No, String Theory’s Competitor Has Not Been Disproven

I was recently alerted to a video by my friend and colleague Brian Keating that claims Loop Quantum Gravity (LQG), string theory’s biggest competitor, has been disproven.Brian is reporting on a paper about Lorentz-invariance violation. The story is that about 20 years ago, some people in LQG said that the theory would give rise to such violations and sold it as an advantage over string theory because it made LQG testable. If Lorentz-invariance violations would be found, they said, that would support LQG. Others in LQG disagreed that the theory gave rise to such violations. 20 years later, those who once claimed that LQG is testable have become very quiet. If you are pro-LQG you can now claim it hasn't been disproven. If you’re anti-LQG you can claim it isn’t testable. Personally, I don’t understand why people waste time on this one way or another.

This episode of Science News covers gravitons. Gravitons are one of the most sought-after particles in physics. They could help physicists combine quantum physics with gravity to create a theory of "quantum gravity." We thought until recently they were for all practical purposes impossible to detect, but now scientists are coming up with some ideas for how graviton-detecting experiments could work for real. Let’s take a look. You can take the quiz here.

You can now create and share your own quizzes on QuizWithIt – for free! Just set up an account and creator profile and you are good to go. Create quizzes to go with websites, videos, blogposts, podcasts, or as standalone. Your audience can support you by subscribing to your content, which allows them to collect points by taking your quizzes. Each quiz has a unique URL, can be embedded into websites or newsletter, and be shared on X, Facebook, or LinkedIn. Happy quizzing!

Modified Gravity vs. Dark Matter: The Fight Continues

Wide binary system, illustration. Credits: NASA/Chris Smith

Wide Binaries – systems of two stars orbiting each other at a large distance – have recently attracted attention as a promising way to tell dark matter from modified gravity. Unfortunately, different analyses of the same data gave different results, some speaking for modified gravity, some against it. To make a long story short, the analysis that spoke for modified gravity had been criticised on the grounds of using only part of the available data. Following that criticism, the author repeated his analysis with the full samples. He says the result still speaks for modified gravity at more than 5σ significance. Paper here. Press release here.

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Leading Quantum Computing Company to be Investigated for Potential Tax Misuse

Design of PsiQuantum’s scalable Quantum Computing platform, arXiv: 2404.17570

PsiQuantum has emerged as one of the most promising companies to build a useful quantum computer. Their tech is built on photonic computing, and they claim to have developed a scalable platform that would allow them to reach a million qubits easily. PsiQuantum has partnered with Global Foundries to produce their microchips, and some headlines said they’ve even bought land for the factory (I talked about this previously here). However, a big chunk of PsiQuantum’s funding was most recently provided by the Australian government, a whopping 940 million Australian dollars. Given that PsiQuantum is now a U.S. company, this struck some Australians as decidedly odd. Some members of the Australian parliament have requested an investigation into whether the investment is an appropriate use of public money. The Australian National Audit Office now says that they will look into the matter. You can read the letters here.

I will be in London at the HowTheLightGetsIn Festival at Hampstead Heath on Saturday, Sep 21. I have attended this festival several times and it always gives me something to think about. So if you're in the area, maybe consider dropping in? Tickets available here: https://howthelightgetsin.org/festivals/london