**Nov 8, 2023 09:55 PM (This post was last modified: Nov 8, 2023 09:57 PM by C C.)**

**C C**
Can we fit the universe in a box?

https://www.symmetrymagazine.org/article...entity=und

EXCERPT: . . . 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...

[...] Cosmologists and physicists use simulations to better understand how the universe works over cosmic time: How do certain structures form? How do typical galaxies evolve? Simulating specific aspects of the universe is certainly helpful, but it’s impossible to glean the bigger picture of how the universe works by looking at just one aspect...

[...] 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 Big Bang.

The other three forces certainly aren’t easy to simulate, either.

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 quantum computing to run numerical simulations using statistical sampling that yields probabilities of various outcomes—but only on a timescale that differs from reality. “So that means we don't actually simulate QCD as it appears in our universe,” Grabowska says. “We simulate one that is similar and can be directly connected, but it's not the same.”

For the most complicated simulations, scientists have come up with calculations to compensate for what they don’t understand and to make assumptions based on what they do. “Simulations of the universe can show us what’s plausible, given what we already know,” Pontzen says. “The simulations just carry with them a range of caveats to make the simulation work.”

The power to simulate the universe

Even if scientists could figure out how to describe all four fundamental forces across real time, and even if they understood all the laws of physics, the computer power they would need to simulate the universe is still far out of reach... (MORE - details)

https://www.symmetrymagazine.org/article...entity=und

EXCERPT: . . . 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...

[...] Cosmologists and physicists use simulations to better understand how the universe works over cosmic time: How do certain structures form? How do typical galaxies evolve? Simulating specific aspects of the universe is certainly helpful, but it’s impossible to glean the bigger picture of how the universe works by looking at just one aspect...

[...] 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 Big Bang.

The other three forces certainly aren’t easy to simulate, either.

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 quantum computing to run numerical simulations using statistical sampling that yields probabilities of various outcomes—but only on a timescale that differs from reality. “So that means we don't actually simulate QCD as it appears in our universe,” Grabowska says. “We simulate one that is similar and can be directly connected, but it's not the same.”

For the most complicated simulations, scientists have come up with calculations to compensate for what they don’t understand and to make assumptions based on what they do. “Simulations of the universe can show us what’s plausible, given what we already know,” Pontzen says. “The simulations just carry with them a range of caveats to make the simulation work.”

The power to simulate the universe

Even if scientists could figure out how to describe all four fundamental forces across real time, and even if they understood all the laws of physics, the computer power they would need to simulate the universe is still far out of reach... (MORE - details)