It's all speculative

 

It's all speculative ... time travel and living in a simulation as both connect to relativity and quantum mechanics along with the wild card of chaos and the law of initial conditions as nothing ever repeats a given path exactly whether it be earth circling the sun once a year or a pendulum on a clock as an exact tracing of a given path is forever not a given.

The map defined by x → 4 x (1 – x) and y → (x + y) mod 1 displays sensitivity to initial x positions. Here, two series of x and y values diverge markedly over time from a tiny initial difference.

To whit. 

Time travel or the push to reverse entropy, the "arrow of time" or heat death equation, as governed by the two laws of thermodynamics, is something SyFi writers and scientists, since the beginning of time, have wrestled with in trying to solve this wicked problem for the ages. 

Tenet gets points for its creative use of entropy but this bit of 19th-century science is not convincing. Though increasing entropy does indeed track the forward flow of time, there is no evidence that entropy controls time. In fact, entropy decreases locally in our own bodies, yet we move forward in time, not backward. That may explain why, when Nolan consulted Caltech theoretical physicist Kip Thorne—who had worked on Nolan’s earlier film Interstellar (2014)— Nolan had to promise, “I wasn’t going to bandy his name around as if there was some kind of scientific reality to Tenet. It’s a very different kettle of fish to Interstellar.”2

Do any real scientific ideas support time travel? Do they provide a way to resolve its paradoxes? The answers lie in relativity and quantum physics. Einstein’s relativity—especially general relativity, his theory of gravity—treats time directly together with space as the spacetime continuum, the fabric of the universe that has cosmic physical effects. Quantum theory describes subatomic behavior, but is also necessary to explain cosmic processes where general relativity breaks down, as it does inside a black hole, and during the earliest moments of the universe. That is why physicists are working to combine both theories into a unified theory of quantum gravity that is a more complete description of the universe.

One real result from general relativity is that the flow of time is variable. This is gravitational time dilation, where time flows more slowly the stronger the gravitational field. It appears in a crucial Interstellar scene where spacecraft pilot Cooper (Matthew McConaughey) has aged only by hours in the powerful gravity near a black hole, but realizes that Murph, the young daughter he left back on Earth, has meanwhile aged by decades. He desperately wants to travel back in time to communicate with her at age 10; but this interaction should not carry information from future to past, another of the violations that time travel would create. Thorne finessed the problem by using ideas from quantum gravity that allow Cooper to travel back and communicate with Murph by pushing objects to create gravitational forces that she senses, without violating anything. Thorne also describes another form of time travel in the book he wrote to accompany the film, where a wormhole makes it possible to reach the past.

Awesome take that has legs. 

 Love Fouad Khan's take on the simulation bit.

All computing hardware leaves an artifact of its existence within the world of the simulation it is running. This artifact is the processor speed. If for a moment we imagine that we are a software program running on a computing machine, the only and inevitable artifact of the hardware supporting us, within our world, would be the processor speed. All other laws we would experience would be the laws of the simulation or the software we are a part of. If we were a Sim or a Grand Theft Auto character these would be the laws of the game. But anything we do would also be constrained by the processor speed no matter the laws of the game. No matter how complete the simulation is, the processor speed would intervene in the operations of the simulation.

Here’s a simple example. A 64-bit processor would perform a subtraction between say 7,862,345 and 6,347,111 in the same amount of time as it would take to perform a subtraction between two and one (granted all numbers are defined as the same variable type). In the simulated reality, seven million is a very large number, and one is a comparatively very small number. In the physical world of the processor, the difference in scale between these two numbers is irrelevant. Both subtractions in our example constitute one operation and would take the same time. Here we can clearly now see the difference between a “simulated” or abstract world of programmed mathematics and a “real” or physical world of microprocessor operations.

If we live in a simulation, then our universe should also have such an artifact. We can now begin to articulate some properties of this artifact that would help us in our search for such an artifact in our universe.

Awesome to a fault.