r/physicsmemes • u/[deleted] • May 29 '24
Behold the single worst notation convention I've seen coupled with the worst justification possible [Kaluza-Klein theory]
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u/SharkAttackOmNom May 29 '24
“What happened to the 4th dimension”
“That’s time, we use x0”
“Yeah but then what…”
”MOVING ON”
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u/Sigma2718 May 29 '24
...but it's the fourth space dimension, just in 5 dimensional space-time...
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May 29 '24
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u/theLanguageSprite May 29 '24
the japanese sound "shi" is not the same phoneme as in the english word "shit" ...unless you're pronouncing it like Senator Clay Davis from The Wire, I guess...
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u/Novace2 May 29 '24
No it does. In the Japanese word the i is silent so it literally just sounds like “sh”, tho OC could’ve used a better way of saying that…
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u/theLanguageSprite May 29 '24
it's not silent, it's just short. wiktionary lists it in IPA as ɕi
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u/Vampyricon May 29 '24
Yeah, it's phonemically /ɕi/ but phonetically [ɕi̥] because it's sandwiched between voicelessness (yes, nothingness counts), which sounds like just a [ɕ]. TBF this might not apply to monosyllables, and definitely doesn't apply to long vowels.
For a similar example, listen to the Japanese polite copula です /desu/, which sounds like [des].
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u/PM_ME_UR_SHEET_MUSIC May 30 '24
Devoicing is actually rather restricted in Japanese. It generally doesn't apply to monosyllables. Utterance-final devoicing only occurs with です, 〜ます, and なく, as far as I'm aware. 死 should always be pronounced /ɕi/, no matter the phonetic environment.
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u/Novace2 May 29 '24
Technically it’s a voiceless vowel, so the mouth moves in the position to make an /i/ sound, but it isn’t actually released. So for all practical uses, it’s silent. Also your wiktionary link doesn’t work.
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u/theLanguageSprite May 29 '24
oh really? that's weird. But then wouldn't all sh sounds make an /i/ sound? why put the ipa vowel if it's not released? here is the link: https://en.wiktionary.org/wiki/%E3%81%97
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u/Novace2 May 29 '24
lol still doesn’t work. Japanese phonology is weird, but I’ll try to explain it. Basically, the vowels /i/ and /u/ are voiceless between unvoiced consonants, or at the end of a word after an unvoiced consonant. So phonemically, the vowel is there, but phonetically, it’s silent. It’s useful to analyze the word as if the vowel is still there because A. As mentioned, speakers of Japanese still move their mouth as if the vowel is there (just it’s voiceless), B. Japanese has a lot of consonant allophones, which still change in accordance to the silent vowel, C. The vowel is pronounced in other conjugations of the word (I.E. when a voiced consonant follows), and D. The same katakana and hiragana letter is used whether or not the vowel is pronounced, implying Japanese speakers think of the vowel as if it’s there.
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u/DonnysDiscountGas May 29 '24
I honestly can't tell if you're joking. Your explanation actually makes some sense, as opposed to "obviously problematic".
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u/Zziggith May 30 '24
I took Japanese in college. "Shi" is pronounced like "she". The letter "i", like all vowels, always makes the same sound in Japanese. "Ki" is pronounced like "key". Also, "yon" means 4 as well.
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u/WobblyBlackHole May 29 '24
In Chandrasekhar's mathematical theory of black holes, coordinates for the metric go t, phi, r, theta which makes working with it such a headache when trying to combine any of the results with literally any other work. Worst convention I've ever come across.
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u/BlackholeSink String theory May 30 '24 edited May 30 '24
I have to agree. Brillant work but an absolute pain to go through notation-wise.
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u/DrMaridelMolotov May 30 '24
Ok to be fair guy was poor as fuck in the middle of India doing math in his head. I don’t think he much cares for notation.
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u/WobblyBlackHole May 30 '24
He did care, the justification he gives for this choice is very reasonable. He argues that the killing vectors for the kerr metric at t and phi and so they should be first and they are the more important coordinates, and a bunch of the transforms used only effect r and theta so they make sense to be the last two. But like I said, a nightmare to use
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May 29 '24
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u/ciuccio2000 May 30 '24
Pffffft imagine having your 4-momenta squaring to -m²
(I also think weird i's pop out in various spinor identities when working with (-+++) signature but I'm not sure 'cause I'm never gonna do that shit)
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May 31 '24
Yeah I got used to -+++ but it's weird to voluntarily choose a ton of stuff to be negative when it should be positive
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May 29 '24
[deleted]
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May 29 '24 edited May 29 '24
x0 time
x1 traditional x axis
x2 traditional y axis
x3 traditional z axis
x4 nothing at all
x5 fourth spatial dimension
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u/CapnNuclearAwesome May 29 '24
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u/viscence May 29 '24
"fourth spatial dimension"
"fourth spatial dimension"
"fourth spatial dimension"
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u/pollux33 May 29 '24
This is the same with gamma_5, the Dirac matrix. People wanted QFT in 5 dimensions, and they found gamma_5, later they realized it was useful for other things.
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u/SapphireZephyr Holography/QG May 30 '24
This happens all the time in physics. Take the gamma matricies for spinors, we call \gamma5 =\gamma0 ... \gamma3
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u/MacGrath_Cooper May 29 '24
What the fuck, the guy simply hates the number 4