Why am I certain that God is real? In facing a question like this one it is important on the one hand to distinguish between "what has to exist" (sometimes called "necessity"), and what is "in need of an explanation" on the other hand. Many questions about god, I will claim, are questions about what is necessary. An example will help. There is a formula for solving quadratic equations, which every high school student learns in algebra; but there is no formula for the general quintic. This latter fact is a result that every first-year college algebra student learns. It follows from this that if god were to exist god might know the solution to any quintic, but god would not be able to write down a general solution because it is possible to prove that no such equation exists. Every quintic has a solution (in fact it has 5 of them and for the same reason that a quadratic has 2). This is a necessary feature of algebra; that is to say, it is necessarily true once one discovers algebra. Since this fact is logically necessary does it make sense for someone say, "Well, do you have any evidence for that?" Well, no there is no "evidence" that a formula for solving the general quintic does not exist. Indeed, it doesn't make sense in this case to ask for evidence: the assertion that there is no formula for solving the general quintic is still true because it is necessary. This is a product of how one works through the questions arising from thinking algebraically. Moreover, anyone asking for evidence completely misunderstands what algebra is about.
There are, however, lots of situations where asking for evidence, asking for an explanation, seems to make good sense. Physics, chemistry, biology, botany and astronomy are good cases in point. It makes sense to ask, for example, "Why does the DNA in my mitochondria come only from my mother and not my father?" There is something very different about this question than the question about algebra, and it seems to be of a type where asking for evidence seems warranted. Physicists, likewise, are bent on providing explanations of this sort, and they are careful when they meet questions of the former kind not to confuse the two. So, for example, good physicists will happily assert that everything we see around us is subject to needing an explanation: people, trees, water, the solar system, galaxies, volcanic sand, bacteria, states of mind; all stand in reference to this latter sort of questioning: "Why are things this way and not some other way?" This happens in the Astronomy section of Y!A all the time. "Why is the sky blue," "Why is the sun yellow," "Where does the universe end," "How old is the earth," all these questions and more show up with astonishing regularity! So, why is the sky blue and not red? Why are all large solid bodies roughly spherical in shape? Why is the sun yellowish? Why is the solar system stable over long periods of time?
To move on, care needs to be taken when lumping individual items into systems because not every attribute of a planet, say, becomes an attribute of a solar system. The importance of this will be apparent in a moment. It is not always clear how explaining the individual parts of a system explains the whole system. For example, no good physicist would claim that a wall made of small bricks was, therefore, a small wall; but it would still be a brick wall. A pile of $10.00 on a table isn't an "empty" pile when the money is spent. None of us would assert --except as a joke-- that the world is littered with empty piles of $10.00 dollar bills. So, it makes sense to ask "How did this pile of $10.00 dollar bills get here" without the answer being "Well, the pile was always here, it just has $10.00 dollar bills now, whereas before it was just an empty pile." The pile of $10.00 dollar bills itself is susceptible to the same sort of questioning that the sky is, that the solar system is. There are planets and stars, is there such a thing as a solar system? Sure. Is there such a thing as "the universe as a whole?"
At each step in this process of asking questions we always ask for a set of reasons (sometimes those reason give evidence and sometime they do not) which give us some explanation for what we see. Now for the question that leads to the concept of "god." When do we ever stop asking for an explanation or for evidence? When we cite reasons which are perforce necessary. When the chain of reasons, of lists of evidence finally rests on a reason that is necessary, we are done. For example, there is no equation from which one can derive the positions of the planets of our solar system. This is called, in the parlance of mathematicians, the "n-body" problem. If the solar system were composed of exactly two bodies which were themselves perfectly rigid spheres, and if they were reasonably small and at a great distance from each other, then there is such an equation, which was derived by Isaac Newton. But when the number of bodies is greater than 2 then no such formula exists; and it can be proved that there is no such formula. There are *numeric* solutions which can be quite good over long spans of time; but no general solution. No physicist searches for one; what's the point? Likewise, absolute zero is what it is. Occasionally on Y!A physics, one sees the question "can something get colder than absolute zero?" Asking that question makes clear that the person asking does not understand what "absolute zero" means, nor why it follows from the way one thinks in the process of discovering physics. Questions into the nature of what is necessary have to be asked with great care, or one starts talking nonsense without realizing it. If Einstein is correct, then on cannot travel faster than light. Yet, people persist in posing a question such as, "Well, suppose one could travel faster than light..." All answers to questions that start out like that are nonsensical unless the answer is "One cannot travel faster than light..." It is a necessary condition of General Relativity that one cannot travel faster than light.
So, when one faces all that physicists, biologists, psychologists, chemists, geologists and astronomers have discovered it does indeed make sense to ask, "Is there a reason for all of that?" Is there a reason for the "Universe as a whole?" One can, of course, choose not to face ths question, one can minimized the question, but those are personal issues of integrity; yet as the discussion shows this question still makes sense to ask.
The answer to that question is what Muslims, Jews, Christians, Taoists, Wiccans, and the like refer to when they use the term "god." As a consequence, there is no "evidence" for god, nor does god need further explanation. Quadratic equations have a general formula for their solution, the n-body problem is not solvable, god is the answer to a particular question and there is no "going beyond" these. There is no good way to answer the question, "Well, can you give me some evidence that every quintic has a solution without an explicit formula?" It follows from a whole way of thinking about algebra that it is so. The same is true for the speed of light. It is a necessary consequence. The same is true for god. As I pointed out, god is the answer to, god follows from, a whole system of questioning.
HTH
Charles