第 376 期·中文精讀

斯蒂芬·沃爾夫勒姆:ChatGPT 與真理、現實和計算的本質

Stephen Wolfram: ChatGPT and the Nature of Truth, Reality & Computation

計算科學家談 ChatGPT 的工作原理、語言模型與真理的關係,以及計算視角下的宇宙觀。

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2023年5月,斯蒂芬·沃爾夫勒姆(Stephen Wolfram)第四次坐到 Lex Fridman 的麥克風前。就在這期節目上線前不久,他把 ChatGPT 接進了 Wolfram Alpha 和 Wolfram Language。

兩個系統的底層邏輯差得很遠。ChatGPT 從人類寫在網上的一萬億詞文字里學出“下一個詞大概是什麼”,然後一個詞一個詞往外吐。Wolfram Alpha 背後是四十多年積累的形式化知識體系,把數學、科學、系統化的事實翻譯成機器可以一步步推演的結構。

沃爾夫勒姆自己的總結很乾脆:ChatGPT 寬而淺,他這四十年在做的東西也寬,但真正關鍵的是深。

這句判斷解釋了一個反覆出現的現象。同一個模型,寫一首模仿莎士比亞的詩幾乎無懈可擊,算一個三位數乘三位數再開平方就開始犯迷糊。

兩條技術路線,兩種對世界的理解

先說 ChatGPT 在做什麼。

你給它一段提示,它試著把這段提示按照人類寫作的統計規律續下去。技術上,它做的事情和人腦處理語言最初的那幾百毫秒有相似之處:神經元被啟用,訊號在層與層之間擴散,最後落在一個詞上。這種計算很淺,淺到只有幾十層,但它鋪在一萬億詞的語料上,覆蓋面極廣。

再說 Wolfram 那條路。

從他二十歲出頭開始,他就在琢磨一件事:能不能把人類文明裡所有能形式化的知識,都變成機器可以執行的計算。數學公式、物理常數、化學元素、地理資料、歷史時間線,這些內容現在都能被 Wolfram Language 呼叫,能參與多步推演,能算出從沒被任何人算過的結果。

兩條路的成本結構完全不同。收集網頁文字便宜,幾乎免費;把知識一條條形式化,貴得離譜,需要人力、專家、幾十年的耐心。沃爾夫勒姆認為,只有後者能壘起真正的高度。

ChatGPT 那種做法,是從人類為了別的目的寫下的東西里覓食。我們做的是搭建計算系統,讓整個人類文明的專家知識變成可以可靠算出來的東西。(斯蒂芬·沃爾夫勒姆)

這裡有個隱含的賭注:可靠。語言模型的輸出永遠帶著機率的味道,同一句話問兩遍可能得到兩個答案。計算系統的輸出不這樣,只要輸入和規則確定,結果就確定。在需要負責任的場景裡,這個差別是生死線。

人類真正的分水嶺,是學會了搭塔

沃爾夫勒姆把人類的能力切成兩層。

第一層是幾千年前普通人的日常智慧。什麼東西一眼能看出來,什麼判斷靠天生的神經結構就夠,什麼經驗是活一輩子自然長出來的。這一層,人和不少動物共享,差別沒有我們想的那麼大。

第二層出現得晚得多。邏輯、數學、科學,這一整套形式化工具,是文明史上真正的分水嶺。有了它們,人能搭塔:拿一條規則推出一個不顯然的結論,再拿這個結論推出下一個,一路往上,直到抵達一個憑直覺永遠夠不著的地方。

這兩層的區別可以這樣感受。第一層是“我一眼就知道答案”。第二層是“我拿這套規則一步一步推出來,推完才發現答案和我猜的相反,但我信這個推出來的結果”。

Wolfram Language 的全部野心,就是造這種塔。ChatGPT 那種“我好像在哪兒見過類似的句子”,始終停在地面那一層。

這個區分也解釋了語言模型的邊界在哪裡。它在地面層強得驚人,因為人類寫下的文字絕大多數都是地面層的產物。一旦任務需要爬塔,它就沒有梯子,只能從記憶裡翻出形狀相似的段落去蒙。

一行不到的程式碼,跑出一整個宇宙

要理解沃爾夫勒姆為什麼對計算有這麼強的信心,得回到1980年代初。

他當時在幹一件看起來毫無用處的事:隨手造一些極小的程式,小到不足一行程式碼,有些規則甚至是隨機拼出來的,然後把它們跑起來,看會發生什麼。

結果把他自己震住了。即使極度簡單的程式,跑起來也會產生極其複雜的行為。複雜到沒有語言能描述,複雜到像生物,像雪花,像一整片森林。

他花了好幾年才消化這件事。真正讓他震住的,並非複雜本身,而是複雜從哪兒來。程式裡沒有寫“長出森林”,程式裡只有一條重寫規則,森林是自己冒出來的。

他後來把這件事讀成自然界的底層運作方式。規則可以極簡,結果可以極繁。物理世界看起來也是這樣:幾條基本定律,演化出星系、生命,以及正在爭論這件事的兩個人。

問題在於,知道規則這件事,在實踐上能換來什麼。

知道規則,和能預測,中間隔著一條鴻溝

這期訪談裡最重要的概念在這裡出現:計算不可約性(computational irreducibility)。

設想你掌握了某個系統的全部規則。按直覺,你就掌握了一切,因為你可以把規則跑一遍。真正的問題是:你能不能跳過那些步驟,直接說出跑一百萬步之後的結果?

