For nearly 20 years, physicists have known that the expansion of the universe has begun to speed up. An unproven hypothesis. Twenty years before that, they KNEW that the universe was collapsing.
We cannot see to the 'end' of the Universe, and do not even know if there is an 'end'. We cannot detect that which we have not , and never will see.
All discussions that physicists make about the universe take as a given that they are discussing the observable universe, not the universe as a whole. Just because they don't bother to restate that every time doesn't mean it isn't taken into account.