Objects in the game view only and not in the scene view

I am following along with the Space Shooter tutorial and after adding the Quad to hold the bacgkround (in video 4) i did something and now i cannot see anymore objects in the scene view, while i see them in the game view.

Basically my scene view is empty, while i see the ship and the quad in the game view. i guess there is some shortcut or flag that removes all and i would like to reset it again.

Any idea?

After trial and error i found. What was happening was that i zoomed out too much (probably with some shortcut) and so all the objects were too far away.
So my problem is solved, i keep the question for reference.