大多數時候不能。唯一的辦法就是老老實實跑那一百萬步。

如果你能約化掉那個計算,那個計算本身就沒有任何意義了。計算之所以有價值,恰恰在於你必須真的做它,才能知道答案。(斯蒂芬·沃爾夫勒姆)

這句話的殺傷力超出技術範疇。它意味著宇宙自己算得飛快,而身處宇宙內部的我們,沒有任何辦法提前知道它會算出什麼。宇宙用宇宙能有的最快速度在跑,我們連插隊的資格都沒有。

按他的估計,宇宙每秒重寫自己 10 的 100 次方次。這個數字遠超人類任何計算能力,也遠超任何可以想象的模擬能力。所以“我們有朝一日能模擬整個宇宙”這句話,在物理上就是空想。

那科學為什麼還有意義?

不可約的世界裡,總有可約的口袋

因為不可約的計算裡,永遠散落著可約化的口袋。

你沒法跳過全部,但你總能在某些區域性提前知道結果。科學的整個故事,人類幾乎所有重要的發明,很大一部分就是找到這些口袋,然後把自己掛上去。

沃爾夫勒姆說他意識到,我們恰好活在一個可預測性密度合適的位置上。房間裡的空氣分子在亂飛,理論上是一個複雜到無法追蹤的故事,但你不必追蹤。你只需要知道,這幾秒鐘空氣還是空氣,不會有大事發生。這種可約化的口袋你抓住了,才能在房間裡正常走路、正常說話、正常思考。

生命本身就建立在大量可約化口袋之上。如果世界處處都無法壓縮成簡潔敘述,你連下一秒該做什麼都決定不了。每一刻都要從原子層面重新算起,這種存在方式撐不過一秒。

他還提到,壓縮這件事有代價。你抓的口袋越大,丟掉的細節越多。科學的進步經常表現為換一個更大的口袋,或者發現原來那個口袋在某個方向上漏了。

這套視角還有一個副產品,沃爾夫勒姆說這是他近幾年最喜歡的發現。

觀察者:把無數構型壓成一個數字

把底層的計算不可約性,和“我們是計算能力有限的觀察者”這兩件事放在一起推,能推出二十世紀發現的主要物理定律。這是他自己的評價,也說明他為什麼認為觀察者這個概念值得單獨立項研究。

這個專案被這波 AI 熱潮打斷了。他本來想搞清楚:什麼是觀察者?

他的定義很物理。拿一箱氣體舉例,你測的是壓強。氣體分子撞擊活塞的方式有無數種,你在意的只有總和。無數種微觀構型,在你眼裡完全等價。

觀察者的核心動作,就是把大量不同構型歸併成“我只關心這一個聚合特徵”。

這類歸併在物理裡到處都是。溫度是歸併,密度是歸併,顏色是人類視網膜對波長的歸併。每一次歸併,都換來了一個可以拿在手裡討論的東西,代價是丟掉了底層細節。

但歸併本身還不夠。要讓物理定律出現,還差一個條件,看起來平淡無奇,實際非常關鍵:我們相信自己在時間中持續存在。

為什麼你相信自己還是剛才那個你

微觀上看,這件事很古怪。

按照他的理論,每一刻鐘的我們,都由不同的空間原子組成。上一刻的你和這一刻的你,在微觀層面沒有任何共享的部分。就像一條河,每一秒流過的水都換了一遍,可你還叫它同一條河。

那為什麼我們覺得自己始終是同一個人?

因為意識擁有一條單一的經驗線索。這條線索把破碎的微觀事件縫成了一段連續敘事,於是才有“剛才發生了一件確定的事,現在又發生了一件”這種感受。

沃爾夫勒姆強調,這條線索來自計算受限系統的一種簡化。宇宙本身並沒有這種普遍特徵。一般的計算系統可以並行分裂出無數條經驗線,人類必須把它們壓成一條,否則沒法做決策,也沒法說話。

量子力學就是一個例子。系統內部在分裂成多條經驗線,人類必須在感知層面把它們縫合起來,才能說“測量得到了一個確定值”。縫合動作發生在觀察者這邊,代價是我們永遠看不到縫合之前的全貌。

順著這個思路,他還說了一句挺刺人的話:很多人預設意識是宇宙中最高階的東西,他不這麼看。意識算不上宇宙的通則,它只是一種特化。特化意味著能力上的取捨,你換來了連貫的自我,同時失去了同時活在多條經驗線裡的可能。

