[I was just sitting here – thinking about where the fun speculations of 19th century Mormonism might lead, and this is what came out. Excuse its ragged form.]
Mormonism has a uniquely materialist bent. It posits that the material is necessary for complete happiness. That while the world is biphasic, physical and spiritual, both are material. Modern physics divides much of its attention between the very large (cosmology) and the very small (quantum phenomena). In the large, physics tells us of a universe whose center is everywhere and whose circumference is nowhere and yet expanding. That expansion is apparently going on forever, never to stop.
The expansion of the universe along with the laws of thermodynamics dictate both a lessening of temperature variations among different spatial locations (proceeding to eventual uniformity) and a dissipation of energy, overall system organization degrading to near non-existence. Barring a “big rip,” the first major end stage is the cessation of star formation in about 1013 years from now. It’s all down hill from there.
The quantum world is mysterious by “design” apparently, with probability dictating the predictions of the relevant equations. Weird is the rule here: disappearance and reappearance of particles, time reversals, creation and destruction of “matter.” I’ll come back to this in a moment.
While the Mormon view of reality is biphasic, the material worlds are linked. Wherever there is regular matter, there is “spiritual” matter. The latter is apparently matter, but difficult to detect, something on the order of “dark matter.” Living beings are formed of both types of matter, and possibly all of the physical world overlays its doppelganger “spirit matter” version. This has support in some of Joseph Smith’s early revelations (JST, say) and their interpretations by the Pratt brothers in particular.
The “small” universe contains restrictions on what may be known. Further, depending on whether proton decay exists, the progress to an eventual universe steady-state varies. But no matter which version is correct, the large universe cannot support life as we know it beyond about 1050 years from now. The so-called “dark-era” begins about a googol of years from now.  Two different fates are possible from this point depending on whether protons are stable. If not, a sparse-state, where roughly all there is left locally will be electrons and positrons wandering at great distances from one another and that makes for not only a very dark place but an exceedingly cold one, eventually dipping to absolute zero. (There are various possible intermediate states I won’t consider here.) If protons are stable, then all matter will decay to iron isotopes which collect in “iron stars” and eventually these may disappear into quantum black holes. In any event, things get dark and as cold as can be.
The Mormon God is some kind of material being, and at least some strands of Mormon theology describe God as a part of the present physical world, even a resident on a physical planet. For purposes of this post, let us suppose this is the case. While God may be highly accomplished in manipulating the material universe on very short (not quantum) time scales, the speed limit of the universe (essentially the speed of light – although that must be defined more precisely than I will do here) defines the maximum rate of information transfer. Additionally, God is required to be local, very local indeed if he were to make visits to earth.
The physical universe offers somewhat limited possibilities in the way of building/sustaining life. Life – at least as we understand it – probably can’t exist outside a star system like our solar system. Moreover, in each such system there is a “sweet spot” – not too far from the central star – not too close. The earth’s orbit defines what is roughly that sweet spot in our particular system. Further, magnetic fields of some strength must exist to protect a planet in the sweet spot (from the rain of charged particles) which requires an internal dynamo system, like our own liquid iron core complex whose useful operation may depend on the moon’s existence. Additionally, solar systems are not generated in any useful stable fashion outside the “sweet spot” of spiral galaxies. Too near the central mass and the density of interstellar objects is too great for solar system mechanics to remain stable long enough to support life and its development (I’m assuming that evolutionary processes account for life here – but claiming some other mechanism doesn’t alter the essentials much). Too far from the central galactic mass and not enough metal is around to allow for planet formation (I use “metal” in a somewhat generalized sense). Our own solar system can be taken to define the galactic sweet spot orbit – though that is naturally considerably larger than the solar system sweet spot orbit. These are a few of the factors necessary to support life as we know it. If God shares the physical world with us and is embodied in matter (protons, neutrons, electrons, etc.) then God is subject to similar conditions and barring technological solutions, would be found in the galactic sweet spot. However, speed limits still apply. No complex material system like a biological organism could approach the speed of light (except in science fiction). The amount of energy required would involve something like converting a large fraction of the mass of the moon to energy. And no material object may travel at the speed of light.
But we are speaking of God here and therefore it seems permissible, within the boundaries outlined here (material body) to allow for God being able, by some sort of technology, to travel near the speed of light. Say 90% of c (or about 168,000 miles per second). Getting up to such a speed would involve reasonable rates of acceleration and deceleration. That adds significantly to any journey time. But let’s assume that God is only minimally inconvenienced by such things. In order to visit the earth, say, to speak face to face with Moses for example, requires that God is relatively close during potential communication episodes. Say within a few light years (how about 12,000,000,000,000 miles). His other administrative domains might require absence of many years, perhaps a few hundred or maybe even a few thousand years. That seems to require an established administrative network, under long-term contract so to speak. I’m ignoring questions of reliability here. Presumably if there is one God-being, and he is in the process of building others like himself, then the existence of reliable administrative networks (think, the steward system in Gondor (grin)) is tenable. All this fits our heavy theological emphasis on obedience and consistency.
