There are many popular hypotheses with all kinds of different implications related to time in some way, but those aren’t part of standard textbook physics. They’re proposed extensions of our current models. I’m talking about plain old general relativity+Standard Model QFT here. Spacetime is a four-dimensional manifold, fields in the SM Lagrangian have support on that manifold, all of those field have CPT symmetry. Don’t go asking for quantum gravity or other matters related to UV-completion.[1]
All that gives you is an asymmetry, a distinction between the past and future, within a static block universe. It doesn’t get you away from stasis to give you a dynamic “moving cursor” kind of present moment.
Combined with locality, the rule that things in spacetime can only affect things immediately adjacent to them, yeah, it does. Computations can only act on bits that are next to them in spacetime. To act on bits that are not adjacent, “channels” in spacetime have to connect those bits to the computation, carrying the information. So processing bits far removed from t at t is usually hard, due to thermodynamics, and takes place by proxy, using inference on bits near t that have mutual information with the past or future bits of interest. Thus computations at t effectively operate primarily on information near t, with everything else grasped from that local information. From the perspective of such a computation, that’s a “moving cursor”.
(I’d note though that asymmetry due to thermodynamics on its own could presumably already serve fine for distinguishing a “present”, even if there was no locality. In that case, the “cursor” would be a boundary to one side of which the computation loses a lot of its ability to act on bits. From the inside perspective, computations at t would be distinguishable from computations at t+1 and t−1 in such a universe, by what algorithms are used to calculate on specific bits, with algorithms that act on bits “after” t being more expensive at t≤t1. I don’t think self-aware algorithms in that world would have quite the same experience of “present” we do, but I’d guess they would have some “cursor-y” concept/sensation.
I’m not sure how hard constructing a universe without even approximate locality, but with thermodynamics-like behaviour and the possibility of Turing-complete computation would be though. Not sure if it is actually a coherent set-up. Maybe coupling to non-local points that hard just inevitably makes everything max-entropic everywhere and always.)
I mean, do ask, by all means, but the answer probably won’t be relevant for this discussion, because you can get planet earth and the human brains on it thinking and perceiving a present moment from a plain old SM lattice QFT simulation. Everyone in that simulation quickly dies because the planet has no gravity and spins itself apart, but they sure are experiencing a present until then.[2]
Except there also might not be a Born rule in the simulation, but let’s also ignore that, and just say we read off what’s happening in the high amplitude parts of the simulated earth wave-function without caring that the amplitude is pretty much a superfluous pre-factor that doesn’t do anything in the computation.
Combined with locality, the rule that things in spacetime can only affect things immediately adjacent to them, yeah, it does.
Along a worldline, you have a bunch of activity at time T0 that is locally affecting stuff, a bunch of stuff at time T1 that is locally affecting stuff, and so on. They’re all present moments. None is distinguished as the present moment, even from the perspective of a single worldline..
In that case, the “cursor” would be a boundary to one side of which the computation loses a lot of its ability to act on bits.
There could be any number of such approximate “boundaries” along a worldline.
Except there also might not be a Born rule in the simulation,
Assuming you mean collapse—the Born rule is a just a timeless relationship between probability and amplitude—there could be one in reality as well. That’s one of the reasons there isn’t a single model of time in physics. Collapse actually is a moving cursor.
There are many popular hypotheses with all kinds of different implications related to time in some way, but those aren’t part of standard textbook physics. They’re proposed extensions of our current models. I’m talking about plain old general relativity+Standard Model QFT here. Spacetime is a four-dimensional manifold, fields in the SM Lagrangian have support on that manifold, all of those field have CPT symmetry. Don’t go asking for quantum gravity or other matters related to UV-completion.[1]
Combined with locality, the rule that things in spacetime can only affect things immediately adjacent to them, yeah, it does. Computations can only act on bits that are next to them in spacetime. To act on bits that are not adjacent, “channels” in spacetime have to connect those bits to the computation, carrying the information. So processing bits far removed from t at t is usually hard, due to thermodynamics, and takes place by proxy, using inference on bits near t that have mutual information with the past or future bits of interest. Thus computations at t effectively operate primarily on information near t, with everything else grasped from that local information. From the perspective of such a computation, that’s a “moving cursor”.
(I’d note though that asymmetry due to thermodynamics on its own could presumably already serve fine for distinguishing a “present”, even if there was no locality. In that case, the “cursor” would be a boundary to one side of which the computation loses a lot of its ability to act on bits. From the inside perspective, computations at t would be distinguishable from computations at t+1 and t−1 in such a universe, by what algorithms are used to calculate on specific bits, with algorithms that act on bits “after” t being more expensive at t≤t1. I don’t think self-aware algorithms in that world would have quite the same experience of “present” we do, but I’d guess they would have some “cursor-y” concept/sensation.
I’m not sure how hard constructing a universe without even approximate locality, but with thermodynamics-like behaviour and the possibility of Turing-complete computation would be though. Not sure if it is actually a coherent set-up. Maybe coupling to non-local points that hard just inevitably makes everything max-entropic everywhere and always.)
I mean, do ask, by all means, but the answer probably won’t be relevant for this discussion, because you can get planet earth and the human brains on it thinking and perceiving a present moment from a plain old SM lattice QFT simulation. Everyone in that simulation quickly dies because the planet has no gravity and spins itself apart, but they sure are experiencing a present until then.[2]
Except there also might not be a Born rule in the simulation, but let’s also ignore that, and just say we read off what’s happening in the high amplitude parts of the simulated earth wave-function without caring that the amplitude is pretty much a superfluous pre-factor that doesn’t do anything in the computation.
Along a worldline, you have a bunch of activity at time T0 that is locally affecting stuff, a bunch of stuff at time T1 that is locally affecting stuff, and so on. They’re all present moments. None is distinguished as the present moment, even from the perspective of a single worldline..
There could be any number of such approximate “boundaries” along a worldline.
Assuming you mean collapse—the Born rule is a just a timeless relationship between probability and amplitude—there could be one in reality as well. That’s one of the reasons there isn’t a single model of time in physics. Collapse actually is a moving cursor.