Ask HN: Ideas/problems that are hi-tech in nature and hard to implement.

From last few years I have been doing many interesting projects that aimed to solve some real world problems but they were mostly not too technical in nature(mostly web application involving db or simple mobile apps).

Now, I am craving to write some code that solves some technologically difficult problem(but still worth solving).

Do you have any such ideas? Do you have any such technological problems with no solution available at this moment?