Two universes

I started The Impossible Us by Sarah Lotz last night. It's about a couple who meet online but turn out to be living in (slightly) different universes. In another timestream Tom and I would be married 42 years today. A friend who was married a week before we were posted a picture from their wedding a few days ago. In the background was Tom, who had been a groomsman. It was if he had casually dropped into my universe for a second, to say hello.

The story is leaving me to wonder a bit what my life would have been like in that other universe. Would that Michelle be here at the shore this week? Might I run into her on my morning walk, when for a brief second the two universes intersect? Or catch her out of the corner of my eye?