# Cosmic-Time Generative Presentism (CTGP) — Explained Part 10 of 26 (1,273 words) 9.4 Cosmological Simultaneity and Relativistic Locality ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ CTGP distinguishes three senses of “present” that are often conflated in objections to the framework. Local physical present: what an observer experiences at their worldline. This is the phenomenological present, dependent on local physical processes and subject to the usual relativistic effects of time dilation and gravitational redshift. Cosmological present: the foliation naturally selected by the large-scale matter distribution of the universe, approximated observationally by the CMB rest frame. This is a physically motivated but not observer-dependent quantity: any observer can in principle determine the CMB frame and locate themselves within it. Ontological present: the boundary between the generated domain M(σ) and the ungenerated future. This is the active edge at which new hypersurfaces are produced, parameterized by σ. CTGP’s present edge Σ_σ is identified with the cosmological present rather than with Newtonian absolute simultaneity or with any particular observer’s local present. Consequently, CTGP preserves local Lorentz invariance while maintaining a physically motivated global generation parameter. The resulting “universal tick” is therefore not a universal clock visible identically to every observer but a cosmologically grounded ordering relation associated with the generation of new hypersurfaces. Much confusion disappears once these three senses of present are kept distinct: local simultaneity is observer-dependent and Lorentz-relative; cosmological simultaneity is physically selected by the matter distribution; ontological simultaneity concerns what has been generated and what has not. 9.4.1 Co-presence, Cosmic Time, and Synchronization Co-presence is not a relation added to existence but a consequence of it. Since only the present exists — earlier stages have ceased to exist and later ones are ungenerated — everything that exists belongs to a single generative stage. This is why CTGP requires a global foliation: existence cannot be frame-relative, so there must be one fact about which events constitute the present. Cosmological time specifies which surfaces these are (§6.1). Membership in Σ_σ is co-presence, and because Σ_σ is a level set of the generation parameter, co- presence is equality of σ: two co-present events occur at the same cosmological generation stage because they carry the same value of σ. This is not a correlation between two facts but a single fact stated twice. In the emergent geometric regime, where σ is a monotone relabeling of cosmological time (Postulate 3), this is what “same cosmic time” refers to; prior to geometric emergence σ remains an ordering parameter and the equality still holds, without presupposing proper time. What does not follow from equality of σ is equality of proper time, which differs between worldlines under relative motion and differing gravitational conditions; synchronization in any operational sense, since co-present events may exchange no timing signals and need not be in causal contact; or sameness of rate, since systems undergoing radically different physical processes are generated within the same Σ_σ. The point is clearest for spacelike-separated events. Consider a person on Earth raising an arm and, billions of light years away, another person raising an arm. Neither event lies in the other’s past light cone; neither can influence the other, and in an expanding universe the two may never enter causal contact at all. CTGP nonetheless holds that there is a fact of the matter as to whether the two events belong to the same Σ_σ, and that this fact is fixed by the cosmological foliation rather than by any observer’s frame. The two movements are unrelated, uncoordinated, and unsynchronized. What they share is the same cosmological generation parameter σ, and therefore the same generative stage — and that equality carries no implication of shared proper time, shared rate, or any coordination whatever between them. The non-synchrony is quantitative and already carried by the formalism. The norm condition of §6.3 fixes the lapse of the cosmological foliation: N = f(σ)^{−1/2}, which is constant on each level set and equals 1 for the canonical labeling σ = τ. The observers normal to Σ_σ are therefore the maximizing geodesics themselves, and a system moving with speed v relative to them accumulates proper time dτ_local = N√(1 − v²/c²) dσ. Gravitational time dilation enters through the same factor, since a clock held at rest in a gravitational well is not in free fall and moves relative to the geodesics passing through it. Systems co-present at Σ_σ therefore accumulate different amounts of proper time between Σ_σ and Σ_{σ+dσ}. Both arm-raisers are co-present; neither is a clock the other could read, and the local simultaneity surface of each is in general tilted relative to Σ_σ. CTGP therefore does not claim that either observer’s own present is the privileged one. It claims that the generative ordering is settled by a foliation that neither of them occupies. Both facts hold at once, and neither displaces the other. The value co-present events share is itself a proper time: σ is a monotone relabeling of cosmological time, the maximal proper time accumulated since the initial singularity, which in cosmology is the proper time of the comoving matter congruence. Each co-present system also carries its own proper time, which in general differs from it — a system with peculiar velocity accumulates less between Σ_σ and Σ_{σ+dσ} than a matter- frame worldline does, and a clock at rest in a gravitational well accumulates less for the same reason. The two arm-raisers therefore share one cosmic proper time and carry non-identical local times simultaneously. This introduces no second kind of time. There is one quantity, proper time, evaluated along different worldlines; what distinguishes the cosmic value is the congruence along which it is measured and the fact that its level sets foliate the spacetime, not that it is a different sort of thing. This is why the matter-frame congruence enters as a realization rather than as a criterion of membership. Cosmological time is attained along the maximizing geodesics, which in cosmology are the comoving worldlines. Systems carrying peculiar velocity — essentially all systems, including the Earth — do not lie on those worldlines, and are co-present nonetheless. The construction selects the parameter; it does not impose a shared clock on the events the parameter orders. This also settles what would otherwise be an awkward case. Suppose a physical system underwent no change of any kind between two successive stages — no alteration of internal or spatial state. CTGP still distinguishes Σ_σ from Σ_{σ+dσ} as a progression in cosmological generation. Participation in the advancing present is not conditional on possessing a changing state variable: under Postulate 2, persisting at all is being generated at successive stages, and an unchanging configuration is one in which successive stages produce the same state rather than one exempt from generation. In brief. CTGP's simultaneity isn't Newton's absolute 'cosmic now.' Newton's time is imposed from outside and flows identically everywhere, so every clock in the universe ticks at the same rate and agrees on the same reading. CTGP rejects that. In CTGP, two events are co-present when they belong to the same generative stage of reality, the same step in the present's unfolding. The dividing line isn't imposed from outside. It's fixed by the geometry the universe's own matter produces, and on large scales it's the frame in which the cosmic microwave background looks uniform. Co-present events don't share proper time, clock rates, or any synchronization, and relativity's local effects like time dilation stay fully intact. Picture two people raising their arms billions of light years apart. They can never signal each other, and their clocks don't agree, but they still belong to the same stage of the present. Think of a computer’s shared system time, with each program showing its own timer — except that no clock anywhere keeps the present; the universe’s own structure does.