Cosmology Using Numerical Relativity: A New Paper by Eugene Lim and Colleagues

Zeeya Merali

We’re often told it is “unscientific” or “meaningless” to ask what happened before the big bang. But a new paper by FQxI cosmologist Eugene Lim, of King's College London, UK, and astrophysicists Katy Clough, of Queen Mary University of London, UK and Josu Aurrekoetxea, at Oxford University, UK, published in Living Reviews in Relativity, in June 2025 proposes a way forward: using complex computer simulations to numerically (rather than exactly) solve Einstein’s equations for gravity in extreme situations. The team argues that numerical relativity should be applied increasingly in cosmology to probe some of the universe’s biggest questions–including what happened before the big bang, whether we live in a multiverse, or whether our universe cycled through a series of bangs and crunches. Read more at qspace.fqxi.org/news.

GALE

Often people say that asking “what happened before the Big Bang” is meaningless, because time and space themselves began at that moment. But I wonder if “non-existence” here simply reflects the fact that we have not yet established a way to observe or model it. In that case, the real task of science is not to dismiss the question, but to invent the tools that could make such questioning meaningful.

History shows this pattern: atoms, galaxies, even gravitational waves were once said to be “non-existent” simply because they could not be observed. Later, with new instruments and theories, they became part of established science. Why should the “pre-Big Bang” be treated differently?

In cosmology, scenarios like cyclic universes, bounces, or multiverse models already attempt to extend our reach into what was once declared meaningless. Perhaps what we call “nothingness” is only the next frontier, waiting for science to define the methods to glimpse it.

To me, the spirit of science is not to declare limits too quickly, but to embrace the challenge: what we cannot yet observe may still be there, and the joy is in learning how to reach it.

Amrit Sorli

The Einstein tensor and its equations are a mathematical masterpiece, but are limited in practical use. With the GR mathematical model, you cannot calculate the gravitational force between Earth and the Sun. I developed a model where the curvature of space is replaced with the variable energy density of space; the mass-energy equivalence principle is extended to superfluid space. The article was published in the International Journal of Quantum Foundations under the title: Einstein Legacy: Ether Relativity and Cosmology https://ijqf.org/archives/7583
In this model, there is no Big Bang; the universe is a non-created system, and SMBHs are rejuvenating systems of the universe. I think the Big Bang model belongs to the history of physics. The idea of some explosion out of nothing is more philosophical than physical.
Maybe is time to be more critical of Big Bang cosmology also on FQXI. We had long discussions in the past years that there is no physical time (Julian Barbour). If there is no physical time, the universe cannot exist in time. The universe is timeless. It would be nice to extend this subject on FQXI: TIME AND COSMOLOGY.

GALE

Amrit Sorli
Thank you very much for your thoughtful analysis.
Indeed, my intention was to emphasize the practical limitations of GR when applied beyond its elegant mathematics. By replacing “spacetime curvature” with “variable energy density of space,” I believe we can obtain a more physical and testable description of gravitational phenomena.

Regarding cosmology, my model views SMBHs not as destructive endpoints, but as rejuvenation engines of the universe, leading to an eternal, non-created system without a Big Bang. In this sense, I agree with you: the Big Bang belongs to the history of physics, not to the future of it.

I also find Julian Barbour’s arguments about the non-existence of physical time very stimulating. If physical time does not exist, then the universe itself cannot be said to “begin” or “end” in time. My model aims to be consistent with this timeless perspective, treating the cosmos as an atemporal structure of energy renewal.

I strongly agree that FQXi could provide a valuable stage for a deeper critique of the Big Bang paradigm. Extending this discussion under the theme of “Time and Cosmology” would be an excellent opportunity.

dhelaM

The reality as we perceive it we call it Universe. The vacuum and space-time as background are assumptions. If we dismiss this assumptions, the Reality is just energy and we are part of it. How to explain than the reality? First the reality it is is not substance but a process is dynamic and nonlinear energy structuring. Time itself is an dual operator that we process to observe this reality by 1: separate the observed from the field, than 2: invert the image in the brain (structured energy) to process the separation of the observed (identity) from ourself (identity) and ourself from the field. This dual time is observed by qualia that label the observed and acknowledge the observation. So the reality is a coherent labeling chain of energy.
With no space/time preexisting there was no big bang.
Is non sense to try to explain multiverse before we truly understand our Universe.

GALE

Your framing of reality as a dynamic, nonlinear process of energy structuring resonates with me. I also see reality not as a fixed substance but as a recursive process, where observation and identity continuously interfere and evolve.
The idea of “dual time” is fascinating—I imagine it as a Möbius-like recursion, where separation and continuity coexist.
Maybe the real challenge is to find ways to model this nonlinear process so that it bridges both physics and the lived experience of qualia.

onetomany

Some spoilers:
The truth is stranger than the fictions so far hypothesized.
We don't live in a multiverse.
There was not a single big bang, there is a continuous stream of bangs, still going on today, which are increasing in scale perpetually forever, we, as a vast collection of neighboring galaxies, are speeding away from the origin of our bang much faster than it is growing.
Our previous life cycle, before we were a galaxy as we know it today, is that we were part of a much denser cloud of matter that eventually slowly decomposed into trillions of galaxies.
Our life cycle in the future, or our galaxies fate, is that we will continue to slowly decompose until every single particle disentgrates into its primary building blocks, never to take part in an interaction with other particles of any kind.
The fuel that feeds the engine behind us which generates more matter (and eventually more galaxies), is flowing between the gaps of particles, so far undetected.
There is only one substance in the totality of the universe, the only difference is how it is geometrically arranged - for example it can be part of a particle, or not, or part of a system of particles, of which there are countless variations and nested systems: protons, planets, galaxies, etc to name a few. The true fundamental building block has yet to be discovered, it is far too tiny. It exists primarily as a zero-viscosity fluid and is infinite in this form. The particles in the universe, and therefore the atomic-universe, is finite, but will continue growing in scale forever.
Because of the sheer size and scale of the atomic universe, countless intelligent evolved animals, mechanical intelligent creations, etc have already existed and died out, as well as exist alongside us, but likely very far away. Anything we discover is a rediscovery, it's only new to us.
Olympus Mons on Mars is not a volcano, it's an eruption point of one of the cores of Mars. When it ejected out of Mars, it took the atmosphere with it. This is an event that can happen to any planet with more than one core, although it's very rare and unlikely.
The Sun is not hotter or hottest at its center, it is actually hottest near its outer bands. Science fundamentally does not understand solar power or energy in general.
The good news: The future potential for energy and prosperity is unlimited.
The bad news: We only exist as cells which make up our animal because the alternative was to go extinct, we have no third-party purpose, our purpose is whatever we think it is, and unfortunately, we are not mini gods, there is no free will, we are merely biological machines, no more free from physics than a rock. Whether the ride is enjoyable or not is entirely up to chance. I suppose this could be good news for those that believed they were going to burn in hell forever.