The multiverse theory posits the existence of multiple, possibly infinite, universes that exist alongside our own. These universes, collectively known as the "multiverse," may differ in fundamental ways—from the laws of physics and constants of nature to the very structure of space and time.

Several interpretations and models support the multiverse concept. In cosmology, the theory arises from inflationary models of the early universe. According to eternal inflation, as proposed by physicist Alan Guth and others, inflation never completely ends but continues in different regions, producing "bubble universes" with potentially varying physical parameters.

In quantum mechanics, the many-worlds interpretation, introduced by Hugh Everett in 1957, suggests that all possible outcomes of quantum measurements are realized, each in a separate, non-communicating branch of the universe. This leads to a vast array of parallel universes, each containing a different version of reality.

Another line of reasoning comes from string theory, which allows for a vast "landscape" of solutions—potentially on the order of 10^500 different configurations of compactified dimensions—each corresponding to a different possible universe.

It is important to emphasize that while the multiverse theory is grounded in respected scientific frameworks, it remains highly speculative. Empirical verification is extraordinarily difficult, as these other universes, by definition, may be causally disconnected from our own. Thus, the multiverse is a profound and contentious idea—one that challenges the very limits of scientific inquiry and philosophical interpretation.