Material systems probably age in a very fundamental sense. Aside from electrons and their antiparticles, the rest may be unstable (folks are looking for evidence of proton decay now) possibly over huge time scales – that only shortens the estimates for time until the “dark era” etc. above. In the end, all material objects will disintegrate, including God’s body – assuming it is some kind of biological system. Thus, in spite of a resurrection and “eternal life,” after interminable years (see above) all biological forms will disappear from the universe. Hence God will have a finite (if extremely large) lifespan. Given the apparent tie (see above) between spirit matter and physical matter, there could be no refuge in retreating from the physical universe.
Hence a theology of the material requires a finite God-span if you will. On the other hand it clearly suggests a progressive God, perhaps even one who evolved from a man-like state.
Further, some ideas in Mormonism must be reinterpreted in this case. The idea of truly infinite lifespans must be cast aside. Intelligence should be thought of as an emergent quality, independently in the physical and spiritual realms. Not in terms of some kind of eternal consciousness, but having finite, perhaps unfathomable spans, not infinite in any objective sense though. A being may perceive its own lifespan as so long that its ending is functionally infinitely far in the future. There are various scenarios to rescue this part of classical Mormon theology, but the idea of ending life is coherent with early Utah speculations of Brigham Young, Heber C. Kimball, the Pratt brothers and others.
So, we can be thought of as existing in the “sweet spot” of time as well as space. The universe is at present life-sustaining, (and in this sense, God-sustaining if you will).
Theological considerations like justice, mercy, atonement, sin, repentance, commandments, revelation, prayer may all be reinterpreted in a finite system like this one. In some cases, they are not as satisfying or may seem less effective, but given the fundamental limitations that exist in the universe, they are the best of all possible versions.
Could God be material and yet somehow unaffected by space and time? Not in the physical sense of this excursion. Other distinctions may be possible but they distance God from man in important ways that are, at least in classical Mormonism perhaps, almost heretical. (Part of the point of this business is to trace some of the consequences of the naive materialism of the 19th century when accepted uncritically.)
It may seem fatalistic, but the potential future is so long as to be beyond the ken of anyone. Nevertheless, it will come to an end. Omnipotence in the classical sense is certainly sacrificed. Its logical limits are undoubtedly far outside its practical limits in a material system like this one. Hence, scripture and theological language terms like “forever” and “eternal” and such would have to be thought of as “very long indeed.” Omniscience also cannot exist in the classical sense. While administrative domains might be set up to perceive and react to things, God could not know instantaneously what is happening anywhere. Even if God is present locally then we have to allow for the idea that he receives information at the speed of light, but no faster. Another issue with a material God is the question of knowledge. Distributed knowledge is a possibility, but “infinite” knowledge seems an impossibility. Even extremely large caches of information require technological assistance to a material brain. “Perception” leads to other questions that suggest physical limitations on incoming information. I won’t explore these here except to say they are serious problems and involve us in questions of speed again.
The end of “time” will be a slow process. Eventually new life ceases to come forward, so more intelligent beings cease being produced. Those intelligent beings in existence would still have a “work and a glory” but the end of all things would be in sight. Our present mortal lives are models of this in miniature. Or they can be. Loving and caring for one another is the essence of the good life, even if it is finite.
It seems clear that most religions are quite willing to give up materiality in favor of an unfettered God (or an unfettered soul perhaps). But in Mormonism, the choice seems more difficult and fraught with curious assertions sometimes made in favor of science fiction rather than science.
Personally, I find myself stuck in Joseph Smith’s claims on reality. I have faith in the restoration and I’m a believer. But I also find myself puzzled by the way Mormons often approach science. We’ve got a lot of weird cognitive dissonance sitting around (not that we have a corner on the market).
Rather than the extreme materialist view, I tend to believe that we take some passages of modern scripture too seriously and acontextually (such as the Pratt extraction from the Ramus reports). I’m not taking a materialist theology to heart because I reject the limitations it offers. But that is a matter of faith.
 D&C 93:33-4, 45:17, 138:50. I’m not suggesting that this post is anything more than thinking out loud.
 See Orson Pratt’s extraction forming D&C 131:7.
 Second law. Closed systems suffer entropy-death.
 The “big rip” is a strange kind of expansion that tears everything apart only a few billion years hence. (Caldwell, et al., “Phantom Energy and Cosmic Doomsday”. Physical Review Letters 91 (2003).)
 A “googol” is 10100, a number so astoundingly large as to be beyond discussion. The numbers get much larger in the iron decay scenario.
 Here I’m not allowing for the rather silly speculations that propagate like living things traversing “worm holes” and such. Even assuming such things exist, regulating them is something for Star Trek, not star fact.
 D&C 88 might be taken to suggest that there are 12 such domains. But that is outside the realm of the present discussion.
 J. R. R. Tolkien’s The Lord of the Rings.
 Given the spiritual domain as material, it is not be exempt and there is no real “eternal now” available for refuge here. Such language must be thought of as poetic as it appears in scripture for example.
 It may be that in a subjective sense, life might be eternal or that under some circumstances an observer may think another’s life lasts forever.
 The material nature of the spiritual was exploited to a large degree. The “recycling” of spiritual beings was an occasional theme as was emergent intelligence/individuality.