May the Fourth Be With You

I don’t remember exactly where I was or even exactly when it was, but my earliest memory of being transported to that galaxy a long time ago and far, far away was watching the Battle of Endor, rooting for Han and Leia as they attempted to turn off a force field protecting the half-completed second Death Star, which turned out to be “quite op-er-ational” and able to destroy Rebel ships in an instant. I remember sitting in front of the TV gripped by the fight between good and evil, father and son: a pair of space wizards wielding lightning swords. And, of course, the final redemption of the ultimate bad guy, when he throws his boss into a chasm, guarded only by a railing that quite frankly isn’t up to the job.

The Death Star is, in many ways, a Health and Safety nightmare. Maybe it’s something about being evil, but there seems to be very little concern for the welfare of workers in the Empire. There are numerous (some would say too many) ledges with no railings, warning signs or places to attach harnesses, alongside open pits in floors, and doors that seem to be designed to be just short enough for unwary Storm Troopers to bang their heads. At least the helmet offers something in the way of Personal Protective Equipment to prevent head injury, though little protection against blasters, it’s actual supposed purpose.

And this is before we have even got to the workers forced to stand metres from a superlaser designed to destroy whole planets. These poor technicians stationed beside the huge, bright green beams were at least given visors that were designed to cut out the laser light. Unfortunately for them, the effectiveness of a piece of glass against a Doomsday weapon may be minimal.

This is because destroying a planet isn’t easy. It needs a LOT of energy. Although gravity is the weakest of the fundamental forces (no, not The Force…), it surrounds us, binds us (really, NOT The Force…). It causes mass to bind together – and there’s a LOT of mass in a planet. Let’s take our very own planet Earth as an example. To overcome this gravitational binding energy and turn the Earth from a near-sphere into an expanding cloud of rock and sorrow would take somewhere in the region of 224 trillion exajoules: 224,000,000,000,000,000,000,000,000,000,000 J, which in scientific terms is a ridiculously large number. I got tired and confused just typing it out. This figure represents the total energy output of the Sun for a week. Looking at it another way, it’s just a little less than all of the sunlight that has landed on Earth since the dinosaurs died out, 65 million years ago, or firing the most powerful laser ever made on Earth continuously for about 7,000,000,000 years. It’s a lot of energy. This means that the Death Star needs to pack a great big punch.  Fortunately it is possible to transport that amount of energy in a relatively small space. And by small I mean on a planet-destroying space station like the Death Star which is a whopping 160 km in diameter!

Einstein showed us that the amount of energy in an object is equal to its mass multiplied by the speed of light multiplied by the speed of light again, or to put it much more elegantly, E=mc2. This means that every kilogram of mass could be turned into 9×10¹⁶ J of energy. By dividing this by our ridiculously large binding energy figure it turns out the Empire would only need to turn 2.5 trillion tonnes of matter into energy to reach their goal. Simple! Granted, a trillion tonnes is a lot of matter, but for a military industrial complex like the Galactic Empire, it should be within their grasp. For instance, in 2017 a 5,700 km² iceberg broke away from Antarctica’s Larsen C ice shelf. Scooping a couple of ‘bergs that size from an ice planet like Hoth would give you the required mass. Even easier, they could just grab a conveniently-sized asteroid from one of the many asteroid belts. One with a diameter of 5-6 km would have about the right mass.

There is, however, a problem. Turning all of that mass into energy is going to be tricky. But who ever said planetary destruction would be easy? The Empire has been shown to be in possession of some incredible technology, but it’s never explained in too much detail, so do they have the means to feasibly convert all that mass into energy? One method would be to not use matter at all, but instead use antimatter. Antimatter is matter’s ‘evil’ twin, like Star Trek’s Mirror Universe Spock, only instead of a beard to signify its sinister intentions, it has an opposing charge. Antimatter and matter annihilate one another when the two come into contact with each other, explosively turning 100% of the mass into energy in an instant. The benefit of this would be that you would only need half the required mass as per Einstein’s equation – the doomed planet would supply the other half, so you would only need a little over a trillion tonnes of antimatter. Win! The downside is that antimatter (at least on Earth) is the most expensive substance ever created. Estimates vary, but NASA suggested that a single gram of antihydrogen could be made for a mere $62.5 trillion. That would mean that to fire the Death Star weapon just once would cost $300 for every joule in our ridiculously big gravitational binding energy that we need to overcome. That’s 3 followed by 34 zeros; an expenditure that even a galactic civilisation might think twice about.

