A god is a being that's claimed to exist in a "mythical realm" and "outside of" the natural world. If something does not reside in the natural world then its existence cannot be tested or disproved by those who do reside in the natural world. Its existence also cannot be proven so any claim of its existence would be a dishonest one equal to saying, "it exists because I want it too."

There are two basic types of gods. A deistic god is claimed to be a conscious creator of the universe. A theistic god, aka a "personal god," is claimed to also interact with our daily lives. Both of these claims can in fact be tested through science, the study of the natural world. It is the claimed interactions with the natural world than we can prove or disprove the existence of.
 

"God" As A Term

In a poetic non literal use of the word "god" some philosophers and scientists like Albert Einstein have used it to describe a oneness of the universe. That oneness or "god" is however not a conscious being but rather a math equation or the smallest building block that all of existence is made out of. In a 1954 letter Einstein actually called the belief in a theistic god a "childish superstition."

Supernatural Interactions? All of nature follows certain basic "laws" that we have a firm understanding of. These laws are not guidelines or policies like human laws but rather observations of the constants and limitations of what nature can and cannot do without supernatural or divine intervention. In the case of Christianity its holy texts describe a personal god that regularly interrupts the known constants and limitations of nature. Such gods are said to interact with our daily lives through supernatural acts which go against all that we know about the laws of nature. Yet in real life we see nothing like this at all, the closest we get are non-supernatural miracles that tend to be nothing more than simple coincidences. Never in the known history has their been any sign of a being (or anything for that matter) interrupting the laws of nature.

Natural Interactions? One could try to argue that a god interacts with our daily lives by controlling natural events instead of supernatural events like the Bible claims. This is a stretch but thankfully there is still a way to test this claim with one simple question. Do natural events favor particular actions or groups of people? Native Americans noticed that after doing a certain dance rain fell from the sky and in hopes to make rain fall again they would repeat this dance until it did. We now know that this was just a superstition and that the weather is not influenced by what dances we do or don't do. The same goes with all natural events as nature is not influenced by attempts to please a possible personal god. Weather rewards us and punishes us equally no matter our moral path or what god we pray to. We now have an in depth understanding of how nature operates and no longer have a need to place hope in ancient superstitions.

 

Thanks to modern studies in the field of cognitive science we have a rather in depth understanding of how the brain functions and more impressively what causes and is required for consciousness. The consciousness, intelligence, and thinking ability of all known conscious beings are constructed by, formed by, and dependent on the physical structure and neuron patterns of the brain. Which means all known examples of consciousness cannot exist without a physical structure and thus the material world had to came first, before consciousness could exist. So a conscious force could not have created the material world.

Before basic cognitive science it was imagined that consciousness was a magical entity separate from the material world. This is where the concept of souls came from along with the idea of a conscious force being a possible option for what created the universe. The next question is, if consciousness could not have created nature could nature have created consciousness? The answer is a solid yes. Science has explained how complex conscious brains evolved by means of a natural non-conscious designer from primitive nervous systems like that of the hydra, a tiny aquatic invertebrate. We also now known that every part of all conscious beings are formed out of non-life, atoms. And those atoms that build up our bodies, brains, and give us the ability to have consciousness were literally formed in by the stars. To answer the initial question, the material world came first, then consciousness.
 

The Conclusion...

Creator gods are all based on a lack of knowledge about life's and earth's origins. Not being content with the absolute lack of known evidence to explain our origins ancient man imagined their own stories. Since man was the one who came up with the creation stories there usually was an emphasis on man putting him above all other creations. Over time these stories gathered believers and made their way into religions/cults. Personal gods are based on the assumption that nature was controlled in the same way we control inanimate objects. Ancient man knew that when an arrow is shot across the sky it was done so by a conscious being so when they saw lightning shot across the sky it was only natural to assume it too was done so by a conscious being. Since we are dependent on nature ancient man tried to seek ways to appease the supposed conscious being they thought was controlling the world around us. Bottom line, all gods are based on nothing more than a lack of knowledge, a lack of understanding, and pure wishful thinking.

Every single phenomena where a god was invented for its explanation now, thanks to modern knowledge, has a more elegantly simple natural explanation. We have come to know a lot about the universe and how nature operates since the time of gods and every explanation never required the involvement of a conscious being intervening. If everything which no longer has an unknown explanation required no need to invoke a god then why should we assume those that currently still have unknown explanations require the need to invoke a god? Lets face it, we were wrong about the whole god thing.