...but the adjective automatically includes "in principle"...
I have discussed several answers to the annual (and problematic) Edge.org question Which scientific ideas should be retired? but Sean Carroll's answer wasn't among them.
Falsifiability needs to be retired (Carroll's answer at Edge.org)Sean Carroll mentioned his answer on his blog, The Preposterous Universe, and he got largely criticized, especially by commenters like Doc C, Bruce Caithness, Dan, John Duffield, Andy Odell, and DEL. I mostly oppose these critics (who got most of the positive votes) and sympathize with Carroll's spirit but I would still disagree with the main thesis that "falsifiability may/should be retired".
What Scientific Ideas Are Ready for Retirement? (Carroll's blog)
Karl Popper became famous for the observation that the scientific process is a sequence of falsification events in which older, insufficient theories are abandoned so that they must eventually be replaced by less bad ones. Ideas that can't be superseded in this way are unscientific.
If one carefully studies what he really said about this process, I would endorse Popper's theses (although I would say that the claims are kind of trivial and many other philosophers and philosophical clubs, like the Vienna Circle, said similar things with a different focus that could get a higher rating from your humble correspondent). He also correctly said that the authorship of a hypothesis is a creative inductive act but the resulting scientific knowledge is deductive.
One of the often overlooked details – and Carroll realizes this detail very well – is that Popper acknowledged that the falsifiability that must be possible for a statement to be scientific really means "falsifiability in principle".
It's a very important subtlety. After all, Popper wanted to eliminate Marxist economics and Freudian psychoanalysis that were arguably never falsifiable, not even in principle. I would say that the same thing holds for many religious and spiritual interpretations of physics and many of the vague and permanently flexible claims rooted in the anthropic principle. But by demanding that statements in science must be falsifiable in practice – or even soon or cheaply – would mean to throw out the baby with the bath water.
We often discuss examples of theories and propositions that are perfectly scientific yet probably unfalsifiable in practice – in a foreseeable future – like string theory and some claims from the cutting-edge cosmology (not all of them, and many cosmologists' and surely Carroll's bizarre musings may be falsified very easily because they are utterly wrong).
But it's important to notice that science depends on many claims that are unfalsifiable in practice but we still choose to believe them because they naturally follow from theories that have been tested or established. In principle, these claims are falsifiable.
For example, take the existence of other (distant) galaxies. One may invent an alternative explanation. They are just some collections of light dots on a celestial sphere, a screen that is some millions of light years away from the Earth and someone is projecting these dots over there. Our explanation is that the light actually comes from collections of stars that are analogous to the Milky Way, our galaxy.
Which explanation is the right one? An extremist Popperazi would be forced to admit that this question is unscientific. We can't really travel to the other galaxies – which are millions of light years away from us – anytime soon. We can't really prove the other galaxies' finite distance from us by the method of parallax, either. The parallax is too small. And so on.
However, we still prefer to say that the other galaxies are as real as the stars in the Milky Way. It is definitely a part of our scientific image of the Universe. This explanation can't be compared to the bizarre alternative explanations by a doable experiment but we still have rational reasons to conclude that the alternative explanations are much less likely. They (the theories with distant galaxies as movies) are more contrived, less unifying, less symmetric, depending on too many exceptions, and so on. We know that this question makes sense because in principle, we could travel to the other galaxies (at least there surely seems to be no potential, unavoidable restriction that could prevent us from travelling millions of light years).
The other galaxies' guts are inaccessible to "easy testing" because they are too far. Other scientific concepts are extremely separated from the everyday life when it comes to different quantities. For example, our theories of the Sun imply that the Sun will keep on burning for 7.5 billion years or so before it becomes a red giant. This follows from the models describing the conditions and reactions inside the stars. But this statement about the far future of the Sun is also unfalsifiable in practice. No lab paid by the taxpayer can really wait for 7.5 billion years.
Grand unified theories, supersymmetry, and string theory are probably (let's assume that there are no large/warped ADD/RS extra dimensions) unfalsifiable in practice (at least if we talk about some direct testing that doesn't allow us to include any sophisticated calculations or argumentations) because they deal with phenomena that occur at too short distance scales, too short time scales, and that require too high temperatures or energies per particle to be probed by accelerators. But these theories, concepts, and propositions about them are exactly as scientific as the statements about the distant galaxies or the distant future of the Sun. They're unfalsifiable by direct experiments that are doable in practice because they are extreme in certain respects. However, they are clearly physical and in some important sense, string theory is much more tangible and precise physics that allows one to calculate things (like cross sections of particle collisions) more accurately than any other theory. Any analogy with Marxism, Freudism, religion etc. is totally absurd.
