What phenomenon is created by the air returning to vacuum caused by lightning?

The phenomenon created by the air returning to vacuum caused by lightning is thunder. When lightning strikes, it rapidly heats the surrounding air to extremely high temperatures (around 30,000 degrees Fahrenheit), which causes the air to expand explosively. This rapid expansion creates a shock wave, which we hear as thunder.

The sound of thunder can be quite distinct and varies depending on the distance from the lightning strike and the surrounding environment. It is a direct result of the rapid movement of energy through the air rather than any other natural phenomena such as earthquakes, hurricanes, or the lightning strike itself, which is a visual display rather than an auditory one.