世界線

• 読み: せかいせん
• ローマ字: sekaisen
• 漢字の分解: 世 (world) + 界 (boundary) + 線 (line)
• 発音: /se.ka.i.seɴ/

意味

Worldline/timeline — borrowed from Steins;Gate to describe an alternate reality, unexpected development, or a scenario that feels like it belongs in a parallel universe.

世界線 is originally a physics term (worldline, from general relativity) that was popularised in everyday Japanese through the visual novel and anime Steins;Gate (2009/2011). In the show, characters leap between 世界線 — different timelines where events play out differently. Fans adopted the term to describe real-life situations that feel surreal or like they belong in an alternate timeline. 'What 世界線 is this?' became a standard reaction to bizarre news, unexpected celebrity couples, or any development that seems to defy normal reality.

例文

1. あの二人が付き合ってるって、どの世界線の話？
2. コロナ前の世界線に戻りたいって時々思う。
3. 推しがうちの地元に来るとか、どういう世界線？

使い方ガイド

場面: social media, internet culture, casual conversation, reactions

トーン: bewildered, amused, surreal

正しい言い方

• この世界線だと俺たち同僚なのウケるな。 (It's funny that in this timeline we're coworkers.)
• どの世界線でもあの人は成功してそう。 (I bet that person succeeds in every timeline.)

避ける言い方

• 物理学の文脈で冗談として使うと専門家に嫌がられることがある (Using it jokingly in a physics context may annoy experts who use the term precisely)

よくある間違い

• Assuming everyone knows the Steins;Gate reference — older generations may only know it as a physics term
• Using it too literally as if discussing actual parallel universes in a serious context

起源と歴史

From the physics concept of a worldline (Minkowski spacetime), massively popularised by the visual novel/anime Steins;Gate (2009). The show's central mechanic of shifting between timelines made 世界線 a household word among anime fans, which then spread to general internet slang.

文化的背景

時代: 2009-2011 (Steins;Gate release), widespread by mid-2010s

世代: Teens to 30s, especially anime fans

社会的背景: Otaku origin, now broadly understood online

地域メモ: Used across Japan. Steins;Gate is one of the most influential anime/VN franchises, making this term widely recognised even outside core fandom.