Watch one hour near a black hole cost seven years on Earth. Gravity bends time.

Send a twin near light speed and bring them home. See who aged less and by how much.

Launch a photon and fast-forward. Watch your signal reach Proxima Centauri, Andromeda, and beyond.

Throw a clock off from various heights on earth (and elsewhere!). Watch how long it takes to reach the ground and how it accelerates!

Frequently asked questions

Wiki - for a further taster...