The subject of this article has never been observed, and on its own theory cannot be – not for want of instruments, but because one of them does not last long enough to be one. It is described here only in the plural.

| Type | Proposed elementary particle |
|---|---|
| Of | the luminiferous aether |
| Composition | A single twist of the medium |
| Observed | Never |
| Found singly | Never – see below |
| Detectable properties | None |
The rentup is the proposed elementary particle of the luminiferous aether: the smallest possible twist of the medium, the ground-state knot from which, on the aether theories, all matter is built.[1] It has never been isolated; and on the theory's own terms it cannot be, a circumstance its proposers regard not as an embarrassment but as a confirmation.
A rentup is defined as a twist in the aether – and a twist, the theory holds, must twist against something.[2] A single rentup, alone, has nothing to oppose; it untwists in the instant of forming and is gone. The aether therefore contains a great many rentups and not one rentup – conditions its theorists insist are wholly different. The particle is, in consequence, only ever plural: one does not encounter a rentup, only rentups, and never fewer than the medium will bear.
The rentup is defined less by what it is than by what it is needed for.[3] Every aether theory requires an elementary unit, so that its equations should close; none has produced one; and rentup is the name reserved for the unit each theory assumes and none has shown. It has no detectable property – not mass, not charge, not extent – a fact its proponents hold to be the signature of a truly fundamental thing rather than of an absent one. (Ezekiel Quartz's vortex-solitons are the rentup writ large.)
The word is modern, coined – in the plural, rentups – by whoever first had need of it; and it stands, in garble and likewise plural, on the 33,666th tablet of the ancient Obed, one of five terms that stone is held to have pre-named by accident.[4] That the tablet gives the word in the plural is, the faithful observe, the single respect in which it is correct: the rentup having no singular, rentups is its only proper form, cut so three thousand years before the particle was thought of.
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