What is Hackers' Pub?

Hackers' Pub is a place for software engineers to share their knowledge and experience with each other. It's also an ActivityPub-enabled social network, so you can follow your favorite hackers in the fediverse and get their latest posts in your feed.

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John Carlos Baez @johncarlosbaez@mathstodon.xyz
Public

New result: you can build a universal computer using a single billiard ball on a carefully crafted table!

More precisely: you can create a computer that can run any program, using just a single point moving frictionlessly in a region of the plane and bouncing off the walls elastically.

Since the halting problem is undecidable, this means there are some yes-or-no questions about the eventual future behavior of this point that cannot be settled in a finite time by any computer program.

This is true even though the point's motion is computable to arbitrary accuracy for any given finite time. In fact, since the methodology here does *not* exploit the chaos that can occur for billiards on certain shaped tables, it's not even one of those cases where the point's motion is computable in principle but your knowledge of the initial conditions needs to be absurdly precise.

This result is not surprising to me - it would be much more surprising if you *couldn't* make a universal computer this way. Universal computation seems to be a very prevalent feature of sufficiently complex systems. But still it's very nice.

• Eva Miranda and Isaac Ramos, Classical billiards can compute, arxiv.org/abs/2512.19156.

Classical billiards can compute Eva Miranda, Isaac Ramos We show that two-dimensional billiard systems are Turing complete by encoding their dynamics within the framework of Topological Kleene Field Theory. Billiards serve as idealized models of particle motion with elastic reflections and arise naturally as limits of smooth Hamiltonian systems under steep confining potentials. Our results establish the existence of undecidable trajectories in physically natural billiard-type models, including billiard-type models arising in hard-sphere gases and in collision-chain limits of celestial mechanics. Significance statement. Billiards are a textbook model of deterministic motion: a particle moves freely and reflects specularly from rigid walls. We show that, even in two dimensions, billiard trajectories can simulate arbitrary Turing machines. This universality implies a sharp limit on prediction: there is no general algorithm that can decide basic questions such as whether a trajectory is periodic. Because billiards also arise as limits of smooth Hamiltonian systems with increasingly steep confining potentials, these algorithmic barriers are not confined to idealized hard-wall models. Our results place undecidability, alongside chaos, as a fundamental obstruction to long-term prediction even in low-dimensional classical dynamics. From here: https://arxiv.org/abs/2512.19156
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한겨레 @hanibsky.bsky.social@bsky.brid.gy
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정부가 2030년까지 플라스틱 쓰레기를 30% 줄이기 위한 ‘탈플라스틱 종합대책’을 내놨습니다. 그러나 일회용품 사용을 금지하는 정책이 미약하고 플라스틱 사용 자체를 줄이는 계획이 포함되지 않아 실제 효과를 거둘 수 있을지 의문이 나옵니다.

‘탈플라스틱’ 종합대책 대국민 토론…“2030년까지 3...

‘탈플라스틱’ 종합대책 대국민 토론…“2030년까지 30% 감축”

정부가 2030년까지 플라스틱 쓰레기를 30% 줄이기 위한 ‘탈플라스틱 종합대책’ 초안을 내놨다. 그러나 일회용품 사용을 금지하는 정책이 미약하고 플라스틱 사용 자체를 줄이는 계획이 포함되지 않아 실제 효과를 거둘 수 있을지 의문이 나온다. 정부는 23일 오후 서울 영

www.hani.co.kr · 한겨레

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Hacker News 100 @hn100@social.lansky.name
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Universal Reasoning Model (53.8% pass 1 ARC1 and 16.0% ARC 2)

Link: arxiv.org/abs/2512.14693
Discussion: news.ycombinator.com/item?id=4

arXiv logo

Universal Reasoning Model

Universal transformers (UTs) have been widely used for complex reasoning tasks such as ARC-AGI and Sudoku, yet the specific sources of their performance gains remain underexplored. In this work, we systematically analyze UTs variants and show that improvements on ARC-AGI primarily arise from the recurrent inductive bias and strong nonlinear components of Transformer, rather than from elaborate architectural designs. Motivated by this finding, we propose the Universal Reasoning Model (URM), which enhances the UT with short convolution and truncated backpropagation. Our approach substantially improves reasoning performance, achieving state-of-the-art 53.8% pass@1 on ARC-AGI 1 and 16.0% pass@1 on ARC-AGI 2. Our code is avaliable at https://github.com/zitian-gao/URM.

arxiv.org · arXiv.org

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[랜선효도] 제주감귤🍊 @jejuorange.bsky.social@bsky.brid.gy
Public
Shared by Dolmengi

AI 가짜 의사 막는다…포털·플랫폼·게시자에 ‘AI 생성물 표시제’ 적용 정부, 정보통신망법 개정 예고 www.hani.co.kr/arti/politic... "인공지능 기반의 ‘가짜 인간’이 광고에 나오면 해당 인물이 인공지능 기반임을 표시하도록 하는 내용의 법 개정도 추진"

AI 가짜 의사 막는다…포털·플랫폼·게시자에 ‘AI 생...

