Time runs at different speeds depending on how fast you are moving and how strong the gravity around you is. That is not a thought experiment, it is measured daily, and your phone's navigation would fail within minutes if we ignored it. We work through special and general relativity in plain language, without the mathematics.

You'll come away understanding why nothing can exceed the speed of light, what the twin paradox really shows, and why gravity may not be a force at all.

Talking Science is sponsored by Kinsoft. Visit www.kinsoft.com.au

Further reading: Einstein Online (Max Planck Institute); NASA relativity resources; Royal Institution lectures on spacetime.