The Massive Bang is commonly described because the explosive beginning of the universe—a singular second when area, 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 identical time?
In a brand new paper, revealed in Bodily Evaluation D (full preprint right here), my colleagues and I suggest a hanging various. Our calculations counsel the Massive Bang was not the beginning of every part, however fairly the end result of a gravitational crunch or collapse that fashioned a really large black gap—adopted by a bounce inside it.
This concept, which we name the black gap universe, affords a radically totally different view of cosmic origins, but it’s grounded solely in identified physics and observations.
As we speak’s customary cosmological mannequin, primarily based on the Massive Bang and cosmic inflation (the concept the early universe quickly blew up in measurement), has been remarkably profitable in explaining the construction and evolution of the universe. But it surely comes at a worth: It leaves a number of the most basic questions unanswered.
For one, the Massive Bang mannequin begins with a singularity—some extent of infinite density the place the legal guidelines of physics break down. This isn’t only a technical glitch; it’s a deep theoretical downside that means we don’t actually perceive the start in any respect.
To clarify the universe’s large-scale construction, physicists launched a quick part of speedy enlargement into the early universe known as cosmic inflation, powered by an unknown subject with unusual properties. Later, to clarify the accelerating enlargement noticed at the moment, they added one other “mysterious” element: darkish vitality.
In brief, the usual mannequin of cosmology works effectively—however solely by introducing new substances we’ve got by no means noticed straight. In the meantime, probably the most fundamental questions stay open: The place did every part come from? Why did it start this manner? And why is the universe so flat, easy, and enormous?
New Mannequin
Our new mannequin tackles these questions from a special 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 think about what occurs when an excessively dense assortment of matter collapses beneath gravity.
It is 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 beneath very common circumstances, gravitational collapse should result in a singularity. This consequence, prolonged by the late British physicist Stephen Hawking and others, underpins the concept 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 atypical macroscopic objects. If we embody the consequences of quantum mechanics, which guidelines the tiny microcosmos of atoms and particles, as we should at excessive densities, the story could change.
In our new paper, we present that gravitational collapse doesn’t have to finish in a singularity. We discover a precise analytical answer—a mathematical consequence 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 straightforward mathematical answer describes how a collapsing cloud of matter can attain a high-density state after which bounce, rebounding outward into a brand new increasing part.
However why do Penrose’s theorems forbid such outcomes? It’s all all the way down to a rule known as the quantum exclusion precept, which states that no two similar particles referred to as fermions can occupy the identical quantum state (equivalent to 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 shouldn’t be solely attainable—it’s inevitable beneath the fitting circumstances.
Crucially, this bounce happens solely inside the framework of common relativity, which applies on giant scales equivalent to stars and galaxies, mixed with the essential rules of quantum mechanics—no unique fields, additional dimensions, or speculative physics required.
What emerges on the opposite facet of the bounce is a universe remarkably like our personal. Much more surprisingly, the rebound naturally produces the 2 separate phases of accelerated enlargement—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—that means the universe shouldn’t be 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, equivalent to the continued Euclid mission, affirm a small constructive curvature, it could be a robust trace that our universe did certainly emerge from such a bounce. It additionally makes predictions concerning the present universe’s charge of enlargement, 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 customary cosmology. It may additionally shed new gentle 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 area missions equivalent to Arrakihs, which can examine diffuse options equivalent to 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 are troublesome to detect with conventional telescopes from Earth and can assist us perceive darkish matter and galaxy evolution.
These phenomena may also be linked to relic compact objects—equivalent to black holes—that fashioned through the collapsing part and survived the bounce.
The black gap universe additionally affords 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 fashioned in some bigger “father or mother” universe.
We’re not particular, not more than Earth was within the geocentric worldview that led Galileo (the astronomer who steered the Earth revolves across the solar within the sixteenth and seventeenth centuries) to be positioned beneath home arrest.
We’re not witnessing the beginning of every part from nothing, however fairly the continuation of a cosmic cycle—one formed by gravity, quantum mechanics, and the deep interconnections between them.
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