多線索並存的心智是什麼感覺,很難想象,但在他看來那才是更一般的狀態。我們這種“一條線”的心智,在整個可能性空間裡屬於稀有配置。

雪花:一次漂亮的科學失敗

訪談裡有一段長長的雪花故事。表面在聊物理,落點在科學方法論上的一個陷阱。

雪花有形狀。它從六邊形起步,長出枝杈,枝杈再長枝杈,最後填回一個更大的六邊形。原因挺有意思:一塊冰凝結時會釋放熱量,把周圍區域性加熱,於是緊鄰的位置不容易再結冰。這個抑制效應把枝杈推開了,讓它們彼此分離地長。

沃爾夫勒姆用極簡單的離散模型復現了這個過程。他還發現一件事:當枝杈長回去填滿那個大六邊形時,會留下一些填不上的小孔。他起初不確定,就去翻雪花的實拍照片,果然,照片上真有這些小孔,像生長過程留下的疤痕。

有意思的地方在後面。幾十年前有一批關於雪花生長的文獻,給出了漂亮的曲線,算出了生長速率,數字看著還挺準。

他仔細一看:按照那些模型,雪花應該是球形的。

生長速率對了,形狀全錯。而形狀恰恰是雪花最顯眼的特徵,是任何人第一眼就會注意到的東西。模型抓住了沒人關心的一項,漏掉了所有人都在看的那一項。

沒有哪個模型是正確的,除了實際系統本身。問題只在於:它有沒有抓住你在意的東西?(斯蒂芬·沃爾夫勒姆)

什麼樣的模型算好模型?答案取決於你打算拿它幹什麼,取決於你要用它造什麼技術。同樣的系統,做氣候預測的人和做材料設計的人,需要的模型完全不同,評價標準也不同。

科學上大量爭論(“你這個模型不對”“不對是因為它沒抓住我在意的那個特徵”)本質上都在這一點上打架,只不過雙方經常沒說清自己在意的到底是什麼。說清楚了,很多爭論會自動消失。

唯一的例外是:如果你聲稱自己建模了整個宇宙,那才有“正確”這回事。但也僅限於底層意義。而且就算你有了正確的模型,你也跑不動它,因為計算不可約。宇宙的唯一一次執行,就是宇宙本身。

符號:把世界塞進腦子的唯一辦法

從物理回到工程,中間隔著一個問題:我們憑什麼能把複雜世界塞進腦子裡?

看一個房間。視網膜上有幾百萬個畫素,但你記住的是“那裡有兩把椅子、一張桌子”。畫素被壓縮成了符號。人類認知的核心動作就在這兒落地,把無限細節壓成有限的東西。

自然語言是最初的壓縮形式,也是人類文明共享的一套符號系統。它有個致命缺點:它不夠精確,沒法直接計算。你說“兩把椅子”,這句話本身算不出任何東西。

於是就有了符號程式設計。1979年前後,沃爾夫勒姆在設計他第一個大型計算機系統時,想出了一個表示方式:把一切寫成“函式加引數”的結構化表示式。這個函式不一定立刻求值,它就靜靜待在那裡,代表一個結構。

他自己也沒想到這套東西能撐四十多年。這種結構化表示式,恰好非常貼近人類概念化高層事物的方式。語言的模糊性被消解掉,剩下的東西可以餵給機器一步步推演。

Wolfram Alpha 的全部工作就是幹這件事。把“我們關心什麼”這個非常人類的判斷,翻譯成機器能算下去的符號系統。資料庫裡不存電影的每一個畫素,存的是片名、導演、票房、上映日期,這些是人會問的東西。

他對“理解”這件事下過一個定義,很值得記住。

理解可以有一個可驗證的標準

我們總問:它真的理解了嗎?

在計算的世界裡,這個問題可以有明確答案:能不能把它轉成符號化的計算結構,從而算出各種後果。

按這個標準,“能不能續寫一段文字”和“有沒有理解這段文字”,是兩件不同的事。前者它做得極好,後者它給不出可驗證的證據。你可以讓它解釋一個物理概念,它說得頭頭是道;你讓它算這道題的數值,它可能編出一個漂亮但錯誤的數字。

這也說明兩個系統為什麼該合作。ChatGPT 負責接住人類的模糊表達,把一大段自然語言裡的意圖摳出來;Wolfram 負責把意圖變成可計算的結構,然後算出答案。入口可以很寬,底座必須很硬。

沃爾夫勒姆說,四十多年來他一直在擴這塊可計算的疆域,讓世界上儘可能多的東西能被可靠算出來。這件事很慢,很費人力,遠不如收集網際網路文字那麼便宜。他認為這是唯一能把文明往上壘的路。

背後有一個更長的判斷。人類文明的成果,絕大部分體現在形式化的知識裡:數學定理、物理定律、工程規範、法律條文。這些東西之所以能代代積累,正因為它們能變成符號,能被機器接著往下推。不能形式化的部分,只能靠口傳心授,一代人一走就散了。

