On a contemplative night, I found myself confronted by a profound question regarding the very nature of reality: How might space and time simply be distinct manifestations of the same fundamental entity? This inquiry was not merely scientific but deeply philosophical, gravitating around the essence of the universe and, perhaps, my own existence.

Seeking answers on ChatGPT quickly directed me into the intricate webs of general relativity theory. Inevitably, this journey drew me towards one of modern physics’ most intriguing phenomena: if black holes continuously absorb matter, where precisely does this matter end up? The concept of singularity - an infinitely dense point where all known laws of physics seemingly collapse - not only challenged my logic but also unsettled my most fundamental beliefs about reality itself.

Gripped by a deep existential crisis, I finally encountered a daring hypothesis with the help of AI: what if, upon reaching a critical threshold inside a black hole, all this accumulated matter breaks the boundaries of our known universe, giving rise to a new spacetime? What if each black hole acts as a cosmic seed, nurturing child-universes, potentially explaining the ultimate mystery of the origin of our own universe?

So, I would like to share the paths I’ve traveled, demonstrating how artificial intelligence can serve as a powerful ally in exploring the deepest and most meaningful questions about the universe, life, and the very meaning of existence.

You Came From a Black Hole, and So Did Everything Around You

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No, I don't believe that if we fell into a black hole we'd be simply teleported into another universe - at least we would not survive to it. 

This article explores the hypothesis that our universe might have originated from the gravitational collapse of a black hole existing in a previous universe, transforming the energy from the donor universe into our Big Bang - a notion which has evolved from philosophical speculation into a serious scientific investigation due to recent advances in quantum cosmology and quantum gravity.

Foundational Theories and Background

The notion of baby universes born inside black holes has its roots in the late 20th century, as physicists pondered the fate of matter in gravitational collapse and the limits of Einstein’s theory. In classical general relativity, a black hole features a central singularity where volume shrinks to zero and densities diverge – a clear sign that new physics is needed.

Early conceptual work suggested that black hole interiors might connect to other regions of spacetime. For example, the maximally extended Schwarzschild solution includes an Einstein-Rosen bridge (wormhole) connecting two asymptotically flat universes, hinting that a black hole could be a throat to another universe. While that specific solution is an idealization (eternal, unchanging black hole), it planted the seed that a collapsing black hole might dynamically lead to a new expanding region rather than a true end of spacetime.

By the 1980s, theorists like John Wheeler had popularized the idea of a “spacetime foam” where baby universes could branch off, and Stephen Hawking speculated that black holes might spawn baby universes, possibly carrying away information. Hawking suggested that anything falling into a black hole could re-emerge in a new universe, making the black hole a one-way portal. This was one proposed resolution of the black hole information paradox – information isn’t destroyed but simply moves to a place inaccessible from our universe.

Quantum Gravity and Black Hole Bounces

A central question for the baby universe scenario is: Do black hole singularities get resolved by quantum effects, enabling a “bounce” into a new region? Several independent approaches to quantum gravity suggest that the answer could be yes. We review two prominent frameworks – Loop Quantum Gravity (LQG) and Einstein–Cartan theory – which provide mechanisms for nonsingular black hole interiors. These approaches, while different in detail, yield a picture in which a contracting spacetime region (inside a black hole) transitions into an expanding region (a baby universe or white hole), rather than terminating in a singular point.

Loop Quantum Gravity and Interior Bounce

Loop Quantum Gravity is a non-perturbative approach to quantizing spacetime geometry. In LQG, space is not continuous but comprised of discrete “atoms” of geometry (quantized volumes and areas). This discreteness acts as a natural regulator that can potentially avert the formation of singularities. Over the past two decades, LQG techniques have been applied to cosmology (resolving the Big Bang singularity via a Big Bounce) and to black hole interiors. In 2006–2010, a series of studies explored models of Schwarzschild black holes using loop quantum geometry modifications.

