This question may seem, on first inspection, to be simple, but it’s not. We will see that this question is phenomenally complex. Indeed this seems to be a pattern of many questions on religious topics. Once more, the complicated nature of the question is revealed through the definitions used to express it.
We need to define evidence, existence, and most importantly, whatever this god character is. But rather than waste time investigating the possibilities and realities of existence, we will just use the common understanding of the term. The same goes for evidence.
Let’s start by looking at one of the simplest definitions of a god. We define this god to be a singular, supernatural, transcendent being, by which we mean that its state of existence is not controlled by the universe. It is not part of the universe, nor subject to its laws. We ascribe no further properties or functions to this being. It is not necessarily intelligent or powerful in any way.
You might question whether there would be any point calling this being a god, because it is so vastly different to the common understanding of a what a god is. For this definition, there is no evidence. We didn’t specify whether this being could interact with the universe, nor whether it would have any reason to, nor whether this being could reason at all. No information passes from this being to things within the universe. So this being has no footprints, no evidence. But then, we’re not really interested in this type of being.
Now let’s elucidate upon the definition. Let’s say that this being is the cause for the universe to exist. Now we have not said that the universe requires a cause. We simply stated that in this case, we’re giving the universe a cause and this god being is it.
Well, our definition is still very simple, all we’ve essentially done is state that the universe has a trigger, and the trigger is god. If the universe did indeed need a cause, then that would count as evidence in favour of this very simple definition of a god. But remember that this god is not necessarily sentient, nor involved with the events in the universe in any way. This god so far is not personal, nor communicative. This god doesn’t know, or even care, who you are or what goes on in your life.
Furthermore we don’t know whether the universe requires a trigger. This is discussed more comprehensively in another article on this site. Ultimately, philosophy alone is not capable of determining whether the universe requires a cause. The main problem is that if a god does not require a cause, why must a universe require a cause? So we’ll have to wait until physics finds out, which could be a long time if ever.
Note also that so far we’ve seen only simple definitions of a god. Some consider the idea that simple things do not require a cause and complex things do. But as we increase the complexity of this god character, this notion gets turned on it’s head, and it becomes less and less reasonable to suggest that a god might not need a cause.
Now there are a variety of intermediate stages between the previous definition and the next one. However most people who claim that there is evidence for a god will tend to claim that divine intervention is directly responsible for making life possible in the universe. So we need to give this god some properties which mean that it can be responsible for life. If this is true then it needs to be immensely knowledgeable, though not necessarily omniscient, because this god needs to be able to figure out what life is and how to create it. This god also needs to have some degree of access to the control panel of the universe. What we have essentially a defined, is a god that created the universe with intent that life would be in it. We’re not saying yet that the god has any involvement with the day-to-day running of the universe.
Many people will claim that the evidence for this initial divine intervention is everywhere. They will claim that without the specific intention of something to create life, life could not have formed. Now we have reached the world of mainstream debate on this subject. The evidence that is claimed to prove this notion is taken from all the sciences, but the majority from evolution. That’s right, we’ve reached creationism. Every time a species is discovered, either living or fossilised, and this species has some feature that is difficult to explain with evolution, a gang of creationists jumps on it. They clearly have ulterior motives for proclaiming that their beliefs are true, but try to suggest that they have scientific evidence in their favour.
Science always looks for the best explanation of all the facts. The explanation that a god did it is a terrible explanation, because it merely states that the willpower of a supernatural being is enough for something to happen. No scientific theory in history has been this simple, and none has carried with it so many assumptions (this article is already getting too long, so I won’t list these here). This notion does not explain the fact that around the animal kingdom, there are many features which would exhibit absurd design. Animals are full of imperfections. It would be a better explanation that a sentient species of another planet was the progenitor for life on planet earth, as this could explain imperfections, as well as difficulties with abiogenesis.
Bizarrely, others will increase the complexity of the god they believe in, only to have the god do less. The more liberal minded religious people tend to think that a god may have started the universe, and may have limited intervention with it, though is not quite so responsible for existence of life. It is now that we increase the definition of a god to one which can communicate with human beings at least, and any object at most. This god must now be sentient, thoughtful, insightful. This god must be reasonably powerful, as it has not only created the universe with design, but can communicate with things in it. This god is intelligent.
Again, we’ve jumped across many possible definitions of a god to arrive at one which many people believe in. People will cite their own personal experiences for the existence of this god. This is often the only evidence that is put forward, but it’s not even evidence. Science relies on the fact that evidence can be obtained any number of times. Scientific claims are testable, cross-examinable, and unbiased. It is not possible to know whether or not you genuinely had some communicative experience with this intelligent, transcendent being. Many people who think they’ve had this experience might be delusional, only under the impression that they had this contact.
I could go on, but it would get tiresome. It is now obvious just how difficult it is to answer what would appear to be such a simple question. Hence the position of atheism is that if there is any real evidence, it is at most inconclusive.