聊天框裡冒出一段漂亮的文字,那停在地面層。能在上面搭出一步推一步、推完還能繼續推的東西,才進入了塔的內部。人類之所以區別於其他物種,靠的從來是後一層。

給從業者的幾條可操作建議

  • 在系統設計裡明確區分“接住模糊表達”和“算出可靠答案”。前者交給語言模型,後者必須有可驗證的計算後端,別指望用機率補上精確性。
  • 判斷一個模型好不好,先寫下你在意哪些特徵,再對照模型抓沒抓住。別隻看它給出的那個數字準不準,雪花模型算對了生長速率,卻給出了一個球形。
  • 遇到無法預測的系統,別去找全域性捷徑。去找那些區域性的可約化口袋,把工程和決策押在可預測的切片上,其餘部分接受不可約。
  • 做知識庫和工具鏈時,優先投資符號化和結構化表示。自然語言是入口,不是底座,能參與推演的只有精確結構。
  • 評估模型會不會“理解”,別隻看它續寫得像不像。設計需要多步推演的測試,看它能不能把結論一路算出來。
  • 對自己也要留一份清醒:你相信的那條連續自我敘事,是計算受限系統的一種簡化。它有用來由,不是宇宙的真相。
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Lex Fridman Podcast #376 – Stephen Wolfram: ChatGPT and the Nature of Truth, Reality & Computation Machine transcription by Qwen3-ASR 0.6B (MLX, local, Apache-2.0). May contain recognition errors. The following is a conversation with Stephen Wolfram, his fourth time on this podcast. He's a computer scientist, mathematician, theoretical physicist, and the founder of Wolfram Research, a company behind Mathematica, Wolfram Alpha, Wolfram Language, and the Wolfram Physics and Metamathematics projects. He has been a pioneer in exploring the computational nature of reality, and so he's the perfect person to explore with together the new, quickly evolving landscape of large language models as human civilization journeys towards building super intelligent AGI. And now a quick view second mention of his sponsor. Check them out in the description. It's the best way to support this podcast. 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This is the Lex Friedman podcast to support it. Please check out our sponsors in the description. And now dear friends, here's Stephen Wolfram. You announced the integration of ChatGPT and Wolfram Alpha and Wolfram Language. So let's talk about that integration. What are the key differences from the high philosophical level? Maybe the technical level between the capabilities of. Broadly speaking, the two kinds of systems large language models and this computational gigantic computational system infrastructure that is Wolfram Alpha. Yeah, so what does something like ChatGPT do? It's it's mostly focused on make language like the language that humans have made and put on the web and so on. So you know it's it's primary sort of underlying technical thing is you've given a prompt. It's trying to continue that prompt in a way that's somehow typical of what it's seen based on a trillion words of text that humans have written on the web, and the way it's doing that is. With something which is probably quite similar to the way we humans do the first stages of that using a neuron that and so on and just saying given these given this piece of text, let's ripple through the neuron that one word and get one word at a time of output, and it's kind of a shallow computation on a large amount of kind of training data that is what we humans have put on the web. That's a different thing from sort of the computational stack that I spent the last I don't know forty years or so building, which has to do with what can you compute many steps potentially a very deep computation. It's not sort of taking the statistics of what we humans have produced and trying to continue things based on that statistics instead. It's trying to take kind of the formal structure that we've created in our civilization whether it's from mathematics or whether it's from kind of systematic knowledge of all kinds and use that to do arbitrarily deep computations to figure out things that that aren't just let's match what's already been kind of said on the web, but let's potentially be able to compute something new and different that's never been computed before. So as a practical matter, you know the the what we're you know our goal is to have made as much as possible of the world computable in the sense that if there's a question that in principle is answerable from some sort of expert knowledge that's been accumulated, we can compute the answer of that question and we can do it in a sort of reliable way that's that's the best one can do given what the expertise that our civilization has accumulated. It's a very it's a it's a much more sort of labor intensive on the side of kind of being creating kind of the the computational system to do that. Obviously the in the the kind of the ChatGPT world, it's like take things which were produced for quite other purposes namely all the things we've written out on the web and so on and sort of forage from that things which were are like what's been written on the web. So I think you know as a practical point of view, I view sort of the ChatGPT thing as being wide and shallow, and what we're trying to do with sort of building out computation as being this sort of deep also broad but but most importantly kind of deep type of thing. I think another way to think about this is if you go back in human history, you know I don't know thousand years or something, and you say what what can the typical person what's the typical person going to figure out. Well the answer is there certain kinds of things that we humans can quickly figure out that's sort of what what our you know our neural architecture and the kinds of things we learn in our lives let us do. But then there's this whole layer of kind of formalization that got developed in which is you know the kind of whole sort of story of intellectual history and whole kind of depth of learning that formalization turned into things like logic, mathematics, science and so on, and that's the kind of thing that allows one to kind of build these towers of of of sort of towers of things you work out. It's not just I can immediately figure this out. It's no I can use this kind of formalism to go step by step and work out something which was not immediately obvious to me, and that's kind of the story of what what we're trying to do computationally is to be able to build those kind of tall towers of what implies what implies what and so on, and as opposed to kind of the yes I can immediately figure it out. It's just like what I saw somewhere else in something that I heard or remembered or something like this. What can you say about the kind of formal structure, the kind of formal foundation you can build such a formal structure on, about the kinds of things you would start on in order to build this kind of deep computable knowledge trees. So the question is sort of how do you how do you think about computation, and there's there's a couple of points here. One is what computation intrinsically is like, and the other is what aspects of computation we humans with our minds and with the kinds of things we've learned can sort of relate to in that computational universe. So if we start on the kind of what can computation be like, it's something I've spent some big chunk of my life studying. Is imagine that you're you know we we usually write programs where we kind of know what we want the program to do and we carefully write you know many lines of code and we hope that the program does what we what we intended it to do. But the thing I've been interested in is if you just look at the kind of natural science