One striking result came from Dah-Wei Chiou (2008), who investigated the Schwarzschild interior with LQG-inspired dynamics. In one of the quantization schemes he studied, the classical singularity was eliminated and replaced by a quantum bounce. On the other side of this bounce, the black hole interior smoothly continued into what looks like the interior of a white hole. In other words, an infalling observer would encounter a minimum volume (Planck-scale) and then find space start expanding again, as if entering a new region that eventually behaves like a white hole ejecting matter. 

In Chiou’s model, the black hole effectively gives birth to a daughter black hole (or white hole) with much smaller mass, contained within the original horizon. This process can repeat in theory – each “baby” black hole could itself eventually produce another via its own quantum bounce, leading to a nested, fractal structure of universes within universes. While the details are model-dependent, the qualitative picture is that LQG’s quantum geometry can avoid the infinite crunch and instead cause a rebound. The spacetime continues beyond where classical GR breaks down, which is exactly the requirement for baby universe formation.

More recent and refined LQG-based analyses have reinforced this general scenario. In 2018, Abhay Ashtekar, Javier Olmedo, and Parampreet Singh (building on a line of work in loop quantum cosmology) showed that when quantum gravity effects are carefully included, spacetime continues across the classical singularity into a new region with the geometry of a white hole interior. In their model, the black hole does not last forever – instead, after a possibly long lifetime, it transitions into a white hole. From the outside perspective, this might appear as a highly delayed explosion (a black hole turning into a white hole and releasing its contents). 

From the inside perspective, the infalling matter never hits an infinite-density point; instead it passes through a “quantum bridge” and out the other side. The new region formed by the bounce is to the future of the black hole collapse (not spatially elsewhere but temporally later in an extended spacetime diagram). This is important: it means the baby universe (white hole interior) is not pre-existing but created by the collapse itself. Crucially, such a scenario does not violate known physics so long as quantum gravitational effects (which are negligible outside or before the singularity forms) become dominant and allow a temporary departure from classical Einstein equations in the deep interior. 

Whether the expanding region is a separate baby universe or re-connects to our external universe as a white hole is a subtle point. In some models (including Ashtekar et al. 2018), the bounce leads to a white hole that might, after a long time, appear in our universe – essentially the black hole turns inside-out into a white hole in the far future. In other models, especially older “mass inflation” or cosmological-type extensions, the new region might be entirely separate (except for the wormhole connection at the bounce itself). For the purposes of the baby universe hypothesis, we generally imagine the new region as an entire new universe, mostly disconnected from the original. LQG results do not forbid this – they simply show the interior becomes a white hole region. 

It’s worth noting that LQG-inspired ideas have led to the concept of a “Planck star” – a core of extremely high density that resists collapse – which is essentially the rebound point of a black hole. Carlo Rovelli and Francesca Vidotto proposed that a black hole’s interior might eventually re-expand as a Planck star, releasing its contents. In their scenario, the baby universe is not a separate permanent universe but rather ejects back into ours (so it’s a slightly different outcome). Nonetheless, both outcomes involve a bounce. Depending on initial conditions and the model’s parameters, the rebound could either appear in our universe (as a white hole explosion) or create a separate universe that does not communicate back. Both possibilities are compatible with the broad idea of “no singularity, new expanding phase”.

Einstein–Cartan Gravity and Torsion-Induced Bounces

A different route to eliminating singularities comes from an extension of general relativity that includes torsion. In standard GR, spacetime is curved by mass-energy but is assumed torsion-free (torsion relates to how spacetime can twist due to spin). Einstein–Cartan theory relaxes this assumption by allowing spacetime to have torsion in the presence of spin-angular momentum of matter. Notably, torsion in this theory does not propagate as waves – it’s non-zero only where matter is present, and at usual densities its effects are negligible. However, when matter is extremely dense (on the order of nuclear densities and above), the spin-spin interaction via torsion becomes significant and effectively produces a repulsive force. This prevents densities from reaching infinity.

