What do you think dark matter really is?
Why do you think it is important?
And does it REALLY matter?
Is that so, cosmo?
Then you can tell me what you think it is and why it we wouldn’t exist without it.
I assume you know exactly what it is after spending half your life studying?
Or have you no real answer?
I like how you stated your question – very clever!
First – what is dark matter. Dark matter is dark because it is unseen and because it is unknown or more importantly unexplained. Lord Kelvin in the 19th Century estimated that if the Sun burned do to chemical reactions it would burn out in 30,000 years. But as it was discovered that the earth had a history much older than that, there must be something else that fuels the Sun and stars. It was not until nuclear energy was discovered and investigated in the 20th Century that we understood what happens within a star like the Sun.
Dark matter represents a similar mystery. If galaxies represent all the matter that matters, then as Zwicky first discovered we would expect a drop off in the velocities of stars as they orbit further from the center of the galaxy. Instead, Zwicky saw that galaxies have rotation curves as though they were orders of magnitude greater than what we see. The same holds for galaxy clusters of all sizes. So a mystery.
The other part of darkness – unseen – comes from the fact if we have unseen matter all over the place but yet can see back to the beginning of the universe, then the dark matter cannot interact strongly with light. Call that our first clue.
As to the second part of your question. It matters only if faced with a mystery you must find an answer. Of course it would be difficult to accept any of our current physical theories if they cannot explain this mystery, and in turn the validity of any scientific pursuit if mysteries as fundamental as where is matter can be left unanswered. Whether or not it is a big deal once the answer is found – don’t know, but maybe.