18 Inches

If I remember correctly -- or I could have made this up -- there is an invisible bubble with an 18 inch radius around each of us. It encompasses our personal space. Maybe for some people, the bubble is smaller, and for some I'm sure its diameter is even wider. However, most of us know the moment that bubble has been breached. For some reason, if someone we don't normally allow in our personal spaces decides to move within that 18 inches, we sense it immediately. Personally, I instantly feel my shoulders tense up, and my jaw clenches. It's as if I'm bracing for an imminent invasion. While I could be an extreme case (which I doubt), I know I'm not the only one who reacts this way; check your own response. Given the universality of this experience, it completely blows my mind when idiots get on an almost empty elevator with me and proceed to invade my 18 inches when they could be taking up space several feet away from me.