In the late 2000s and 2010s, physicist Nikodem Popławski revisited Einstein–Cartan theory as a natural mechanism for Big Bounces. He found that torsion would avert the formation of a singularity inside black holes: instead of collapsing indefinitely, the core would stop collapsing at an extremely high but finite density, then rebound. The collapsing matter “bounces at a finite density and then expands into a new region of space on the other side” of the black hole. Popławski explicitly developed the idea that every black hole might create a new universe. In a 2010 paper, he showed through a simple model that an infalling geodesic observer in a black hole governed by Einstein–Cartan equations would see a minimum radius and then expansion – mathematically, the interior solution can be extended to a new, growing universe. 

According to Popławski’s hypothesis, the black hole’s interior becomes a one-way tunnel to a baby universe. The spacetime is continuous: the baby universe is not “created from nothing” but rather pinched off from the parent universe at the black hole singularity (which is no longer a singular point but a bridge). The event horizon of the black hole from the parent side acts like a boundary – once matter passes through, it cannot return, but it appears in the baby universe as an initial expansion. He points out that this one-way passage (an Einstein–Rosen bridge with a past horizon in the parent universe and future horizon in the child universe) naturally imposes an arrow of time in the new universe: time’s flow in the baby universe is such that everything there moves away from the bridge (just as we only move forward in time away from our Big Bang). This could explain why time asymmetry (the “arrow of time”) exists in the baby universe – the formation of the horizon itself breaks time-reversal symmetry.

One appealing aspect of the Einstein–Cartan baby universe scenario is that it provides an origin for our own Big Bang. Popławski has argued that perhaps our universe is the inside of a black hole existing in some parent universe. In this view, the observed Big Bang singularity was not an absolute beginning but rather the continuation of a collapse from a prior realm. The extreme torsion-induced pressure at high density would have caused a bounce that became our expanding universe. Intriguingly, this scenario can produce inflation-like expansion naturally: torsion-driven particle production in the newborn universe can generate huge amounts of matter and rapid expansion (solving horizon and flatness problems in a novel way). It also offers a neat answer to where all the mass that falls into countless black holes goes: it seeds new universes (solving any “mass loss” puzzle by relocating mass-energy to a new cosmos).

Quantum Field Implications, Information Paradox and Entropy

Any discussion of baby universes inside black holes is tightly connected to the black hole information loss paradox and quantum field theory in curved spacetime. If a black hole truly funnels content into a separate universe, what becomes of quantum information and the laws of physics as seen by an external observer?

If a black hole creates a baby universe, an outside observer in the parent universe would never see the information that fell in come back out. Hawking radiation, according to Hawking’s original calculations, is completely thermal (random) and carries no information about what formed the black hole. Thus, by the time a black hole evaporates away, any information about the initial state appears lost – presumably transferred to the baby universe. Hawking argued in the 1980s that this implies pure quantum states evolve to mixed states, meaning quantum unitarity is violated in our universe. 

He was willing to accept this radical conclusion, positing that quantum gravity allows topology change (splitting off baby universes) which leads to a non-unitary evolution in a single universe, though overall unitary if one includes the baby universes. In this picture, each black hole’s formation and evaporation is like a quantum process where the wavefunction’s support is partly carried away on a new topologically disconnected branch. Stephen Hawking even published an essay titled “Black Holes and Baby Universes” discussing these ideas for a general audience.

Many physicists found this solution unsatisfying because it essentially gives up on predicting the information – it says “it’s gone elsewhere”. Nevertheless, it might be true; the test would be whether some subtle signature of information loss could be observed in our universe’s physics (such as violation of quantum correlations or conservation laws). Over the last 20 years, the mainstream view (especially with the rise of string theory and holography) shifted towards believing unitarity is preserved within our universe, meaning no loss to inaccessible universes.

