Lay down your lightsabers, Star Wars fans.
Scott Engle likes the galactic movie franchise as much as the next person. But he is also an astronomer at Villanova University, and he has just a few quibbles with the way science is portrayed in Star Wars: The Last Jedi, the newest installment of the series.
A research assistant professor of astrophysics and planetary science, Engle pursues the answers to a variety of cosmic questions, such as studying planets outside our solar system to determine whether they could support life. But he also likes a bit of escapist fun, and he has seen all the Star Wars movies except the Rogue One offshoot that came out in 2016.
We took Engle to see Last Jedi on opening day, and he gave it a thumbs-up for entertainment. But the physics? No spoilers, but here are five things the filmmakers got wrong (or right):
Noise. Like its predecessors, Last Jedi is a movie about conflict in outer space, so it gives nothing away to say the film portrays a few explosions. Just one problem: we should not be able to hear them.
In order for humans to hear, sound waves need to travel through a medium of some sort, such as air or water. But in space, gas particles are too far apart from one another to transmit energy that would register on the human eardrum — at well under one-trillionth the density of air at sea level on Earth.
"It's nowhere near dense enough to carry any kind of sound that we could hear," Engle said.
This phenomenon starts at just 100 miles above the Earth's surface, the beginning of a region called the anacoustic zone — the zone of silence.
And while we're on the subject of explosions — Engle said they would not look as fiery as they do in the movie due to the lack of oxygen in space. There is oxygen inside a ship, but that gas would rapidly escape an explosion and expand into the vacuum of space. Sorry, Hollywood.
"Any fireball after an explosion would be very short-lived," Engle said.
Cold. At one point, a major character finds herself floating in space without any protective gear, and immediately a layer of frost forms on her body. Wrong, the Villanova astronomer said.
It is true that space is very cold, with temperatures far below zero. But the character would not freeze right away for the same reason there is no sound in space: very low density.
Heat energy is conducted primarily through the movement of atoms. The denser the environment, the more efficiently it is conducted.
"That's partly why being submerged in cold water is so much more dangerous than being exposed to cold air, because it's so much more dense," Engle said.
In space, on the other hand, Engle estimated it would take many hours for a person to freeze.
Pressure. Though the character would not freeze right away, there are other issues. A big one is air pressure, which declines with altitude.
In Philadelphia and other places near sea level, the boiling point of water is 212 degrees Fahrenheit. In the thinner air of mile-high Denver, that number drops to 203 degrees.
In space, the scarcity of gas molecules means the "air" pressure is ultra-low, close to a total vacuum. Despite the extreme cold, any liquid water would boil — turn into a gas — instantaneously, Engle said.
So if a person goes out in space without a helmet, saliva and tears on the surface of the eye would boil away. This happened once in a vacuum chamber on Earth, in a 1966 test of an early spacesuit, according to Space Safety Magazine.
"As I stumbled backwards, I could feel the saliva on my tongue starting to bubble just before I went unconscious, and that's the last thing I remember," test subject Jim LeBlanc recalled.
What's more, Engle said, the low pressure in space would cause the person's body to swell up a bit, which does not occur in the movie. Count on lung damage, as well.
Gravity. In a pivotal scene early in the movie, bombs are dropped on a spaceship, appearing to accelerate at a rate close to what would occur on Earth. Not accurate, Engle said.
The action appears to take place far from the surface of any planet, so the pull from any planetary gravity would be low. There would also be a small amount of gravitational pull between the bombs and the spaceship itself, but nowhere near enough to cause the kind of acceleration depicted in the movie, in Engle's eyes.
"The rate at which they fall is simply too fast," he said.
Another glitch related to the motion of objects: in the movie, at least one ship appears to slow down or start listing to one side as it runs out of fuel. That would not happen, Engle said. As described in Newton's first law of motion, the ship would continue forward at the same rate of speed, much like the controversial "lateral" pass that Seattle Seahawks quarterback Russell Wilson threw against the Eagles on Dec. 3.
Stars. On one planet depicted in the movie, two suns are visible from the surface. That also was the case on Tatooine, the planet where Luke Skywalker lived in the original Star Wars movie, now known as Episode IV — A New Hope.
The filmmakers get credit in this case, Engle said.
And one more bit of credit. At one point in the movie, a character fires a blaster pistol at Capt. Phasma, the Stormtrooper commander. Yet the "light-based energy" appears to bounce off her polished, mirrorlike armor. Engle figures that makes scientific sense, more or less.
Scientific accuracy or no, Engle liked The Last Jedi. Good thing, because he was already planning to go see it again with his family.
The U.S. Department of Energy got in on the fun, too. Watch here for expert musings on lightsabers and more: