Boundary Conditions of Cosmology
The View from Oregon — 313: Friday 01 November 2024
In last week’s newsletter, in a discussion of the cosmological constraints on human history, I suggested that the different views of the heavens from different planets would inspire different attempts at explanation of these cosmological phenomena, as indeed the cosmological phenomena human beings observed throughout our history have inspired many explanations. Many years ago I read Poul Anderson’s World Without Stars, which is the story of an inhabited planetary system that formed outside the Milky Way, so the night sky has no stars, but it does have a magnificent view of the entirety of the spiral of the Milky Way. If memory serves, Anderson had the natives of the planet in question worship the Milky Way as it rises in the night sky. This would be a particularly dramatic illustration of what I was writing about last week, though it would not be difficult to formulate a number of other celestial phenomena that would puzzle and inspire any intelligent beings in a position to observe them.
One use of computer simulation that I would find fascinating would be to show what the universe would look like from planets in other planetary systems. While the resolution of our current telescopes would not allow us to reconstruct a planetary system in sufficient detail to illustrate this realistically, we will have this technology long before we have the technology to actually visit these places. The enormous variety of planetary systems that have been revealed to us by the Kepler telescope, and which will now be supplemented by the observations of the James Webb Space Telescope, suggest an equal variety of alien skies. I don’t think we could make any concrete predictions about what these skies would mean for an intelligent observer on these worlds, but it would give us a kind of cosmological connection to see what the universe would look like from these vantages.
Such views don’t hold for subsurface ocean biospheres, which would have no view of the heavens and no possibility of cosmological observation for any intelligent observers. This is significant because it now appears that the bulk of water in our solar system is locked up in subsurface oceans out beyond the Frost Line. We have reason to believe that this will be the case in other planetary systems. If following the water leads us to life, it could well be the case that the bulk of life in the universe is locked in subsurface ocean biospheres. If this is the case, then the Great Filter may be the unusual good fortune of life evolving on the surface of a planet instead of a subsurface ocean biosphere. I have several times (maybe not in these newsletters, but elsewhere) quoted a paragraph by Hans Blumenberg on having an atmosphere thick enough for us to breathe but not so thick that we can’t see through it. This is a boundary condition for an intelligent observer engaging in cosmology. Recently I’ve found a much older quote on the related importance of viewing the stars, this from Plato’s Timaeus:
“The sight in my opinion is the source of the greatest benefit to us, for had we never seen the stars, and the sun, and the heaven, none of the words which we have spoken about the universe would ever have been uttered. But now the sight of day and night, and the months and the revolutions of the years, have created number, and have given us a conception of time, and the power of enquiring about the nature of the universe; and from this source we have derived philosophy, than which no greater good ever was or will be given by the gods to mortal man.”
According to the cosmological principle, there are no privileged observers in the universe. This means that there are no privileged observers of the universe as the universe, but there are without doubt privileged observers of particular planetary systems. We are privileged observers of our own planetary system, but not privileged observers of the universe. This would hold good, under the cosmological principle, for any planetary system in which observers evolve. Recent cosmology has started to cast some uneasy doubts on this, as our improving telescopes (and technologies like adaptive optics) seem to be revealing large-scale features of the cosmos, and if there are singular and distinctive large-scale features of the cosmos (like the Great Attractor, the Sloan Great Wall, or the Hercules–Corona Borealis Great Wall), that means that the universe isn’t homogenous and isotropic, and that in turn means that there could be privileged observers who see some features of the universe that are not seen by others, or not seen as well by others — and underprivileged observers who don’t see these features, and who therefore have a false conception of the structure of the universe.
No one seems to be seriously put out about this yet. It’s kind of like the anomalies that showed up early in the twentieth century and which we now attribute to dark matter. We know that our theories don’t explain how the universe looks, but we entertain them anyway because we don’t have anything better at the moment. Perhaps someday, if the anomalies are sharpened to the point that they can no longer we hand-waved away, then they will cause a re-thinking of the cosmological principle, which seems to be secure for the time being. In any case, the level of abstraction that cosmologists employ is such that the distinctive features in the skies of any inhabitable planet — the features an intelligent observer would notice first, like the moon — don’t even count for cosmology. This is worth thinking about for a moment. Any intelligent observer that evolves on a planetary surface will first be aware of its place in the cosmos by the distinctive local features of its own planetary system. It would not be until much later, thousands of years later in the development of a civilization, that the intelligent observers would be able to conceive the cosmological principle and observe themselves as orbiting a star in a galaxy, and with the universe on the whole composed of galaxies all flying apart from each other.
