A myth? What a boon to layabouts in string theory that would be!
Our philosopher and photographer friend Laszlo Bencze kindly writes to point out,
Don’t know about String theory but the multiverse theory is definitely a metaphysical speculation. It is no kind of science and most certainly not a scientific theory for the simple reason that the multiverse is by definition unobservable. All those other supposed universes have no connecting point with our own. We might as well be talking about Valhalla or Hades which are likewise metaphysical suppositions.
“A theory is to be called ‘empirical’ or ‘falsifiable’ if it divides the class of all possible basic statements unambiguously into the following two non-empty subclasses. First, the class of all those with which it is inconsistent (or which it rules out, or prohibits): we call this the class of the potential falsifiers of the theory; and secondly, the class of those basic statements which it does not contradict (or which it ‘permits’). We can put this more briefly by saying: a theory is falsifiable if the class of its potential falsifiers is not empty. —The Logic of Scientific Discovery, Karl Popper, p. 82 – 83 “
Multiverse theory has no falsifiers. It excludes nothing. No potential fact of existence can falsify it. By contrast Relativity has plenty of falsifiers: Something exceeding the speed of light, gravity having no effect on the flow of time, apparent time not slowing down as the speed of light is approached. Any of these will do.
See also: At Scientific American: Falsifiability in science is a myth. If propositions in science cannot be falsified by evidence, they aren’t propositions in science. They are simply things many scientists believe for a variety of reasons.
Falsifiability is overrated, cosmologists say. Many cosmologists don’t like Karl Popper’s concept of falsifiability because it gets in the way of simply assuming that concepts like string theory and the multiverse are correct because, well, because they just must be. Many would like to loosen the concept of falsifiability to allow for such cool but unfalsifiable concepts in science.