The moment one characterizes God (i.e. "Almighty," "Never-ending" etc.), thereby ascribing some form and shape to God, one has created a false image (see Rambam, Hilkhot Yesodei Ha-Torah 1:7-12). The non-believer, therefore, can at best deny a form of God which he has developed in his mind. This is indeed true, because in order to negate a concept one first needs to define that which he denies, prior to declaring that it does not exist. Once a person paints a static picture of God, by definition he has limited God: the real character of God can never be defined by human faculties.