There is only matter and light and the great flux of forces which constitute existence. When we look inside ourselves we find nothing but a material brain and its electrical activity. There is no consciousness, no mind, no soul, no spirit.
If we put a person on a scale as they are dying, there is no change in weight and no discernible departure of anything. Even with our most delicate instruments we detect no fleeing of energy into the nether world. There is, as far as we can observe, nothing but the flux in the form of bodily remains.
If we look outward into the vastness and minuteness of the universe it is both grand and glorious. But wherever we look and however closely we look, the universe stands alone, self-animated and self-contained.
Perhaps, in the beginning, there was a force in the universe that some people call God. From an infinitely small speck of nothingness it sparked into existence everything that is. Then this God withdrew back into that nothingness to wait, to rest a billion billion years until the next time. But no matter how closely we look we see nothing of that presence in what appears to be our self-animated and self-contained universe. Thus there may be no God in us and no God around us. As frightening as it may seem to some, we and the universe may stand alone and are one.
Thales talked of water, that is, essentially, substantial existence. He wanted to look, to observe, and think about the relationships between the objects of the world he could sense. The world of the Gods? No one had ever actually seen them, so who could say or know if they existed.
Emanuel Kant in the Critique of Pure Reason formalized the epistemological boundary between what we could expect to know via rational observation of the world and what we could hope to know via rational speculation regarding any transcendent reality. These two forms of knowledge could no longer legitimately inter-penetrate each other. As a result, in the two hundred years since the Critique, science has been left largely free to pursue its project of accumulating worldly knowledge, unhindered by the shackles of religion.
Educated and intelligent people increasingly accepted rational scientific investigation as the only legitimate means of accumulating real or at least useful knowledge. The more sophisticated accept the Kantian argument that science can make no epistemological judgments regarding the transcendent; that the two are separate projects. However, with the passing of time, the scientific project has become a far more powerful aspect of historic human consciousness. Thus, even though science can not technically make truth claims about transcendence, it has nevertheless made speculation largely meaningless.
Minds of the quality of a Leibnitz or Spinoza no longer trouble themselves with serious rational speculative efforts. At best, ironically, transcendence is left to strive for scientific validation, and scientific metaphors of truth: The hand of God is in the laws of nature discovered by science. We can infer that God's presence is in the clockwork precision of universal mechanics. In complexity we can see the evidence of design rather than the chaos of chance.
But we are still left with the reason of transcendent speculation attempting to draw wider conclusions from the ultimately more simple scientific project of fact gathering in the world. In this project we find no evidence of transcendence, only its inference. Given the lack of evidence one way or the other, and given science's lack of interest in seriously examining its own foundational first premises, there is an indifferent shrug. Or, with a slash from Ockam's razor, it is said with increasing confidence that the universe at all levels is self-animated and self-contained; that it does what it does because of what it is.