There is a whole movement that bastardizes Popper's dictum to claim that science has to be practical – something that Popper surely didn't want to say (after all, philosophy in general has been less practical than the least practical parts of physics at least since the birth of physics). The very first comment on Carroll's blog is extremely explicit about this delusion.
Doc C: Either science is a tool to answer practical questions, or it is a tool to satisfy our anxiety over the uncertainty we experience in our existence. It can’t be both. Falsifiability makes science practical rather than psychotherapeutic.Science is a systematic process of learning how Nature works because the knowledge of the truth is assumed to have a very high, independent value. The knowledge often may and does bring us practical advantages, too. But they're not the main raison d'être of science. After all, science in the modern sense was founded by Galileo Galilei and Isaac Newton and they were surely not studying the motion of planets or moons or balls near the tower in Pisa to solve practical problems. They wanted to know how the world works.
Put another way, In deciding to spend our money, how much should we devote to speculative imagination, and how much to practical solutions? Does it really matter how well we understand string theory if its not going to be testable or yield practical applications in any foreseeable time? Are there better problems to focus on? Who gets to choose, the academics, or the indigent?
So in the first paragraph by Doc C, the second answer is much more correct than the first one, despite the dishonest attempts to present the thirst for the truth as a psychiatric disease. It may be a psychiatric disease but those who don't suffer from this disease are just healthy animals, just slightly more refined equivalents of pigs and cows. Activities counted as science are sometimes motivated by practical applications, especially "applied research", but they're also and primarily motivated by the thirst for the truth, especially the "pure science". The purer the scientific research is, the more it is motivated by the thing that Doc C presents as a psychiatric illness.
We are not studying string theory to improve the life of primitive mammals like pigs or cows or Doc C. We don't throw copies of Polchinski's textbook to the pig sheds or Doc C's house because it would be a waste of resources. We grow pigs because pork is a pretty good meat. I am not sure why we grow the likes Doc C but let me assume that someone would be able to find a reason, too.
At any rate, the money for advanced science that makes us human is clearly not willingly contributed by Doc C or the dozens of scumbags who upvoted his idiotic comment. The money is being contributed by much more spiritually refined people who actually appreciate the intrinsic value of the scientific truth – individuals like Kavli, Lazaridis, or Milner as well as millions of similarly feeling citizens of most countries in the world. Those would like a much higher percentage of their taxes to be paid for science. The actual result – something like 1% of the GDP for science – is some kind of the (weighted?) average of all the citizens' opinions.
But the result is that some money is being paid to science and science, by definition, cannot be affected by unscientific pressures such as the question whether a primitive moron nicknamed Doc C finds something useful for himself. Science has its own rules and the search for the truth in particle physics simply isn't affected by the impression of practical use in the eyes of Doc C. His "demand" that such factors should be taken into account is completely analogous to the wishes of a "sports fan" who pays to watch a baseball match but demands one goal to be added to the score whenever a cheerleader of that team performs a strip tease (he wants this modification of rules because he finds the strip tease much more interesting than some collisions of bats and balls and running men – and so do I but that's not the point here LOL).
The rules of baseball just don't allow such a thing; it would be against the whole spirit of the game. Baseball is about the bats, balls, and running men, not about strip tease. And exactly the same is true for science and the unacceptable demands by Doc C and others. Someone is paying for science which means a rather particular thing and has some pretty well-defined rules; it is surely not what Doc C demands science to be. If a "sports fan" came to a baseball match and aggressively demanded strip teases, he would probable be given a proper thrashing, and that's exactly what should be done with Doc C and dozens of similarly aggressive anti-science Mujahideens.
I am still puzzled by the dozens of aggressive foes of pure science who keep on visiting science blogs like Sean Carroll's blog in this case but who hate science so much that they demand research in science to be practically useful for their lives. Why don't they spend their time with things they actually like or find practical? Sean Carroll's blog has never been about applied physics, has it?
Almost nothing in science is useful for your lives because you are primitive morons, Doc C et al. The stupider you are, the less useful to you science seems to be. It's that simple.