Ask A Genius 1324: Entropy, Information, and Cosmological Models
Author(s): Rick Rosner and Scott Douglas Jacobsen
Publication (Outlet/Website): Ask A Genius
Publication Date (yyyy/mm/dd): 2025/03/28
Scott Douglas Jacobsen: Why do you think the universe might last for trillions of years? And if it does last that long, what would that imply for the net informational history of the universe?
Rick Rosner: It’s likely far beyond just trillions of years. Depending on what we mean—whether it’s heat death, proton decay, black hole evaporation, or some more speculative long-term outcome—the timeline could span where “trillions” is a major underestimate. The universe has only existed for 13.8 billion years, barely a blink on that scale.
Jacobsen: So, what does that say about the accumulation of information?
Rosner: If we think of the growth of information in the universe—meaning entropy or distinguishable microstates—it might behave like a kind of “random walk” through configuration space. In a random walk, particularly in two dimensions, your average distance from the starting point increases as the square root of the number of steps. That is, ⟨r⟩∼t. In higher dimensions, similar behaviour holds, though the formalism changes.
But the universe’s information doesn’t grow via a pure random walk. It increases due to irreversible processes—stars burning hydrogen, black holes forming, entropy increasing—which are more directional than a random walk. So, rather than a symmetric, aimless path, it’s more of an entropy gradient, constantly climbing toward maximal disorder.
Still, if we were to model information growth as a kind of diffusion, it would be fair to say the total information content might grow with time, possibly non-linearly—perhaps proportional to time or time to some power greater than one. But we do not have a single, unifying equation for how information (or entropy) scales with cosmic time in all cases.
Jacobsen: What about the idea that the amount of matter determines the universe’s age or size?
Rosner: That’s not quite how it works. The universe’s age is the time that elapsed since the Big Bang and its size (meaning the observable universe) expands due to the dynamics of spacetime governed by general relativity. It’s influenced by the total energy content—matter, radiation, dark energy—but not directly determined by information.
Jacobsen: Could we be missing a constant that makes our universe’s age longer than it appears?
Rosner: Possibly in some exotic models, but in mainstream cosmology, the observable age is derived from cosmic microwave background (CMB) observations and redshift data, constrained by general relativity and ΛCDM (Lambda Cold Dark Matter) models. Though future physics (like quantum gravity) might revise our understanding, these methods are robust.
Jacobsen: What if the universe was semi-engineered? Could it have started with more than zero information?
Rosner: That enters speculative territory. Standard cosmology assumes the universe began in a low-entropy state (possibly not zero, but very low). The reason why it started with such a special, ordered configuration is still an open question in cosmology and physics. Ideas range from inflationary theory to multiverse proposals, but none are yet confirmed.
Jacobsen: What about cyclical models—the big bounce, the universe expanding and collapsing over and over?
Rosner: Yes, those models are mathematically permitted under general relativity. There are “big bounce” and “ekpyrotic” models where the universe undergoes repeated expansions and contractions. But current observational evidence (like the universe’s accelerated expansion due to dark energy) suggests that our universe is more likely headed toward heat death—a cold, dark, and diffuse state—rather than a cyclical one.
Jacobsen: So, what kind of model makes the most sense?
Rosner: I lean toward a model in which the universe’s information content increases over time and is tied to irreversible thermodynamic processes, not cyclical collapse and rebirth. The universe appears to be on a one-way path—at least from what we know. Whether or not that path is random is up for debate, but it’s not static.
Jacobsen: And what about the substrate of the universe—what is it built on?
Rosner: That’s one of the deepest questions in theoretical physics. Whether spacetime is fundamental or emergent—perhaps from quantum information, strings, or some more abstract mathematical structure—remains unknown. But whatever that substrate is, it could define the ultimate rules for how the universe behaves, evolves, or ends.
It’s not that there’s no uniformity—it’s just a different kind. On large scales, under the Big Bang model, the universe is spatially isotropic and homogeneous. That means that no matter where you are, space looks roughly the same in every direction. But temporally, it is not uniform. Time has a clear direction and structure: it starts at the Big Bang, at t=0, and evolves outward.
So, every moment in a Big Bang universe is different because the universe has a different density, temperature, and scale factor at each point. It’s completely non-uniform in time but relatively uniform in space.
An Informational Cosmology universe—hypothetically—might be roughly isotropic across time, meaning it looks about the same 30 billion years from now as it did 30 billion years ago. You’re trading one kind of symmetry for another—spatial for temporal.
Jacobsen: That sounds a lot like steady state theory. How does that compare?
Rosner: The steady state theory, which was largely debunked in the mid-20th century—especially with the discovery of the cosmic microwave background—was isotropic in space and time. It proposed that the universe had no beginning or end and always looked the same. But observations didn’t support it.
Interestingly, that theory required continuously creating new matter to maintain a constant density as the universe expanded. So, as galaxies moved apart, new galaxies would supposedly form in the space between them, keeping the universe looking “steady” over time.
IC doesn’t do that. Instead, in IC models or Big Bang cosmology, new galaxies “appear” in observational terms because we’re seeing further back in time as light from more distant regions reaches us. In both frameworks, the deeper you look into space, the further back in time you see.
The difference is that in a 13.8-billion-year-old universe, there’s a hard observational limit—you can’t see anything older than 13.8 billion years. But as time progresses, the observable universe gets larger. If the universe reaches 16 billion years old, you can observe regions that were previously beyond your cosmological horizon.
Jacobsen: Does that change how we interpret visibility over cosmic time?
Rosner: Yes, and that has to do with cosmic expansion. As the universe expands, very distant regions move away faster than the speed of light due to the expansion of space itself—not because objects are breaking the cosmic speed limit. As the expansion slows (which, to be clear, current data suggests accelerating due to dark energy, not slowing), those regions might re-enter our observable horizon if their recession speeds dip below light speed.
So, in both Big Bang and IC frameworks, there’s a mechanism for new matter to “appear” in our view—though not because it’s being newly created, but because we’re just now seeing it.
We were talking about information in an IC or quantum-informed universe. We know some things about information, but thinking about it in cosmological and quantum contexts is still relatively new.
Jacobsen: I’d argue that information isn’t even properly defined yet—not in a way that’s universally agreed upon in physics.
Rosner: My idea is that information requires a unitary context. You can work with information in a fragmented or local way, but to fully define and understand it, you need a unified framework—a whole universe that provides coherence. Without that, what you call “information” might be an approximation.
The same goes for things like entropy and gravitation. Locally, you can define and measure them. But globally, they may behave very differently across the whole universe—and need to be understood as part of a unitary structure.
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