Hm. It is Ok. Well, if you mean "physics is what everybody needs". If you mean it the other way round, probably a change of intonation would be required.
So "физика всем нужна" would mean that everyone needs physics, possibly in addition to other things, but "всем нужна физика" would imply that what everyone needs is physics and not something else? Which is a theoretically possible but quite odd interpretation of the English sentence.
Yeah, it is like "I know what you need!" sentence. Физика всем нужна / Физика нужна всем is a more neutral sentence, suggesting that physics is among the essential things (for all people or for some group you are discussing).
If "наш учитель говорит, что всем нужна физика" is not acceptable, why the sentence is not "Our teacher says that Physics is needed for everybody"? How should I find out the word order change?