The multiverse is a theoretical framework in modern cosmology (and high energy physics) which presents the idea that there exist a vast array of potential universes which are actually manifest in some way. There are a number of different types of potential universes - the many worlds interpretation (MWI) of quantum physics, braneworlds predicted by string theory, and other more extravagant models - and so the parameters of exactly what constitutes the multiverse is different depending on whom you speak to. It's unclear how this theory can actually be applied scientifically, so it's still controversial among many physicists.
One application of the multiverse in modern discourse is a means of invoking the anthropic principle to explain the finely tuned parameters of our own universe without recourse to the need of an intelligent designer. As the argument goes, since we are here we know that the region of the multiverse in which we exist must, by definition, be one of the regions that have the parameters to allow us to exist. These finely tuned properties, therefore, require no more explanation than explaining why humans are born on land instead of under the ocean surface.
Also Known As:
- multiple universe hypothesis
- parallel worlds
- parallel universes
Is the Multiverse real?
There's solid physics supporting the idea the universe we know and love could be one of many. Partly this is because there's more than one way to make a multiverse. Take a look at five types of multiverses and how they could actually exist:
- Bubble Universes - Bubble universes are fairly easy to comprehend. In this theory, there could have been other Big Bang events, so far away from us that we can't conceive of the distances involved yet. If we consider our universe to consists of the galaxies created by a Big Bang, expanding outward, then eventually this universe might encounter another universe created much the same way. Or, maybe the distances involved are so vast these multiverses would never interact. Either way, it doesn't take a huge leap of imagination to see how bubble universes might exist.
- Multiverse from Repeating Universes - The repeating universe theory of multiverses is based on infinite space-time. If it's infinite, then eventually the arrangement of particles will repeat themselves. In this theory, if you travel far enough, you would encounter another Earth and eventually another "you".
- Braneworlds or Parallel Universes - According to this multiverse theory, the universe we perceive isn't all there is. There are additional dimensions beyond the three spatial dimensions we perceive, plus time. Other three-dimensional "branes" may co-exist in higher-dimension space, thus acting as parallel universes.
- Daughter Universes - Quantum mechanics describes the universe in terms of probabilities. In the quantum world, all possible outcomes of a choice or situation not only can occur but do occur. At every branch point, a new universe is created.
- Mathematical Universes - Mathematics is considered a tool used to describe the parameters of the universe. However, it's possible there could be a different mathematical structure. If so, such a structure could describe a completely different sort of universe.
Edited by Anne Marie Helmenstine, Ph.D.