‘Spooky action at a distance’ is now used to describe quantum entanglement. But forces, like gravity, appear in the form of action at a distance too. Are forces spooky too? Physics professor, Sverre Holm, journeys the occult origins of forces, and the mysteries still looming over modern science. 

Isaac Newton is well known for having added, "I frame no hypotheses" to the second edition of Philosophiæ Naturalis Principia Mathematica in 1713, meaning that he could not explain the cause of gravitation.

Gottfried Leibniz’ view was that if such attraction at a distance is not explainable then it is a perpetual miracle, and added that it is “a chimerical thing, a scholastic occult quality.”

Leibniz’ dismissal is all the more strange in light of Newton’s seeming agreement with Leibniz. Newton himself had after all dismissed the medieval scholastics for their belief in substantial forms, like “sympathies” between similar objects. He had written that “to tell us that every Species of Things is endow'd with an occult specifick Quality by which it acts and produces manifest Effects, is to tell us nothing.”

How could Newton be so sure that his theory of gravitation did not fall under the category of such a scholastic form, and thus that Leibniz arguments were not valid?

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Newton called the presence of forces without an intervening medium an absurdity.

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In retrospect, we know that Newton was right and Leibniz wrong. The field concept, which plays such an important role in today’s physics, was well established by the end of the 19th century. Michael Faraday and James Clerk Maxwell played major roles through their work with electric and magnetic fields. Mary Hesses’s classical book from 1961 is the definite guide to this history.

Action at a distance, sympathies, and tides 

Leibniz was right that Newton’s gravitational action at a distance shares the property of the medieval substantial form in that it is fundamentally inexplicable. The main difference is that the gravitational law is quantitative, and Newton could demonstrate for the first time that the same law describes the moon’s orbit and a falling apple on earth. This was the definite break with the Greek separation between a heavenly and an earthly physics.

From antiquity, it had also been known that the moon and the tides were linked. The scholastic way was to say that the moon had a “watery nature” and thus attracted seawater on the Earth through joint “sympathy”. This could explain the tidal bulge on the side facing the moon, but not the bulge on the opposite side of the Earth. Galileo had sought for decades to develop an alternative model that was meant to prove that tides instead were caused by the combined motion of the Earth around the Sun and the Earth’s rotation. It was all a part of his failed attempt to prove Copernican heliocentrism. Newton, however, could show that gravitational attraction would explain both tidal bulges.

Three important aspects

To understand the novelty of Newton’s approach one needs to see that there was a subtle change in the meaning of the word “occult” in the early modern period. Over the course of the 17th century, the meaning changed from encompassing both lack of sensibility and lack of intelligibility, to mean only unintelligible. Historian Keith Hutchison emphasizes three important aspects to consider for the Leibniz-Newton debate to be comprehensible:

1. Experience or detectability is the fact that although we cannot sense the gravitational field from the moon with our five senses, we experience its effects indirectly in the form of the tides.