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# 1: Foundations of Relativity

• 1.1: The Relativity Principle
Our journey begins with Einstein's big idea, and the greatest null experiment of all time.
• 1.2: The Nature of Time
We continue in the same manner as Einstein – with what he called "thought experiments." These are simply logical arguments that lead to inescapable conclusions if the relativity principle is correct. Some of the most startling of these conclusions are related to the nature of time.
• 1.3: More Thought Experiments
Considering how universally important the measurement of time is throughout physics, it shouldn't be too surprising that there many more interesting results to coax from thought experiments.