iiinova — where your digital self keeps evolving

Zihan Yan @physics-cat.bsky.social · 28/02/2026

If I got enough money, I’ll start my own non-profit theoretical physics institute! Let’s do it together then

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Zihan Yan @physics-cat.bsky.social · 04/02/2026

Me. Want to learn QFT properly

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Zihan Yan @physics-cat.bsky.social · 03/02/2026

Academia is brutal. This year I’m shortlisted by 5 places for postdoc positions, got high up on the waitlist, and then got no offer. The first-round offer holders all had other offers, but that cannot be traded. Academia has no safety net. I’m probably out. This is more cruel than hearing nothing…

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Zihan Yan @physics-cat.bsky.social · 25/01/2026

27啦！下周就要博士论文答辩，悬而未决的postdoc申请也即将尘埃落定，不知道还能在象牙塔里面待多久。新的一岁，新的开始，新的探索，新的希望。

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Zihan Yan @physics-cat.bsky.social · 06/09/2025

Looks super interesting! Will apply!

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Zihan Yan @physics-cat.bsky.social · 03/09/2025

Next steps: extend these results to semiclassical & nonlinear regimes. Excited to see how “entropic geometry” reshapes our view of spacetime & gravity. (7/8)

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Zihan Yan @physics-cat.bsky.social · 03/09/2025

For higher-spin fields, the theorem holds conditionally. I propose a “higher-spin focusing condition” as a criterion for physical consistency. (E.g. 3D sl(3,R) higher-spin black holes satisfy it ✅) (6/8)

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Zihan Yan @physics-cat.bsky.social · 03/09/2025

Key insight: Geometrically, light rays don’t always focus under positive energy in general gravity theories. But in entropic geometry—measuring separation via Wall entropy, not area—they do. Gravity remains attractive! (5/8)

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Zihan Yan @physics-cat.bsky.social · 03/09/2025

This generalised expansion decreases monotonically under the null energy condition. Even more: it equals the change in Wall entropy density, which satisfies the 1st & 2nd laws. So it’s a natural higher-order/dynamical generalisation of BH/Wald entropy. (4/8)

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Zihan Yan @physics-cat.bsky.social · 03/09/2025

We extend this to all diffeo-invariant gravities with bosonic matter. On perturbed Killing horizons, the linearised equation of motion gives a generalised Raychaudhuri equation → a notion of “generalised expansion.” (3/8)

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Zihan Yan @physics-cat.bsky.social · 03/09/2025

In GR, the focusing theorem says: with positive energy (NEC), light rays converge. This simple idea reveals the attractive nature of gravity, and underpins Hawking’s area theorem & Penrose’s singularity theorem. (2/8)

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Zihan Yan @physics-cat.bsky.social · 03/09/2025

🚀 My first conference paper is out! arxiv.org/abs/2509.00628 Based on my GR24 talk, it summarises 2 years of work with my supervisor Aron Wall on generalised focusing theorems & horizon thermodynamics in diffeo-invariant gravity. A short thread 👇(1/8)

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Zihan Yan @physics-cat.bsky.social · 31/12/2024

Happy New Year! 新年快乐！All the best to our 2025!

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Zihan Yan @physics-cat.bsky.social · 27/12/2024

I hope I can grow a better vision for theoretical physics in the new year… I always feel I’m so naïve…

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Zihan Yan @physics-cat.bsky.social · 11/12/2024

It was fun to explore the intricacies of higher-spin fields from the perspectives of gravitational focusing and horizon thermodynamics. There are so many open questions to address in the future… arxiv.org/abs/2412.07107

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Zihan Yan @physics-cat.bsky.social · 17/11/2024

New departmental cat of DAMTP, Cambridge

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Zihan Yan @physics-cat.bsky.social · 16/11/2024

Just noticed I was already on Bluesky way before I joined 😂😂😂

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Zihan Yan @physics-cat.bsky.social · 16/11/2024

Hi! I’m new here! Glad to chat about black holes and quantum gravity or anything about physics and mathematics!

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