This is a completely post-scarcity society. Robots and automated systems run the economy and most research. AIs are commonplace, and available to all in the human-like, completely obedient, and super-intelligent varieties. Carbon nanotubes and diamond filament structures are old news. Asteroids are left alone in the name of environmental conservation, and material is either recycled or starlifted. Medical technology has made everyone ageless, and capabilities of genetic engineering technology has long exceeded the creativity of its users. Interstellar travel is boring, and relies on a combination of laser sails and antimatter rockets, powered by Dyson swarms. Nearly every star in the galaxy has something built around it.

This civilization wants to build some giant space pets. Fish, snakes, dragons, butterflies, squids, worms, anything vaguely Earth-like goes. They can make lifeforms out of carbon, silicon, or both simultaneously. They've already spent eons making terrestrial creatures hilariously large. The bodies of these animals can be internally reinforced programmable material trusses that change length and shape as the animals move.

They want to make the largest space creature possible. It doesn't have to get closer than a lightyear or two to any stars, and pretty much any amount of both macro and micro cyborg enhancement is possible.

Essentially, if they can get right to the limit of currently theorized material science, how large can the space creatures get?

  • $\begingroup$ Please clarify your specific problem or provide additional details to highlight exactly what you need. As it's currently written, it's hard to tell exactly what you're asking. $\endgroup$
    – Community Bot
    Commented Apr 24 at 18:50
  • 2
    $\begingroup$ Something like the Silk God from the Orions Arm Project $\endgroup$ Commented Apr 24 at 20:45
  • $\begingroup$ You've listed so many hypothetical technologies that you're well past "science based" here! This is a Star Trek kind of situation - it only needs enough pseudoscientific filler to sound plausible, not an actual scientific basis. $\endgroup$
    – Graham
    Commented Apr 25 at 5:41
  • $\begingroup$ @Graham Fair enough! I've removed that tag. I'm trying to go for the most advanced technologies that should be possible under current understandings. In this world, antimatter rockets are allowed, even though there aren't any great concepts yet for how to get the energy from antimatter annihilation into usable thrust, but warp drives aren't, because there's no evidence of negative matter existing, and the practicalities of how much of it you would need. It's essentially the most optimistic interpretation of currently known limitations. $\endgroup$
    – user107900
    Commented Apr 26 at 0:58
  • $\begingroup$ @user107900 Fair enough. :) Re plausibility, there's one SF writer (my bad, can't right now remember who it was) who came up with the concept of two levels of suspension-of-disbelief on hard SF. Their basic idea was to be able to answer every "but what about" with an extra level of handwavy detail, and then to be able to answer every "but what about" on that level of detail with another level of handwavy detail. They reckoned two levels of that was enough for every reader to just go "OK, fair enough", and it didn't have to be massively accurate, just have a not-completely-fake answer. $\endgroup$
    – Graham
    Commented Apr 26 at 8:56

1 Answer 1


Planet sized.

Biological organisms are limited by evolution and what it can achieve, e.g. they can't have multiple lungs and hearts wherever needed to maximize blood flow.

But if you have unlimited funds and genetic engineering, you can just make something that works. It won't start to break down till gravity becomes an issue. Stick enough hydrogen in a small space, and you get a star, not an organism.

The exact size would depend on real life science about how to build a planet sized creature. We haven't actually done that, so you can put the limits wherever you like. Just, if it gets too big, it will collapse due to gravity.

  • $\begingroup$ With the right body shape, you should be able to organize an arbitrarily large amount of mass without gravitational collapse. It won't look much like any kind of earth pet, but rather a large network of widely distributed mass pockets connected by thin tendrils. $\endgroup$ Commented Apr 24 at 19:26
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    $\begingroup$ " Fish, snakes, dragons, butterflies, squids, worms" they require animals in those shapes, not tentacle monsters. $\endgroup$
    – Nepene Nep
    Commented Apr 24 at 19:32
  • $\begingroup$ @NepeneNep squids aren't tentacle monsters now? $\endgroup$ Commented Apr 25 at 8:29
  • $\begingroup$ Squids don't have long tentacles connecting large parts of their body. $\endgroup$
    – Nepene Nep
    Commented Apr 25 at 12:24
  • $\begingroup$ @NepeneNep You left off the most important part of that list - "anything goes". $\endgroup$ Commented Apr 25 at 12:49

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