Dark energy conundrum

[water rat]

I'm relatively new to astronomy (just putting the finishing touches to my viewing plinth in the back garden) and I'm puzzled. We're told that the more distant objects are the faster they are travelling away from us which "proves" that universal expansion is accelerating and that supposedly proves that dark energy exists. How can this be? Surely if distant objects are travelling faster that means the universe was expanding faster in the distant past, so universal expansion is slowing down or have I misunderstood something? I'd appreciate your views on this.

[Stephen]

I think you got the initial assumption wrong.

Distant objects travelling faster proves expansion - not acceleration.

Type 1a supernovas being 15% further away than an non accelerating model predicts proves acceleration?

I could be wrong but I thought it was something like that