This is a companion piece explaining the worldbuilding behind “The Relentless Gardner” from A Consensus in Time.

Warning: Spoilers for A Consensus of Time

The Gardner, in his quest to run independent parallel experiments with civilizations, needs to contain them to their local area [1] and prevent cross-contamination. This is especially important given how abundant with life the universe is. Intelligent species are intrinsically motivated to figure out “what’s out there.” They’re curious. Therefore, they’ll try to reach outwards and make contact with other civilizations.

The Gardner is of the opinion that passive discouragement trumps active prevention. For example, if a civilization observes that interesting places are moving away faster than they could ever travel to them, they’re likely to give up before they try [2]. If instead they were completely isolated in a smaller local cluster, they’re likely to probe the edges and break down the fence. In summary, a sufficiently intelligent civilization trying to contain us would make it appear that everything beyond our local area is redshifting [3].

However, redshifting has problems. The speed things move away can’t be so fast that it affects the structural integrity of local matter. It also can’t induce total hopelessness. It must be sufficiently slow for civilizations to advance without despair, but sufficiently fast that they don’t bother trying to leave.

The Gardner is not omnipotent. There are limits to his technology. Even while using superluminal energy, he has to spend time traveling. We can safely assume he has not mastered the dimension of time. His subjects can’t travel at the same speed he can, but he also can’t be everywhere at once. He can’t intercept a poorly controlled civilization from contaminating others while he’s not attending them.

The curtains are somewhat translucent, letting in some light while blocking the rest. Manipulating this light is the Gardner’s way of allowing controlled observations from the planet. However, the light that gets in also brings evidence of matter interacting gravitationally with celestial bodies - but without the corresponding visible light that would explain it. This is what appears as dark matter to us [4].

[1] The “local area” is arbitrary - it could be as small as a solar system and its Oort cloud, or much larger - depending on the objectives the Gardner has set for that particular civilization.

[2] Imagine you’re on a treadmill that’s moving backwards faster than you can run forwards. You’d stop trying to reach the front pretty quickly.

[3] Redshifting is when light from distant objects stretches into longer, redder wavelengths. We observe this happening to distant galaxies, and the further away they are, the faster they appear to be receding from us. This is currently interpreted as evidence that the universe is expanding.

[4] Dark matter is something we can’t see directly, but we know it’s there because of how it pulls on things gravitationally. Galaxies spin faster than they should given their visible mass, and light bends around empty-looking space. We infer there’s invisible mass causing these effects. In this framework, it’s mass behind the curtain that we can detect gravitationally but can’t see optically.