"God of the Gaps": When God is invoked to fill in the blanks in scientific knowledge. An old-fashioned and doomed theological approach, but one that is nevertheless very much alive in the minds of many.
In the General Scholium, a sort of epilogue to his monumental Mathematical Principles of Mathematical Philosophy (here is a translation of the 3rd edition by Ian Brice available on the Web; there are others), Isaac Newton wrote (I use the I. Bernard Cohen and Anne Whitman translation):
"This most elegant system of the sun, planets, and comets could not have arisen without the design and dominion of an intelligent and powerful being.
And if the fixed stars are the centers of similar systems, they will all be constructed according to a similar design and subject to the dominion of the One ... And so that the system of the fixed stars will not fall upon one another as a result of their gravity, he has placed them at immense distances from one another."
We can see that Newton made direct use of the God of the Gaps approach, whereupon God is invoked to explain something science can't. In Newton, things are more complex than just that, given that he saw the cosmos as an imprint and direct manifestation of God's mind and plan. Perhaps shockingly, to Newton — the architect of mechanics and the universal law of gravity, co-inventor of calculus and discoverer of some of the fundamental laws of optics, inspirer of the Enlightenment and quintessential model of rationality — God was an integral and essential part of the universe.
Of course, historical context is essential here. Newton's long life covered the second half of the 17th century and beginning of the 18th, when the schism between science and religion, and between science and philosophy, was not out in the open. Ironically, the schism came about mostly due to the success of Newton's remarkable science: If it was possible to compute with high precision the motions of celestial and terrestrial objects, reducing the cosmos to material particles acting under the influence of forces, might not everything be thus reduced, including the affairs of men?
Newton's God got squeezed into increasingly smaller gaps due to the advances of the science he had created. A famous example is the formation of the solar system, the sun, planets, comets and moons, which, as we see from the quote above, Newton attributed to divine intervention. The French physicist and mathematician Pierre-Simon Laplace — in the early 1800s — proposed a purely physical origin of the solar system based on the contraction of a huge spinning gas cloud due to gravity, an idea very close to what we consider today. The spinning ball would flatten at the poles and grow at the equator, even "breaking" into separate rings where the planets would form. (Planetary formation is somewhat more complicated than that.)
The interesting part of this story comes when Laplace gives Napoleon a copy of his Celestial Mechanics, describing in great detail the motions of the planets and comets in the solar system. Napoleon invites Laplace to his palace and, after congratulating the sage, expresses his astonishment at not seeing God mentioned in the manuscript. Laplace's famous answer tells it all: "Sir, I have no need for that hypothesis."
I tell this story because it so well illustrates how science moves. Of course, Laplace was being his arrogant self; but he was also being dishonest. Not because he needed God to explain what he didn't know, but because there were many things he didn't know. For example, he didn't explain where the gas cloud came from. Did God put it there? Laplace would have none of that, but he also wouldn't have an answer.
It took a while for the modern theory of cosmology to propose a mechanism for the formation of stars and galaxies, as due to a combination of unlikely ingredients: normal matter (stuff we are made of, like electrons and protons), dark matter (stuff that is about six times more abundant than matter but we don't yet know its composition), dark energy (stuff we don't really understand but know it's there and in dominant quantities — about three times more than dark matter), and tiny fluctuations in the values of fields that we presume existed very early on in the history of the universe. Once we put all these ingredients together — and they are all well-justified from observations — even if the list appears quite bizarre, we can reproduce the universe pretty nearly as we see it with our tools.
The main difference between Newton, Laplace and modern cosmology is that we don't presume (or shouldn't) to know all there is to know about the universe. Even as we strive to know more about nature — and this is what science is supposed to do — we also realize (or should) the vastness of what we don't know. One thing should be clear to all who share a scientist's urge to learn about the world: To put God in our current knowledge gaps certainly would not further our understanding of the universe. For that we need science and its stubbornly secular modern approach.
Marcelo Gleiser is a theoretical physicist and cosmologist — and professor of natural philosophy, physics and astronomy at Dartmouth College. He is the co-founder of 13.7, a prolific author of papers and essays, and active promoter of science to the general public. His latest book is The Island of Knowledge: The Limits of Science and the Search for Meaning. You can keep up with Marcelo on Facebook and Twitter: @mgleiser.