(Aug 10, 2020 04:27 AM)zhangjinyuan Wrote: If the Big Bang hypothesis is true, was time at rest relative to the outside world in the infinitely massive universe? After all, the universe is more massive than any black hole
Let's say we have an observer out in the universe, or somebody in the future will walk out of the universe
So when he looks at the universe, does it appear that there is no change in the horizon of the universe, but in fact tens of billions of years have passed inside the universe.
In what's apparently one of the "newer"
pregeometry proposals, spacetime as a kind of figurative hologram emerges from a boundary of quantum entangled
qubits with accordingly very complicated relationships. A view from outside the (entire) global entangled system of qubits for the cosmos wouldn't be literally possible. But imagination-wise it would be static (timeless), while "inside" its subsystems things seem to be evolving -- there are conscious agents who are experiencing changes or what they believe is a transistion from one different state to another.
How to understand the universe when you're stuck inside it
https://www.quantamagazine.org/were-stuc...-20190627/
Lee Smolin: [...] The statement that there’s nothing outside the universe — there’s no observer outside the universe — implies that we need a formulation of physics without background structure. All the theories of physics we have, in one way or another, apply only to subsystems of the universe. They don’t apply to the universe as a whole, because they require this background structure. If we want to make a cosmological theory, to understand nature on the cosmological scale, we have to avoid what the philosopher Roberto Unger and I called “the cosmological fallacy,” the mistaken belief that we can take theories that apply to subsystems and scale them up to the universe as a whole. We need a formulation of dynamics that doesn’t refer to an observer or measuring instrument or anything outside the system. That means we need a different kind of theory.
It’s a theory about processes, about the sequences and causal relations among things that happen, not the inherent properties of things that are. The fundamental ingredient is what we call an “event.” Events are things that happen at a single place and time; at each event there’s some momentum, energy, charge or other various physical quantity that’s measurable. The event has relations with the rest of the universe, and that set of relations constitutes its “view” of the universe. Rather than describing an isolated system in terms of things that are measured from the outside, we’re taking the universe as constituted of relations among events. The idea is to try to reformulate physics in terms of these views from the inside, what it looks like from inside the universe.
[...]
It reminds me of a lot of work that’s going on now in physics that’s finding surprising connections between entanglement and the geometry of space-time.
Lee Smolin: I think a lot of that work is really interesting. The hypothesis that’s motivating it is that entanglement is fundamental in quantum mechanics, and the geometry of space or space-time emerges from structures of entanglement. It’s a very positive development.
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Quantum gravity's time problem
https://www.quantamagazine.org/quantum-g...-20161201/
EXCERPT: . . . One clue comes from theoretical insights arrived at by Don Page and William Wootters in the 1980s. Page ... and Wootters ... discovered that an entangled system that is globally static can contain a subsystem that appears to evolve from the point of view of an observer within it. Called a “history state,” the system consists of a subsystem entangled with what you might call a clock. The state of the subsystem differs depending on whether the clock is in a state where its hour hand points to one, two, three and so on. “But the whole state of system-plus-clock doesn’t change in time,” Swingle explained. “There is no time. It’s just the state — it doesn’t ever change.” In other words,
time doesn’t exist globally, but an effective notion of time emerges for the subsystem.
A team of Italian researchers experimentally demonstrated this phenomenon in 2013. In summarizing their work, the group wrote: “We show how a static, entangled state of two photons can be seen as evolving by an observer that uses one of the two photons as a clock to gauge the time-evolution of the other photon. However, an external observer can show that the global entangled state does not evolve.”
[...] As I described in an article this week on a
new theoretical attempt to explain away dark matter, many leading physicists now consider space-time and gravity to be “emergent” phenomena:
Bendy, curvy space-time and the matter within it are a hologram that arises out of a
network of entangled qubits (quantum bits of information), much as the three-dimensional environment of a computer game is encoded in the classical bits on a silicon chip. “I think we now understand that space-time really is just a geometrical representation of the entanglement structure of these underlying quantum systems,” said Mark Van Raamsdonk, a theoretical physicist at the University of British Columbia.
[...] On the timeless boundary of our space-time bubble, the entanglements linking together qubits (and encoding the universe’s dynamical interior) would presumably remain intact, since these quantum correlations do not require that signals be sent back and forth. But the state of the qubits must be static and timeless. This line of reasoning suggests that somehow, just as the qubits on the boundary of AdS space give rise to an interior with one extra spatial dimension, qubits on the timeless boundary of de Sitter space must give rise to a universe with time — dynamical time, in particular...
[...] Other theoretical work has led to similar conclusions. Geometric patterns, such as the amplituhedron, that describe the outcomes of particle interactions also suggest that reality emerges from something timeless and purely mathematical. It’s still unclear, however, just how the amplituhedron and holography relate to each other. The bottom line, in Swingle’s words, is that “somehow, you can emerge time from timeless degrees of freedom using entanglement.”
Aug 10, 2020 04:27 AM
