Warren D Smith <warren.wds@gmail.com> wrote:

In short, dark matter cannot be a particle at all subject to any of the forces were are aware of, it must be subject to some new force we have never yet found.

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) since this conversion sometimes happens spontaneously near lightning bolts. He and two children visiting the lab discover this the hard way when an accident causes the whole lab to be transported to this other form, with him and the children in it. Can they survive in this parallel world? With the equipment in the lab, can they return home, or at least send a signal? Even though nobody else knows about this discovery? I like it because it makes me think. The physics is radical, but not totally implausible. It implies that Earth's true density is only about half what it's said to be, since half of the gravity comes from the other Earth. Is that possible? How can the rotation rates just happen to be the same? (I came up with an explanation, can you?) How much can the terrain differ between the worlds without someone having already noticed? (If there were a mountain range in parallel- Florida, would anyone have noticed its gravity? Or if they had, would they have come up with another explanation, such as mass concentrations close underground?) If you converted a rocket to "vacuum Earth" and let it fall to the center of the world before you lit its engines, how much extra boost would you get? And how many times could you do this before an accumulation of spent rocket exhaust at the center made this unworkable? And how can property be protected if burglars can walk through walls and snatch it from a parallel world?