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This drawing is from Alan Guth, MIT Dept. of Physics. It is what physicists call an 'embedding diagram'. It represents three-dimensional space as a two-dimensional surface that is 'bent' or curved by gravity. This diagram depicts one of the basic ways that an existing universe (e.g., the one we live in) can generate, via quantum tunneling, an entirely new and separate child universe. Currently known and accepted laws of physics appear to allow this — a quantum 'phase change' of a small 'seed' of matter (just a few grams) into a peculiar state called a 'false vacuum' or something like it, which has negative pressure, and can therefore expand into a whole universe at an astounding rate. The diagram depicts the moment that the 'umbilical cord' (wormhole or Ellis Drainhole) connecting the parent and child universe snaps, and the child universe becomes a completely separate new universe. See Farhi, Guth, and Guven (Nuclear Physics B, Volume 339, Issue 2, 30 July 1990, Pages 417-490) for all the detail. |
(last updated 17 June 2025)
This post is devoted to the simple, hard, physical argument of whether and how a universe with the physical laws that ours has can self-replicate, the five main ways this can occur based on the known laws, and the far-reaching consequences that seem to inevitably result.
Question 1: Does a universe with the physical laws that our observed universe currently exhibits permit self-replication?
Answer: We do not understand the full set of physical laws describing all aspects of our universe's behavior. In particular, the earliest period (the 'birth') of our universe seems to be best described by extrapolating toward high energy and small dimensions, which is the realm where the two highly successful models we have of our universe, Quantum Mechanics and General Relativity, would need to merge (actually emerge [going forward in time] perhaps via some form of symmetry-breaking in a more fundamental, more general theory). To date, despite at least a century of intensive theoretical and experimental study, no satisfactory (generally accepted, experimentally confirmed) form of such a theory has been identified.
One way of attacking this question is to assume that the two models of our universe are both correct, and that no fundamental merger is required because self-replication can occur within the framework (domain of scales) of either model. The physical systems that both Quantum Mechanics and General Relativity describe include mechanisms that do appear to allow self-replication (see next question).
We have no experimental evidence that self-replication has happened, though there are scenarios where the event could be undetectable. Importantly, there is also no evidence that self-replication is impossible.
Question 2: What are the five ways that our currently accepted physical laws permit this to happen?
First way: Within Quantum Mechanics: a natural, spontaneous quantum tunneling. It seems to require very high density and high energy, states that have very low probability, but not zero probability. A number of papers, over the years, have been published describing how a universe could spontaneously form from vacuum fluctuations. The intent of these papers is usually to explain how our universe could appear 'from nothing,' i.e. from no prior universe, but since vacuum fluctuations are an essential part of the quantum theory of our universe, the arguments would seem to be just as valid if some pre-existing state of our universe was the starting point of the tunneling process.
Second way: From General Relativity: Lee Smolin has discussed the reproduction of universes on the inside of black holes. His 'Cosmological Natural Selection' theory, and the related 'Black Hole Cosmology' are not commonly accepted General Relativity solutions. Standard General Relativity solutions lead to intractable singularities at the heart of Black Holes, but in the process, they concentrate matter and energy into arbitrarily high densities, within which conditions found at the earliest times of our universe would be replicated. This is a generalization rather than a theory, but if Quantum Mechanics is then invoked to describe what is possible within such high-density matter, the probability of quantum tunneling producing a 'false vacuum'-like (inflation) state should steadily increase as the density increases.
Third Way: 'Creating a baby universe in a test tube.' In general, there is no theoretical prohibition to generating the kind of high energy density that black holes produce within 'normal' space, i.e., not beyond the event horizon of a black hole. This is the thought experiment discussed in the 1990 Nuclear Physics B article mentioned in the caption to the introductory image at the top of this post—Creation of a child universe in the laboratory or in a particle accelerator. We do not possess the technology to achieve these conditions, but there seems no theoretical barrier. It boils down to an engineering problem, and the successful creation of a child universe should produce a detectable signature. Perhaps the application of metamaterials can bring the needed conditions closer to achievability in the less-remote future.
