What do you mean? There's lots of evidence that the expansion of the universe is accelerating and that's the whole reason we believe that dark energy exists. Most cosmologists do believe we're heading for a big rip.
No, "big rip" and "accelerating expansion" are not the same thing. A big rip would require that the density of dark energy in the universe is increasing with time. We have no evidence that it is, and most cosmologists do not believe we are heading for a big rip.
No, most cosmologists believe we're heading for the Big Freeze.
The Big Rip would require something called "phantom energy", a special form of dark energy. While not entirely ruled out, our observations disfavor it and it would be problematic from a theoretic standpoint.
According to TFA, it's the "most direct and strongest evidence for the accelerating universe" that's now possibly an artifact. As I understand it, "dark energy" is fundamentally just another way to say "accelerating expansion".
The big rip would imply that eventually, all points in space are accelerating away from one another faster than the speed of light, which would tear apart atoms, subatomic particles, and everything down to the smallest divisible units of matter and energy. The accelerating expansion doesn't imply this at all, and would instead leave big dense things like galaxies intact to burn out and fade away.
Acceleration comes from the cosmological constant - more volume means more dark energy, which means more velocity (acceleration). Only if the cosmological constant isn't constant would we expect a big rip.
Now, we're questioning the acceleration part also apparently.
