> To me, again as an outside observer, it feels so counter-intuitive to _invent_ a new type of matter you can't observe than to just say that your calculation is close but not right and to start over. Is it not a crutch?
Physicist here. If you're doing applied physics or engineering, this certainly would be a crutch. But when we're talking about fundamental physics, talking about new kinds of matter that nobody has seen before is not a crutch -- it's literally the core thing we do. That's what makes it fundamental!
Saw a track in the bubble chamber curving the wrong way? Invent a new kind of matter: antimatter.
Saw short-lived particles in the bubble chamber that shouldn't have made it there? Invent a new kind of matter: mesons that decay into the observed particles.
Problems with getting solar reactions to work out right? Invent a new kind of matter: neutrinos.
Amount of neutrinos detected not quite right? Invent multiple neutrinos and neutrino oscillations.
Saw some weird long-lived particles? Invent a new kind of matter: "strange" mesons and baryons.
Want to explain the pattern of mesons and baryons? Invent a new particle: "quarks", along with the stipulation that they can never be observed, even in principle.
Standard Model seems a little off-balance at this point? Invent a new particle: "charm" quarks to balance out the strange ones, at an energy high enough that nobody has seen them yet.
But the mesons and hadron patterns still aren't consistent with the Pauli exclusion principle! Invent a new force: color charge, carried by "gluons", which are also postulated to be unobservable.
Some particular meson and baryon decays acting weird? Invent a new force: the weak force, carried by "weak bosons", which are too heavy to be observable at the time.
Can't get the weak bosons to have mass? Invent a new interaction, the Higgs interaction, carried by an invented new field, the Higgs field, which gets a vev from an invented new function, the Higgs potential, whose elementary excitations are an invented new particle, the Higgs boson.
Of course, not every weird thing is explained by a new type of matter; many anomalies fade away after careful checking. But the anomalous observations that motivate dark matter persisted for almost a century, they're been only building in strength as we get more data, and all attempts we've made to explain them in terms of "normal" physics have failed. So the case for explaining it in terms of something new is at least as strong, in fact far stronger, than the examples I gave above.
I guess what is different about dark matter is that it has to outmass regular matter by a large factor. It feels unparsimonious to invent four-five times the mass of the known universe just to patch a discrepancy between observations and a theory of gravitation. It feels like the theory would better be adjusted to match observation than to patch observations to match theory.
Today I learned that the mass of the neutrinos we know about (which were similarly invented, though since detected) about matches the mass of all the stars.
Actually, in the context of astrophysics, that exact objection has been employed many times. For example, the most famous argument against heliocentrism was that it would require the stars to be ridiculously far away and ridiculously big to patch away the lack of parallax, which felt unparsimonious. Similarly, people believed that galaxies weren't galaxies, because it seems unparsimonious to expand the universe far beyond the Milky Way just to patch up some weird features of fuzzy nebula. And even in our galaxy, the mass in dust and interstellar gas exceed that in stars.
Literally all progress in fundamental physics is "just" "invented". Each time it must triumph against the objections of the same, thousand-year-old philosophical arguments.
Physicist here. If you're doing applied physics or engineering, this certainly would be a crutch. But when we're talking about fundamental physics, talking about new kinds of matter that nobody has seen before is not a crutch -- it's literally the core thing we do. That's what makes it fundamental!
Saw a track in the bubble chamber curving the wrong way? Invent a new kind of matter: antimatter.
Saw short-lived particles in the bubble chamber that shouldn't have made it there? Invent a new kind of matter: mesons that decay into the observed particles.
Problems with getting solar reactions to work out right? Invent a new kind of matter: neutrinos.
Amount of neutrinos detected not quite right? Invent multiple neutrinos and neutrino oscillations.
Saw some weird long-lived particles? Invent a new kind of matter: "strange" mesons and baryons.
Want to explain the pattern of mesons and baryons? Invent a new particle: "quarks", along with the stipulation that they can never be observed, even in principle.
Standard Model seems a little off-balance at this point? Invent a new particle: "charm" quarks to balance out the strange ones, at an energy high enough that nobody has seen them yet.
But the mesons and hadron patterns still aren't consistent with the Pauli exclusion principle! Invent a new force: color charge, carried by "gluons", which are also postulated to be unobservable.
Some particular meson and baryon decays acting weird? Invent a new force: the weak force, carried by "weak bosons", which are too heavy to be observable at the time.
Can't get the weak bosons to have mass? Invent a new interaction, the Higgs interaction, carried by an invented new field, the Higgs field, which gets a vev from an invented new function, the Higgs potential, whose elementary excitations are an invented new particle, the Higgs boson.
Of course, not every weird thing is explained by a new type of matter; many anomalies fade away after careful checking. But the anomalous observations that motivate dark matter persisted for almost a century, they're been only building in strength as we get more data, and all attempts we've made to explain them in terms of "normal" physics have failed. So the case for explaining it in terms of something new is at least as strong, in fact far stronger, than the examples I gave above.