You are one human (at least, I’m going to assume you’re a human, no aliens allowed) out of over 7 billion, on a planet out of billions, in a galaxy out of millions, in a Universe. That makes you rather small. What if there’s more than one Universe? That’s bound to make you utterly insignificant compared to the scale of the Universe, or possible Universes. This is what we usually refer to as the Multiverse.

The Multiverse (meta-universe/metaverse) is the hypotheical set of multiple possible universes. We tend to assume that if there is more than one Universe, they’d be just like us, with the same physical laws. There is said to be various universes within the multiverse that are called parallel universes.

You may have only heard about Multiverses in Science-Fiction and Fantasy litterature or films, however, it’s a common fact that science fiction often becomes science fact! Multiverses have been hypothesized in astronomy, religion, cosmology, physics, philosophy and transpersonal psychology. Therefor, there are many different theories of how they would be. Mentioning only a few:

An infinite Universe: This theory proposes that there are an infinite amount of Universes, containing an infinite number of Hubble volumes (http://en.wikipedia.org/wiki/Hubble_volume), all having the same physical laws.

Chaotic inflation theory: The Multiverse is seen as a whole that is forever stretching, however, some regions of space stop stretching and form bubbles. You can think of it as gas pockets in a loaf of rising bread (apart from the fact that we don’t get bread that stretches forever, that’d be a bit scary). These bubbles are embryonic level 1 multiverses.

Picture above: Every disk is a bubble Universe (Universe 1 to Universe 6 are different bubbles, they have physically constants that are different from our Universe).

The cycle theory: An infinite amount of Big Bang crushes. The big bang never ending. (http://en.wikipedia.org/wiki/Cyclic_model)

Great 10 minute video on the Multiverse with Dr. Michio Kaku explaining:

http://www.youtube.com/watch?v=nZiROWO6iVs

The theory that is mentioned in the video, that we live in a soap bubble among other soap bubbles is being tested by physicists. They are currently searching for disk-like patterns in the cosmic microwave background (CMB) radiation. Relic heat radiation left over from the Big Bang could provide evidence of collisions between other universes and our own. However, physicists needed to be sure whether the patterns were the results of collisions or random patterns in noisy data.

A team of cosmologists based at University College London, Imperial College London and the Perimeter Institute for Theoreotical physical are trying to solve this problem and think they have tackled it. The team ran simulations of what the sky would look like without cosmic collisions and developed an algorithm (http://en.wikipedia.org/wiki/Algorithm) to determine which fit better with the wealth of CMB data from NASA’s Wilkinson Microwave Anisotropy Probe.

Stephen Feeney (PhD student at UCL) created the powerful computer algorithm to search for the tell-tale signatures of collisions between bubbles universes and said: “The work represents an opportunity to test a theory that is truly mind-blowing: that we exist within a vast multiverse, where other universes are constantly popping into existence.”

Now with the team’s algorithm, which is much harder to fool when it comes to telling the difference between universe collisions and random noisy data.

This theory has received a lot of criticism for being “unrealistic”. However, they tend to forget about the fact that humans got executed for saying their thoughts out loud on possible extraterrestrial life or perhaps going against the theory of the Earth being the center of the Universe.

Sources:

http://www.zeitnews.org/space-science/first-observational-test-of-the-multiverse.html

http://www.youtube.com/watch?v=39qmbl7mpJQ

http://en.wikipedia.org/wiki/Multiverse