Biggest Computer Simulation for Galaxy Formation Ever

Credit: Argonne National Laboratory, U.S. Dept of Energy

Astrophysicists have used the Frontier supercomputer at Oak Ridge National Laboratory in the U.S. to perform a simulation of galactic structure formation at the highest resolution yet – or so I believe, because, aside from a press release with a video, I haven’t been able to find details about exactly what they did. Such structure formation simulations can, in principle, be used to test mathematical descriptions of the universe (e.g., the amount of dark matter or dark energy) against observations. In practice, the computer simulations have so many unconstrained parameters (mostly stemming from subgrid physics) that they can be made to fit anything. I like them anyway because they look pretty – and I hope a paper will appear soon.

Check out this video about the universe! Is the universe really infinite? Or could it close back on itself like a sphere? If it’s infinite, how can it expand? And is it true that there might be copies of you in it? Today I want to explain how much we know about those questions and what the expansion of space has to do with Hilbert's Hotel. You can take the quiz here.

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IBM Entangles Two Quantum Computing Chips In A Big Step Towards Scalability

Figure: Vazquez et al, Nature (2024)

Researchers at IBM have succeeded in combining two quantum computing chips with superconducting circuits with 127 qubits each, demonstrating that they could use at least 142 qubits in total. The major difficulty with this is maintaining the entanglement between qubits on different chips. It is not the first time that qubits on two different chips have been entangled, but the first time between such large chips. It is a big step on the way to scaling up quantum computers to commercially interesting use cases, which will require about 1 million qubits. Paper here.

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A Limit to Growth of Everything?

In a pre-print that just appeared, Toby Ord, the Australian philosopher known for his work on existential risk, proposed that nature might have a fundamental limit to growth. He speculates that the laws of nature must be computable, a property defined by them being executable on a standard computer. However, it seems that such computable functions cannot grow arbitrarily quickly. Even if you don’t believe his conjecture, it might be a way to test whether we live in a computer simulation. At the very least it’s given me something to think about. Paper here.

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