The exception to observing a universe in which all galaxies are flying away from each other are the gravitationally-bound galaxies of the local cluster. The first galaxies other than the Milky Way of which human beings became aware were the Large and Small Megellanic Clouds, and the Andromeda galaxy, which is, in fact, gravitationally bound to us and rushing toward us. So even an observer of a certain degree of sophistication, able to construct a cosmological distance ladder and thus to confirm that other galaxies exist outside their own galaxy, may see only other galaxies in their local cluster. For example, if an intelligent observer evolved on a planet orbiting a star that was part of a galaxy that was in turn part of a much larger local cluster than our local cluster, it might be quite some time before that observer reached a level of observational sophistication that they would be able to view anything beyond their local cluster.
Quasars (which we are now more likely to call active galactic nuclei) are sufficiently bright that they can be seen across the distances of the observable universe, and a sophisticated observer would be able to determine their recession by red shift, so eventually a civilization should be able to discover the large-scale structure of the universe, even if they evolve deep inside a local cluster than obscures their view of the universe beyond, but we only figured out what quasars are in the past few decades, so this level of observational sophistication in cosmology is only recently won by our species. A civilization, or many civilizations, that never experienced a scientific revolution and an industrial revolution would never reach this level of observational sophistication, which requires technologically advanced instrumentation. If the Great Filter is science and the industrial technology that science enables, then all societies that fail to pass the Great Filter (presumably the majority of them, given the lack of an SETI detections) do not achieve the observational sophistication to determine their place within the cosmos. And we implicitly acknowledge industrial technology as a great filter insofar as SETI is predicated upon sending and receiving radio or other EM spectrum signals over interstellar distances, which is an activity reserved for societies that have achieved industrial technology.
If the principle of mediocrity holds, our galaxy should be located in a mediocre local cluster. I take this to mean that there should be local clusters much larger then our local cluster, and local clusters much smaller than our local cluster. Local cluster size should describe a bell curve, and if our local cluster exemplifies the principle of mediocrity, our local cluster should be in the bump of the bell curve of local cluster size. Of course, there may be other ways to measure the relative mediocrity of local clusters — for example, by their mass, by the number of galaxies they contain, by the ratio of spiral galaxies to dwarf galaxies or to elliptical galaxies, and so on. Mass and number of galaxies would roughly correlate with size, so all these of these metrics should give us approximately the same result in terms of the mediocrity of our local cluster.
With this in the back of my mind, every so often I go searching through papers on cosmology to try to find the largest discovered local cluster, but I haven’t had any success in finding this, either because I don’t know how to read (or search for) cosmology papers, or because astronomers just aren’t interested in the question. However, this strikes me as one of the most important questions in cosmology. As the universe expands, local clusters will be drawn together, while non-gravitationally bound clusters will eventually pass over the cosmological horizon until each local cluster is an island universe stranded in a sea of cosmological nothingness. The largest of these clusters will have the greatest quantity of resources, so that any intelligent beings that set out to sustain themselves for as long as possible in our universe will have the most resources to do so in the largest local clusters.
From this we can derive yet another “solution” to the Fermi paradox: all intelligent beings are racing to get to the largest local clusters while these clusters are mutually visible to each other in the observable universe. Since we know, ex hypothesi, that our local cluster is not the largest, all the aliens are headed away from us, bent on the race against time to colonize the largest local clusters before they pass beyond the cosmological horizon. Once a cluster passes beyond the cosmological horizon, it lies beyond our light cone and its resources are lost to us. There is only a finite period of time during the Stelliferous Era when it would be possible to make this determination and to take action, hence the aliens are in a race against time, and we aren’t part of that race so we are irrelevant to the biggest story in the universe.
