Alright time to get off RQ=PD theorycrafting and get back to the purpose of this blog: real science concepts in Steven Universe. I’m very tardy to this party (TVTropes editors noticed this the day the episode aired), but I want to cover this before moving on to some of the more recent stuff.

When the rubies’ ship leaves for Neptune at the end of “Hit the Diamond,” It makes a little black hole in front of itself before warping away.

What would happen if you created a miniature black hole just above the surface of the earth? The exact diameter of the black hole in the show isn’t clear (the sizes of objects and characters in Steven Universe aren’t very consistent anyway), but given the theme of the episode we’ll say it’s the size of a baseball, with a radius of 4.7 cm. A black hole with a Schwarzschild radius of 4.7 cm would have a mass about 5.3 times the mass of the earth, or 96 times the mass of the planet Mercury.

(More science under the break.)

Having something like that just a few feet off the surface of the earth would be very bad news for us. There’s no chance of the earth peacefully falling into the black hole because the earth would explode. According to Frank Heile, Ph.D. in physics from Stanford University, if even a coin-sized black hole were made on the surface of the earth:



…not all of the Earth would simply be sucked into the black hole. When the matter near the black hole begins to fall into the black hole, it will be compressed to a very high density that will cause it to be heated to very high temperatures. These high temperatures will cause gamma rays, X-rays, and other radiation to heat up the other matter falling in to the black hole. The net effect will be that there will be a strong outward pressure on the outer layers of the Earth that will first slow down their fall and will eventually ionize and push the outer layers away from the black hole. So some inner portion of the core will fall into the black hole, but the outer layers, including the crust and all of us, would be vaporized to a high temperature plasma and blown into space. This would be a gigantic explosion—a significant fraction of the rest of the mass of the Earth matter that actually fell into the black hole will be converted into energy… This radiation will be absorbed by the outer layers of the Earth and will vaporize them.

Ok, well since Leggy didn’t accidentally destroy the earth by turning on the black hole generator before reaching a safe distance, I think we can safely say that’s not how the rubies’ ship works.

Presumably, what the crewniverse is trying to get at with this visual is that the rubies’ ship moves by somehow manipulating spacetime itself, rather than just moving through spacetime. Warp drives, or hyperdrives, have long been a staple of science fiction, with writers wanting to acknowledge the real world cosmic speed limit of the speed of light, but also get their characters to other planets in a reasonable amount of time.

Inspired by Star Trek’s warp drive, in 1994 Mexican theoretical physicist Miguel Alcubierre (pronounced Al-coo-bee-air) realized that although it is physically impossible for the relative speed of two objects in spacetime to be greater than the speed of light, there is no limit on the relative speed of two separate patches of spacetime itself.

Alcubierre proposed creating a wave that would cause the fabric of space ahead of a spacecraft to contract and the space behind it to expand. The ship would then ride this wave inside a region of flat space, known as a warp bubble, and would not move within this bubble but instead be carried along as the region itself. To use a Star-Trek-esq analogy: it’s a bit like surfing on a wave instead of having to paddle through the water.





Although Alcubierre’s warp bubble is a mathematically valid solution of Einstein’s field equations, it also requires that we have some exotic matter with negative mass. As far as we know, no such thing exists. It’s a bit like having a workable design for a car engine that runs on unicorn blood. There are also some other potential problems involving time travel paradoxes, negative energy density and being vaporized by Hawking radiation. That’s all outside the scope of this post, but suffice it to say, we won’t be using Alcubierre drives to commute to the Andromeda Galaxy anytime soon.

Ok, well, let’s say that since the Gems are an advanced race who were already colonizing other worlds when we were just starting to get the hang of agriculture, that they somehow figured out how to make exotic matter with negative mass and overcome the other technological challenges. We’ll also ignore the fact that this would mean the rubies could use their ship to send signals into their own past and create paradoxes. What does it mean for the show that this is how their FTL travel works?

One nice feature of Alcubierre’s drives is that they get rid of the real kind of time travel: time dilation. As a consequence of relativity, on a spacecraft moving close to the speed of light, time will move more slowly than time back on Earth. For example, if the Rubies traveled from the their homeworld in Bode’s Galaxy to Earth, in a very powerful rocket ship that travels through spacetime at 99% the speed of light, 12.13 million years would pass on earth before they got here, but the Rubies would “only” experience 1.71 million years of time in their rocket ship. If the Rubies could travel at 99.9999999999999% of the speed of light, 12.01 million years would pass on Earth during their journey, but the Rubies would only experience about six and a half months of time on their ship. So while the Rubies wouldn’t have to wait that long, Jasper would be stuck on Earth for a very, very long time.



So, with his new Alcubierre-drive-powered-ruby-ship, Steven doesn’t have to worry about taking the ship out for a spin at relativistic speeds and coming back to find Connie is an old woman (and former president). Since the ship is sitting inside a moving patch of spacetime rather than moving through spacetime, however much time passes on Earth will be about the same amount of time that passes on the spaceship.

To learn more, checkout PBS Spacetime’s video on the Alcubierre drive. (Really just watch all their videos, they’re amazing)