Hi all.

As I know 'what in the world' is an idiom. Am I right?

So, can you guys tell me what does it mean? First off give me some examples, please and then tell me when should I use it in my speaking?

In the meantime, does 'what on earth' have the same meaning of 'what in the world '?

Thank you.

Jeff.
I'm quite sure that what on Earth and what in the world are synonyms, you can use both of them and the meaning will be the same.

I think you use those idioms to intensify. For instance....you're telling your child to prepare a meal and he/she does it all wrong and in order to underline how astonished/disappointed/surprised you are you will say: What on Earth/in the woeld have you done!!!! instead of just What have you done.

It's stronger, that's all Emotion: smile

^_^
Emotion: it wasnt me woRld*
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Question words (what, who, where, how, etc.) can be intensified by

in the world, on earth, the heck, and several other vulgar expressions as well.

(You can add in tarnation as well. tarnation is a very old-fashioned word. It's a corruption of damnation.*)

They all communicate the same basic idea, namely, that the speaker is experiencing some strong emotion about the question.

What in the world do you think you're doing? (to someone doing something that is irritating the speaker)

How on earth are we going to get this piano up to the tenth floor? (a very frustrating problem without an obvious solution)

Where the heck did you put the scissors? (I need them immediately, and they are not where they should be.)

CJ

*Mark Twain uses "in the nation". Here a few examples from Huckleberry Finn:

How in the nation did they ever git into such a scrape?

What in the nation do they call it the mumps for?

How in the nation are these fellows going to be ransomed?

CJ