroup$ Is the life created with the planet, or is it going to need to evolve? $\endgroup$ Mar 30, 2017 at 21:06
  • $\begingroup$ We are on what is for the most part a ball of magma. We live on a cold crust floating on top. You can go down a kilometer in some tunnels here. $\endgroup$
    – user25818
    Mar 30, 2017 at 21:08
  • $\begingroup$ A god can do whatever they want to do. For example they can surround the world with a firmament (meaning strongness in Latin) and place on the said firmament a great luminary for the day, and a smaller one for the night, together with countless tiny luminaries serving as indicators of fate. Gods and science-based cannot mix: gods are gods and science doesn't do gods, because gods are by definition super-natural (in Latin) or meta-physical (in Greek, same meaning). $\endgroup$
    – AlexP
    Mar 30, 2017 at 21:14
  • $\begingroup$ @JoeKissling Evolution is not necessary. Lifeforms are created along with the planet. $\endgroup$
    – Sazanami
    Mar 30, 2017 at 21:17
  • 2
    $\begingroup$ Gods are immune from tedium simply because they can create beings to do the tedious bits for them. Let's call them angels. Delegation can work fine for Gods. $\endgroup$ Mar 30, 2017 at 21:23

2 Answers 2


There's a bit of a problem with the premise of the question to have God create a universe, but "still adhere to the laws of nature" and "have some kind of scientific basis". Presumably this God can make any laws of nature they like. But let's talk about that second bit, "have some kind of scientific basis".

"Science" is often misused to mean a model of how the world works; $E = mc^2$ and so on. That's not science, it's a result of science. Science is a method of looking at the universe in order to make predictions about the universe. For a world to have a scientific basis, that just means it follows its own rules. It means if you do the same thing twice, you get the same result (even the "randomness" of Quantum Mechanics follows probability equations). For more on this, I recommend Harry Potter and the Methods of Rationality in which a scientific minded Harry Potter uses science to puzzle out the rules of the Wizarding World.

That said, I'm going to hold on to some fundamental physical principles like the Principle of Locality, an object is only influenced by its immediate surroundings; no instantaneous action at a distance (except God). Also the Principle of Relativity, that the rules are the same no matter your frame of reference; a car coming towards you at 100 kph is the same as you rushing towards the car at 100 kph. And finally that the laws of physics work the same everywhere, no exceptions; this means God can't decide to have something hanging in the sky defying their laws of gravity.

In my answer I'm going to have God make a viable planet using rules as close to our own physics as possible, with as few special cases as possible, and with as little direct intervention or sculpting as possible.

A single planet floating in an endless void seems like a waste of space. Let's use that space and literally turn the idea inside out.

Make the planet a true, rigid Dyson Sphere where the inhabitants live on the inner surface. This provides an enormous volume of living space. At 1 AU, the distance from the Earth to the Sun, that gives 2.8e17 km2 of surface area as compared to just 5e8 km2 for the entire Earth. A billion times more room! As we'll see below, it doesn't have to be 1 AU, it can be as big as God likes.

God can tinker with the parameters of the Universe to make a rigid Dyson Sphere work. There's a few practical problems with rigid Dyson Spheres: material strength, how do you hold together a 1 AU sphere?; gravity, how do you keep people stuck to the inner surface?; position, how do you keep it centered around the star? We can solve all that in our universe with minimal changes.

They can make it a completely closed system bounded literally by the edge of the universe. The edge of the universe can radiate a gravity-like force to hold everyone on the "surface" and reduce to 0 at the center. In effect, the ground is dirt and rock that piled up on the edge of the universe.

The center of the sphere would act like an L1 Lagrangian point, a point of free-fall, but also an unstable point so anything there will drift one way or the other and fall back to the surface. Since that point is unstable, you can't put a star there (God could decide to just pin it at the center, but that's the kind of special case we're trying to avoid). That's ok, it doesn't need one.

Since it's a closed system, there's no need for a central star to provide energy. The inner volume of the sphere started with X amount of energy and it is neither created nor destroyed nor can it leave. There's no need for a star to warm the surface, it's already warm and always will be so long as that energy doesn't get locked up. On the flip side, any technological society would have to worry about the consequences of waste heat from industry as it would have no where to radiate to.

Light sources could be... well anything you like. There wouldn't be a day/night cycle in the traditional sense. That's fine, because this biosphere doesn't require plants and photosynthesis. Since it's a closed system there's no need to have organisms which gather energy from "outside" (on the Earth that's the Sun) to be at the bottom of the food chain. Instead that would be scavengers and lithotrophs.

Similarly, sight using visible light isn't a requirement for humanoid light. They'd probably use some other part of the spectrum. It's possible you'd see organism evolve to use active sensing, basically have built in flashlights. Or just not bother with vision at all, in a world without natural light, eyesight is not a big enough evolutionary advantage to offset the energy spent on it. Maybe echolocation.

Eventually entropy will become a problem and the usable energy in the sphere will start to become less dense. But God can step in to tidy that up every once in a while, that's inescapable in a small universe.

He prefers to mass produce as much as possible.

I have good news for God! They can make this inside-out universe in a few easy steps!

  1. Create a spherical universe with a hard edge.
  2. Imbue that edge with its equivalent of gravity.
  3. Add raw material at the center.
  4. Let it fall.
  5. Wait.

Note that there's no need to add energy, manifesting material at the center adds energy. When it appears, it suddenly has gravitational potential energy. As it falls and expands to fill the vacuum, that's converted to kinetic energy, and then heat and sound when it crashes down.

After that, normal chemical processes take over. Though without plate tectonics or any sort of a core or planetary rotation to stir things up it might take a bit longer. If God specifically wants humanoids, they'll have to engage in some artificial selection.

  • $\begingroup$ After reading it 4 times and letting the implications sink in a bit, I think I can safely conclude that this is absolutely perfect! Thanks for taking the time to write it all up! $\endgroup$
    – Sazanami
    Mar 31, 2017 at 9:41

It isn't orbiting anything

So there is no sun and no stars and no moon. No seasons, no day/night, no tides (actually no water on the surface at all because it'll be frozen). None of these are super necessary to life. No external source of energy would be a killer because Newton says entropy will increase forever. However -

The god may do some maintenance work every now and then.

Means that we have an energy source, so we probably don't need to break any (apart from creating an almost empty universe) laws of physics.

The god would like to add handcrafted, inhabitable tunnels and other underground structures to the planet.

Great. Make some dwarves that live underground, with industry powered by deep geothermal generators. Since god can just reheat the core every thousand years it's an infinite power source. You don't have to worry about the surface being frozen because there will be a comfortable temperature somewhere between the core and the surface.


No sun = no photosynthesis. You can have microorganisms that can grow in dirt (possibly using heat), which support some fungus or mold, which might be able to support tunneling rodents. Maybe there are larger creatures that live in cave systems. The dwarves can farm mushrooms and whatever eats mushrooms.


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