General relativity is about gravity {gravitation, relativity}| and accelerations. For small gravity, observers calculate that gravitation and acceleration have the same local effects on space-time curvature. Because gravitational field strength varies inversely with distance, observers calculate that gravitation and acceleration have different global effects on space-time curvature.
time
Because stationary observers calculate that gravity rotates space-time time and radial-space coordinates toward each other, clocks in gravitational fields, or undergoing accelerations, run slower. People age slightly more quickly on Moon than on Earth, because Moon has smaller gravitational field. People age more slowly on accelerating rockets than on Earth.
object length
Observers calculate that accelerating massive objects decrease length. After accelerating finishes, observers calculate that length returns to previous amount.
object mass
Observers calculate that accelerating massive objects increase mass. However, mass increase increases inertia and resists further acceleration. After accelerating finishes, observers calculate that mass returns to previous amount.
energy
Gravity depends on mass, directed potential energy, directed kinetic energy, and random-energy temperature. Mass and random energy are always positive. Gravity fields cannot cancel, because they are only positive. Because gravity is infinite and is only positive, gravity can have unlimited energy amounts.
sources
General-relativity stress-energy tensor has ten independent gravitational-field sources and ten independent internal-stress sources. Sources all conserve energy and momenta. Field equations are d'Alembert potential equations.
physical-law invariance
Gravitation and acceleration curve space-time, so non-locally physical laws vary under coordinate transformations.
uncertainty principle
Gravitational-field values correspond to position. Field-value-change rates correspond to momenta. Therefore, uncertainty principle applies to gravitational-field values and value-change rates.
black holes
Because gravity is unlimited, gravity can become strong enough to overcome all object accelerations, so even light cannot escape the space region. Outgoing geodesics converge. Space curves so much that it closes on itself, forming a region separate from space-time, not observable from outside. Only gravity can cause space-time singularities, because it is never negative.
gravitational entropy
Spaces have entropy that depends on topology (Euler number). Gravity curves space-time and creates different topologies, so gravity has entropy. Because only gravity is always positive, only gravity has entropy. Other forces cannot curve space-time, because they are not infinite and/or are both positive and negative.
gravitational entropy: black hole
Because gravity has entropy and forms black holes, black holes trap entropy. Black-hole trapping amount depends on event-horizon radius, so black-hole entropy depends on event-horizon spatial area.
Because black holes have entropy, they have surface temperature at event horizon. At event horizon, virtual-particle creation can allow one virtual-pair member to tunnel through event horizon to space, causing black hole to lose matter and eventually dissipate. Entropy decreases, rather than always increasing. Black holes disrupt quantum-state deterministic development and mix states {mixed quantum state}.
repulsion
Perhaps, gravity can temporarily repulse, and cause universe origin. Exotic particles can have negative pressure, causing repulsion. Larger spaces have more repulsion because pressure is in space, not in ordinary particles.
Physical Sciences>Physics>Relativity>General Relativity>Gravity
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Date Modified: 2022.0224