Star Wars exists in the world as science fiction, perhaps as “soft” science fiction that deviates from established science when desired for story or choking Imperial officers. Nevertheless, it’s affected whole generations’ understanding of outer space with its blend of fantasy and starships. On May the Fourth, Discover takes a look at the science behind this pop culture phenomenon to celebrate Star Wars Day.

Where has the mega-franchise gotten science right, and where has it done a Kessel Run around reality? Here are six eye-opening facts to explain the science behind Star Wars Day.

1. Lightsabers

Could such a weapon exist in our mundane world filled with gas-fueled cars and laser pointers? It would have to meet certain standards: visible at a distance and capable of slicing through metal but not other lightsaber blades. This rules out lasers, which would only be visible in a fine mist or fog. And since the photons (the light) would have boson properties, the “blades” would pass right through each other during any climactic confrontations.

Plasma, as in modern-day plasma cutters, might form the basis for a lightsaber, but even this super-charged substance has issues, according to the Connecticut Science Center. Plasma cutters heat gases to about 40,000 degrees Fahrenheit, hot enough to slice into metal.

The problem is, “A beam of plasma as big as a lightsaber blade would produce enough heat to instantly fry the hands of anyone holding the hilt,” writes Andrew Fotta, an educator at the center, in an article. “A lightsaber made from plasma would also require an enormous amount of power, requiring a very large power source. Kind of puts a damper on those lightsaber duels where they run around all over the place, leaping and jumping.”

2. Ion Engines

The pretty blue flames that propel many starships in the Star Wars films, including Star Destroyers and TIE Fighters, emanate from so-called ion engines. And we’re closer to a real life equivalent of these engines than you might think.

With help from the Joint Propulsion Laboratory, NASA is working to develop large ion drives that will be more efficient and maneuverable than current rocket engines.

Certain satellites already use small versions to stay in orbit, and the retired Dawn space probe used so-called electric drives to visit the Ceres dwarf planet in 2015.

3. The Force

A. Nepomuk Otte, a physicist at Georgia Tech, argues that The Force ignores a central pillar of physics by acting in a one-sided manner, as when Kylo Ren choked General Armitage Hux from a short distance.

“Didn’t we learn from physics classes about Newton’s third law?” he writes in an article. “For every action, there is an equal and opposite reaction.”

He takes issue with Yoda’s casual raising of an X-Wing fighter from the dredges of Dagobah (in The Empire Strikes Back).

“So why doesn’t the little fella get squished like a mosquito?” Otte says.

4. Faster Than Light Travel

When called upon, Han Solo’s Millenium Falcon can jump to light speed and hurtle to 1.5 times the speed of light, which is sadly impossible under our current understanding of the universe. A velocity of this kind would require an infinite amount of energy.

The faster the spaceship goes, the more energy it has. And because of Einstein’s mass-energy equivalence, the more energy it has, the more mass it has. Accelerating further requires more energy, in a compounding fashion, so the spaceship can never reach the speed of light.

But Han Solo does, and what’s more, he survives the G forces involved in the quick transition, which should transform him into tomato soup.

All this means the Falcon’s heavily-modified hyperdrive is working some kind of magic, or relativity doesn’t work the same way in a Galaxy Far, Far Away.

5. Force-Training Droids

In A New Hope, an untested Luke Skywalker spars against a small, spherical droid that pelts him with blaster bolts. His student, Rey, squares off against the same type of droid in The Rise of Skywalker.

Similar round robots called SPHERES live on the International Space Station, where they have been used for experiments regarding satellite and rocket movement. In 2011, astronauts outfitted them with smartphones and upgraded their intelligence so they now move around and perform various tasks.

6. Mustafar

The famous/infamous battle between Anakin Skywalker and Obi-Wan (Revenge of the Sith) takes place on Mustafar, a lava planet wracked by gravitational forces, something that exists in consensus reality.

“A comparable world would be Jupiter’s moon Io, which gets flexed on the inside by the gravitational pull of Jupiter and other Jovian moons,” writes Sonia Tikoo-Schantz, an assistant professor of geophysics at Stanford, in an article. “However, the gases in the atmosphere of such a volcanic world would be noxious and surface temperatures would likely be too hot for anything to survive, much less get in a fight.”

May the fourth be with you on this planet.