That something can't be falsified right now does not make it unscientific. As long as something can, in principle, be falsified, it's a valid scientific hypothesis - but perhaps not a useful one.
For the record, I haven't read the article in question closely enough to know if what's being proposed can even be falsified in principle.
True, neither multiverse theory nor a singleverse theory can be proven. But both are scientific in the sense that they (sort of) predict the structure of our universe. The question then becomes how to select one of the theories. Occams razor provides little help, since both theories are similarly complex, so one possible way to select a theory is to use Bayes rule. I'll sketch this reasoning:
The laws of physics are governed by equations which output only a probability distribution P(x) for various quantities (positions of particles, the values of certain fundamental constants).
(Note: I really don't understand any of this stuff well, so if someone (Dani?) with better knowledge can correct me or clarify, I'd love to see it.)
In a single-universe theory (SUT), one postulates that a particular x is selected, at random, relative to P(x) dx. In this theory, it is highly unlikely that the universe can support life (or at least life like us). In a multiverse theory (MUT), one postulates that all x are selected in parallel. In this case, our particular x will be chosen; the fact that we live in a good universe is not luck, merely natural selection. So the probability we exist is close to 1.
Both these theories are more or less equally "simple" (think Kolmogorov complexity), so let us assume they each "occur" with the same or similar "probability" (i.e., p(SUT)=p(MUT)=1/2). Then we use Bayes rule:
So multiverse theory is more "probable" than single universe theory. This remains true even if you wildly alter the complexity of competing theories, e.g. p(SUT)/p(MUT) = 1e6.
It's true, we can never falsify SUT or MUT relative to each other. But we can make educated guesses as to which one is more "probable". And yes, this is pretty sketchy, hence my use of scare quotes everywhere. But it's the best we can do right now.
I guess for lack of scientific rigour? Theories aren't scientific because of the maths, they're scientific because of the approach, which involves creating testable hypotheses that can be determined to be right or wrong. The reason why these two are not scientific theories is not because no one can come up with some maths to support them, but because there is no way to observe them.
I did a physics degree. I studied atomic physics and quantum mechanics. We briefly brushed on the multi/single universe, but largely that was not examined in too much detail in the physics cursus. People who were doing Physics & Philosophy, however, got plenty of detail in their course. My point being: this is philosophy, not science.
[edit: my turn to wonder why I am being downmodded, lol]
Both theories are testable. They both (sort of) successfully predict the structure of the universe, up to some parameter choices (e.g., fine structure constant). There are ways to falsify both theories simultaneously since they make nearly the same predictions, we just don't have ways to falsify one but not the other.
The question is 'absent plausible experiments, how do we choose between single and multiple universes?' And that is done using occams razor; the 'simpler' or 'more probable' theory is chosen, for a somewhat (but not completely) arbitrary definition of 'simpler'.
Occams razor is a philosophical point, as is (to some extent) your definition of 'simpler'. I thought I was careful to highlight those points.
I was merely trying to explain the reasoning multiverse theory, but in a less vague manner than the article did (I trust most of HN to know Bayes rule).
Incidentally, this thread is bringing out behavior which is weird for HN. Someone downmodded your comment, also for reasons which are completely inscrutable to me.
Don't worry. The writer just (unfortunately) phrased it that way for a lay audience. It is in no way a reaction or an alternative to anything to do with creationism.
