In the Newtonian picture of gravity, space and time are absolute, fixed quantities, while in the Einsteinian picture, spacetime is a single, unified structure where the three dimensions of space and the one dimension of time are inextricably linked. (NASA)

Ask Ethan: Is Spacetime Really A Fabric?

In General Relativity, even space and time themselves aren’t what they seem.

Gravity might have been the first fundamental force ever discovered, but in many ways, it remains the least-well understood. We know that it’s always attractive, and that any two masses in the Universe, no matter where they are, will experience its force. When Einstein concocted his general theory of relativity, one of the great advances was to recognize that space and time were combined into a single entity: spacetime. Another was that the presence of matter and energy curved the very fabric of this spacetime, and that curved spacetime, in turn, dictated how matter moved. But is this picture right? Mariusz Wroblewski is skeptical, asking:

I’d like somebody to finally acknowledge and admit that showing balls on a bed sheet doesn’t cut it as a picture of reality.

I freely acknowledge and admit it. As ubiquitous as pictures of bent sheets or coordinate systems are, they aren’t exactly reflective of the reality we inhabit.

The spacetime curvature around any massive object is determined by the combination of mass and distance from the center-of-mass. However, this two-dimensional grid-like depiction of spacetime isn’t necessarily the most accurate way to perceive it. (T. PYLE/CALTECH/MIT/LIGO LAB)

If you’ve ever seen a picture of a bent, two-dimensional grid with masses on it…