What Happens Before the Big Bang? New Simulations Are Revealing a Violent Pre-History
By David Freeman - August 25, 2025
The traditional image of the Big Bang, a smooth and sudden explosion from nothing, is being replaced by something much more turbulent. Behind closed doors and inside high-performance computing labs, physicists are running full-scale simulations that trace the origins of our universe in ways never before possible. These simulations no longer begin at the Big Bang. They pass through it.
For decades, cosmology has relied on a simplified picture of the early universe. The equations that describe it assumed perfect uniformity across space, treating all directions as equal and all regions as nearly identical. This worked well enough for calculating expansion rates and matching predictions to cosmic microwave background data, but it left the most extreme questions untouched. What if space was never uniform? What if the Big Bang was not a singular beginning? What if the events leading into the expansion phase were more violent, more chaotic, and more structured than previously admitted?
Physicists using numerical relativity are now confronting these questions directly. These are not thought experiments. They are full simulations of spacetime under conditions so extreme that traditional models break down. The key difference is that these simulations do not assume a background geometry. They solve the full Einstein equations with no simplifying assumptions, allowing spacetime to evolve based on the matter and energy within it. The result is a model of the early universe that is no longer hypothetical. It is computationally realized, and it behaves in ways the standard picture cannot accommodate.
Some of these models start not with an explosion, but with a collapse. Instead of a universe beginning at a point of infinite density, the simulations are seeded with a contracting space. As the contraction continues, regions of high curvature begin to form. Space does not shrink evenly. Some areas compress faster than others. Distortions form. These are not small corrections. The geometry becomes unstable. Shear and anisotropy grow. What began as a gradual contraction transforms into a chaotic prehistory.
At high enough energy densities, the collapse reaches a critical threshold. In certain conditions, instead of terminating in a singularity, the collapse reverses. The simulated universe bounces. Time continues. Space expands again. Matter fields stretch. The geometry flattens. This sequence, collapse followed by rebound, becomes the backdrop for everything that follows. The Big Bang, in this view, is not a beginning but a transition.
The idea of a cosmic bounce is not new. What has changed is the ability to test it using full relativistic models. Past theories assumed symmetry or treated matter as smooth. They could not capture the nonlinear feedback between geometry and energy. These new simulations do. When a local overdensity forms, the surrounding geometry curves. That curvature, in turn, affects the motion of nearby matter. This two-way interaction is not just a technical detail. It is essential to capturing the true behavior of the early universe.
In these bounce scenarios, space undergoes rapid distortions that leave behind persistent features. These are not temporary fluctuations. They are embedded in the geometry itself. Scalar fields collapse into localized clumps. Gravitational waves are generated spontaneously. Some simulations show the formation of structures resembling early black holes, formed not from stars but from pure gravitational instability.
There is no indication in these models that the bounce erases the memory of what came before. This suggests the possibility of a connected sequence, where each expansion phase is preceded by a collapse. A cyclic framework emerges, not because it was imposed, but because it arises from the equations when simulated without constraints.
Other models take a different route. They begin not with collapse, but with disorder. Instead of a smooth start, the early universe appears fragmented. Numerical relativity allows researchers to initialize simulations with irregular matter distributions and distorted geometry. The outcome is not noise. It is pattern. High-density pockets form. Fields interact. Some regions expand while others lag. The geometry shifts in real time, responding to the irregularities. This behavior is not predicted by perturbative theories. It cannot be captured by averaging equations. Only full general relativity reveals how this kind of disorder unfolds.
This has direct consequences for inflation. Inflation theory requires a specific set of conditions to function. Traditionally, these conditions were assumed. Now, they can be tested. Researchers input rough, uneven initial states into their simulations and observe whether inflation still triggers. In many runs, it does. The exponential expansion smooths out the early chaos. But in others, it does not. The field fails to dominate. The irregularities persist. Inflation stalls. The universe expands unevenly or not at all.
This challenges the notion that inflation is inevitable. If its success depends on a narrow set of initial conditions, then some prior structure must be responsible for setting them. That structure, whatever it was, now becomes a new frontier of study. The simulations do not provide answers to where it came from. But they allow researchers to test what happens if it existed.
Some of the most violent scenarios involve mixmaster dynamics. These are characterized by rapid oscillations in the shape of space. Instead of stretching equally in all directions, the universe distorts. One axis may contract while another expands. These shifts cycle repeatedly. The result is a geometric turbulence that defies simplification. The term for this is anisotropic chaos. It emerges near singularity thresholds and is common in simulations that allow for full inhomogeneity. This kind of behavior would leave clear signatures in the energy distribution and structure of the early universe, if it occurred.
Another frontier being explored involves the formation of oscillons. These are localized energy concentrations that form from scalar fields in the early universe. Unlike black holes, oscillons are not formed from collapse. They emerge from field interactions and remain stable for extended periods. In some simulations, oscillons dominate the energy budget of the universe after the bounce or after inflation. They clump, collide, and affect the expansion rate of space. If they decay, they release energy back into the field. If they persist, they can distort local curvature. These objects do not appear in traditional models. They arise only when matter and geometry are evolved together without approximation.
Primordial black holes are also under renewed scrutiny. In a universe with large fluctuations, some regions may exceed the collapse threshold even before stars or galaxies exist. These simulations allow researchers to model that process from first principles. They track how overdense zones evolve under full gravity. The curvature increases. Collapse begins. Horizons form. These are not hypothetical scenarios. They are consistent with the mathematics of general relativity when applied under extreme initial conditions. Whether these black holes survived, and whether they account for any of the dark matter, is still being explored.
