Is it possible to believe in nothing?

I don't think that the definition of an "atheist" is "someone who believes in nothing". An atheist is someone who does not believe in the existence of a god or gods, as the term itself suggests (compare to "monotheism" - belief in one god, and "polytheism" - belief in many gods). An atheist, therefore, has a set of beliefs, but at the top of his pyramid you won't find a god, but something else (rationalism, science etc.).

I consider myself an atheist, and I can personally admit that to an objective observer who will try to compare my motivation to believe that there is no god to the motivation of a religious person to believe that there is a god, both motivations will bear some resemblance. At the very core, they're both irrational, since they're both based not upon empiric data and knowledge, but upon a "hunch", if you will. This "hunch" is the tool through which both the atheist and the religious person interpret the world. An earthquake, for instance, can be a sign of God's wrath (as an Israeli Knesset member from a ultra-religious party claimed recently), or it can be a result of geological activity with no moral value (As I believe).

As an atheist, I think the fundamental difference between an atheist and a person who believes in the existence of a god or gods lies in the "burden of proof". If I'm to believe that a god exists, I need to see a solid proof to that existence, that will lead to the inevitable conclusion that there is a god (mind you: it needs to be a positive proof, and not a proof that wil say, by way of elimination, "there's no other known explanation to account for a certain phenomenon"). The religious person, on the other hand, needs to see a positive and solid proof that there isn't any god. I don't believe that either proof can be found, and that the debate is pretty much at a deadlock. It's all a matter of belief.

An atheist doesn't believe in nothing.  He accepts those things that are logically plausible or proven by scientific reality.  It isn't a matter of being religious.  It is simply that an atheist has no reason to "believe" in something that can't be proven.

But an atheist would tell you it "is possible to believe in nothing" -- look at all the God-fearing believers in the world.

Is it possible to know anything?

Atheism, as a philosophical view, is the position that either affirms the nonexistence of gods or rejects theism (wikipedia)

In other words, atheism in its positive form affirms that there is no God or in its negative forms rejects the possibility of the existence of a supernatural being, whatever its shape or content.

Essentially atheism does not equal to believe in nothing, because that would be impossible. Even to acknowledge the world around us, as exposed through our senses is a form of belief.  How can we be absolutely sure that what we see is really there? Belief in essence is a form of knowledge, and knowledge is a form of belief. To believe in nothing would amount to not being alife. So the answer to your question is no, it is not possible to believe in nothing.  

Atheism is not to be confused with secularism, which tends to advocate freedom of religious feeling. Secularist thinkers such as Voltaire or Rousseau for instance, admitted they believed in God, although they refused to follow a set of rules dictated by a religious system such as Christianity, Judaism etc.

My personal question to any self-proclaimed atheist is “If the supernatural does not exist, How is possible to explain the world in purely empirical terms” The creation of the world for instance… An atheist will certainly not contradict that matter can not come into existence by itself. If nothing exists above matter, how is possible that matter came into being?  

If this "nothing" you refer to is "God" then yes. Seriously though, atheism just means one thing (a lack of belief in all the God claims out there) any idea beyond that can differ from atheist to atheist.