Spacetime foliation is the mathematical operation that slices a four-dimensional universe into three-dimensional sheets of 'now.' In general relativity, the slicing is a gauge choice. This is the physics, the ADM formalism, and why no universal present exists.
Julian Barbour's Platonia replaces time with a static landscape of every possible 'Now.' This is the physics, the equations, and the deep questions it cannot answer.
White holes are the time-reverse of black holes, a region nothing can enter and everything escapes. Long dismissed as mathematical curiosities, they may now be the physical exit from every black hole that ever formed.
In 1974, Frank Tipler showed that an infinite, ultra-dense, fast-spinning cylinder would drag spacetime hard enough to permit time travel into the past. This is the physics, the specifications, and the universe's response.
In 1991, David Deutsch wrote down the mathematics of what quantum mechanics does when a particle is forced to loop back through its own past. The paradox dissolves. The price is your continuous identity.
Spin networks are the central objects of loop quantum gravity, the theory that space itself is built from discrete quanta of geometry. This is the physics, what it actually says, and what it doesn't.
The absolute elsewhere is the third region of spacetime, sealed away from cause and effect, where the word 'now' loses all meaning. This is the physics, the Andromeda paradox, and the question the picture cannot answer.
If the block universe is real, you may not be a single self moving through time but a four-dimensional worm of temporal parts. This is the physics, the philosophy, and the question the picture cannot answer.
The Growing Block universe says the past and present are real, but the future is literally not yet there. This is the physics, the philosophy, and the unresolved question both sides share.
The block universe theory holds that past, present, and future are equally real, frozen together in a four-dimensional spacetime. This is the physics, the argument, and the unsettling implication.
