Why are some people so adamant intelligent life on Earth is unique, even though the universe is so vast?
It puts a bit of a dent in their narcissism, I guess. Narcissism and monotheism go hand in hand after all.
I suppose this explains the fact that when asked about Jesus' comment that he has 'other sheep which are not of this fold' (John 10:16), very few Christians - at least - will say that they know what this means since there is no indication whether the 'other folds' referred to, are earthly or universal. As such, Christianity says absolutely nothing about humanity having a cosmic uniqueness.
I guarantee that if signals from another civilisation are ever discovered, Christians will very quickly find a passage in the bible that predicted it!
With 2 billion or so people identifying as Christians, I am sure there will be some.
Do you know of any passages in the Bible which says or implies there is no intelligent life apart from on this planet?
No, but then I do not expect the writers of the bible to have given it any consideration due to the fact they they were totally ignorant of the universe they were in.
I expect what will happen, as has happened in the past, that when some new discovery is found, some idiot will point the some vague passage in the bible and claim it foretold or predicted the event. This is of course nonsense and simply interpreting some vague text to mean what you want it to.
An example might be that some chistians claim that the bible new the world was a sphere and that it hung in space hence it new all about the orbit of the Earth around the Sun etc. Complete nonsense.
The bible only seem able to predict scientific discoveries AFTER science has discovered them.
That shoud give those christians pause for thought.