Interestingly, recent developments show that these two perspectives might not be as contradictory as once thought. The replica wormhole/island paradigm has given a semi-classical calculation of the Page curve (the entropy evolution of an evaporating black hole) that implies information is not lost after all. In these calculations, spacetime wormholes (called “replica wormholes”) effectively allow Hawking radiation to be correlated with degrees of freedom behind the horizon in such a way that the entropy begins to drop after the Page time, indicating information recovery. The new ingredient is the appearance of an “island” in the entanglement entropy calculation – a region inside the black hole that is entangled with the outside radiation and must be included to get the correct entropy. This island is essentially the remnant of the black hole interior that is no longer accessible once the hole has largely evaporated; it behaves like a sealed-off baby universe from which no influence can escape.

Another way to phrase it: the Hawking information paradox is resolved if each black hole’s interior becomes a baby universe that takes the entropy with it. What remains in our universe (the Hawking radiation) can then be thermal without violating global unitarity. Essentially, the entropy “missing” from the radiation is accounted for as the entanglement entropy between our universe and the baby universe. Once the black hole fully evaporates, the two are causally disconnected, and one ends up with two separate, pure systems (a pure state of radiation here, a pure state that is an entire other universe there), which if considered together form a pure entangled state. To observers in either universe alone, the state appears mixed. This scenario is a beautiful synthesis of ideas from decades prior with modern calculations.

It should be noted that not everyone interprets the island result as literally creating a new universe – some view the “island” as just a part of the same quantum gravity system. However, the mathematics (using gravitational path integrals) is very much analogous to older wormhole “baby universe” discussions initiated by Coleman, Giddings-Strominger, etc., in the late 80s. Those works suggested that spacetime wormholes could lead to an ensemble of universes and soften constraints like global charge conservation or fixed coupling constants. 

In fact, Marolf and Maxfield (2020) revisited that paradigm in the AdS context, finding that baby universes and wormholes can induce a sort of ensemble average in boundary theories. The upshot for black hole info is that while any single universe evolves unitarily, an observer who doesn’t realize they are in an ensemble might see an apparent mixed state. This rather abstract line of reasoning has bolstered the idea that baby universes need not contradict quantum mechanics – they might be an integral part of a consistent quantum gravity theory.

From a more practical QFT standpoint, one can ask: if black holes produce baby universes, could we ever tell from outside? Conservation laws offer one clue. If a black hole carries certain conserved charges (like electric charge, baryon number, lepton number, etc.), and it disappears into a baby universe, one worries about violation of those conservation laws in the parent universe. In classical GR, a black hole can carry charge and when it evaporates via Hawking radiation, that charge is released in the radiation (charged black holes radiate charged particles). If instead the black hole “disappears” into a baby universe (say it pinches off without fully evaporating into our space), we’d better have that charge go somewhere. 

One possibility: the baby universe carries away the charge (so charge is still globally conserved, just not in the parent universe). This would appear as charge non-conservation from our perspective – something we do not observe in electromagnetic charge, for example. Thus, most scenarios assume that any charge a black hole had does get reflected in our universe (either via remaining evaporation or perhaps the wormhole cannot pinch off if it carries gauge charge). Indeed, there are arguments that quantum coherence plus gauge charges constrain baby universe formation, or that only gauge-neutral combinations can disappear. For the most part, the baby universes discussed are assumed to carry away only quantum state information and possibly any global charges (like baryon number, if that isn’t fundamentally conserved in our universe anyway). This remains a topic of debate.

