At the Edge, Sean Carroll argues that falsifiability should be retired:
My answer was “Falsifiability.” More of a philosophical idea than a scientific one, but an idea that is bandied about by lazy scientists far more than it is invoked by careful philosophers. Thinking sensibly about the demarcation problem between science and non-science, especially these days, requires a bit more nuance than that.
Modern physics stretches into realms far removed from everyday experience, and sometimes the connection to experiment becomes tenuous at best. String theory and other approaches to quantum gravity involve phenomena that are likely to manifest themselves only at energies enormously higher than anything we have access to here on Earth. The cosmological multiverse and the many-worlds interpretation of quantum mechanics posit other realms that are impossible for us to access directly. Some scientists, leaning on Popper, have suggested that these theories are non-scientific because they are not falsifiable.
The truth is the opposite. Whether or not we can observe them directly, the entities involved in these theories are either real or they are not. Refusing to contemplate their possible existence on the grounds of some a priori principle, even though they might play a crucial role in how the world works, is as non-scientific as it gets.
More crucially, again as pointed out by Baggott, the reasoning basically boils down to: we have this empirically unsubstantiated but nice theoretical complex (the multiverse) that would very nicely solve this nagging fine tuning problem, so we think the theoretical complex is on the mark. This is dangerously close to being circular reasoning. The fact, if it is a fact, that the idea of a multiverse may help us with cosmological fine tuning is not evidence or reason in favor of the multiverse itself. The latter needs to stand on its own.
And yet Sean comes perilously close to proposing just that: “We can’t (as far as we know) observe other parts of the multiverse directly. But their existence has a dramatic effect on how we account for the data in the part of the multiverse we do observe.” I truly don’t think I’m reading him uncharitably here, and again, I’m not the only one to read some cosmologists’ statements in this fashion.
None of the above should be construed as suggesting that ideas like the multiverse or string theory are somehow pseudoscientific. They are complex, elegant speculations somewhat grounded in well established physics. Nor is anyone suggesting that barriers be put around the work or imagination of cosmologists and string theorists. Go ahead, knock yourselves out and surprise and astonish the rest of us. But at some point the fundamental physics community might want to ask itself whether it has crossed into territory that begins to look a lot more like metaphysics than physics. And this comes from someone who doesn’t think metaphysics is a dirty word…
Some of us think there is no question that the fundamental physics community has crossed over into metaphysics. A while back. Here’s a question: Would it have been possible to develop a cosmology where avoiding the concept of God is a goal (and that is clearly what this whole fine-tuning issue is about) without the cosmology becoming a metaphysic?
See also: Copernicus, you are not going to believe who is using your name. Or how.
The Science Fictions series at your fingertips
Note: Pigliucci crossed our screens before here, in “Pigliucci: nothing makes sense in biology except in the light of evolution — NOT!” and here on the frequent imprecision of the science/pseudo-science divide in medicine (no surprise, given the strength of the placebo effect).