For decades, the Big Bang has stood as the cornerstone of modern cosmology: a moment when the universe exploded from an infinitely dense point into existence. But what, if anything, came before that moment? The question once seemed meaningless, but recent breakthroughs in numerical relativity—a computational approach to solving Einstein’s notoriously complex equations—are revealing that the universe’s earliest history may be far stranger than previously imagined. Scientists are now glimpsing the potential for pre-existing universes, colliding realities, and even the possibility that the Big Bang wasn’t a beginning, but a transition.
Rewinding the Cosmos: Numerical Relativity’s Breakthrough
The core challenge lies in the fact that the equations describing gravity break down at extreme densities. Physicists have long attempted to sidestep this issue by using approximations, plugging conditions into supercomputers and letting them run simulations. This isn’t about finding exact solutions; it’s about extracting meaningful insights from rough estimates. As Eugene Lim of King’s College London explains, this field is now uncovering answers to questions once considered unanswerable.
The power of this approach emerged from gravitational wave astronomy. After decades of theory, scientists finally observed ripples in spacetime in 2016. That success emboldened researchers to apply the same techniques to the far more difficult problem of the early universe, building “death star” level models to simulate conditions near the Big Bang.
The Inflationary Puzzle and the Case for Bouncing Universes
One of the leading theories about what happened before the hot, dense phase of the early universe is inflation : a period of exponential expansion that smoothed out initial irregularities. However, inflation relies on a hypothetical field—the “inflaton”—with poorly understood properties. Simulations are now revealing that certain configurations of this field are more likely to produce inflation than others, creating tension with observations from the cosmic microwave background (CMB).
This uncertainty has opened the door to alternative models, including the bouncing universe hypothesis. Instead of exploding from a singularity, the universe may have contracted from a previous state before rebounding. Numerical relativity supports this idea, showing that contraction can smooth out irregularities just as effectively as inflation, and potentially avoid the problematic singularity altogether. Recent data even suggests the universe’s expansion is slowing down, making a future contraction more plausible.
Evidence of Colliding Universes?
Perhaps the most radical implication of these simulations is the possibility that our universe isn’t alone. If inflation created “bubbles” of slower-expanding space, those bubbles could have formed close enough to collide. Models suggest such collisions would leave detectable scars in the CMB. While early searches for these imprints yielded inconclusive results, researchers are refining their methods and exploring more realistic scenarios.
Experiments are even being conducted in labs to simulate colliding universes using exotic fluids, seeking to validate the theoretical predictions.
The Future of Cosmological Inquiry
Numerical relativity isn’t just testing existing theories; it’s also probing the foundations of theoretical physics. The shapes of the inflaton field required to produce inflation, for example, clash with many models of string theory, yet align with specific variations. This suggests that some approaches to unifying gravity with quantum mechanics may be more promising than others.
With faster computing power and more sophisticated simulations, scientists are poised to push the boundaries of cosmological knowledge even further. The era of blindly accepting the Big Bang as an absolute beginning may be drawing to a close. We’re entering a phase where the universe’s origins can be tested, challenged, and potentially rewritten based on the relentless pursuit of computational truth.
The simulations are beautiful pieces of work, but still incomplete. The models can’t yet fully explain the universe as we see it today, but they’re getting closer to answering the biggest question in cosmology: what came before everything?
