astronomy Cosmology Creation/evolution Physics Science

Why is Dark Matter everywhere in the cosmos?

A product of the Dark Side

Sombrero Galaxy Credit: NASA/ESA and The Hubble Heritage Team (STScI/AURA)

Why is dark matter assumed to exist in the cosmos? From reading news headlines you would think it has been clearly identified and that we now know so much about this once elusive stuff. It has been sought in many different laboratory experiments for more than four decades now, but never found. Why then are astronomers so confident it is out there? Let me try to put this into context and I hope it will become clear.