Our cosmology assumes that most matter comes in a “dark” form that hasn’t yet been detected. It relies on Albert Einstein’s cosmological constant, a seemingly arbitrary addition, to explain why the universe’s expansion is apparently speeding up. Even if you are prepared to overlook these difficulties, there is the unsolved question of what the universe was doing before it was expanding.
… I introduced the mystery elements of dark matter and dark energy into our standard cosmology. So is the model I helped construct right; is our cosmology a true reflection of reality? In what follows, I will strongly argue yes – but only as far as that goes.Jim Peebles, “Why the universe I invented is right – but still not the final answer” at New Scientist (paywall)
Throw in a multiverse and pop science will believe. Hey. We can’t help that.