The Great Cosmic Roller-Coaster Ride
Could cosmic inflation be a sign that our universe is embedded in a far vaster realm?
But one of the emerging themes of 21st-century cosmology is that the known universe, the sum of all we can see, may just be a tiny region in the full extent of space.
Various types of parallel universes that make up a grand “multiverse” often arise as side effects of cosmological theories. We have little hope of ever directly observing those other universes, though, because they are either too far away or somehow detached from our own universe. Some parallel universes, however, could be separate from but still able to interact with ours, in which case we could detect their direct effects.
The possibility of these worlds came to cosmologists’ attention by way of string theory, the leading candidate for the foundational laws of nature.