SelfAwarePatterns made me aware of this essay by theoretical physicist Sean Carroll who expressed opinion that some scientific theories can still be called scientific, even though they are claimed to be unfalsifiable:
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.
The falsifiability criterion gestures toward something true and important about science, but it is a blunt instrument in a situation that calls for subtlety and precision. It is better to emphasize two more central features of good scientific theories: they are definite, and they are empirical. By “definite” we simply mean that they say something clear and unambiguous about how reality functions. String theory says that, in certain regions of parameter space, ordinary particles behave as loops or segments of one-dimensional strings. The relevant parameter space might be inaccessible to us, but it is part of the theory that cannot be avoided. In the cosmological multiverse, regions unlike our own are unambiguously there, even if we can’t reach them. This is what distinguishes these theories from the approaches Popper was trying to classify as non-scientific. (Popper himself understood that theories should be falsifiable “in principle,” but that modifier is often forgotten in contemporary discussions.)
Carroll suggests to replace the requirement of falsifiability for a scientific theory with two requirements: being “definite” and being “empirical“. IMO, it’s the same as falsifiability. A few points:
- “Unfalsifiable with today’s technology” and “unfalsifiable in principle” are two different matters. E.g., we may be able to observe some effect of the multiverse on our universe in the future.
- “Unfalsified” and “unfalsifiable” are different matters. Just because a theory has not been proven false, does not mean that it cannot be proven false.
- “True” and “useful” are different matters. Scientific models and theories are created to explain empirical data and make useful predictions. If a theory does not do that, it can still be scientific, but it is rejected as useless (e.g. aether theories) The concepts of electron or radio wave are not “true” or “false”. The fact that we cannot “see” them does not seem to embarrass any scientist. We imagine electrons to be particles and it helps to explain empirical data. But electrons are not “particles” per se. We imagine electrons to be waves and it helps to explain empirical data, but electrons are not exactly like the waves on the surface of an ocean, for example. As long as these models and visualizations help explain empirical data, these models are empirical and falsifiable because if they fail to explain empirical data, they will be falsified.
- The question “can a theory be proven false?” is ambiguous. It can mean two different things: (1) “Is the theory likely to be false?” or (2) “Can the theory be proven false, in principe?” These questions are not to be confused. E.g. Evolution appears to be falsifiable because, if we found human remains predating dinosaur fossils, evolution would be proven false, but it’s unlikely we ever will. “The universe appeared from nothing” appears to be unfalsifiable theory because I cannot imagine what evidence of “nothing” might look like, even in theory. I don’t even know what “nothing” is. I don’t even know if I can say “nothing is” or “was“.
Regarding high energies, we don’t necessarily need to “have access” to them on Earth (e.g. build huge particle colliders). We can observe phenomena happening at these high energies in the space.
Multiverse is just a concept or a model that is supposed to explain certain empirical data. It’s completely possible to use this model to predict phenomena that we can observe. If these predictions prove to be incorrect, we can say that we have falsified the multiverse as a useful scientific theory. I think, the falsifiability principle still stands. What do you think?
See also: “Evolution and Philosophy: Is Evolution Science?”
Update 1/21/2014: This video explains the different concepts of “multiverses” mentioning that there <em>can</em> be experimental evidence of them, in principle. So, these hypotheses are not unfalsifiable.