Philosophers distinguish between "Soft Atheism" and "Hard Atheism."
"Soft Atheism" is the position that, as long as there is no evidence for the existence of a God, there is no more reason to believe in a God than to believe in gremlins or unicorns. In the absence of evidence, a reasonable human holds that gremlins, unicorns and gods are fictions that don't exist in reality.
"Hard Atheism" is the position that a belief in the existence of a God would contradict known facts of reality. Historically, "hard" Atheism was typically associated with the position that the properties attributed to the God or Gods of some specific religion were mutually contradictory, or stood in contradiction to known facts. This is not difficult to establish with respect to, for example, the attributes of omnipotence, omniscience and benevolence traditionally ascribed to God in Abrahamic monotheisms. But the attributes ascribed to God differ from religion to religion; a Hindu or a Deist need not ascribe to her God any of the traditional attributes from this list. Until the last half-century, hard Atheism was always associated with preclusion of some specific religious conception of God, rather than of God/Gods in general.
A "hard Atheism" independent of any specific religious conception of God can only be based on a contradiction between reality and those attributes that are shared by every conceivable God of any conceivable religion. There are two such attributes: consciousness and non-measurability. A measurable entity cannot be "transcendent," and an entity incapable of awareness cannot be "spiritual" in any religious sense of those terms. Thus, a demonstration that the same entity cannot be simultaneously non-measurable and aware would be a foundation of a Hard Atheism independent of any specific religion's list of the attributes of its God. It would be the foundation of a simultaneously "hard" and universal Atheism.
The steps in demonstrating the contradiction are as follows:
(1) Mass and energy are measurable. To be non-measurable, a God cannot be physical in the sense of being composed of, or containing, matter or energy. A God is non-physical.
(2) To be aware is to be aware of the identity of something. To be aware, an aware God must have information about the identity of whatever it is ware of. A God must have information.
(3) The quantity of information in an entity, is given by Shannon's Law applied to the range of possible states of its physical attributes. For that quantity to be non-zero, the entity must have physical attributes with measurable properties. But only physical entities composed of matter and energy can have measurable properties and states. Therefore only physical entities composed of matter and energy can contain or carry information. (For more detail on this, an explanation of the need in every data network protocol stack, for a physical layer to carry the information, can be found in any standard textbook on data networks.)
(4) Therefore only a physical entity can be aware.
(5) Therefore a God, being non-physical, cannot be aware. QED.
Thus Shannon's Law precludes the possibility of there being a God who is simultaneously non-measurable and aware. If one understands Shannon's Law, and the evidence on which it stands, one must be a Hard Atheist - or incoherent.