Why do all languages share the same intonation for questions?
I could be wrong here, but it seems to me that a common aspect amongst all languages is the tendency to raise the pitch of your voice slightly when asking a question. Especially at the end of a question sentence.
If I'm wrong about this raised pitch being common amongst all languages, at the very least do all languages change their tone slightly to indicate that a question is being asked?
I guess there needs to be some way to indicate what is and isn't a question. Perhaps a higher pitched voice reflects uncertainty. Is this something deep rooted in humans, or just an arbitrary choice when language developed?
"Rhetorical" questions - like this one - are specially interesting because, while they follow the syntax of a genuine question, they're pragmatically assertions. You're implying "this is not true", even if you're phrasing it as a question.
And that phrasal pitch contour that you see in yes/no questions is dictated by the pragmatical purpose of the utterance, so if the "question" is not actually a question, it doesn't get it.
Russian does, because the rising intonation is the only thing that differentiates a statement from a question in many cases. Eg "You a good driver." Vs "You a good driver?" Both are grammatically correct, and only the intonation makes it a question.
Vietnamese doesn't really rise at the end of the question unless that's the way the last word is anyway. Some questions end with a low sound. Some questions are evident by a small word cluster (sounds like "Fai La") after the subject but before the object that basically mean "this is a question and not a statement." Or "I'm asking not telling"
I was expecting Mandarin to be an exception, since the language uses pitch to encode different words; apparently it isn't, the speakers simply "abstract" the phonemic vs. phrasal pitch variations as two different things, when interpreting the sentence. Check figure 6.
And while there is a particle overtly conveying "this is a question", ⟨吗⟩ /ma⁰/ (the "0" indicates neutral tone), it seems that you can couple it with an assertive phrasal pitch to convey rhetorical questions. And other languages (like e.g. German and English, that overtly mark questions with verb fronting) show a similar pattern.
I also found some literature claiming that it might be cross-linguistically consistent
The most important observations are the following:
pitch tends to decline from the beginning of an IP [intonational phrase] to the end, a tendency known as declination;
the beginning of an IP may be marked by a local sharp rise in pitch or “reset”;
in IPs that are utterance-final and/or in statements, there may be a local drop in pitch at the end of the IP in addition to any overall declination spanning the IP as a whole;
in IPs that are in questions and/or are not utterance-final, declination may be moderated, suspended or even reversed, i.e. the overall trend may be less steeply declining, level, or even slightly rising;
in addition to exhibiting reduced declination, non-final and interrogative IPs may also have a local rise in pitch at the end, or at least have no local
drop.
The validity of these observations, as general tendencies, is not in doubt.
The article also lays out some potential explanations for this. The basic gist of it is, nobody knows why but everyone has a guess.
EDIT: as another user (ABCDE) correctly pointed out, keep in mind that this works differently for open-ended vs. yes/no questions.
That’s just a coincidence. 吗, meaning “what?”, is pronounced má which has the ascending tone. This is not true of all questions in Chinese. For example: 谁在你的右边 meaning “who is on your right?” does not end with 吗, and 边 is pronounced bian which has the flat tone.
"How are you?" Is "you're good, no?" But the word "no" does not have a rising tone.
Tonal languages are hard for non-tonal language speakers to pick up because of this. On the flip side, it can be tough for tonal language speakers to grasp the tonal inflections in English, and sometimes speak like robots before they understand how to use them.
As I checked from an article, at least in Mandarin the usage of particles happens alongside the change in intonation, not at the expense of it.
Also note that even [some? all?] Germanic languages show something similar - but instead of a particle, you get a syntactical movement (verb fronting) overtly marking the question. Examples:
English
German
This is an apple.
Das ist ein Apfel.
Is this an apple?
Ist das ein Apfel?
The cat meows.
Die Katze miaut.
Does the cat meow?
Miaut die Katze?
In English this is slightly obscured by do-support being obligatory for most verbs, but note how it's the same process - if you were to insert the "do" without a question, in the third sentence, it would end as "the cat does meow".
Semi-related question since people have shown counterexample for OP's question: Are there English sentences where the tone goes up at the end, but is not a question? It feels like that particular tone is exclusive for questions.
That's a sexist stereotype, but it's true for anyone feeling really unsure about their statement. You don't even have to change the note at the end of the sentence. Could just trail off... or add a whole new half sentence like "thoughts? "
Your second question has a general answer. Most languages use tones, which means tones change in the course of a sentence. If the tone changes for all sentences, then it also changes for questions. I know that's not what you were trying to ask, but that's the answer to the question you did ask.
If you need a way to indicate that something is a question, you could do what English does... You could use question words at the beginning of the sentence. You could change word order. You could add extra words... Which is to say, you're not dependent on intonation, though you could use it if you want to.