of programs. So you just say I'm going to make this program it's a really tiny program maybe I even pick the pieces of the program at random but it's really tiny and by really tiny I mean you know less than a line of code type thing. You say what does this program do and you run it and big discovery that I made in the early 80s is that even extremely simple programs when you run them can do really complicated things. Really surprised me it took me several years to kind of realize that that was a thing so to speak, but that that realization that even very simple programs can do incredibly complicated things that we very much don't expect. That discovery I mean I realized that that's very much I think how nature works that is nature has simple rules but yet does all sorts of complicated things that we might not expect. You know as big thing of the last few years has been understanding that that's how the whole universe and physics works, but that's a quite separate topic. But so there's this whole world of programs and what they do and very rich sophisticated things that these programs can do. But when we look at many of these programs, we look at them and say well that's kind of I don't really know what that's doing. It's not a very human kind of thing. So on the one hand we have sort of what's possible in the computational universe, on the other hand we have the kinds of things that we humans think about the kinds of things that have developed in kind of our intellectual history, and that's and really the challenge to sort of making things computational is to connect what's computationally possible out in the computational universe with the things that we humans sort of typically think about with our minds. Now that's a complicated kind of moving target because the things that we think about change over time. We've learned more stuff. We've invented mathematics. We've invented various kinds of ideas and structures and so on. So it's it's gradually expanding. We're kind of gradually colonizing more and more of this kind of intellectual space of possibilities. But the the real thing the real challenge is how do you take what is computationally possible. How do you take how do you encapsulate the kinds of things that we think about in a way that kind of plugs in to what's computationally possible, and and actually the the the big sort of idea there is this idea of kind of symbolic programming symbolic representations of things, and so the question is when you look at sort of everything in the world and you kind of you know you take some visual scene or something looking at, and you say well how do I turn that into something that I can kind of stuff into my mind. You know there are lots of pixels in my visual scene but the things that I remembered from that visual scene are you know there's a there's a chair in this place. It's a kind of a symbolic representation of the visual scene. There are two chairs on a table or something rather than there are all these pixels arranged in all these detailed ways. And so the question then is how do you take sort of all the all the things in the world and make some kind of representation that corresponds to the types of ways that we think about things and human language is is sort of one form of representation that we have. We talk about chairs that's a word in human language and so on. How do we how do we take but human language is not in and of itself something from that plugs in very well to sort of computation. It's not something from which you can immediately compute consequences and so on, and so you have to kind of find a way to take sort of the the the stuff we understand from human language and make it more precise, and that's really this story of symbolic programming and you know what what that turns into is something which I didn't know at the time it was going to work as well as it has, but back in the 1979 or so I was trying to build my first big computer system and trying to figure out you know how should I represent computations at a high level, and I kind of invented this idea of using kind of symbolic expressions you know structured as it's kind of like a a function and a bunch of arguments, but that function doesn't necessarily evaluate to anything. It's just a a thing that sits there representing a structure, and so building up that structure and it's turned out that structure has been extremely it's it's a good match for the way that we humans it seems to be a good match for the way that we humans kind of conceptualize higher level things, and it's been for the last I don't know forty five years or something, it's served me remarkably well. So building up that structure using this kind of symbolic representation, but what can you say about abstractions here because you could just start with your physics project you could start at a hypergraph at a very very low level and build up everything from there but you don't you take shortcuts, right? You take the highest level of abstraction, convert that, the kind of abstraction that's convertible into something computable using symbolic representation, and then that's your new foundation for that little piece of knowledge. Somehow all that is integrated, right? So the sort of a very important phenomenon that that is kind of a thing that I've sort of realized is just it's one of these things that sort of in the in the future of kind of everything is going to become more and more important is this phenomenon of computational irreducibility, and the the question is if you know the rules for something you have a program you're going to run it. You might say I know the rules, great I know everything about what's going to happen. Well, in principle you do because you can just run those rules out and just see what they do. You might run them a million steps, you see what happens, et cetera. The question is can you like immediately jump ahead and say I know what's going to happen after a million steps, and the answer is 13 or something. Yes, and the the one of the very critical things to realize is if you could reduce that computation, there is in a sense no point in doing the computation. The place where you really get value out of doing a computation is when you had to do the computation to find out the answer, but this phenomenon that you have to do the computation to find out the answer this phenomenon of computational irreducibility seems to be tremendously important for thinking about lots of kinds of things. So one of the things that happens is okay you've got a model of the universe at the low level in terms of atoms of space and hypergraphs and rewriting hypergraphs and so on, and it's happening you know 10 to the 100 times every second let's say. Well you say great then we've we've nailed it we we know how the universe works. Well the problem is the universe can figure out what it's going to do. It does those 10 to the 100 you know steps, but for us to work out what it's going to do we have no way to reduce that computation. The only way to do the