This section expands relativity to include gravity. Einstein describes gravity not as a force between objects, but as a curvature of spacetime caused by mass and energy. He uses the "Principle of Equivalence" to show that being in a gravitational field is indistinguishable from accelerating.

Read the full text at the Project Gutenberg or Marxists Internet Archive.

Einstein applies his theories to the entire universe, discussing its potential shape and whether it is finite or infinite. Key Features for Readers

Modern editions with introductions by renowned physicists like Roger Penrose are available through retailers like Amazon .

The text is famous for its "Gedankenexperimenten" (thought experiments), such as observers on moving trains and flashes of light, to make abstract concepts concrete.

The book is divided into three main parts that build from the basics of motion to the grand structure of the cosmos: