Is the Moon still there when Einstein stops looking?

[magus]

Gavin,

Thank you for this excellent review. I’m glad you found the book fascinating, as I did.

@Gavin

The movement of stars around the galactic core is anomalous – so we invoke “dark matter” (which we cannot observe) to make the observations consistent with the theory.

The invention of “dark matter” seems similar to Ptolemy’s creation of epicycles to explain the retrograde motion of planets. The Ptolemaic system can predict the movement of planets from the vantage point of Earth pretty well, but it is not how the planets actually move. Likewise, dark matter might help us explain other eccentricities we observe in outer space, but it does not mean that dark matter actually exists. Is this a fair comparison?

Edit: Despite relying on epicycles, the Ptolemaic system lasted a long time because its predictions were good enough for most practical purposes. Even Copernicus used epicycles in his heliocentric model of the solar system. It was not until Kepler supplanted circular orbits with elliptical ones that epicycles were abandoned. Perhaps our contrived “dark matter” will last a long time, too. I suppose it will depend on whether it is capable of explaining newly discovered anomalies or not. When the anomaly to explainable phenomenon ratio grows uncomfortably large, we might be due for a paradigm shift.