Sean Carroll takes the idea of many universes seriously, even if they can't be observed yet:
We find ourselves surrounded by an opaque barrier past which we can’t see—the Big Bang. The distant universe might be uniform, or it might be full of different universes scattered throughout space. The conditions of our local environment might be the unique consequence of fundamental laws of physics, or they might just be one possibility out of a staggering number.
Right now we don’t know, and that’s fine. That’s how science works; the fun questions are the ones we can’t yet answer. The proper scientific approach is to take every reasonable possibility seriously, no matter how heretical it may seem, and to work as hard as we can to match our theoretical speculations to the cold data of our experiments.
(Image: The Bubble Nebula by Larry Van Vleet via NASA's Astronomy Picture of the Day)
The Dish 