When Christopher Nolan's "Interstellar" begins, on an Earth of the near future, it's not quite apocalypse now, but it will be soon. Crops are failing everywhere. Humanity's final generation on Earth has been born. We've got to get off the planet. And not just off to a nice moon in our solar system: We've got to go interstellar.

This is going to require some serious science.

The film's hard-science pedigree is guaranteed by its science adviser and executive producer, Kip Thorne, one of the world's leading experts on Einstein's theory of general relativity. "The things he was able to open up for me were far more exotic and exciting than anything I could have come up with as a screenwriter," Nolan said.

Some critics have said they wished they'd brushed up on their physics before seeing the film, so here's a spoiler-free guide to everything you need to know before you see "Interstellar."

Q: What is this "dust" that threatens the Earth's food supply?
A: The agent of destruction is a blight fungus. In the film it is sweeping across the world and has already destroyed wheat and okra crops. In the real world, blight is indeed a serious threat: One strain was responsible for the Irish potato famine, for example, and another, Ug99, now threatens wheat. Norman Borlaug, dubbed the father of the Green Revolution, said Ug99 "has immense potential for social and human destruction."

Nolan was influenced by the Dust Bowl in 1930s North America, when rich top soil essential to farming dried out and blew away, desolating vast areas and causing famine and mass human displacement, a situation that could happen again with a severe, ongoing drought in the United States.

But chin up, people. Consider the movie's tagline: The end of Earth will not be the end of us.

Q: How can we ensure the survival of the human race?
A: Colonizing neighboring planets and their moons will be the first step. Once we've arrived at our new home, we will need to grow crops and establish a viable population.

Poor Anne Hathaway, playing "Interstellar's" only female astronaut, Amelia Brand, isn't expected to do all this herself: She is taking a load of frozen human embryos with her. (Presumably some artificial wombs, too.)

But as Stephen Hawking has argued, the long-term survival of our species depends on our developing interstellar travel.

Even if we don't render our planet uninhabitable, the sun will eventually swell up and engulf Earth. This won't happen for 5 billion years, but nevertheless, Michael Caine's character in the film — based on Thorne — insists we have to travel through a wormhole to another galaxy. "We must confront the reality that nothing in our solar system can help us," he says.

Q: How could we travel to planets beyond our solar system?
A: It's a long way to the nearest exoplanets. To get there without spending thousands of years on the journey, the options are limited. Physics won't let us go faster than the speed of light, but it will allow for radical shortcuts. There are efforts to devise "Star Trek"-inspired warp drives, but even if they were possible, they could be deadly. That leaves the main contender: wormholes.
Wormholes are hypothetical tunnels through space-time — predicted by Einstein's theory — that can connect distant parts of the universe.

Until recently, wormholes have been seen as unworkable curiosities. That's changing. Physicists have described how you could make a wormhole big enough to send a message or a spaceship through — or perhaps reunite star-crossed lovers. We can even visualize with graphics software what it might look like to travel through one.

We won't manage to make a wormhole for a while; that will take a highly advanced civilization. And if we ever get to go through one, who knows what we'll find? The crew on the "Interstellar" spaceship, the Endurance, discovers an unwelcome beast at the other side of theirs: a supermassive black hole.

Q: What are the real dangers of approaching a black hole?
A: The beautiful black hole in "Interstellar" is not just visually stunning, it is scientifically accurate.

At the heart of a black hole is a singularity, a point of effectively infinite mass. This exerts a lot of gravity, which drags matter toward it, spiralling into the hole in a vast swirl called an accretion disk.

Thorne worked out the mathematics of what happens to the accretion disk and found that the intense gravity warps the disk around the black hole, creating the spectacular halo that is one of the movie's visual highlights.

If you fall into a black hole or get too close to its intense gravity and somehow survive, you'll notice weird things happening to time. This is a favorite Nolan trope, one that he also used in "Inception," the Leonardo DiCaprio film in which time moved at different speeds depending on the dream state his characters were in.

In "Interstellar," gravity's time-warping effect intensifies the heart-wrenching separation between Matthew McConaughey's character, Cooper, and his 10-year-old daughter, left on Earth. The ages of real-life astronaut twins Mark and Scott Kelly diverged by roughly 10 milliseconds when one was on the International Space Station, but in the movie Cooper can't know how old his daughter will be if he ever gets back to Earth.

By Rowan Hooper