CosmicReplay

Hands-on

Play with the universe

Reading about space is good. Poking at it is better. Every toy here runs on real physics — and tells you honestly where the estimates end.

A futuristic spacecraft cruising through deep space toward a glowing ringed planetLive

Trip planner

Space Travel Calculator

Pick an origin, a destination, and an engine — from a 3-day Moon hop to a 50-billion-year crawl to another galaxy.

Open
Mars mid-transformation: one hemisphere red desert, the other blooming with oceans and green landLive

Simulator

Terraform Mars

Push the sliders — temperature, air, water, oxygen — and watch the red planet come alive. Can you make it breathable?

Open
A supermassive black hole with a glowing orange accretion disk warping starlightLive

Comparer

How Big Is a Black Hole?

Drag the mass slider and watch the event horizon grow — from city-sized stellar remnants to monsters that swallow solar systems.

Open

In the lab

Drake equation explorer — soon