Black holes have a thermodynamic entropy given by the Bekenstein-Hawking formula: S = (k_B * c^3 * A) / (4 * G ħ). If a black hole forms a baby universe, does that process consume entropy? One interpretation is that the Bekenstein-Hawking entropy represents information hidden behind the event horizon—which, in the baby-universe scenario, corresponds to the entropy contained in the baby universe itself, since from outside we cannot distinguish internal states. The generalized second law of thermodynamics states that the total entropy (horizon entropy plus outside entropy) must never decrease, mathematically expressed as d(S_horizon + S_outside)/dt ≥ 0. Thus, when a black hole evaporates and leaves behind a disconnected baby universe, the entropy associated with the Hawking radiation in our universe still satisfies this condition. Baby universes, therefore, are consistent with thermodynamic principles, provided entropy is carefully accounted for.

Cosmological Consequences and Multiverse Scenarios

If baby universes are indeed born inside black holes, the implications extend far beyond individual black hole physics – they paint a picture of a self-reproducing multiverse with potentially profound cosmological consequences.

A Multiverse of Black Hole Offspring

The baby universe scenario naturally leads to a branched multiverse structure. Imagine a “family tree” of universes: our universe might contain millions of black holes, each of which (if conditions are right) could spawn a new universe. Those offspring universes in turn may develop their own black holes and spawn further universes, and so on. Over cosmic time (and across generations), this could produce an ever-growing (possibly infinite) ensemble of universes. 

This vision is quite different from the eternal inflation multiverse (where bubble universes nucleate in an inflating false vacuum sea) – here, the process is more akin to cell division or reproduction through black holes. One universe gives birth to “baby” universes from its black holes, which remain hidden from the parent (cloaked by the event horizons) except for their gravitational effects. Each baby universe is initially connected via a wormhole, but as time progresses that connection likely pinches off, leaving the child universe causally isolated.

One consequence of this model is that the Big Bang of a new universe is the time-reverse of a black hole collapse. The spacetime diagram would show a contracting region (in the parent) that crosses a throat and emerges as an expanding region (the baby universe’s big bang). To inhabitants of the baby universe, the beginning of time (t=0 for them) might look like a hot, dense state – similar to our Big Bang – but it actually had a pre-history in another universe. This neatly addresses the question of what “caused” the Big Bang or what preceded it: in this scenario, it was caused by the collapse of a massive star (or other mass concentration) in a parent universe that formed a black hole. 

The new universe’s initial conditions could be influenced by the properties of that collapse (e.g. rotation might induce a preferred direction, etc., although many studies assume symmetrical non-rotating black holes for simplicity). Some researchers have speculated that the slight anisotropies in our cosmic microwave background – usually explained by quantum fluctuations amplified by inflation – could alternatively reflect asymmetries in whatever collapsed to form our parent black hole. These ideas are speculative, but they illustrate how the model provides a different angle on cosmological initial conditions.

Cosmological Natural Selection

Lee Smolin’s cosmological natural selection (CNS) hypothesis is a direct consequence of the black-hole multiverse picture. Let’s examine it a bit more deeply.

In CNS Each universe’s fundamental constants (parameters like particle masses, coupling constants, etc.) can vary when a new universe is born. The variation is assumed to be small – analogous to mutations. There isn’t a detailed mechanism in the original proposal; it’s an assumption perhaps justified by quantum gravity’s probabilistic nature (similar to the “baby universes” of Coleman where coupling constants can differ in different branches).

Universes that have constants resulting in more black holes will have more offspring. For example, consider a constant like the neutron-proton mass difference: if it were much larger, perhaps stars couldn’t synthesize heavy elements efficiently, leading to fewer stellar remnants and black holes. If it were much smaller, maybe all hydrogen converts to helium early, altering star formation in a way that also reduces black hole production. The actual dependence is complex, but one can imagine that our universe’s value is in a range that yields plentiful massive stars and black holes. Indeed, Smolin pointed out that our universe seems to sit near a peak of black hole fecundity – change things too much and you’d get either fewer stars (thus fewer black holes) or stars that end their lives differently.

