For a layman&#x27;s mathematical understanding of relativity I recommend &quot;Why does E=mc^2&quot; by brian cox and jeff forshaw, which explains both the theory and why the equations used to describe the theory, well, describe the theory. It does it all with a nice just-so narrative that builds on physics from galileo all the way through to einstein and ends up at particle physics. It&#x27;s just a very good book.