The multiverse theory is a speculative idea in cosmology that suggests the existence of multiple universes or "parallel" universes beyond our own. These universes may have different physical laws, constants, and properties.
The multiverse theory is often proposed to explain certain features of our universe, such as the fine-tuning of physical constants. It posits that if there are many universes with different properties, then it's more likely that one of them would have conditions suitable for life.