An easier method (and again, everything is relative…) would be to drop the mass onto a spinning black hole in the Death Star’s core. At maximum efficiency this would convert 42% of the mass into energy, so you would need a bigger asteroid. While that may not be a problem, there may be one or two technical hurdles involved in taming a black hole… however I can’t imagine this method costing more than the antimatter route. All of this suggests that the Death Star’s weapon might not be laser-based as we presume, but something much more exotic.

A quick mention of another laser-like but DEFINITELY not laser-based weapon that fans of Star Wars may be aware of: The obscure and little known Jedi weapon called a “lightsaber” (WARNING: previous sentence contains at least 400% too much sarcasm). Possibly the most famous weapon in all of fiction, owning a lightsaber is the dream of every child (and almost every adult) who has seen a Jedi using one. From toys to videogames, they are EVERYWHERE; lightsaber-duelling has even been recognised as an official sport in France as of February 2019, although it does use a less… powerful version of a lightsaber (ie. glowing plastic batons).

At first glance lightsabers may look similar to lasers, but there are a few fundamental differences; the main ones being that you can see the blade, and that the blade is only 3 foot long. Let’s look at these one at a time. The first point might seem counterintuitive but the truth is that light is invisible. If it wasn’t, we wouldn’t be able to see anything as every beam of light that crossed our vision would stop you seeing what’s on the other side. You only see light when it interacts with your retina. This means in general a laser is only seen as a dot on a wall as the light reflects off the wall into your eye (you should never look directly at a laser, even if they aren’t Death Star-powered; even a laser pointer has the potential to permanently damage your eyes). You may have seen the beam from a green laser pointer as it crosses a darkened room or is shone into the sky, but this is caused by Rayleigh scattering; the same phenomenon that makes the sky blue. The scattered laser light that enters your eye allows you to see it. For a lightsaber to be seen from the side suggests it must be radiating light towards you, rather than just being a laser beam emitted straight up from the handle. The other main difference is the length of the blade. Lightsaber blades are usually around 1 metre in length, but if the blade were laser-based, it would shoot out of the handle and carry on forever, or until it hits an object. Lightsaber blades are therefore much more likely to be an “energy” or plasma blade, rather than a laser.

So could you make a real lightsaber? Without the force-imbued Kyber crystal, it’s going to be difficult, however there was a brief glimmer of hope in 2013 when scientists from MIT published a paper in Nature suggesting that they had turned light into molecules. Would it be possible to construct a blade using these exotic photons? This might be a moot point. Going back to my earlier point about Health and Safety, I think there is a very strong argument for NOT building lightsabers, even if they were possible. They may be, as Ben Kenobi states, “an elegant weapon for a more civilised age”, but the risk assessment alone would mean that only a very select few would ever be able to hold one, never mind wield it in battle. The huge power requirements needed to produce a plasma (or “energy”) blade capable of cutting through nearly any substance is going to be a problem. Even if batteries could be made with the energy density necessary, they would basically turn the lightsaber handle into a rather unstable bomb, projecting a blade of at least several thousand degrees in temperature – not something you want to hold anywhere near your face, or have idly hanging from your belt… I’d also suggest that holding a very light object that can effortlessly slice through nearly anything might be a tad dangerous.

Lets face it, the Force is not strong in our galaxy (or at least we haven’t found a way to manipulate it – yet…) so it is likely that the very first thing that will happen after the first lightsaber gets turned on is the very first lightsaber-related self-amputation, and that’s just setting ourselves up for a lot of paperwork. So while the science of Star Wars may be edging closer to becoming a reality, perhaps we should be careful – or at least have a COSHH form ready for – what we wish for.

I heard the sad news Peter Mayhew’s death just before publishing this article.

RIP Chewbacca. May the Force be with You.

About the author:
Karl is an award winning Science Communicator, trainer and Public Engagement Consultant and is currently the Public Engagement Manager at the London School of Hygiene & Tropical Medicine. Originally from Northern Ireland but now living in London, Karl graduated from the University of Edinburgh with a degree in Virology in 2002. He then worked in laboratories in Edinburgh and Belfast for the next 6 years on a range of subjects including HIV, Hepatitis C, the MMR vaccine and lung diseases caused by smoking,

He has been actively involved in science communication and public engagement since 2000. His previous roles include Christmas Lectures Manager at the Royal Institution of Great Britain, where he produced Professor Saiful Islam’s 2016 lectures TV series, and Senior Programme Coordinator at Cheltenham Science Festival. He also lectures on public engagement, and has trained scientists and public engagement professionals to be better communicators in over 15 countries, on 4 continents.

In his spare time, Karl is an avid fan of cinema and has written and presented numerous shows looking at the science behind science fiction, as well as the “Science Friction” podcast.