(March 2, 2018 at 6:55 pm)polymath257 Wrote: Well, in a sense, that is how we discovered dark matter and how we investigate its properties. Dark matter doesn't interact with ordinary matter or light very strongly (if at all). So in a sense, it satisfies your criteria.
We use the way that dark matter bends light to map out where it is and how much is there. We do that by looking at slight distortions in the way light travels from more distant objects. So, there is a sense in which we are detecting the water just as you suggested.
That's what I was thinking, although I haven't heard of applying dark matter to light bending.
