Unpopular Science
Sidenote illustration by Jess DG Hayes for chapter 6, “The Apple Falls the Slowest from the Tree”
Sidenote illustration by Jess DG Hayes

Chapter 06 of 50

The Apple Falls the Slowest from the Tree

“Spacetime tells matter how to move;matter tells spacetime how to curve.”
John Archibald Wheeler, 1962
“We have ways of making people talk...by giving them fresh apple slices.”
Kenneth Parcell, 2010

General relativity formulates gravity as spacetime curvature where time and space metrics are affected by mass and energy. Contrary to the depiction of gravity as bending space, as in the rubber sheet visualizations, in cases in which masses are small (the Earth, for example) it is the gradient in time’s rate that creates gravitational attraction, guiding objects towards regions of slower time. The reason an apple is falling is not because it is affected by force radiated by Earth, nor is it due to the curvature of space, but rather because it is following the shortest path through curved time.

Topics

  • Equivalence Principles
  • Free Fall as Geodesic
  • Spacetime Metric gμνg_{\mu\nu}
  • Gravitational Time Dilation
  • g00g_{00} Component
  • Falling Into Slower Time
  • Local Inertial Frames
  • Tidal Effects
  • Einstein’s Elevator
  • Proper Time Maximization
  • GPS Clock Corrections

Sidenote

Top (GR — Falling Toward Slow Time): An apple follows a curved free-fall trajectory toward Earth. Along the path, it is shown accompanied by clocks, which tick progressively slower as they get closer to Earth. This is an insight relativity: free-falling objects move toward regions where proper time is maximized — in other words, where the time component of the metric, g00g_{00}, decreases. The apple is not being pulled by a force, but slides through spacetime toward slower time.

Middle (Misleading Space Bending): Two “rubber sheet” grid diagrams are shown. The top depicts an exaggerated funnel-shaped distortion caused by a black mass — a common pop-science depiction of gravity. The bottom shows the Earth resting on a seemingly flat grid, emphasizing that for small masses such as Earth, spatial curvature is negligible. What matters is the distortion of time, not space. Gravity in this regime is governed almost exclusively by the g00g_{00} gradient.

Bottom (Aristotle to Newton): Left: Aristotle’s model shows apples falling back to Earth because they “belong” there — matter returning to its natural place. Right: Newton’s model depicts a single apple being pulled downward by an invisible gravitational force, with spring lines suggesting mutual attraction between masses. This is Newton’s universal law of gravitation — a force acting at a distance.

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Beyond Popular Science: the films

Each chapter is becoming a short film: the book’s own words, read to camera, with its figures, sources and equations animated alongside.

The films go out under the UK edition’s title, Beyond Popular Science. The fifty chapters are the same in both editions.

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Front cover of Unpopular Science by David H. Silver: hand-drawn science doodles by Jess DG Hayes around the title

This chapter is one of fifty in Unpopular Science.

For readers curious enough to want the actual mathematics, tired of science communication that oversimplifies or sensationalizes. Science as it actually is: demanding, complex, but well worth the effort.