AI 가짜 의사 막는다…포털·플랫폼·게시자에 ‘AI 생성물 표시제’ 적용

정부가 인공지능(AI) 기반 생성물 표시를 의무화하는 ‘인공지능 생성물 표시제’를 인공지능 사업자뿐 아니라 포털·플랫폼·게시자에게도 적용하는 법 개정안을 추진하기로 했다. 인공지능이 만든 ‘가짜 전문가’가 나오는 식·의약품 광고 행위를 금지하고, 긴급시정조치 등 인공지

www.hani.co.kr · 한겨레

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🫧 socialcoding.. @smallcircles@social.coop
Public
Shared by 🫧 socialcoding..

Any developers on this here delightful commons?

Any lovers?
Any geek out there?
Searching for and ?

:blobaww: Then this may be for you..

codeberg.org/socialcoding/deli

Summary card of an issue titled "Candidate curated list delightful-gleam-standards" in repository socialcoding/delightful-commons

Candidate curated list delightful-gleam-standards

First inkling of an idea to start a curated list on the Venn diagram topics of: 1. Open standards 2. Open technologies 3. Gleam best practices Collecting open standards based libraries is particularly interesting, as robust Gleam (reference) implementations can be feature-complete, their...

codeberg.org · Codeberg.org

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🫧 socialcoding.. @smallcircles@social.coop
Public
Shared by 🫧 socialcoding..

:blobhyperthink:

Compare activists who refuse to join and use proprietary platforms and tools on sheer principle, not even to try to rescue fellow afficionados who are captured there, suffering or just misguided.

To the North-Korean liberation movement, refusing to rescue dissidents, on sheer principle, because Kim-Jong Un is still in proprietary power. Instead they build a big fat signpost at the border, saying "Come here, it is the better choice!"

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nafumofu :vivaldi_red: @nafumofu@vivaldi.net
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約30年の歴史を持つ「WebMoney」2026年3月末で「プリペイドカード」がサ終へ―事業承継のため | Game*Spark - 国内・海外ゲーム情報サイト
gamespark.jp/article/2025/12/2

約30年の歴史を持つ「WebMoney」2026年3月末で「プリペイドカード」がサ終へ―事業承継のため | Game*Spark - 国内・海外ゲーム情報サイト

1998年から使われている「WebMoney」がビットキャッシュへ事業承継。「WebMoneyプリペイドカード」は2026年3月をもって停止予定です。

www.gamespark.jp · Game*Spark - 国内・海外ゲーム情報サイト

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(っㆆᴗㆆ)っ(ΦωΦ) @gev@fedibird.com
Public
Shared by MJ+

尼泊爾警方會配合中國的立場，在西藏抗暴，或達賴喇嘛生日等敏感紀念日前後，控制反華挺西藏的活動，甚至提前抓人。

尼泊爾首都普裝監視器 助中國監控流亡藏族 news.pts.org.tw/article/787057

尼泊爾首都普裝監視器 助中國監控流亡藏族 ｜ 公視新聞網 PNN

施慧中 · 尼泊爾政府以建設智慧城市之名，大量在首都加德滿都街頭裝設監視攝影機，從城市到邊境山頂，隨處可見監控設施，而系統設備主要來自中國廠商，在流亡藏人聚集的社區更是密集，讓他們的不安全感大幅增加。尼泊爾警方會配合中國的立場，在西藏抗暴，或達賴喇嘛生日等敏感紀念日前後，控制反華挺西藏的活動，甚至提前抓人。

news.pts.org.tw · 公視新聞網 PNN

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European Commission @EUCommission@ec.social-network.europa.eu
Public
Shared by Chao-c'

Europe is making a list, checking it twice… and upgrading its trains to high-speed – nice! 🚄

While you are sipping hot chocolate, we are cooking up 200+ km/h rail magic:

✨ Faster journeys: Berlin → Copenhagen in 4hr instead of 7hr
🚆 New routes: Lisbon–Madrid–Paris and Tallinn–Riga–Vilnius–Warsaw
🌙 More night trains for long trips
🎫 One ticket for your whole journey, and easier booking across borders

By 2040, your holidays might just start on the rails.

👉 link.europa.eu/hDyYBG

A watercolour-style illustration depicting a sleek, red and white high-speed train, labelled "EU Holiday Express in the making," speeding out of a swirling, abstract representation of the blue European Union flag with its yellow stars. In the background, there are snow-covered Christmas trees and picturesque, snow-dusted houses. The EU logo is also visible in the bottom right corner.
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Stefano Marinelli @stefano@fedihome.stefanomarinelli.it
Public
Shared by Stefano Marinelli

The Gray Teacher

On a gray winter morning, memory drifts back to an old classroom, a stern teacher, and the thin line between mist and humidity.

https://my-notes.dragas.net/2025/12/23/the-gray-teacher/


The Gray Teacher | MyNotes

On a gray winter morning, memory drifts back to an old classroom, a stern teacher, and the thin line between mist and humidity.

my-notes.dragas.net

Link author: Stefano Marinelli@stefano@bsd.cafe

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