We all know the universe exists. Some people offer the hypothetical that many universes could co-exist. What concrete proof is there for a multiverse?
Has our universe ever bumped into another one?
First, let me suggest an article in First Things by Catholic theoretical physicist, Stephen Barr:
firstthings.com/blogs/firstthoughts/2013/06/the-large-hadron-collider-the-multiverse-and-me-and-my-friends
There really is no concrete proof that more than one universe exists. Theories of a āmultiverseā are one type of mathematical-physical model for explaining bizarre phenomena that occur at the edges of the two major fields of modern physics: general relativity and quantum mechanics.
From my perspective, there are four important problems that give rise to speculation about the multiverse (more actually, but to simplify the discussion):
(1) the wave-particle nature of light, in particular, as demonstrated in the ādouble slitā experiments;
(2) āfine tuningā of fundamental constants of the universe;
(3) the āanthropic principle,ā which just means that we only see what we are able to see, based on the speed of light and our current position in spacetime; and most importantly,
(4) the preference in modern science for mechanistic explanations of physical phenomena (which in atheist circles reduces to philosophical naturalism and total rejection of God, but in theist circles is constrained by limits of mathematics, observations, and experiments we can run economically).
Multiverse theories can have different underlying assumptions, and can include notions of:
- āparallel universesā that weakly interact with ours,
- ālocal universesā donāt interact with each other because theyāre separated by a large distance in spacetime
- eternal expansion of the multiverse, within which new universes emerge or ānucleateā
- proliferation of universes, with one universe created for every possible alternative possibility that has ever occurred within the universe
- an infinite number of alternative universes that have all possible ranges of fundamental constants (e.g., the magnitude of gravitational force, the cosmological constant), so that by necessity ours ā which bears life ā must exist.
To my understanding, positing a multiverse is not the only way to solve the conundrum posed by problems 1-4, above. For example, John Wheelerās āParticipatory Anthropic Principleā extends some āspookyā properties of quantum mechanics (based on the double-slit experiments and an experiment called delayed choice) to posit that the entire past spacetime history of the universe (including, possibly, the values of fundamental constants) reshapes itself to ensure that the observations made by living observers occur. Hereās an article on that theory, which to me is a thoroughgoingly modern restatement of teleology, but a potential nightmare for epistemology and science in general:
discovermagazine.com/2002/jun/featuniverse
There are other approaches to the problem.
