Breaches

A breach is hole or rift in the dimensional barrier, bridging worlds together. Fifty-two breaches between Earth One and Earth Two were created when time was tampered with in "Fast Enough." Normally only speedsters can pass through breaches, but somehow Harry was able to cross over to Earth One using a breach. It was said that Zoom could see and hear through the breaches, but it's unclear whether he could himself or was using Reverb to do it, who could at least open portals to Earth One, and potentially more, and so can Vibe.