The origin of the universe is one of the greatest scientific mysteries of all time. Scientists have developed numerous theories and testable predictions about how the universe began, including the Big Bang model, cosmic inflation and quantum-cosmology proposals.
To test those theories, researchers from the Center for Astrophysics, a collaboration between Harvard and the Smithsonian, assembled the Lumina Project, a simulation of the early universe far larger than any prior one.
The details of the simulation, published in the Monthly Notices of the Royal Astronomical Society (PDF), describe how regular matter, dark matter and radiation likely interacted during the first 2 billion years of the universe, covering a region equivalent to a cube roughly 1.5 billion light-years on each side.
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For reference, the prior champion for the largest early-universe simulation was the Thesan simulation in 2022, which simulated about a billion years of the early universe across a region roughly equivalent to a 300-million-light-year cube.
It does all of this in incredible detail, largely due to observations made by NASA’s James Webb Space Telescope and other telescopes that spend considerable time observing the oldest celestial objects. By looking at those ancient space objects, scientists have been able to piece together at least some ideas of what the early universe may have looked like.
There’s a lot of science at work here
The simulation was made on the Frontier supercomputer at Oak Ridge National Laboratory in Tennessee. Frontier has around 37,000 GPUs across its system, and the Lumina Project used about 15,000 of them.
That’s what helped the simulation become the largest and most detailed simulation ever made, giving researchers plenty of unique features to work with.
One example is helium reionization, a process that scientists believe took place in the early universe. Back then, the universe was so hot that virtually all matter was ionized, meaning it consisted of charged particles. When the universe cooled about 380,000 years after the Big Bang, atoms started combining together to make regular hydrogen and helium. Then, a short time later (comparatively speaking), the first generation of stars emerged and emitted enough ultraviolet light to reionize nearby hydrogen and helium atoms.
“Lumina follows both hydrogen and helium reionization,” Zier told CNET in an email. “This allows us to study these processes together in one self-consistent simulation, meaning it captures reionization as it occurred while allowing its effects to immediately influence the evolving universe within the model.”
Aaron Smith, an assistant professor of physics at the University of Texas at Dallas and an author on the paper, said the team is incredibly fortunate to be building simulations like Lumina. “For the first time, we can follow along as both hydrogen and helium changed into their modern form across such an enormous volume of the universe, while still resolving the galaxies and other luminous objects driving that transformation,” Smith said in a statement.
The main function of Lumina is to help scientists test and confirm theories about the early universe and gauge whether their understanding of physics aligns with the simulation’s results.
The team has already used the simulation to make some interesting predictions, including that there were “fewer massive galaxies” in the early universe than James Webb Space Telescope observations suggest. The simulation also houses the mysterious little red dots spotted by JWST, which some scientists now believe are black hole stars.
Stunning imagery of the early universe
A side benefit is that the simulation has some truly gorgeous imagery, showing off a lot of interactions of the early universe, including gases at various temperatures mixing together, chemical reactions and the locations of early galaxies and stars. Since the simulation also fills in where dark matter and dark energy would be, the entire thing is a gorgeous litany of colorful clouds, threads and filaments.
Take the above video, for instance. It starts with a wide shot of the entire Lumina simulation volume, then zooms into a single galaxy in virtually empty space, showing how vast this simulation really is. Try pausing the video at almost any point to capture a really cool screenshot.
This next video flies the viewer through a massive halo within the simulation. It starts by adding in various layers, such as dark matter density, gas temperature, gas metallicity (how much heavier elements there are in the cosmic gas, and stellar light. At the end of the video, the layers are turned off, and what you’re left with is a cluster of galaxies.
The Lumina Project has 15 spectacular videos, showcasing everything from gas densities to hydrogen and helium reionization.