computation to see the result of the computation is to do it, and if we're operating within the universe we're kind of there's no there's no opportunity to do that because the universe is doing it as fast as the universe can do it, and that's you know that's what's happening. So what we're trying to do and a lot of the story of science and a lot of other kinds of things is finding pockets of reducibility. That is you could have a situation where everything in the world is full of computational irreducibility. We never know what's going to happen next. The only way we can figure out what's going to happen next is just let the system run and see what happens. So in a sense the story of of most kinds of science inventions a lot of kinds of things is the story of finding these places where we can locally jump ahead, and one of the features of computational irreducibility is there are always pockets of reducibility. There are always. Places there are always an infinite number of places where you can jump ahead. There is no way where you can jump completely ahead, but there are little little patches, little places where you can jump ahead a bit. And I think you know we can talk about physics project and so on, but I think the thing we realize is we kind of exist in a slice of all the possible computational irreducibility in the universe. We exist in a slice where there is a reasonable amount of predictability, and in a sense as we try and construct these kind of higher levels of of abstraction symbolic representations and so on. What we're doing is we're finding these lumps of reducibility that we can kind of attach ourselves to and about which we can kind of have fairly simple narrative things to say. Because in principle you know I say what's going to happen in the next few seconds you know oh there are these molecules moving around in the air in this room and oh gosh it's an incredibly complicated story and that's a whole computationally reducible thing most of which I don't care about and most of it is well you know the air is still going to be here and nothing much is going to be different about it and that's a kind of reducible fact about what is ultimately at an underlying level of computational irreducible process. And life would not be possible if we didn't have a large number of such reducible pockets. Yes, pockets amenable to reduction into something symbolic. Yes, I think so. I mean life in in the way that we experience it, that I mean you know one might you know depending on what we mean by life so to speak the the experience that we have of sort of consistent things happening in the world the idea of space for example where there's you know we can just say you're here you move there it's kind of the same thing it's still you in that different place even though you're made of different atoms of space and so on. This is this idea that it's that there's sort of this level of predictability of what's going on that's us finding a slice of reducibility in what is underneath this computationally reducible kind of system and I think that's that sort of the thing which is actually my favorite discovery of the last few years is the realization that it is sort of the interaction between this sort of underlying computational irreducibility and our nature as kind of observers who sort of have to key into computational reducibility. That fact leads to the main laws of physics that we discovered in the twentieth century. So this is we talk about this in in more detail but this is a to me it's kind of our nature as observers the fact that we are computationally bounded observers we don't get to follow all those little pieces of computational irreducibility to stuff what is about out there in the world into our minds. Requires that we are looking at things that are reducible we are compressing kind of we're extracting just some essence some kind of symbolic essence of what's the detail of what's going on in the world that together with one other condition that at first seems sort of trivial but isn't which is that we believe we are persistent in time. That is yes you know so so that's the causality. Here's the thing at every moment according to our theory we're made of different atoms of space at every moment sort of the microscopic detail of what what the universe is made of is being rewritten and that's and in fact the very fact that there's coherence between different parts of space is a consequence of the fact that there are all these little processes going on that kind of knit together the structure of space. It's kind of like if you wanted to have a fluid with a bunch of molecules in it if those molecules weren't interacting you wouldn't have this fluid that would pour and do all these kinds of things it would just be sort of a free floating collection of molecules. So similarly it is with space that the fact that space is kind of knitted together is a consequence of all this activity in space and the fact that kind of what we consist of sort of this this series of of you know we're continually being rewritten. And the question is why is it the case that we think of ourselves as being the same us through time that's kind of a key assumption I think it's a key aspect of what we see as sort of our consciousness so to speak is that we have this kind of consistent thread of experience. Well isn't that just another limitation of our mind that we want to reduce reality into some that kind of temporal consistency is just a nice narrative to tell ourselves. Well the fact is I think it's critical to the way we humans typically operate is that we have a single thread of experience you know if you if you imagine sort of a mind where you have you know maybe that's what's happening in various kinds of minds that aren't working the same way other minds work is that you're splitting into multiple threads of experience. It's also it's also something where you know when you look at I don't know quantum mechanics for example in the insides of quantum mechanics it's splitting into many threads of experience but in order for us humans to interact with it you kind of have to have to knit all those different threads together so that we say oh yeah definite thing happened and now the next definite thing happens and so on. And I think you know sort of inside it it's it's sort of interesting to try and imagine what's it like to have kind of these fundamentally multiple threads of experience going on. I mean right now different human minds have different threads of experience we just have a bunch of minds that are interacting with each other but we don't have a you know within each mind there's a single thread and that's a that is indeed a simplification. I think it's a it's a thing you know the general computational system does not have that simplification and it's one of the things you know I people often seem to think that you know consciousness is the highest level of kind of things that can happen in the universe so to speak. But I think that's not true I think it's actually a a