Wouldn’t it be nice to have a computer answer all of the biggest questions in the universe?
In his first year of graduate school, in 2013, Michael Wagman walked into his advisor’s office and asked, “Can you help me simulate the universe?”
Wagman, a theoretical physicist and associate scientist at the US Department of Energy’s Fermi National Accelerator Laboratory, thought it seemed like a reasonable question to ask. “We have all of these beautiful theoretical descriptions of how we think the world works, so I wanted to try and connect those formal laws of physics to my everyday experience of reality,” he says.
In response to the question, Wagman says, his advisor chuckled. Simulating the universe is impossible. There are too many variables; there is too much we don’t understand.
But the fact that we can use computers to simulate anything with any semblance of
In The Universe in a Box, published this year, University College London (UCL) professor of cosmology Andrew Pontzen bolsters those efforts by charting humanity’s progress over time toward a simulation of the universe.
A History of Computer Simulations
Simulations are kind of like hypothetical experiments, Pontzen says. “We set up hypothetical situations inside computers that we’ve programmed—in our case, with certain laws of physics—and then we ask the computer to figure out the consequence of that situation. What should happen next?”
Curious minds have been practicing simulations in this way since antiquity, he says. More than 2,000 years ago, ancient Greeks used a rudimentary computer of sorts, called the Antikythera Mechanism, to calculate the occurrence of astronomical events, such as eclipses.
But perhaps the first mention of a more modern concept of simulation appears in the writings of Ada Lovelace, an English mathematician and pioneer of computing. In the mid-19th century, Lovelace worked alongside Charles Babbage, an English polymath and inventor who envisioned a precursor to the modern computer called the Analytical Engine. He didn’t quite manage to build it, but his goal was to create a machine capable of performing an endless variety of calculations just by changing coded instructions fed to it on strips of card.
Lovelace recognized the potential of the Analytical Engine, Pontzen says. “She wrote about the fact that this machine could take [theoretical] science from being a pursuit of abstract equations and turn that into something much more practical.”
In the early twentieth century, mathematician and meteorologist Lewis Fry Richardson proposed building a giant amphitheater filled with mathematicians, calculating together to produce simulations that forecast the weather. “He believed the equations of physics that describe how materials behave could be applied to the material in Earth’s atmosphere,” Pontzen says. “That’s essentially what modern simulations of the weather do today.”
One of the earliest examples of computer simulations advancing the field of cosmology comes from the work of Beatrice Tinsley in the late 1960s. Tinsley, an astronomer and cosmologist (and the first female astronomy professor at
Chipping Away at a Cosmic Problem
Although scientists cannot yet simulate the entire evolution of the universe, they have managed to use simulations to learn about phenomena they are unable to detect directly, like dark matter and dark energy.
“Data from the
“We still have a lot of questions about early universe dynamics, and it’s really hard to figure out how to calculate certain components of that,” Grabowska says. “It would be much easier if I could just plug in an initial state when the universe started out, then just let it naturally evolve with time and take some measurements. But that’s really hard to do, for a multitude of reasons.”
One challenge is that the Standard Model of particle physics explains three of the four fundamental forces of nature—the electromagnetic force, the weak force, and the strong force—but not the fourth—gravity.
“We don’t know how to simulate gravity,” Wagman says. “We know that Einstein’s Theory of General Relativity and Newton’s Law of Gravitation are both good approximations that work very well at low energies, but the math that goes into those breaks down when you try and ask questions about ultra-high energy states,” such as the conditions of the
The strong force, for instance, governs the interactions of fundamental particles that make up protons and neutrons. These interactions—described by quantum chromodynamics, or QCD—are so strongly coupled that there’s no clear delineation of what aspects may be more important than others to even allow approximations to be made. “A lot of our pen and paper methods of trying to calculate it don’t work because we can’t make approximations,” Grabowska says.
To circumvent this, scientists use
If the goal is to capture everything in the universe in a simulation, that means there should be one