A planet of inherent contradictions, whose very existence was theoretically impossible.

Cleverly designed, they would be very difficult, if not theoretically impossible, to detect.

If we accept this theory, the emergence of speech becomes theoretically impossible.

Those who think it is theoretically impossible and would not believe it no matter what they saw.

"As an engineer, you don't try anything that's theoretically impossible."

My ideas are not theoretically impossible in their opinion - only wrong.

Oddly enough, those are two items you mentioned as being theoretically impossible.

"Isn't it theoretically impossible for a giant star to have a planetary system?"

To salivate over something you've never tasted is theoretically impossible.

It is theoretically impossible for a real system to perform better than ideal.