specialization in which among other things you have this idea of a single thread of experience which is not a general feature of anything that could kind of computationally happen in the universe. So it's a feature of a computationally limited system that's only able to observe reducible pockets. So so I mean this word observer it means something in quantum mechanics it means something in a lot of places it means something to us humans as conscious beings. So what what's the importance of the observer what is the observer and what's the importance of the observer in the computational universe. So this question of what is an observer what's the general idea of an observer is actually one of my next projects which got somewhat derailed by the the current sort of AI mania but is there a connection there or is that do you do you think the observer is primarily a physics phenomenon. Is it related to the whole AI thing yes yes it is related so one question is what is a general observer so you know we know we have an idea what is a general computational system we think about Turing machines we think about other models of computation. There's a question what is a general model of an observer and there's kind of observers like us which is kind of the observers we're interested in you know we could imagine an alien observer that deals with computational irreducibility and it has a mind that's utterly different from ours and and completely incoherent with what what we're like. But the fact is that that you know if we are talking about observers like us that one of the key things is this idea of kind of taking all the detail of the world and being able to stuff it into a mind being able to take all the detail and kind of you know extract out of it a smaller set of of kind of degrees of freedom a smaller number of elements that will sort of fit in our minds. And I think this this question so I've been interested in trying to characterize what is the general observer and the general observer is I think in part there are many let me give an example of a you know you have a gas it's got a bunch of molecules bouncing around and the thing you're measuring about the gas is its pressure. And the only thing you as an observer care about is pressure and that means you have a piston on the side of this box and the piston is being pushed by the gas and there are many many different ways that molecules can hit that piston but all that matters is the kind of aggregate of all those molecular impacts because that's what determines pressure. So there's a huge number of different configurations of the gas which are all equivalent. So I think one key aspect of observers is this equilibrating of many different configurations of a system saying all I care about is this aggregate feature all I care about is this this overall thing and that's that sort of one one aspect and we see that in lots of different again it's the same story over and over again that there's there's a lot of detail in the world but what we are extracting from it is something a sort of a thin a thin summary of that of that detail. Is that thin summary nevertheless true is can it be a crappy approximation that on average is is correct I mean if we look at the observer that's the human mind it seems like there's a lot of very as represented by natural language for example there's a lot of really crappy approximation. Sure and that could be maybe a feature of it. Well there's ambiguity. Right right you don't know you know it could be the case you're just measuring the aggregate impact of these molecules but there is some tiny tiny probability that the molecules will arrange themselves in some really funky way and that just measuring that average isn't going to be the main point. By the way an awful lot of science is very confused about this because you know you look at you look at papers and people are really keen they draw this curve and they have these you know these bars on the curve and things. It's just this curve and it's this one thing and it's supposed to represent some system that has all kinds of details in it and this is a way that lots of science has gotten wrong because people say I remember years ago I was studying snowflake growth. You know you have a snowflake and it's growing it has all these arms it's doing complicated things but there was a literature on this stuff and it talked about you know what's the rate of snowflake growth and you know it it got pretty good answers for the rate of the growth of the snowflake and then I looked at it more carefully and and they had these nice curves of you know snowflake growth rates and so on. I looked at it more carefully and I realized according to their models the snowflake will be spherical and so they got the growth rate right but the detail was just utterly wrong and you know not only the detail the the whole thing was was not capturing you know it was capturing this aspect of the system that was in a sense missing the main point of what was going on and what is the geometric shape of a snowflake. Snowflakes start in in the phase of water that's relevant to formation of snowflakes it's a phase of ice which starts with a hexagonal arrangement of of water molecules and so it starts off growing as a hexagonal plate and then what happens is it's a plate oh oh versus sphere sphere well no no but it's it's much more than that. I mean snowflakes are fluffy you know typical snowflakes have little little dendritic arms. Okay yeah and what actually happens is it's kind of kind of cool because you can make these very simple discrete models with cellular automata and things that that figure this out. You start off with this you know hexagonal thing and then the places it it starts to grow little arms and every time a little piece of ice adds itself to the snowflake. The fact that that ice condensed from the water vapor heats the snowflake up locally and so it makes it less likely for for another piece of ice to accumulate right nearby. This leads to a kind of growth inhibition so you grow an arm and it is a a separated arm because right around the arm it got a little bit hot and it didn't add more ice there. So what happens is it grows you have a hexagon it grows out arms the arms grow arms and then the arms grow arms grow arms and eventually actually it's kind of cool because it it actually fills in another hexagon a bigger hexagon and when I first looked at this you had a very simple model for this I realized you know when it fills in that hexagon it actually leaves some holes behind. So I thought well you know is that really right so I look at these pictures of snowflakes and sure enough they have these little holes in them that are kind of scars of the way that these arms grow out. So you can't fill in backfill holes. They don't backfill and presumably there's a limitation on how big like you can't arbitrarily grow. I'm not sure I mean the thing falls through the I mean I think it does you know it hits the ground at some point. I think you can grow I think you can