As Emerson said "round every circle a larger can always be drawn" (paraphrase)
Note that as far as we can tell from scriptural evidence, the historical Buddha answered difficult questions in particular ways, suggesting that debating some questions was a waste of time (relative to the central goal of Buddhism - working to escape suffering and rebirth and achieve englightenment) since no authoritative answer could be meaningfully sought. 'Right speech' is a central pillar of Buddhism's noble eightfold path http://www.accesstoinsight.org/index-subject.html#eightfold, and it means considering all speech and only speaking when it contributes to your path to enlightenment and/or alleviating suffering in others through sharing the dhamma. He also questions the motivation behind those asking answerless questions. http://www.accesstoinsight.org/index-subject.html#questions
He specifically dealt with the question of world-origin in the Acintita Sutta: "Conjecture about [the origin, etc., of] the world is an unconjecturable that is not to be conjectured about, that would bring madness & vexation to anyone who conjectured about it." http://www.accesstoinsight.org/tipitaka/an/an04/an04.077.tha...
As far as Chinese philosophy goes, if you have access to paywalled academic articles http://onlinelibrary.wiley.com/wol1/doi/10.1111/j.1540-6253.... looks to be a good recent review of the emergence of various concepts of the infinite. Less authoritatively, Daoism included direct reference to concepts of the infinite in its key texts (circa 600BCE) - https://en.wikipedia.org/wiki/Wuji_(philosophy) and https://en.wikipedia.org/wiki/Taiji_(philosophy) These concepts were expanded upon by https://en.wikipedia.org/wiki/School_of_Names however most of their work is lost. They were an interesting early school of formal logic based to some extent on a sort of primitive set theory, classification, categorization, and the discovery of formal systems proving statements in informal language anomalous: "a white horse is not a horse", "a dog is not a hound", etc. where the ontological coherence of the statement is based upon disparate formal interpretations of accepted informal senses of the verb to be. (Not enhanced in clarity by the need for translation)
1. A translation of the 8th benefit of mindfulness, as espoused in the Kayagata-sati Sutta: Mindfulness Immersed in the Body. Basically in this text the historical Buddha is saying that mindfulness enables recognition of one's past lives.
2. Iddhipada-vibhanga Sutta: Analysis of the Bases of Power in which loads of supernatural powers are listed as being granted to those who achieve concentration through the "four bases of power", and is essentially similar to the above, though it also lists many other powers like walking on water, diving in to earth and flying and is probably not supposed to be taken as literally as it has been translated. Further, it specifically references pre-Buddhist Brahmanic tradition. http://www.accesstoinsight.org/tipitaka/sn/sn51/sn51.020.tha...
The point though is that there's only a couple useful things you can say about the universe: it has a definite begin and a definite end, an infinite beginning and no end, some combination of that, or it's cyclical... and because there's a very limited set of possibilities it's trivial to find an ancient sage opining on something that sounds like the big bang and the heat death of the universe.
Similarly either this universe is all there is or 'the multiverse' which means it's very easy to find historic sources spouting off things that sound like a multiverse. With out actual evidence, math, science behind it though it's not interesting that they came to this conclusion because simply guessing that this is the way of things doesn't push our understanding forward.
If a thesis is not testable, it's just an idea in millions (i.e. existence of God). The validity will remain undetermined and there is nothing to learn from studying it.
The concept of evidence defines a narrower scope.
The testability is determined by the existence of constrains that must be satisfied.
Cosmologists interested in fine-tuning might.
Quantum foundation theorists often consider alternatives, not because they think they are real, but because it's useful to understand why QM has the form it does. Mostly their results suggest QM is difficult to modify without becoming trivial or useless.
I think the drive comes more from the metaphysical direction. It's hard to imagine why one set of laws would emerge as physical unless all sets of laws are physical, just by virtue of existing mathematically.
Max Tegmark is famous for his occasional crackpot theories. If anything they make for good sci-fi.
It would be a mistake to call back into question the existence of multiverse. And a mistake as big to claim it exist.
Until a method to test it is found, discussing this idea is a waste of time. However I would respect people searching and discussing methods to test it if they have pertinent things to say.
To recreate...click the link and scroll down a bit, they fill your history with the same page, so you can't use the back button.
Dark pattern or honest mistake?
Bruno and Leibniz were arguing from the plenitude principle. The principle asserts "the universe contains all possible forms of existance". The idea is introduced by Plato's ontology from which everything after is arguably a derivative.