ANOTHER great question!
I've broken your question down into 2 parts, one dealing with what the Universe is doing here in the first place, and another part about what will happen in the future.

Here's some thoughts;
1. The Universe – why is it there?
Romans 1 19-20 tells us that God uses the Universe in all its glory, to be a witness to his eternal power and divine nature.

In other words, people with hearts which desire to turn to God will look at the Universe, see his nature and surrender their hearts to him. This is what the Writer refers to in Rom 2 14-15 about Gentiles, who at that time, had not heard about God – they were still expected to see and respond to his nature.

And what does our knowledge of the Universe tell us about the nature of God?
Words which spring to mind:
Power
Design
Joy in creativity
Eye for beauty
Extravagance (Any God who enjoys making every snowflake different has got to be having a whale of a time with quasars, pulsars, black holes, dark matter, galaxies, and other chocolate bars.)
Infinite provision
Desire to bless Man with more than he could ever comprehend

OK, I’m sure I could think of more, but I’ll be sitting here all night!

The other part of your question asks why ever create something which nobody will ever observe?

Ah, but will they?

2. The End
God created this universe for a spotless bride people to live in.

Unfortunately, the earliest members of that race gave away to satan the authority over the universe that they had been given.

(If they had taken of the Tree of Life, instead of the other tree, they would have received resurrection bodies, as we shall do one day, and I think they would have had access to the whole of the Universe.)

But they didn't and the "whole creation" fell into decay (Rom 8 21) -presumably because the authority to take care of it had been surrendered.

And as it turned out, we're told by both Peter and John that there will be, in the end, a "new heaven and a new earth" (2 Peter 3 13 and Rev 21 1).

Jesus tells us that the stars will fall from heaven Mk 13 24

Whether this really means that the whole Universe will be replaced, or just our small part of it, I don’t know, I would suggest the whole will be replaced. However it is certain that this earth will disappear along with at least some part of what the ancients would have termed the “Sky”.

(I think that will mean Sky Sport will go too! {:-O)

So what will it be replaced by? I would suggest that the old will serve as the pattern for the new. This would fit the way in which God works, examples being the Temple being a pattern for the throne room of God in heaven, marriage being the pattern for the relationship between Jesus and the church, sacrifices being the picture of His death for us and so on.

Whatever way it works, there will be a Universe there, just as wonderful, or maybe more so, than the one we have now.

Why?

So we can explore it!

If you now read my post to the questions called “What would Heaven be like?” you’ll find info about this in section 5.