Answer:
The sun is a star
Steps:
The pound is not a finish
Replace one word with an antonym of itself.
The pound is not a start
Remove one letter from one word.
The pound is not a star
Remove one word.
The pound is a star
Change one letter for another letter.
The sound is a star
Remove two letters from one word.
The sun is a star
How I got there:
The antonym is obviously the critical step. If it had to be applied after some of the other steps, the puzzle would have been more difficult. But giving it a shot on the initial sentence, "finish" -> "start" was the obvious candidate, then "scientific fact" suggests "star", making the rest easy.