grow in the lab I think you can grow pretty big ones I think you can grow many many iterations of this kind of goes from hexagon it grows out arms it turns back it fills back into a hexagon it grows more arms again in 3D. No it's flat usually. Why is it flat why doesn't it span out? Okay okay wait a minute you said it's fluffy and fluffy is a three dimensional property no or no it's it's fluffy snow is okay so you know what makes we're really we're really in a in a detail but but as multiple snowflakes become fluffy a single snowflake is not fluffy. No no a single snowflake is fluffy and what happens is you know if if you have snow that it's just pure hexagons they they can you know they they fit together pretty well it's not it doesn't it doesn't make it doesn't have a lot of air in it and they can also slide against each other pretty easily and so the snow can be pretty you know can I think avalanches happen sometimes when when the things tend to be these you know hexagonal plates and it kind of slides but then when the thing has all these arms that have grown out it's not they don't fit together very well and that's why the snow has lots of air in it and if you look at one of these snowflakes you know if you catch one you'll see it has little arms and people actually people often say you know no two snowflakes are alike. That's mostly because as a snowflake grows they do grow pretty consistently with these different arms and so on but you capture them at different times as they you know they fell through through the air in a different way you'll catch this one at this stage and as it goes through different stages they look really different and so that's why you know kind of looks like no two snowflakes are alike because you caught them at different a different time. So the rules under which they grow are the same it's just the timing is. Yes okay so the point is science is not able to describe the full complexity of snowflake growth. Well science if you if you do what people might often do which is say okay let's make it scientific let's turn into one number and that one number is kind of the growth rate of the arms or some such other thing that fails to capture sort of the detail of what's going on inside the system and that's in a sense a big challenge for science is how do you extract from the natural world for example those aspects of it that you are interested in talking about. Now you might just say I don't really care about the fluffiness of the snowflakes all I care about is the growth rate of the arms in which case you know you have you can have a good model without knowing anything about the fluffiness. But the fact is as a practical you know if you if you say what's the what is the most obvious feature of a snowflake oh that it has this complicated shape. Well then you've got a different story about what you model I mean this is one of the features of of sort of modeling in science that you know what is a model a model is some way of reducing the actuality of the world to something where you can readily sort of give a narrative for what's happening or you can basically make some kind of abstraction of what's happening and answer questions that you care about answering. If you wanted to answer all possible questions about the system you'd have to have the whole system because you might care about this particular molecule where did it go and you know your model which is some big abstraction of that has nothing to say about that. So you know one of the things that's that's often confusing in science is people will have I've got a model somebody says somebody else will say I don't believe in your model because it doesn't capture the feature of the system that I care about. You know there's always this controversy about you know is is it a correct model well no model is except for the actual system itself is a correct model in the sense that it captures everything. Questions does it capture what you care about capturing sometimes that's ultimately defined by what you're going to build technology out of things like this. The one counter example to this is if you think you're modeling the whole universe all the way down then there is a notion of a correct model but even that is more complicated because it depends on kind of how observers sample things and so on that's a that's a separate story but at least at the first level to say you know this thing about oh it's an approximation you're capturing one aspect you're not capturing other aspects. When you really think you have a complete model for the whole universe you better be capturing ultimately everything even though to actually run that model is impossible because of computational irreducibility. The only the only thing that successfully runs that model is the actual running of the universe. Is the universe itself but okay so what you care about is an interesting concept so that's a that's a human concept so that's what you're doing with Wolfram Alpha and Wolfram Language is you're trying to come up with symbolic representations. Yes as simple as possible. So a model that's as simple as possible that fully captures stuff we care about. Yes so I mean for example you know we could we'll have a thing about you know data about movies let's say we could be describing every individual pixel in every movie and so on but that's not the level that people care about and it's yes this is a I mean and and that level that people care about is somewhat related to what's described in natural language. But what what we're trying to do is to find a way to sort of represent precisely so you can compute things. See one thing we say you give a piece of natural language question is you feed it to a computer you say does the computer understand this natural language. Well you know the computer processes it in some way it does this maybe it can make a continuation of the natural language you know maybe it can go on from the prompt and say what it's going to say you say does it really understand it. Hard to know but for in this kind of computational world there is a very definite definition of does it understand. Which is could it be turned into this symbolic computational thing from which you can compute all kinds of consequences and that's the that's the sense in which one has sort of a target for the understanding of natural language and that's kind of our goal is to have as much as possible about the world that can be computed in a in a reasonable way so to speak. Be able to be sort of captured by this kind of computational language that's that's kind of the goal and and I think for us humans the the main thing that's important is as we formalize what we're talking about it gives us a way of kind of building a structure where we can sort of build this tower of consequences of things. So if we're just saying well let's talk about it in natural language it doesn't really give us some hard foundation that lets us you know build step by step to work something out

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