He was using some fancier and older form of English. I believe it is grammatically correct, we just don't use those forms anymore. The first translation of the Gita is from 1785 and it is one of the most translated Asian texts. Famously, every translator places emphasis and projects their own personal worldview unto the text. Though Oppenheimer actually could read and had read the Bhagavad Gita in its original Sanskrit, so he was just giving it his own personal twist.

The original line comes from Chapter 11 Verse 32 of the Bhagavad Gita.

कालोऽस्मि लोकक्षयकृत्प्रवृद्धो

(kālo ’smi loka-kṣhaya-kṛit pravṛiddho)

The most literal translation would be: "I am mighty Time, the source of destruction of the worlds." But काल can alternatively mean Death, and it looks like that's the interpretation Oppenheimer chose. The verb here is a simple "am", as in "I am Time/Death". So the "am become" part is not due to any feature of Sanskrit itself.

But people usually take some liberty while translating poetry. Given the context (i.e. Krishna convincing Arjuna to fight, and showing him his true form), it makes sense to use "I have become" or even "I am become" (as explained in the other comments, it's grammatically correct).

It's from English, not Sanskrit. More specifically, an archaic English feature, where you'd use "be" instead of "have" for the present tense, if the main verb denotes a change of state (such as "become"). Note how "I have become Death" sounds perfectly fine for modern readers.

Odds are that Oppenheimer was quoting either an archaic translation Bhagavad Gita, or one using archaic language (this is typical for religious texts).

Also give this a check. English used to follow similar rules for be/have as German does for sein/haben.

[Shameless community promotion: check !linguistics@lemmy.ml ! This sort of question would fit like a glove there.]

Am/is become is an old English biblical phrasing and the material he was translating is religious so he probably used that style to invoke the religious nature of the text. He was very well read so this was certainly a specific stylistic choice on his part.

I was curious about this last week and found an article that provides some other examples of this type of usage:

"The translation’s grammatical archaism made it even more powerful, resonating with lines in Tennyson (“I am become a name, for always roaming with a hungry heart”), Shakespeare (“I am come to know your pleasure”), and the Bible (“I am come a light into the world, that whosoever believeth on me should not abide in darkness”)."

https://www.openculture.com/2023/07/j-robert-oppenheimer-recites-the-line-now-i-am-become-death-the-destroyer-of-worlds.html

The article also provides some commentary from a scholar about how to translate the original Sanskrit that Oppenheimer is referencing.

Edit: This article is referenced in the above article, and provides some interesting insight into why Oppenheimer was thinking of this quote. His situation was very similar to the situation of Arjuna, who speaks the original phrase in the ancient story. It really gives some additional insight into how many different mental levels Oppenheimer must have been able to conceptualize.

https://m.economictimes.com/news/science/of-oppenheimer-and-the-bhagwat-gita-lead-correcting-intro-april-22-is-the-113th-birth-anniversary-of-robert-oppenheimer/articleshow/58315807.cms?from=mdr

He used archaic form of English instead of contemporary, possibly for the sake of dramatic effect.

Imagine that it's part of a longer monologue filled with "thou"s, "betwixt"s, "harken"s and you're on the right track.

There's a discussion here:

https://english.stackexchange.com/questions/3402/is-it-acceptable-to-use-is-become-instead-of-has-become

Old English from a millennia ago sounds like a foreign language, even early modern English from Shakespeare's time sounds pretty odd. So it depends on when the translation was done. With English it's common for newly invented words to get popularized and end up in the dictionary. The same kind of thing happens with grammar. Conversely people still sometimes use obsolete words from early modern English as a way to emphasize a statement.

The grammar of that quote may be due to the English translation of the time or something he simply interpreted in his own way. It sounds grammatically off for contemporary English, but that's relative to the time frame. I imagine the English we speak today may sound odd to someone a few hundred years from now.

Only tangentially related: Latin, the dead language, heavily tied into romantic, classical education. I recently found out that Latin in general wouldn't say, I did this, but instead, this was done. Less of an emphasis on individual agency. Fascinating aspects about linguistics, how thought, sense of self has evolved over millenia.

I have not sure. I am become a suspicion it's from Old English (the malt liquor, not the language).

Students of French will recognize the use of the verb "to be" along with verbs such as "come" or "become". As others have mentioned, we changed this in English, but it remains so in other languages.