Interstellar, for real
The film was built on real physics. Here is the part you can measure and play with: messages that take hours to cross the solar system, ships that spin to make gravity, planets that fling spacecraft onward, Saturn up close, and a wormhole drawn with Einstein's equations.
Messages from home
Radio travels at the speed of light, about 300,000 km every second. Across the solar system that is still slow. In the film, the crew near Saturn watch video messages from home that are already more than an hour old. These are the real one-way delays right now.
The pulse is shown sped up. The clock on the right is real time.
Distances change through the year as Earth and each world move around the Sun. Planet positions use NASA JPL's published orbital elements; the Moon uses its average distance.
A ship that spins for gravity
Space has no "down", so the Endurance in the film spins. Standing on the inside of a spinning ring, the floor keeps pushing you towards the centre, and that push feels exactly like weight. How strong it is depends on two things: how big the ring is and how fast it turns.
Comfort limits come from experiments in rotating rooms: most people cope with about 3 turns a minute straight away, and many adapt to around 6 over a few days. It is turning your head while spinning that makes it dizzying.
Slingshots: stealing speed from a planet
Fly close behind a moving planet and its gravity drags you along with it. Seen from the planet you leave as fast as you arrived, only bent around. Seen from the Sun, you have picked up some of the planet's own speed. Spacecraft use this to cross the solar system without carrying the fuel, and near the end of the film Cooper slingshots around Gargantua.
Jupiter moves around the Sun at about 13 km/s. The maths is the standard "patched conic" flyby used to plan real missions.
Voyager 2's grand tour
Launched in 1977, Voyager 2 used a rare line-up of the outer planets to swing from Jupiter to Saturn, Uranus and Neptune. It is still the only spacecraft to have visited Uranus and Neptune.
Planets are drawn where they really were on each encounter date. The line joins those points; the real path curves gently between them.
Arriving at Saturn
In the film, the Endurance takes about two years to reach Saturn. This is a slow approach rendered in Blender from real maps of Saturn's colours and rings.
A wormhole
A wormhole would be a shortcut through space: a sphere you could fly into and come out somewhere else. General relativity allows the shape, but holding one open would need exotic matter with negative energy, in amounts and forms nobody has ever seen; only tiny laboratory effects of that kind are known. For the film, Kip Thorne and Double Negative described the wormhole with three numbers: the size of its opening, the length of its tunnel, and how gently it bends light. Every ray here is traced through that same kind of shape.
Drag the picture to look around. Our side shows the real Milky Way. The far side's sky is imagined, a made-up galaxy, because nobody knows what would be on the other end.
What's real, and what's imagined?
| Messages that take hours | RealEvery mission beyond the Moon lives with it. Mars rovers are never driven live. |
| Spinning for gravity | Real physicsWell understood and tested in rotating rooms on Earth, though no large spinning ship has been built yet. |
| Slingshot flybys | RealUsed by Voyager, Cassini, New Horizons and many more. |
| Gargantua's look | Real physicsLight bending as traced on the black hole page. |
| Time slowing near a black hole | RealMeasured on Earth and in orbit every day. Miller's planet needs an extremely fast-spinning black hole. |
| A wormhole near Saturn | TheoryAllowed in principle; needs exotic matter nobody has found in the amounts required. |
| The tesseract | FictionA storytelling device, not science. |