This has direct consequences for inflation. Inflation theory requires a specific set of conditions to function. Traditionally, these conditions were assumed. Now, they can be tested. Researchers input rough, uneven initial states into their simulations and observe whether inflation still triggers. In many runs, it does. The exponential expansion smooths out the early chaos. But in others, it does not. The field fails to dominate. The irregularities persist. Inflation stalls. The universe expands unevenly or not at all.
This challenges the notion that inflation is inevitable. If its success depends on a narrow set of initial conditions, then some prior structure must be responsible for setting them. That structure, whatever it was, now becomes a new frontier of study. The simulations do not provide answers to where it came from. But they allow researchers to test what happens if it existed.
Some of the most violent scenarios involve mixmaster dynamics. These are characterized by rapid oscillations in the shape of space. Instead of stretching equally in all directions, the universe distorts. One axis may contract while another expands. These shifts cycle repeatedly. The result is a geometric turbulence that defies simplification. The term for this is anisotropic chaos. It emerges near singularity thresholds and is common in simulations that allow for full inhomogeneity. This kind of behavior would leave clear signatures in the energy distribution and structure of the early universe, if it occurred.
Another frontier being explored involves the formation of oscillons. These are localized energy concentrations that form from scalar fields in the early universe. Unlike black holes, oscillons are not formed from collapse. They emerge from field interactions and remain stable for extended periods. In some simulations, oscillons dominate the energy budget of the universe after the bounce or after inflation. They clump, collide, and affect the expansion rate of space. If they decay, they release energy back into the field. If they persist, they can distort local curvature. These objects do not appear in traditional models. They arise only when matter and geometry are evolved together without approximation.
Primordial black holes are also under renewed scrutiny. In a universe with large fluctuations, some regions may exceed the collapse threshold even before stars or galaxies exist. These simulations allow researchers to model that process from first principles. They track how overdense zones evolve under full gravity. The curvature increases. Collapse begins. Horizons form. These are not hypothetical scenarios. They are consistent with the mathematics of general relativity when applied under extreme initial conditions. Whether these black holes survived, and whether they account for any of the dark matter, is still being explored.
These simulations require decisions about how space is bounded. In cosmology, there are no outer edges. To deal with this, simulations often loop the spatial domain. A cube is defined, and its boundaries are wrapped, creating a topological torus. This allows the simulation to run without artificial borders. But it also introduces discrete structure. The universe becomes periodic at a computational level. This decision affects the behavior of long-wavelength modes and sets a scale for structure formation. Some researchers are experimenting with alternative boundary conditions, matching to expanding backgrounds or allowing waves to exit cleanly. The choice of boundary is not trivial. It determines whether the simulation tracks a local patch of a larger universe or represents a self-contained cosmos.
Gauge choice is another technical decision with deep physical consequences. The lapse and shift functions determine how time and space are sliced during the simulation. Different choices emphasize different observers. In highly distorted geometries, choosing the wrong gauge can hide or misrepresent important dynamics. Simulations must be tested for stability and consistency across multiple gauges. This is not just about mathematical rigor. It ensures that what is being seen reflects the underlying physics, not a coordinate artifact.
What emerges from all of this is a picture of the early universe that is rough, violent, and active. Not a featureless void that suddenly inflates, but a complex system with internal feedback, structure, and memory. A place where space is not passive, but responds dynamically to the matter within it. A place where beginnings are not absolute.
This does not reduce the mystery of existence. It replaces one unknown with another. Instead of a singular creation event, the simulations suggest an ongoing process. They point to the possibility that the Big Bang was not the start of time, but one frame in a much larger sequence. If that sequence includes collapse and bounce, then the horizon of the observable universe is not a limit, but a veil. What lies beyond it remains out of reach for now. But what these simulations are showing is that the Big Bang no longer stands alone.
There is no way to run a definitive experiment on the birth of the universe. But physics does not require direct access to draw conclusions. If a model reproduces known outcomes and evolves consistently under the same laws that describe everything else, then it becomes a legitimate object of study. Numerical relativity provides a way to treat the early universe not as a singularity to be avoided, but as a domain to be simulated.
In doing so, it is revealing structures and behaviors that were hidden by previous methods. This is not about redefining origins in philosophical terms. It is about recognizing that the conventional image was incomplete. The early universe may have been deeply distorted, fragmented, or even cyclic. It may have been shaped by gravitational turbulence. It may have passed through contractions and expansions more than once. The equations allow it. The simulations run it. The outcomes are being published. What happens before the Big Bang is no longer off limits. It is now being computed.
Source:
Aurrekoetxea, J.C., Clough, K., & Lim, E.A. (2025). Cosmology using numerical relativity. Living Reviews in Relativity, 28(5). https://doi.org/10.1007/s41114-025-00058-z
ChristopherBlackwell
I don't know how scientists can actually "know" how the universe actually began
'Scientists estimate the age of the universe to be about 13.8 billion years by measuring the rate of the universe's expansion and "rewinding" it to the Big Bang, using tools like the Cosmic Microwave Background (CMB) for the earliest snapshots and observing galaxy redshifts for current expansion rates. They also study the oldest stars and use models of cosmic evolution, such as the Lambda-CDM model, to confirm these estimates, with the CMB and galaxy data providing remarkable agreement.'-greenman
on August 25, 2025, 12:46 pm
