We had opened the wormhole accidentally, nearly fifty years ago. As it turned out, a glitch in the third Large Hadron Collider caused tiny wormholes to open for nanoseconds at a time. No one noticed. This happened for eight years until one of these tiny holes never closed. The other side of this portal between space and time held a sort of exotic matter with negative energy density which caused the wormhole to stabilize. Then it grew.
After six months it was large enough for a ship to fly through.
After seven months, one did.
And it completely ignored us.