Why haven't we bumped into another universe yet?

The multiverse idea states that there are an arbitrarily large number of Universes like our own, but that doesn’t necessarily mean there’s another version of us out there, and it certainly doesn’t mean there’s any chance of running into an alternate version of yourself… or anything from another Universe at all.

The Universe we inhabit is vast, full of matter and energy, and expanding at a tremendous clip. Looking billions of light years away, we can see billions of years into our ancient past, finding evidence of newly-forming planets, stars, and galaxies. We’ve seen so far back that we’ve identified clouds of gas that have never yet formed a single star, and found galaxies from when the Universe was only 3% of its current age. Most spectacularly, we can actually see the leftover glow from the Big Bang, from a time when the Universe was a mere 380,000 years old. Yet in all of this cosmic enormity, we’ve never found evidence that our Universe has bumped into another one in this vast Multiverse. Why not?