I have been following stories about dark matter and have, I think, a layman's grasp of it, to whit: In 1933 the Swiss astrophysicist Fritz Zwicky, who studied clusters of galaxies while working at the California Institute of Technology, made an inference similar to one previously made by Carl Oort. Zwicky applied the virial theorem to the Coma cluster of galaxies and obtained evidence of unseen mass. Zwicky estimated the cluster's total mass based on the motions of galaxies near its edge and compared that estimate to one based on the number of galaxies and total brightness of the cluster. He found that there was about 400 times more estimated mass than was visually observable. The gravity of the visible galaxies in the cluster would be far too small for such fast orbits, so something extra was required. This is known as the "missing mass problem". Based on these conclusions, Zwicky inferred that there must be some non-visible form of matter which would provide enough of the mass and gravity to hold the cluster together (adapted from Wikipedia). Now I was listening to a radio interview with Laurence Krauss, when he visited Sydney once, maybe 7 years ago. The subject of dark matter was broached, and the interviewer, a very scientifically-literate radio host called Spencer, casually opined that we might be 'sorrounded by' dark matter, even as we speak; that it might, as it were, interpenetrate the everyday domain of experience, but it exists in such a form that we can't detect it. Krauss appeared to assent to that - very casually, I thought - 'indeed, it might' - and the conversation moved on. But that idea has stayed with me ever since. What if, I thought, the actual extent of mass or matter, even right here in front of us, is actually some large percentage more that what we can actually measure? What if 'dark matter' is actually an imperceptible component of everything that exists around us? What if, then, the totality of matter that is detected by both instruments and sense, is less that what is really there? I mean, it is not at all established that dark matter hangs around in interstellar space like a large kind of blob of stuff. This kind of depiction indicated that it might not ever be detectable, even when you're sorrounded by it. So if it is actually all around us, it amounts to a kind of hidden dimension or component of everything that exists. I can imagine an Arthur Conan Doyle, or someone of that ilk, making something of it. But it doesn't sound very 'scientific'. It actually sounds more like science fiction to me.