Substance persists across time as the bearer of Physicality. *That* something persists is structural; *which* specific quantities register the persistence (energy, momentum, charge, baryon number) depends on this universe's specific symmetries (Noether, Emmy, 1918). Within those symmetries, the specified quantities cannot arise from or vanish into nothing. Noether’s -(Noether, Emmy, 1918) theorem establishes that every continuous symmetry of an action functional yields a conserved quantity, and time-translation symmetry yields conservation of energy. The conservation laws of energy, momentum, and electric charge are among the most experimentally robust content of physics: every accelerator experiment and every spectroscopic measurement confirms them within measurement precision. The cosmological regime keeps the same symmetry discipline the theorem imposes: an expanding spacetime lacks global time-translation symmetry, so energy conservation there holds in its local, covariant form rather than as a global budget, exactly as Noether's correspondence directs. Conservation of baryon and lepton number (baryon number: the count of protons and neutrons in a system; lepton number: the count of electrons, muons, taus, and their associated neutrinos) holds at all present experimental scales but is expected to be violated in beyond-Standard-Model regimes (the energy scales and processes where physics beyond the current Standard Model is expected to operate), most consequentially during baryogenesis, where Sakharov's -(Sakharov, A. D., 1967) conditions require a small baryon-number-violating process to explain the observed matter-antimatter asymmetry. The structural claim of [§7.5.3](<7.5.3 Conservation.md>) concerns the *that* of conservation, not the durability of any particular item on the list. Apparent violations (radioactive decay, particle creation in pair production) preserve the underlying conservation when the full Substance-budget (Substance: the bearer of Physicality, the third structural condition of Nature, read here as the total stock of conserved quantities a process moves between) is tracked. What is foreclosed is spontaneous arising or vanishing of Substance-quantities, perpetual motion, *ex nihilo* creation at the level of conserved charges, and any cosmology that requires Substance to appear from no-Substance. As at [§7.4.2](<7.4.2 What is Required.md>) and [§7.5.2](<7.5.2 Field.md>), the framework holds neutrality on whether the fundamental physical object is fields-on-spacetime or wavefunction-on-configuration-space; Noether's correspondence between continuous symmetries and conserved quantities operates under either interpretation, and the *that* of conservation does not depend on the choice.


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← [7.5.2 Field](<7.5.2 Field.md>) | [7.5.4 Symmetry](<7.5.4 Symmetry.md>) →
