The Massive Bang is usually described because the explosive beginning of the universe—a singular second when house, time, and matter sprang into existence. However what if this was not the start in any respect? What if our universe emerged from one thing else—one thing extra acquainted and radical on the similar time?
In a brand new paper, revealed in Bodily Evaluate D (full preprint right here), my colleagues and I suggest a hanging different. Our calculations counsel the Massive Bang was not the beginning of all the things, however slightly the end result of a gravitational crunch or collapse that shaped a really large black gap—adopted by a bounce inside it.
This concept, which we name the black gap universe, presents a radically completely different view of cosmic origins, but it’s grounded solely in identified physics and observations.
In the present day’s commonplace cosmological mannequin, based mostly on the Massive Bang and cosmic inflation (the concept that the early universe quickly blew up in dimension), has been remarkably profitable in explaining the construction and evolution of the universe. Nevertheless it comes at a worth: It leaves a number of the most elementary questions unanswered.
For one, the Massive Bang mannequin begins with a singularity—a degree of infinite density the place the legal guidelines of physics break down. This isn’t only a technical glitch; it’s a deep theoretical drawback that implies we don’t actually perceive the start in any respect.
To clarify the universe’s large-scale construction, physicists launched a quick section of fast growth into the early universe referred to as cosmic inflation, powered by an unknown discipline with unusual properties. Later, to clarify the accelerating growth noticed at this time, they added one other “mysterious” part: darkish vitality.
Briefly, the usual mannequin of cosmology works nicely—however solely by introducing new substances now we have by no means noticed instantly. In the meantime, essentially the most fundamental questions stay open: The place did all the things come from? Why did it start this fashion? And why is the universe so flat, clean, and huge?
New Mannequin
Our new mannequin tackles these questions from a distinct angle—by trying inward as an alternative of outward. As a substitute of beginning with an increasing universe and making an attempt to hint again the way it started, we contemplate what occurs when an excessively dense assortment of matter collapses below gravity.
This can be a acquainted course of: Stars collapse into black holes, that are among the many most well-understood objects in physics. However what occurs inside a black gap, past the occasion horizon from which nothing can escape, stays a thriller.
In 1965, the British physicist Roger Penrose proved that below very basic circumstances, gravitational collapse should result in a singularity. This end result, prolonged by the late British physicist Stephen Hawking and others, underpins the concept that singularities—just like the one on the Massive Bang—are unavoidable.
The concept helped win Penrose a share of the 2020 Nobel prize in physics and impressed Hawking’s international bestseller A Transient Historical past of Time: From the Massive Bang to Black Holes. However there’s a caveat. These “singularity theorems” depend on “classical physics” which describes extraordinary macroscopic objects. If we embrace the results of quantum mechanics, which guidelines the tiny microcosmos of atoms and particles, as we should at excessive densities, the story might change.
In our new paper, we present that gravitational collapse doesn’t have to finish in a singularity. We discover an actual analytical resolution—a mathematical end result with no approximations. Our math exhibits that as we method the potential singularity, the dimensions of the universe adjustments as a (hyperbolic) perform of cosmic time.
This easy mathematical resolution describes how a collapsing cloud of matter can attain a high-density state after which bounce, rebounding outward into a brand new increasing section.
However why do Penrose’s theorems forbid such outcomes? It’s all right down to a rule referred to as the quantum exclusion precept, which states that no two an identical particles often called fermions can occupy the identical quantum state (resembling angular momentum, or “spin”).
And we present that this rule prevents the particles within the collapsing matter from being squeezed indefinitely. Because of this, the collapse halts and reverses. The bounce isn’t solely potential—it’s inevitable below the fitting circumstances.
Crucially, this bounce happens solely inside the framework of basic relativity, which applies on giant scales resembling stars and galaxies, mixed with the essential ideas of quantum mechanics—no unique fields, further dimensions, or speculative physics required.
What emerges on the opposite aspect of the bounce is a universe remarkably like our personal. Much more surprisingly, the rebound naturally produces the 2 separate phases of accelerated growth—inflation and darkish vitality—pushed not by hypothetical fields however by the physics of the bounce itself.
Testable Predictions
One of many strengths of this mannequin is that it makes testable predictions. It predicts a small however non-zero quantity of constructive spatial curvature—which means the universe isn’t precisely flat, however barely curved, just like the floor of the Earth.
That is merely a relic of the preliminary small over-density that triggered the collapse. If future observations, resembling the continuing Euclid mission, verify a small constructive curvature, it could be a powerful trace that our universe did certainly emerge from such a bounce. It additionally makes predictions in regards to the present universe’s price of growth, one thing that has already been verified.
The SpaceX Falcon 9 rocket carrying ESA’s Euclid mission on the launch pad in 2023. Picture Credit score: ESA, CC BY-SA
This mannequin does greater than repair technical issues with commonplace cosmology. It might additionally shed new mild on different deep mysteries in our understanding of the early universe—such because the origin of supermassive black holes, the character of darkish matter, or the hierarchical formation and evolution of galaxies.
These questions might be explored by future house missions resembling Arrakihs, which can research diffuse options resembling stellar halos (a spherical construction of stars and globular clusters surrounding galaxies) and satellite tv for pc galaxies (smaller galaxies that orbit bigger ones) which can be troublesome to detect with conventional telescopes from Earth and can assist us perceive darkish matter and galaxy evolution.
These phenomena may additionally be linked to relic compact objects—resembling black holes—that shaped through the collapsing section and survived the bounce.
The black gap universe additionally presents a brand new perspective on our place within the cosmos. On this framework, our complete observable universe lies inside the inside of a black gap shaped in some bigger “guardian” universe.
We’re not particular, not more than Earth was within the geocentric worldview that led Galileo (the astronomer who recommended the Earth revolves across the solar within the sixteenth and seventeenth centuries) to be positioned below home arrest.
We’re not witnessing the beginning of all the things from nothing, however slightly the continuation of a cosmic cycle—one formed by gravity, quantum mechanics, and the deep interconnections between them.
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