Is the Multiverse Real?

Something is real if it can be causally related to anything else that is real.  Our definition of real is constrained by our own observational limitations.  We can only base our knowledge of the world on our observations of it.  It is only through observations, that evidence for or against a particular position/hypothesis can be gotten.  It is true that what we experience when making an observation is not the thing observed, but an illusion, a reconstruction of reality based on information obtained by our senses and analyzed by our mind.  It is also irrelevant to this discussion.  The human mind has split the atom, written the Koran, eradicated polio, taken us to the moon, and reconstructed long-dead written languages,   It has also devised ever-more effect ways to commit murder, denuded the great forests of the Pacific Northwest, used misinformation to destroy the lives of others, and poisoned children for profit. 

The morality or immorality of these acts is a subject for another day.  They are presented here to demonstrate the potency of the human mind.  We have accomplished all these deeds--both great and nefarious--despite the above limitation.  All of science is built upon our flawed perception of reality.

Science is also built upon causation.  If we didn't live in a causally deterministic universe, then science literally wouldn't work.  An observation today would have no value in other situations and could not be used to support or weaken any hypothesis.  Causality can also be observed.  It is the best candidate to use to determine whether or not something is real.

if a is causally related to anything that is real, then a is real.  If a is not causally related to anything that is real, then a is not real. 

It is worth noting that a direct observation of something creates a causal relationship between the observed and the observer via the information exchanged in the observation.  Observations, of course, can only be made in the present.  But if something in the past can be causally related to something in the present, then it is real.  If you can observe a fossil in the present, then that fossil is real.  If the dinosaur that died is causally related to the fossil observed in the present, then it is also real.  That also means that if something cannot be observed and cannot be related causally to something that can be, then it is not real.

Science concerns itself with physical reality.  Scientific inquiry requires an hypothesis and evidence to support or weaken it.  Any hypothesis that cannot be tested by observation cannot be supported and is therefore, unscientific.  Any competing hypothesis that can be supported by any evidence must be the stronger position and therefore that theory that must carry the day.  A theory that is not testable (falsifiable) is not scientific.

The term "multiverse" refers to a body of multiple, parallel universes, including ours.  This concept is not possible.  Either the alternative universes are causally related to something in our universe, in which case they are real and part of the universe, or they are not causally related to anything, in which case they are not real.  Period.  The universe is, by definition, everything.  To talk about "other" collections of everythings is irrational.

Conceptually, we could describe an alternate universe that has it's own causation which is entirely seperate from this universe but real to anything causally related to it.  Such a universe does not exist because it cannot be connected to anything real.  Any hypothesis regarding such alternative causation falls into the category above:  Hypotheses that are not falsifiable and therefore not scientific.

An article posted online in November by Discover Magazine describes what would happen if one of these other universes collided with ours.  Anthony Aguirre builds upon the prior work of Laura Mersini-Houghton to describe the CBM Cold-Spot.  The Cold Spot is a massive area of the cosmos where there very little energy. 

If such a collision occurred, and was causally related to the CMB Cold-Spot, then that "other cosmos" would be a real part of the universe.  It would not be a separate universe.  It would not have its own unique and separate "causal chain."  Instead, it share's one with us--with every other real thing in the universe.

If there is something like the structures described as the multiverse, new verbage is required.  This new verbiage needs to describe these other structures and our relationship to them.  This verbiage would also need to be rooted in observation to be scientific.