Space has intrinsic negative energy {dark energy}|. Dark energy is 70% of universe mass-energy (ordinary matter and dark matter are 30%). Perhaps, dark energy is virtual particles that have negative energy {vacuum energy} and repulse masses. Perhaps, dark energy involves new forces and interactions, such as quintessence. Perhaps, dark energy uses hidden space dimensions.
As they travel, electron, muon, and tau neutrinos, which have different masses, interconvert. Perhaps, neutrino-mass changes make dark energy, as they oscillate matter quark flavors. Dark-energy density is similar to neutrino density.
Perhaps, supernova changes or distant-particle effects cause space expansion, so there is no dark energy. Perhaps, rippling long-wavelength waves still travel after cosmic inflation and increase in intensity, expanding universe indefinitely, so there is no dark energy. Perhaps, non-linear mass interactions (backreaction) contribute to space expansion.
density
Dark energy density is 10^-26 kg/m^3. Dark-energy density variation over space is zero, because dark-energy particles do not attract each other, so space has constant dark-energy density over time and space.
When energy is negative, force is repulsive, so positive space expansion amount equals added negative energy amount, keeping dark-energy density same when universe is small or large.
space expansion
After cosmic inflation ended, 1 second after universe origin, dark energy causes universe space expansion.
internal pressure
Rubber membranes resist stretching (expansion) and compressing (contraction). Stretched rubber membranes try to contract (like gravity) and have positive (attractive) restoring force, potential energy, and internal pressure. Compressed rubber membranes try to expand (like antigravity) and have negative (repulsive) restoring force, potential energy, and internal pressure. Quantum vacuum has negative (repulsive) force that expands space, increasing negative potential energy (dark energy) by subtracting universe positive kinetic energy, and so cooling the universe. Quantum vacuum has negative internal pressure between one-third and one of mass-energy density, so repulsive antigravity is between zero and negative two times mass-energy density: M + 3 * -(M/3) = 0 and M + 3 * -M = -2*M.
universe
In early universe, dark-energy repulsion and gravitational attraction clustered matter into protogalaxy filaments. Filaments formed galaxy clusters. Galaxy clusters stopped forming six billion years ago, as space expansion made mass-energy density lower and gravity less, while dark-energy density stayed constant. Clusters allow galaxy collisions, so older galaxies have irregular shapes (while younger galaxies are spirals). Colliding galaxies increase star formation. Star formation became low six billion years ago.
Before five billion years ago, mass-energy density was higher than dark-energy density, so universe initial expansion slowed. Five billion years ago, mass-energy density became equal to dark-energy density. After five billion years ago, mass-energy density became less than dark-energy density, and universe expansion accelerated. In the future, dark energy will cause faster separation of galaxy clusters, then galaxies, then stars and planets, then molecules, and finally atoms.
heavy elements
If dark energy was stronger, filaments are fewer, clustering is less, and star formation is less, so fewer supernovas make fewer heavy elements. If dark energy was weaker, filaments are more numerous, and clustering is more, but star formation makes smaller stars, which do not supernova to make heavy elements. Universe dark-energy density maximizes heavy-element formation.
Perhaps, non-linear mass interactions {backreaction} contribute to space expansion.
For ordinary matter, average vacuum fluctuation energy is zero {average weak energy condition}. For exotic matter, average can be negative.
When calculations showed that general-relativity equations require that universe expand forever, Einstein introduced extra space-time force {cosmological constant}|, whose attractive force balanced space expansion and maintained static and infinite universe. However, recent observations show that, though gravity slows expansion, space expansion is accelerating, requiring repulsive cosmological constant. Perhaps, dark energy or quintessence supplies cosmological constant. Perhaps, universe angular momentum causes cosmological constant (but universe does not rotate).
By virtual-particle quantum mechanics, space contains very high vacuum energy. If so, universe has very high curvature. By virtual-particle quantum mechanics, cosmological constant is 120 orders of magnitude greater than cosmological constant that balances gravity, but observations show that space has zero curvature {cosmological constant problem}. Perhaps, space has negative pressure to counterbalance vacuum energy. Perhaps, constant negative dark energy counterbalances vacuum energy.
Observed universe mass-energy density is the density (critical density) that makes space curvature zero. If early-universe mass-energy density was 10^-14 more than early-universe critical density, later-universe density becomes much higher than later-universe critical density, and space becomes more curved and more closed. If early-universe mass-energy density was 10^-14 less than early-universe critical density, later-universe density becomes much lower than later-universe critical density, as space becomes less curved and more open. Therefore, because universe space curvature is zero now, early-universe space had zero curvature, an unlikely situation {flatness problem}. Perhaps, though early universe did not have critical density, early-universe cosmic inflation reduces space curvature.
Perhaps, dark energy can become more repulsive energy {phantom energy} as time increases.
Perhaps, dark energy is repulsive field {quintessence, field}|, not virtual particles or vacuum energy. Quintessence is higher at higher potential energy and zero at lowest potential energy, so quintessence (and cosmological constant) decrease over time as universe expands. Perhaps, space negative pressure or quantum effects cause quintessence.
Quintessence field strength is almost zero. If strength was more, space expansion is so great that only radiation can exist. If strength was less, space expansion is so small that only matter can exist.
When rock hits another rock, pressure waves spread from surface and from inside. When inside pressure wave reaches surface, reflection changes phase by 180 degrees. At a thin layer {spall zone} at surface, pressure wave from surface and pressure wave from reflection almost cancel, and surface pressure is near zero. However, pressure just below surface is high, and rock erupts through surface. In cosmology, expanding universe has spall zones.
5-Astronomy-Universe-Cosmology
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Date Modified: 2022.0225