"We often read that the fastest thing in the Universe is the speed of light. Why do we have this limitation and can anything possibly be faster?" Ali Alshareef from Qatif in Saudia Arabia emailed [email protected] with this puzzling problem.

The team grapples with Einstein's Special Theory of Relativity, with help from cosmologist Andrew Pontzen and a British train, travelling somewhat slower than the speed of light.

Plus physicist and presenter Jim Al-Khalili describes how he nearly lost his boxer shorts in a daring bet concerning the speed of subatomic particles.

Send your questions for consideration to: [email protected]

Presenters: Adam Rutherford, Hannah Fry