'Unchangeable fact' is correct and usable in written English.
It may be used to emphasize the fact that something is definite and cannot be changed. For example, "The law of gravity is an unchangeable fact."
To those who lived behind it, the Berlin Wall had become something almost like the Alps, a seemingly unchangeable fact of physical geography.
That's perhaps the one unchangeable fact about life in your twenties, and it's what ties Friends straight to Broad City: the only show to have pulled the trick off since.
It would also make devices far easier for cyber-criminals to hack and still be ineffective for surveillance.Regardless of the ideological merits of giving authorities access to private communications, it is an unchangeable fact that with modern encryption technology and a bit of forethought a malevolent person can send communications to his collaborators that no carrier or government can see.
Now, with unemployment nearly five times higher than two decades ago, the mood (if not the rhetoric) is oddly more relaxed, as though lack of work were an unchangeable fact of life, like an eclipse of the sun.Not only is there no violence to speak of.
That is an unchangeable fact of life.
But the fundamental and most vicious, swinish, murderous, and unchangeable fact is that we totally misunderstand each other... we operate on alien wavelengths.
But there are unchangeable facts about Vaughn.
Maybe you know one of us — the real ones, bound to allegiance by unchangeable facts of history (which is precisely how you would expect someone to say, "I went to Duke").
She was the same person she had been at six or sixteen, unchanged and unchangeable.
Essentialist meaning a view that detects an unchanging, and unchangeable, essence or identity.
Aristotle's De Caelo added that something is eternally unchanged only if unchangeable.
