Sean Carroll is one of my favorite science bloggers, and you should definitely check out his blog, Preposterous Universe, if you have not done so already. But I don't agree with his idea that it's time to toss out the notion of "falsifiability" in science.
Carroll does make some good points. For example, some theories might be falsifiable in principle but not in practice, given technological limitations. For example, take the tiny strings in string theory, which we could only see if we had a particle accelerator the size of the galaxy. The fact that we'll never build a machine that big doesn't mean the strings aren't there.
Another point Carroll makes is that sometimes, things that aren't currently falsifiable eventually become so. If we toss out ideas too soon because we haven't yet figured out a way to test them, we may cut ourselves off from understanding things.
But Carroll is a bit unclear as to what he means by "falsifiability". For example, he writes:
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.What does he mean by "real"? What does it mean for something to be "real", but to be so hidden from our Universe that we'll never be affected by its "reality"?
Anyway, it seems to me that there are at least three different kinds of "non-falsifiable" theories:
Type 1: Theories that are so vague that they can be used to "explain" anything (e.g. "Every event in history is the result of inevitable historical forces.")
Type 2: Theories that are completely untestable in principle (e.g. "There's a particle that can't possibly interact with anything in our Universe.")
Type 3: Theories that are currently untestable given the limits of our technology.
I propose that we treat these three types differently. As for Type 1 Unfalsifiable Theories, we should run around with squirtguns, soaking anyone who wastes our time with these. The Type 2 theories, we know we'll never need, so scientists can safely forget about them, while amateur philosphers endlessly debate the proper meaning of the word "existence".
But what about the Type 3 theories? We might be able to use them someday, but not yet. Do we throw them out (thus risking cutting ourselves off from the truth), or do we use them as long as they're plausible and cool-sounding (thus risking using bad theories)?
I say we do neither. We humans are trained to use two-valued logic, which labels properties either "true" or "false". But I believe science needs a third category: call it "shrug". True, false, or shrug. The things in the "shrug" category should be placed in a mental bin for safekeeping until such time as they might prove useful to humankind, but not used until there exists enough evidence to verify their usefulness to our own satisfaction.
In fact, I think that three-valued logic is a crucial and innovative feature of scientific thought. You need to have that intermediate category where you defer judgment. Call it "shrug-ability". (Note that sometimes the world forces us to make discrete policy decisions, in which case you can't just shrug. But I'm talking about the decision to use a scientific theory, which is typically less urgent.)
Of course, there's also the question of whether our conclusions about scientific theories should be discrete at all. In reality, of course, they aren't. "Accepting" and "rejecting" theories are just mental shorthand. "Shrugging" at theories is also mental shorthand, it just reminds us to consider our confidence levels in addition to our point estimates.
Anyway, Scott Aaronson has some other good thoughts on falsifiability.