{"topic":{"id":4631,"title":"Universe as Group & Null Space","slug":"topic","userId":1007,"categoryId":4,"createdAt":"2023-07-31 08:56:04.629293","bumpedAt":"2023-08-07 11:01:18.946613","views":289,"postsCount":3,"highestPostNumber":4,"likeCount":1,"closed":false,"pinned":false,"pinnedGlobally":false,"pinnedAt":null,"pinnedUntil":null,"isBanner":false,"excerpt":"一直有人在想象宇宙/时空的边界是什么，甚至提出“宇宙有界无边”这样荒诞的充满辩证法的似是而非的论断。其实宇宙就是一个 Group/Vector Space，定义了多维位移算子的集合，满足 Closure：你怎么位移也移不到它的外面。时间也算维度，你永远在 closure 中，所以不存在时间的开始或者终止。什么宇宙大爆炸、边界在扩张，只不过是人类的观测罢了。人类也只是在一个 Vector Subspace 里面，永远无法 escape，…","deletedAt":null,"isAnonymous":false,"isPrivate":false,"isMembersOnly":false,"category":{"id":4,"name":"谈笑风生","slug":"general","color":"25AAE2"},"author":{"id":1007,"username":"anonymous109","name":"anonymous109","avatarUrl":null},"realAuthor":{"id":1007,"username":"anonymous109","name":"anonymous109","avatarUrl":null},"tags":["academic"]},"posts":[{"id":8315,"postNumber":1,"raw":"一直有人在想象宇宙/时空的边界是什么，甚至提出“宇宙有界无边”这样荒诞的充满辩证法的似是而非的论断。其实宇宙就是一个 Group/Vector Space，定义了多维位移算子的集合，满足 Closure：你怎么位移也移不到它的外面。时间也算维度，你永远在 closure 中，所以不存在时间的开始或者终止。什么宇宙大爆炸、边界在扩张，只不过是人类的观测罢了。\n\n人类也只是在一个 Vector Subspace 里面，永远无法 escape，更没法观测外面。\n\n投射到子空间再多次效果都一样：\n$$\n\\text{For a vector space } V \\text{ and subspace } U \\subseteq V \\\\\n\\forall \\pi : V \\rightarrow U \\\\\n \\pi(\\pi(\\vec{x})) = \\pi(\\vec{x})\n$$\n\n黑洞是不是 Null Space 呢？我们观测到的所谓移动不过是维度是可逆过程，宇宙中也有这种不可逆过程，把你投射到 0，永世不得返回。宇宙是 singular 的。","cooked":"

一直有人在想象宇宙/时空的边界是什么，甚至提出“宇宙有界无边”这样荒诞的充满辩证法的似是而非的论断。其实宇宙就是一个 Group/Vector Space，定义了多维位移算子的集合，满足 Closure：你怎么位移也移不到它的外面。时间也算维度，你永远在 closure 中，所以不存在时间的开始或者终止。什么宇宙大爆炸、边界在扩张，只不过是人类的观测罢了。

人类也只是在一个 Vector Subspace 里面，永远无法 escape，更没法观测外面。

投射到子空间再多次效果都一样：
\n

\n\\text{For a vector space } V \\text{ and subspace } U \\subseteq V \\\\\n\\forall \\pi : V \\rightarrow U \\\\\n \\pi(\\pi(\\vec{x})) = \\pi(\\vec{x})\n

黑洞是不是 Null Space 呢？我们观测到的所谓移动不过是维度是可逆过程，宇宙中也有这种不可逆过程，把你投射到 0，永世不得返回。宇宙是 singular 的。

\n","createdAt":"2023-07-31 08:56:04.807959","updatedAt":"2023-09-09 08:41:16.837585","replyToPostNumber":null,"replyCount":0,"likeCount":1,"wordCount":274,"liked":false,"bookmarked":false,"polls":[],"reactions":[{"reaction":"❤️","count":1,"users":[{"id":426,"username":"Komeiji_Koishi","name":"Komeiji_Koishi"}],"hasReacted":false}],"wiki":false,"version":3,"publicVersion":3,"deletedAt":null,"isAnonymous":false,"user":{"id":1007,"username":"anonymous109","name":"anonymous109","avatarUrl":null,"admin":false,"moderator":false,"signatureRaw":null,"signatureCooked":null}},{"id":8658,"postNumber":2,"raw":"什么西交物理学家","cooked":"

什么西交物理学家

\n","createdAt":"2023-08-07 07:08:55.348547","updatedAt":"2023-08-07 07:08:55.348547","replyToPostNumber":null,"replyCount":0,"likeCount":0,"wordCount":8,"liked":false,"bookmarked":false,"polls":[],"reactions":[],"wiki":false,"version":1,"publicVersion":1,"deletedAt":null,"isAnonymous":false,"user":{"id":1047,"username":"anonymous_coward_old","name":"Anonymous Coward Old","avatarUrl":"/uploads/image/43/32/4332638c11248b8ff07033c11de0759a55205facfbec85e14458245a91991faf.avif","admin":false,"moderator":false,"signatureRaw":null,"signatureCooked":null}},{"id":8677,"postNumber":4,"raw":"支持学术发展！","cooked":"

支持学术发展！

\n","createdAt":"2023-08-07 11:01:18.946613","updatedAt":"2023-08-07 11:01:18.946613","replyToPostNumber":null,"replyCount":0,"likeCount":0,"wordCount":7,"liked":false,"bookmarked":false,"polls":[],"reactions":[],"wiki":false,"version":1,"publicVersion":1,"deletedAt":null,"isAnonymous":false,"user":{"id":307,"username":"Fast","name":null,"avatarUrl":null,"admin":false,"moderator":false,"signatureRaw":null,"signatureCooked":null}}],"hasMore":false,"lastReadPostNumber":1,"hasUrlPostNumber":true}