The quietly commanding Vice Admiral Amilyn Holdo (Laura Dern) may be the true hero of Star Wars: The Last Jedi. And physicists are here to back her up.
This article contains gratuitous spoilers for Star Wars: The Last Jedi.
In one of the most dramatic scenes from The Last Jedi — and possibly all of Star Wars — Vice Admiral Holdo rams the Resistance’s last remaining star cruiser through Supreme Leader Snoke’s flagship in a sacrifice that buys the fleeing members of The Resistance enough time to escape to the surface of Crait. Visually, the scene is breathtaking. But in terms of logistics, it might leave you wondering whether this feat is possible.
Don’t worry, though: We’re not here to give a Neil deGrasse Tyson-style “well, actually” debunk of this scene. Rather, we want to figure out whether Star Wars follows our rules of physics. And if it doesn’t then, well, what would it take?
Let’s start with some numbers.
The Raddus, a Mon Calamari star cruiser, is 11,280.74 feet (2.14 miles) long, 2,318.08 feet (0.44 miles) wide, and 1,514.84 feet (0.29 miles) tall. It’s a massive starship, but onscreen, you can see just how much smaller it is than the hulking Supremacy, which is 43,437.27 feet (8.22 miles) long, 37.6 miles wide, and 13,042 feet (2.47 miles) tall. Despite its comparably puny size, the immense energy generated by the Raddus’s forward momentum becomes a great equalizer in this showdown, and physics tells us it’s plausible that the smaller ship could cut through the First Order’s Star Dreadnought.
“If jumping to hyperspace is just super-quick acceleration where you instantaneously — or close to instantaneously — hit light speed, then what is depicted in the film would be approximately what would happen,” physics professor Patrick Johnson, the author of The Physics of Star Wars, tells Inverse.
As an example of this phenomenon, Johnson asks us to imagine something a little easier to picture: a car running into the side of an eighteen-wheeler truck.
“At a slow speed, it would dent it,” he says. “At a higher speed, [the truck] would really start to bow. And then if the car is going fast enough and is solid enough, it could cut right through it in the way that Snoke’s ship is cut along the path [the Raddus] went through.” It would take an awful lot of energy to get the starship going this fast, which Johnson has attempted to calculate for us.
Estimating the mass of the Raddus, assuming it’s 40 percent steel — or durasteel, more likely — and 60 percent air, Johnson tells us how much energy it would take to accelerate the ship. And since accelerating to the speed of light requires infinite energy, at least based on the way we understand jet propulsion, we’ll settle for a significant portion of light speed in this scenario.
“The force involved in accelerating the Raddus to just 90 percent of the speed of light would be ~6.8•10^21 Newtons,” says Johnson. This is a massive amount of energy, which increases with every tiny increment closer to light speed that the Raddus accelerates.
Once the ships collide, though, Newton’s third law says that the Supremacy exerts an equal and opposite force against the Raddus.
“The moment the Raddus started to make contact, it would experience an extra force going backward,” says Johnson. “Now presumably, that hyperdrive is exerting a force forward, pushing it forward, so there’s a thrust force and a resistance force from the Supremacy. I would guess, based off of the way that it is depicted, that the Raddus is essentially at light speed by the time it makes contact. At that point, there’s only slowing down: Laws of physics dictate that you can’t go faster than the speed of light.” Of course, he notes, the hyperdrive adds a little asterisk: Maybe you can go faster than the speed of light.
Regardless of what speed the Raddus is traveling at when it collides with the Supremacy, Johnson says all of the energy the smaller ship carries with it is spent in cutting through the Supremacy — and some smaller star destroyers — and in completely demolishing the Raddus.
Of course, this is all moot if hyperspace travel means the Raddus would have been in another dimension altogether — which some works in the Star Wars Expanded Universe (now “Legends”) seem to confirm. Hyperspace travel seems to incorporate some elements of string theory. But ships in the Star Wars universe still need to accelerate beyond light speed to enter hyperspace.
For our purposes, let’s assume the Raddus is traveling at or beyond the speed of light. Leia calls hyperdrive “lightspeed” in The Empire Strikes Back, so that’s good enough for us. With that in mind, it seems most likely that a starship accelerating into hyperspace is going at the speed of light but is also still present in the same physical dimension as everything else around it. And even if it’s not, it’s still in the same physical dimension as other space when it comes out of lightspeed.
We have evidence of this in Star Wars: A New Hope, in which Han Solo brings the Millennium Falcon out of hyperspace right in the middle of the field of debris that used to be Alderaan. Since the ship didn’t hit any of the rocks until it came out of hyperspace, this suggests that a ship is susceptible to colliding with objects in physical space once it decelerates out of hyperspace, which also suggests that a ship could still collide with something while it’s accelerating into hyperspace.
To put it simply, Holdo does on purpose what Han Solo did by accident.
“If that’s the way you go to hyperspace, it’s perfectly accurate,” says Johnson.
Jorge Ballester, on the other hand, is not totally sure that the Raddus is tall enough to make it all the way through the Supremacy. Ballester, physics department head at Emporia State University in Kansas, points out that the Raddus is about 1,500 feet tall, while the Supremacy is over 13,000 feet tall.
“The widest part of the Raddus is about one-sixth of the height of the Supremacy,” he tells Inverse. “So I don’t know how the Raddus could extend its interaction out far enough to slice through.” To put it another way, you probably couldn’t use a single pebble to split an entire boulder, since the force wouldn’t spread far enough above and below, even if the pebble had enough force to pass all the way from front to back. He also points out an issue that arises as a result of Newton’s third law.
“I don’t know why the Raddus wouldn’t be completely destroyed after penetrating one or two of its own length into the Supremacy,” says Ballester. “Presumably both sides use roughly similar materials and technologies to build their ships. Similarly, I would not expect a bullet made of wood to penetrate deeply into a wooden block because the bullet itself would be destroyed. The block might explode but I would not expect the wooden bullet to rip through making a narrow hole.”
These points certainly shed some doubt on whether this collison could go down the way it did in the film, if we’re judging based on our universe’s laws of physics.
Whether or not the Raddus could make it all the way through the Supremacy, it’s worth taking a second to consider the passage of time as it’s depicted in The Last Jedi. There’s a cinematic effect to slowing down the action right as the ships collide so the audience can experience the emotional weight of the moment.
And while an observer in the Star Wars universe would see the events unfold at full speed, “from her perspective, time would actually slow down for her compared to everybody else because she is traveling super fast,” says Johnson.
So to sum up: Though there are some variables we simply can’t calculate, such as how ship shields interact in the event of a crash, Vice Admiral Holdo’s gambit to save her people is pretty plausible. And, damn, it looks so good.