What Am I Riddles

Question: i can fill up the entire room and still not take up any space. Who am i?

Question: My memory is good, nay, more like perfect Yet I only remember two things.

Question: You see us everyday, but you never see us together. We appear everywhere but never are we together at the same place. Who are we?

Question: When people cut me, I do not bleed. They use me, but then they leave. I die, but then revive. I change my appearance as time goes by. What am I?

Question: When you are born, all you have is me. And even though you're powerless, you are filled with glee. What am I?