Atheism doesn't mean you believe in nothing. It means you don't believe in god or gods. There are plenty of powers greater than ourselves that are not gods. Gravity, physics, consciousness, the list goes on. Higher power for an atheist does not have to be group consciousness, either.
Agnosticism isn't vacillating atheism, it's more like not taking a stand either way for or against the existence of god or gods. It's quite simply saying, "I don't know", or "it is impossible to know".