This brief and simplified discernment is to further elaborate on the following essay :http://backreaction.blogspot.com/2019/07/why-multiverse-is-religion-not-science.html.
The practices of sciences over the millenniums, in particularly since the start of the development of organized science, have gone from sciences of unobservable realms and worlds and metaphysics to sciences of observable realms and worlds. In other words, what were unobservable and metaphysics are now empirical data sciences with the advancement of scientific knowledge, wisdom, and technology. Had scientists not making efforts and wait until things are observable or becoming observable, then science could never have advance or make progress.
Furthermore, sciences of such as astronomy and cosmology are based on remnants of the cosmos or cosmic formations and entities phenomenology from seconds (such as within solar system) to entities many many billions light years or aeon past. And no longer are what they actually were but rather, again are based of their formation and existence of many many billions or aeon past which no longer are as such or even existed at all (i.e. existed in other form-formless). In simple words, such sciences are based on "Past" nature phenomenology rather than "Now" and "Future". In other words, even through they are objective and empirical, can be considered as illusion and or delusion if improperly decoded and or interpreted. And at best, as relative truth if properly analyze through the scientific method rather than absolute truth or nature of reality and truth.
In addition, science beyond the CMB (and many other unobservable sciences such as particles physics, dark matter, dark energy, and among many others. As matter of facts, objects such as black holes were not parts of science in past centuries since they were unobservable) which presently is considered as detectable (and not yet observable which is why they are still termed black holes), are considered as science, and yet the multiverse cannot be considered as parts of the scientific quest.
And therefore, observable and objectivity alone should be not only be parts of criteria for considering what is science. But rather, for natural and fundamental sciences, the following criteria need to be taken in consideration (and which can be further be broken down into interdependent and interconnected sub-criteria):
Hypotheses, conjunctures, and theories have to be based on the essence, nature, and ground of being. And nature rather than on human constructs:
1.0 Nothing can have its own inherent independent existence.
2.0 Are hypotheses, conjunctures, and theories of the elements and parts interdependent and interconnected sum of parts of the greater whole.
3.0 Are hypotheses, conjunctures, and theories of the elements and parts functional aspects of process of wholeness transformation, evolution, and emergence or greater whole topology, structure, function, process, mechanism, and order of "Dependent and Interdependent Origination" and "Dependent and Interdependent Arising". And it would help if beyond falsification method (https://www.epistemologyontologyfoundationinstitute.org/global-science-technology-and-innovation-movement/april-28th-2019) is applied.
However, in actuality, since life beyond the physical body and known physical realm exist (a few recent discernments among diverse past discernments https://www.epistemologyontologyfoundationinstitute.org/nature-decode and https://www.epistemologyontologyfoundationinstitute.org/philosophy-and-science. Based on the human conditions. And essence and nature of being. Transcendence and metaphysics science need to be integrated in science. And part of the scientific quest as such sciences are emerging in the main stream (as an example https://www.newscientist.com/article/2209213-computer-attempts-to-replicate-the-dream-like-maths-of-ramanujan among others such as science of consciousness), many realms and worlds must exist. And which implied existence of at least a type of multiverse, albeit a non-conventional scientific thinking.
And therefore, essential philosophy and scientific concept, method, and process that are based on the essence, nature, and ground of being. And nature as well as complementary validation or verification concept, method, and process need to be developed to properly defined and guide the scientific framework and quest as had inspired, encouraged, and urged in many past discernments. Which would better guide the scientific quest and accelerate science as well as the common and greater good. All the while prevent and eliminate conflicts and divisiveness within the scientific communities. And better inform and enrich the public and future generations.