Fourth way: 'Mitosis'. This covers any number of related concepts, most of which would benefit from rejecting the Standard Model of Cosmology's hypotheses that the universe is perfectly flat, isotropic and homogeneous. The unexplained phenomenon known as 'Dark Energy' is causing the universe to expand at an accelerating rate. If Dark Energy is constant, as the Standard Model assumes, the result is that parts of the universe that are currently visible to us will eventually be receding from us at greater than the speed of light and will thus causally separate from us. These separated parts then evolve completely independently. If there is any mechanism for 'mutation', by which the laws of physics in these separated regions could diverge from each other, then 'interesting things' such as selection processes could happen. Further, if dark energy is variable in time, which the latest results from the Dark Energy Survey Instrument studies suggest, it could also be variable in space. This is mere speculation, but areas with more rapid expansion would, through time, create voids that would separate individual 'cells' and cell-connecting filaments organized in a manner similar to the structure of galaxies and galaxy clusters in our observable universe.
Fifth way: Simulation. Current computer power allows scientists to simulate selected physical systems in great detail, but such calculations fall far short of being capable of simulating processes in sufficient detail to address some of the fundamental questions that we do not yet have answers to, such as how life emerged and how self-aware 'intelligent' beings emerged. But there does not seem to be any obstacle that would prevent us from someday being capable of answering such deep questions via simulation. If future technology makes such robust simulations possible, and because our known universe contains only a finite amount of information, there is no known physical or philosophical reason to expect that we could not someday create a simulated subset of our universe that could pass any pre-established arbitrarily test of 'adequacy'. The first such simulation is likely to focus on an individual 'AI being' that will surpass human intelligence and will profess to be conscious, and this may not be more than a few years or decades away.
Simulations can be analog models as well as digitized mathematical ones. The creation of physical analog models doesn't seem to get the attention or volume of research work that digital simulations do. But there is an overlap in the area of life's genetic code. Experimental efforts to produce synthetic life starting with inorganic chemicals is a primitive example. There seems no barrier to extrapolating such work toward far more complex systems, perhaps creating an Artificial Biological Intelligence that could rival human intelligence and perhaps exceed the self-replication capability of any digital form of Artificial General Intelligence. This is not a projected area of thought that seems to be given much attention, but perhaps it should.
Simulated universes have some interesting consequences for the world's religious communities. For example, simulations that are intentionally created clearly have a creator, which could be thought of as a true, real 'God.' An archived dataset containing a simulated individual's mind and body could amount to something approaching a true, real, immortal afterlife.
Question 3: What are the consequences if universes like ours can self-replicate?
Answer: Analysis of the potential consequences of this cosmology have been sparse. Three of these consequences are of particular note:
First: Our universe came from a 'preceding' parent universe. If self-replication is occurring, then it is nearly certain that it is the explanation of the origin of the particular universe that we observe. Our universe, with all its complexity, was not original - not cut from whole cloth, so to speak.
Second: The 'Fine Tuning' question: In the cases where self-replication occurs in the 'open' universe, i.e., not inside the event horizon of a black hole, and particularly in any of the set of scenarios where intelligent beings (or even simple forms of life) are present to interact with or direct the replication process, there is a potential for the laws of physics in the offspring universes to be skewed favorably toward the living forms involved. This could provide a natural explanation of what has been called the 'Fine Tuned Universe' conjecture or hypothesis or question, which asks why or how our universe seems to be so well-suited for the development of life, when such an outcome is estimated (by the majority of physicists) to have a prohibitively low probability within the range of possible sets of governing laws and constants.
Third: Evolutionary processes (mutation and some form of selection), analogous to those that pertain to the development of complex life forms from simple ones, if operative during universe self-replication, would push back the difficult question of the ultimate origin of reality (e.g., the mechanism or process that produced the "Big Bang") into a veil of obscurity that might be even more difficult to unravel than the question of abiogenesis—the means by which life emerged from the approximately 92 natural elements of the Periodic Table, as generated by cosmic and/or stellar nucleosynthesis.
The example of the development of photosynthesis in early cyanobacteria, and its consequent Great Oxidation Event is good stark example. New chemical pathways have emerged that did not occur in the evolutionary process that led to them, and the earlier forms of anaerobic life, to which oxygen was poisonous, died out, leaving little trace of the chemical pathways from which these life forms originated. If there is any analog between the evolution of life and a not-prohibited process of universe self-replication with mutations, then the questions of emergent physics and lost physics become relevant. Quantum Mechanics and General Relativity in the form that we observe them could, conceivably, not have directly participated in the physical processes that were extant in simpler ancestor/precursor universes.
