I was seated in my backyard observing sky while playing with my child and at 4:15PDT, I noticed an extremely fast moving object traveling from NE to SE in a straight line. It was completely silent, no smoke trail. Disappeared behind group of trees, got up off chair, ran to see it emerge from behind the trees and it was gone. As a former commercial pilot and 38 year aviation expert, I can not explain what the object was. I have seen meteorites, satellites and other natural and made objects move across the sky, but not at such an extreme speed, especially without a sonic boom.