The Universe is not expanding - it is infinite - what is infinite can not expand.

Dark energy is a misnomer, Fred Hoyle disbuted this back in the 50,s but then we discovered background radiation, even Albert Einstein changed his mind. ,

I have my own view. I feel the universe is growing, ie it is growing more (STUFF) on teh outer edges, and this is pulling it away from the centre rather than it expanding out form a big bang.
I consider it like a catalyst, the stuff we have triggers ther stuff to form, out there is bigger and has more stuff, so more gravity.

The universe is expanding faster now than it has in the past. Under current models of gravity this doesn't make sense. Also under current models of gravity most galaxies don't have enough mass to sustain themselves and should fly apart. Dark matter and dark energy are inferred by some of the data but are not yet proven. Either there is another force acting in the universe that we don't yet understand or some of our current models are flawed.

Ther're not sure what it is at the moment.

Too much fat in its diet. Trump is the dark energy in the Universe.

Billions of $ are being spent to answer your question yearly. I hope they can identify it before I leave this planet. I just love the study of the universe as it has so much to offer.

"Dark energy" is a term used basically as a place holder. We know something is there, but science hasn't yet determined what it is.

My belief is that there's more than one mechanism at play. That would also help to explain why its properties are so difficult to determine. The energy you describe, in my view, is actually creating space because it possesses a property which produces an effect causing a repulsive force that operates like gravity in reverse. The space created causes the formation of virtual particles most of which quickly vanish back into the fabric if spacetime .

I never realized how crazy that seems until I tried to explain it in writing.

Gravity is the cause of the expansion . Not sure if they have found any dark matter yet so can't say anything about that