Came life from space?

[Robert Andersen]

I got a hyphotesis: The sun uses about 270 million years to complete 1 
circle around the center of the milky way, if Earth has existed for about 
5 000 000 000 years we got about 18 trips around the galaxy. In that time 
we will have travelled past a lot of stars in the milky way, stars who 
may had life on one of their planets, perhaps even developed life.
Is this a possibility?