Over many generations, a kind of Darwinian evolution occurs: constants “evolve” to maximize the number of black holes (offspring). Universes with “bad” combinations (producing few black holes) have few or no descendants and thus are statistically rare in the multiverse. Meanwhile, those tuned for prolific black hole production dominate the lineage. We, as observers, should therefore expect to find ourselves in a universe that is a successful replicator – which might coincide with conditions hospitable to life but doesn’t require anthropic reasoning. It’s simply that we’re in a survivor universe.

One concrete prediction Smolin derived was about the upper mass limit of neutron stars (if neutron stars could be slightly more massive before collapsing into black holes, that might reduce black hole production, so our universe should not allow too-high mass neutron stars). At the time, observations suggested neutron stars max out around two sun mass, which was in line with the prediction and thus not falsifying CNS. As of now, this line of testing continues whenever new astrophysical data on black hole formation thresholds or extreme stellar phenomena come in. CNS is not widely accepted as “proven” by any means, but it remains an interesting speculative consequence that at least in principle can be falsified – a rarity among multiverse ideas (which usually can’t be tested easily).

Our Universe’s Origins and “Big Bounce” Cosmology

Beyond the selection argument, the baby universe idea offers an appealing resolution to the question of the Big Bang singularity. In traditional cosmology, t=0 is a boundary (or a singular point) where our theories break down. But if our Big Bang was a bounce out of a black hole, then our beginning was in fact a continuation of a prior collapse. This aligns with a broader class of models called Big Bounce cosmologies, which have gained attention especially through loop quantum cosmology. Most bounce models, however, imagine a whole universe contracting then re-expanding (perhaps cyclically). The black hole bounce scenario is a specific twist where the contraction is not of our entire universe but of a localized region in a parent universe. It localizes the big crunch to within a black hole, which then becomes a big bang for a localized region (the new universe).

One question that arises: Does this imply most universes start very small (inside a black hole) and then grow arbitrarily large? Remarkably, yes – a baby universe can start from an effectively Planck-scale region and then inflate or expand to macroscopic, potentially infinite size. From the parent universe’s perspective, the throat of the wormhole might remain microscopic (a black hole doesn’t let things out, so the “size” of the connection might be tiny), but the internal volume on the baby side can be huge due to hyperbolic geometry. 

This is sometimes illustrated by the concept of a “bag of gold” solution (Wheeler’s term): you can have a small entrance (black hole horizon) but an enormous internal spatial volume like a bag, pinched by the throat. Thus a new universe can have much larger volume and entropy than the black hole that spawned it, without violating any laws in the parent universe because that volume is hidden behind the horizon. Popławski notes that enormous entropy production is possible at the bounce via particle production – effectively seeding a large universe – which matches with the idea that our universe has far more entropy than any single star that collapsed to form a black hole.

Cosmological observations to distinguish such a scenario are subtle. One possible hint could be a slight non-uniformity or anisotropy remnant from the initial conditions. If our universe emerged from a rotating black hole (a Kerr black hole) in a parent universe, the baby universe might inherit a preferred axis (from the angular momentum). This could translate into a subtle anisotropy in the cosmic microwave background (CMB). There have been occasional papers asking if the CMB has any signs of a “universal rotation” or other anomalies that might hint at such initial conditions. So far, the data doesn’t show a clear rotation (the universe looks isotropic to a high degree), though there are always low-level anomalies people debate. 

Another potential signature is if our universe is closed (positive spatial curvature) or other specific geometry – some bounce models naturally produce a closed universe. Interestingly, a black hole interior that bounces often yields a closed FLRW universe model on the other side (since a black hole interior is like a closed trapped region). If our universe is closed (which current Planck satellite measurements allow at small positive curvature, though the best fit is flat), it might be a gentle nudge toward a finite-volume universe which a baby universe would likely be (Popławski’s scenario in particular predicts a closed universe on the other side of a Schwarzschild black hole. These are not smoking guns by any means – many models can produce slight curvature or anisotropy – but they show that the idea isn’t completely divorced from possible observation.

