I exaggerate with the title of this post, but only slightly. The title is a reaction to a strange article on multiple universes written by Tom Siegfried at Science News. It's the kind of article that harms the cause of a field and causes the rest of us to take it less seriously . For those who haven't been following the multiverse mania, multiple universes have been invoked as "explanations" for a variety of conundrums in modern physics; among them, the fine-tuning of the physical constants and the measurement problem in quantum mechanics. All speculation without evidence of course.

But Tom Siegfried tells us that the real reason why people don't believe in the multiverse is not a lack of evidence, it's apparently a lack of vision. He starts by pointing out that just because we can't see something does not mean it cannot exist.

If you can’t see it, it doesn’t exist. That’s an old philosophy, one that many scientists swallowed whole. But as Ziva David of NCIS would say, it’s total salami. After all, you can’t see bacteria and viruses, but they can still kill you.

Yet some scientists still invoke that philosophy to deny the scientific status of all sorts of interesting things. Like the theoretical supertiny loops of energy known as superstrings. Or the superhuge collection of parallel universes known as the multiverse.

That's about as bad an analogy as I can think of. There's massive, and I mean really massive, direct as well as indirect evidence for the existence of bacteria and viruses; the tens of thousands of electron microscopy images over the past five decades for one thing. The same goes for atoms, neutrinos, black holes and supernovae. All these may not be directly felt or seen but there's incontrovertible and overwhelming evidence for their existence; if I were an atom I would be feeling quite insulted by now by this analogy. Siegfried unhelpfully compares those who may not believe in superstrings or the multiverse to Ernst Mach, the strident 19th century German physicist who kept up a dedicated attack on the reality of atoms until he died. And yet, as Siegfried obligingly reminds us, there was massive indirect evidence for the existence of atoms, exemplified by Einstein's explanation of Brownian motion.

Yes, there was. But there's two things to be considered here. Firstly, even the indirect evidence that existed arose from a variety of different fields and was exemplified by a palpable chain of physical reasoning that manifested itself through real entities, for instance pollen grains and elemental spectra. There was a lot of internal consistency between the various explanations put forward for the existence of the subatomic world and the whole package when put together by invoking the existence of atoms made good sense. No such causal chain of physical reasoning exists for the multiverse. All we have are logical and elegant sounding, purely theoretical constructs.

But the most egregious thing in that article is an assertion that we can just use the unobservable for explaining the observable:

Similar reasoning can be applied to parallel universes. If other universes exist, they may well be forever beyond the power of humankind’s observational instruments. But perhaps the laws explaining observable things also require unobservable universes.

Come again? This treads dangerously into the territory of pseudoscience and even crackpot science; after all, every New Age guru and preacher says the same thing, that the world that we can observe is somehow controlled by unobservable entities like spirits, Gods, "chakras" and the like. I can come up with an explanation right now for the simultaneous occurrence of identical thoughts in two individuals on opposite sides of the planet based on a "theory" of telepathy. Basically when you start making connections between untestable and unobservable phenomena and the real world, anything goes.

Siegfried alludes to a paper by physicist Frank Wilczek which is far more circumspect in speculating on the multiverse. Wilczek is right that sometimes scientists don't grasp a whole new domain of physical reality because they lack the vision. But what happens when that domain becomes so far removed from the slightest semblance of observable phenomena that it devolves into a broad realm of symbol manipulation and philosophizing? And more important, when there's not a shred of hard evidence for its existence? We don't believe in the multiverse because we lack vision but because the concept is untestable. Now let me go back and concoct an explanation for why my enzyme is not behaving the way it should; it must be all those darn gnomes messing around again with the amino acids in the active site.

Update: Peter Woit nicely weighs in.