KF Lynch: Is it possible that dark matter particles interact among each other in exactly the same way that matter particles interact among each other? In other words, they have their own exact analogs of protons, electrons, photons, etc., which interact with each other but which only interact with ordinary matter via gravitation? I ask because one of my favorite science fiction novels, _Twistor_ by John G. Cramer, takes this as its premise. It depicts a present-day physicist at the University of Washington (the same university at which he is a professor of physics) discovering a way to convert matter from our form to this other form. Actually, there are several forms. He converts a camera into one of the other forms and back, and captures star field images from his basement lab, similar but not identical to the constellations we know. In one of the forms, there's a planet co-extant with ours. It's been cross-fertilized with small Earth life (or vice versa) --nope, that sci-fi stuff is garbage. Dark matter, whatever it is, clearly is far less interacting than normal matter, and cannot form "molecules" and "atoms" and "planets" and "life". We know this because the dark matter does not clump, does not lose energy via self-scattering, hence does not form disk-like galaxies, etc.