Limits and Open Questions

While the multiverse via black holes is an elegant framework, it remains highly speculative and faces several unresolved questions:

Can we ever observe other universes or effects of them? 

By definition, a baby universe is disconnected once fully formed. We cannot travel through a black hole to go visit the child universe. The only hope of observational evidence is indirect: e.g., finding that our universe’s properties align with CNS predictions (supporting the idea of selection), or catching some phenomenon like a white hole bounce (as a signal in our universe) which implies matter is coming out from a bounce. There have been proposals that maybe some fast radio bursts or other unexpected astrophysical phenomena could be tiny white hole explosions – but nothing confirmed. As of now, observational support is absent; the idea lives purely in theoretical inference.

What about time scales? 

If a black hole bounces internally, one has to consider the clocks. Some models (like the Planck star model) suggest the bounce could occur after a huge time delay due to gravitational time dilation – e.g., a bounce that takes, say, 10^5 years internally might appear to take ~10^60 years from the external perspective (due to time dilation near the horizon). This would mean the baby universe “sprouts” only after the black hole has Hawking evaporated to a tiny remnant. 

In other models, the new universe may form and detach rapidly, essentially at the moment of formation of the singularity (the bounce happens quickly in proper time and the baby universe rapidly becomes its own realm). The timing affects whether any signal could come back out. In the detached scenario, nothing comes back; in the delayed bounce scenario, one might get a late-time white hole signal in the parent universe. It’s an open area of research what typical time scales are predicted and whether that yields any glimmer of testability.

Fertility of universe and measure: 

If indeed universes proliferate through black holes, one could attempt to estimate the “reproductive rate” of the cosmos. For instance, how many baby universes might ours create? (Perhaps on the order of the number of black holes that ever form, which is astronomically large over trillions of years as stars form, etc.) Is there a steady state or an explosion of number of universes? This starts to look like a runaway replication scenario. One has to define a measure on this multiverse to make statistical predictions (a notoriously hard problem in any multiverse theory). 

Smolin’s CNS attempts to do this qualitatively (weighting by number of offspring). Others might wonder if this leads to an infinite regress or if the chain of universes has a beginning. Some bounce models allow an infinite past sequence (each universe born from a BH in another, going back indefinitely), which is conceptually appealing as it avoids an ultimate beginning. However, whether an infinite self-contained lineage is possible or every tree must start from some root (perhaps a universe that was not a baby itself) is unresolved.

Compatibility with Big Bang: 

Our current standard cosmology (Lambda-CDM with an early inflationary phase) doesn’t include baby universes. Could inflation and baby universes coexist? Possibly – one could imagine that once our universe was born (via bounce), it still underwent inflation by whatever mechanism (scalar field, etc.). Or maybe the bounce itself took the role of inflation (for example, Popławski’s calculations hint that torsion-driven effects mimic inflation). These topics are being explored on the fringe of mainstream cosmology. So far, the standard model’s success means any baby-universe theory must reproduce all that success (nucleosynthesis, CMB spectrum, structure formation) while adding its new twist at t=0. This is doable in principle, but detailed models are still in development.

Conclusion 

At this juncture, the baby universe hypothesis inside black holes stands as a compelling example of integrative thinking in theoretical physics – connecting gravity, quantum mechanics, and cosmology. It remains unproven, and perhaps unprovable, yet it provides a cohesive narrative that could answer multiple fundamental questions at once: 

Where did our universe come from? What happens inside black holes? Why are the laws of physics the way they are? 

By suggesting “our universe came from a black hole’s interior; inside black holes, universes are born; the laws of physics might be tuned by an evolutionary process of universe reproduction,” this hypothesis dares to venture answers that lie beyond the comfort zone of testable science, but it does so in a framework that does not obviously contradict what we know. 

However, you might have wondered: if our universe perhaps wasn't the first, then which one was? This could be the topic for an entirely new text on Quantum Field Theory (QFT) and virtual particles.

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