[This is for a course where Richard Grigg’s book has been assigned.]
According to Richard Grigg, pantheism “equates God directly with the whole of reality” [Beyond the God Delusion (Minneapolis: Fortress Press, 2008), p. 68].
In its own way, so does process theism—God is equated with the whole of reality understood as all-inclusively newly interacting.
With that understanding, you could say that, in a way, nature is God. Even Protestant Reformer John Calvin grudgingly recognized this, though not on process terms—“I admit, indeed that the expression ‘Nature is God’, may be piously used” (Institutes 1.5.5). Or you could say that, in another way, God is more than nature (that’s what Calvin recommended).
It all depends on how inclusively, or not, we use “nature.” In any case, process theists don’t equate the whole of reality with the physically measurable universe (as Grigg does), and they don’t like to be called pantheists. They prefer to be called neoclassical theists, dipolar theists or panentheists, insisting that, as ways of newly interacting, the whole (God) and the parts are creatively both in and beyond one another.
Maybe that’s quibbling. Charles Hartshorne did at first call his process theism “The New Pantheism,” before deciding the term was misleading (Christian Register 115 :119-120). The reason he changed his mind is that too many people equate pantheism with Baruch Spinoza’s pantheism. For Spinoza the whole of reality, the one and only infinite substance, is totally active, while its parts are totally passive, so nothing is newly interacting—when parts of reality appear to interact newly with one another, they are actually passively expressing the one and only activity of the whole of reality.
Process thought and process theism reject this—both the parts of reality (all of them) and the whole of reality newly interact, and nothing is totally active or totally passive. The whole of reality influences the parts but does not control them, and the parts of reality influence but do not control the whole. This means that we, as “parts,” can have an intimate, dialogical, interpersonal-like relationship with the whole of reality, something Spinoza could never entertain with his commitment to monism and total determinism. Process theists would tend to agree, fairly or not, with Richard Dawkins (p. 40) in calling Spinoza’s (and Einstein’s) pantheism “sexed-up atheism.” (Of course, if you want to be an atheist, wouldn’t you rather be a sexed-up one?)
And they would probably say the same thing about Grigg’s pantheism, which equates God, the whole of reality, with a “closed system of purely physical cause and effect” (p. 55).
Process thinkers find no evidence for a totally closed system anywhere within the whole of reality, much less the whole of reality itself. There is ample evidence for partly closed systems (and to that extent they illustrate the laws of thermodynamics), but never for totally closed systems (and to that extent such laws don’t apply). (The data pointing to “the Big Bang” do not prove that our universe is totally closed, because cosmologists continue to disagree over what the data mean—more here, pp. 144-147, 401-407.)
And process theists don’t feel obliged to regard newly interactive systems of cause and effect as “purely physical,” since the meaning of “physical” seems to change over time just as much as the meaning of “mental,” “spiritual” or “divine” (more here and here).