Proof: (noun) Evidence or argument establishing or helping to establish a fact or the truth of statement. 

I would like to preface this post with the point that the word proof, by definition, is evidence or argument. A big argument people make is that nobody can prove 100% that God does not exist.  There are two types of proofs. One is common only in mathematics.

"Here is a mathematical theorem: There is no largest prime number. And here is a proof:

Consider the list of all primes, pi, starting with p1 = 2. Suppose that there is a largest prime, p*. Then there are only a finite number of primes. Now consider the number X that we obtain by multiplying together all of the primes pi (exactly once each) from 2 to p* and adding 1 to the result. Then X is clearly larger than any of the primes pi. But it is not divisible by any of them, since dividing by any of them yields a remainder 1. Therefore X, since it has no prime factors, is prime. We have thus constructed a prime larger than p*, which is a contradiction. Therefore there is no largest prime." (Sean, What I Believe but Cannot Prove, Cosmicvariance.com)

   The other kind of proof is what we use everyday. We use it in our court systems, we use it to prove sound travels at 340 meters per second in air, we use it to prove that small capsules of water have certain pH levels. This kind of proof is not infallible. We "prove" their existence or truth with evidence. 

   A philosopher, (and I apologize for not quoting him because I can't remember who it was), once said that he could not prove that everyone wasn't just a detached brain sitting in a vat and having signals sent to it, but it is impractical to think that we are. 

Nearly everything in the world we live in cannot be proven in the same way that mathematics can be proven ("100%"). We rely on evidence. A good system we like to use the scientific method. Which required you to test your hypothesis, and only after the test results are constant with your hypothesis, do you have a theory. This is how the scientific community has been solving the questions of the universe for years. 

   Heres some interesting "theories" that have come out of the scientific method:

sex theory: the theory that sexual intercourse is the process that results in reproduction. 

round earth theory: the theory that states that the earth is spherical.

gravity theory, atom theory, molecular theory, relativity theory, the list goes on and on. We accept these theories because of the evidence that exists to support them. This evidence, by definition, and by law, is proof. 

   Some other theories, equally supported by evidence, are the evolution theory and Abiogenic theory (Origin-of-life theory). These are the scientific systems that break down and disprove the existence of God.

   "God" is the name that Christians call their god. They also call him Lord, Jesus, Elohim. Muslims call their god "Allah", while Jews call their god "Yhwh". Greeks had plenty of names for their Gods. Egyptians had plenty as well. This God is presumed to have created man, created life, and created the universe in seven days time some 6-10 thousand years ago. This can be proven wrong with modern science and physics. Science has proven, with evidence, that the earth is around 4.54 billion years old. Man evolved from primate. Life originated on earth 4.4 billion years ago through a process known as abiogenisis. And the universe from the time of the big bang to present is around 13.73 billion years old. 

   Every publicly accepted definition of God can be proven wrong with evidence. Allah can be proven wrong, the christian god can be proven wrong, the hindu Krishna, the Buddha, Zeus, all can be proven wrong with scientific evidence. When it comes right down to it, proof is evidence. Theism has no physical evidence that supports it's hypothesis. The science that refutes it has endless physical evidence to support it's hypotheses.  

   The only argument that Theists have left is to change their definition of "God" into something that science cannot yet explain. For example "Where did the universe come from? this must be god". We as a human race cannot yet explain a few things, but please note, we were once asking "where did man come from? this must be god",  but in the end we realized, man came from primates, evolving over billions of years. Another argument in the validation of god is to change the definition into anything else. for example "God is love". This is similar to saying "God is the sun, and I believe in the sun, so I believe in god" (even though we all know hat the sun is a giant ball of burning gas in the center of our solar system). Or to quote a member in another discussion on this site "God is everything including nothing". We already have a definition for "everything including nothing", it's called existence. This argument does not validate the existence of a higher being it simply takes the idea of "god" or the word "god"  a puts it safely behind the definition of something else. 

   God, as most of the world defines it,  was disproved some time ago. It's possible people hold onto the notion of god because it brings something important to their life. Meaning, or guidance. But I encourage those who cling to the word "God" as a form of guidance to look in all forms of philosophy. The same teachings that Jesus taught exist in plenty of world philosophies, they are not unique to the bible. Nor are the philosophies of Muhammad unique to the Koran, or ancient asian philosophy unique to Confucius. You can get the same lessons the Jesus taught out of "To Kill a Mockingbird".  There are common philosophies in all cultures to help explain how we should live our lives. That commonality is not, however, a big man in the sky who created the universe. It's morality.

   There is little left in the universe that cannot be explained by science. As the argument for God is dismantled piece by piece, theists like to place their definition of god into the small portion of existence that cannot yet be explained. But at this point, they are no longer asking to disprove God. What they are really asking to disprove is "existence" or "love" or anything else they can put the name God onto. These remaining definitions of god are hypotheses that have not been tested, they hold no ground because they have no physical evidence to support them. 

  Heres a parable for you theists: 

  So if we were to tally up the metaphorical score:

As the game of answering the questions of the universe and all it's workings nears the end of the final quarter the score is: 

   Science has answered, with evidence: 1,025,291 questions

   Theism has answered: 0 questions. 

   30 second to go, before all questions are answered. Good luck, theists, and agnostics.

God: (noun) The creator and ruler of the universe and source of all moral authority; the supreme being. A superhuman being or spirit worshiped as having power over nature or human forces; a diety. 

Proof: (noun) Evidence or argument establishing or helping to establish a fact or the truth of statement. 

Science proves god does not exist.