How can we be sure that dreaming is a real phenomenon? It seems like there is no scientifically objective way to know that a person is dreaming; the most we can do is ask them. We are relying on our own subjective experiences, which we cannot verify, and the words of others, which we cannot verify either. REM sleep is correlated with claims of dreaming, but mental activity isn't granular enough to figure out whether a person is in fact *experiencing* an absurd fantasy world rather than simple darkness.
Is it possible to approach dreams and dreaming scientifically, if we have no way to examine or verify them or their existence in any way beyond subjective claims?