There is a known thought experiment, connected to quantum immortality: a duel between physicist and a philosopher.
Each turn physicist and philosopher fire at each other with a pistol. The quantum immortality predicts that each of the participants will find themselves alive and the opponent dead after a number of shots.
We can modify the experiment in the following ways:
They do not fire at each other, but it is lightning that shots them. The outcome should not change.
There are not two but more participants.
They are located at separate islands in the ocean.
It seems that even if there are hundreds of participants, each of them will eventually find all others killed by lightning. If he could not observe other isles directly, after he discovers and explores other isles, he will find them uninhabitable.
Now pretend that the participants actually live on separate planets, and in each million years there happens disaster that kills all inhabitants on 1% of all planets. It seems that after years the physicist that lives on one of the planets should discover that all other planets are uninhabitable. Even more: there is even no chance that organic matter on each other planet could actually evolve into anything resembling actual life.
That said the physicist will find out that there is no other inhabitable planet in the Uinverse. On the other hand, this does not mean that extraterrestrial life does not exist. It actually cannot not to exist. But it exists in parallel universes (in terms of MWI) and thus unobservable. Both physicist on planet A and philosopher on planet B exist, but will never meet in the same universe.
Thus, QI it seems predicts one concrete observable consequence that extraterrestrial life can be never detected.
What is your opinion?