The whole point of "dark" in the dark matter and energy cases is to indicate "we don't know." It looks like there needs to be something there for everything to

The whole point of "dark" in the dark matter and energy cases is to indicate "we don't know." It looks like there needs to be something there for everything to make sense, but we can't see it. Let's try to work out what the properties of the stuff is based on what we can measure and see if anything starts to make sense.