When the aliens come for our organs, the tides for our coastal cities, the supervillains for their own nihilist world-obliterating amusement, how exactly will we protect ourselves? From decades of sci-fi, the answer is clear: some kind of force shield arrangement. If you’re trying to deflect bullets, impress small children, and/or save a major U.S. metropolis, a big ol’ force shield is just what the doctor ordered. And yet a cursory glance at the research suggests that no one’s bothered to actually invent one: It is still the stuff of fiction, as it has been for decades now. Obviously, someone should rectify this as soon as possible. In the meantime, it’s worth asking — as we have, for this week’s Giz Asks — could force shields ever actually exist?
James Kakalios
Professor of Physics at the University of Minnesota and the author of The Physics of Superheroes and The Physics of Everyday Things
Well, of course you can protect yourself from harm by staying inside a bunker — but if you’re referring to a personal field that surrounds a person, as portrayed in many science fiction movies and comic books, that is invisible to the naked eye — that will take some doing.
You could surround yourself with graphene — an arrangement of carbon atoms in a hexagonal lattice that is only one atom thick (so 97% of the light passes through it), yet is stronger than steel. In fact studies by scientists at Rice University found that graphene is, pound for pound, more bulletproof than kevlar. So this might be a good material to start building your invisible shielding.
As to what is termed a “force field,” one can turn to plasma physics.
Plasmas are gases where the atoms are highly ionized — that is, the atoms either have too many or not enough electrons, and thus are electrically charged. These plasma gases must be contained by strong magnetic fields (challenge number one). This could deflect laser beams directed at you, and any charged particle beams would also be deflected, either by the magnetic bottle or the plasma itself. (One can envision a double layer, with a positively charged plasma layer deflecting positive particle beams, and a negatively charged layer protecting you from negative particle beams). The faster the object is moving, the stronger the deflection from the magnetic container, so you might still be vulnerable to a slow but still painful right hook.
Personally, I have always been fond of a proposal made by the science fiction writer Theodore Sturgeon. This early forerunner of graphene shielding is described in Sturgeon’s story ‘It Was Nothing — Really!’ In that story, an inventor notices that perforated paper, such as paper towels, or toilet paper, always rips at any location except at the perforations. Therefore, he concluded, the perforations must have made the material stronger. By removing more and more matter, he was able to create an invincible and invisible shield composed entirely of the perforations.
Rhett Allain
Associate Professor, Physics, Southeastern Louisiana University
Let me be clear: I love force fields in science fiction. I think they’re a great plot tool, and allow you to do a bunch of cool things narratively. I’m not advocating to get rid of them. But I don’t see how they’d actually work in real life.
Let’s start from the basic interactions that we understand, the fundamental forces. We have the gravitational force, which is an interaction between objects that have mass; we have the electric force, which is an interaction between objects with electric charge; we have the magnetic force, which interacts with objects with charge that are in motion; and then there’s strong and weak nuclear forces. Everything we know or understand takes the form of one of those interactions.
If you wanted to build a force field, you’d have to ask yourself: which of those forces would it be made from? Well, it’s probably not going to be mass, because mass only attracts. We don’t have repulsive masses. So it’s probably going to be some type of electric force. But while you can create strong electric fields, they’re not necessarily going to repel things right away. Experiments have been done on building a force field to prevent explosions from affecting a given area; these involved changing the density of the air, creating a kind of barrier, in the hopes of decreasing the explosion’s impact.
There’s another way you can generate strong electric fields, and that’s with light. When light interacts with matter, it can push on that matter, too. But it’s more like a flashlight than a forcefield. Light is an electromagnetic wave — an oscillation of electric fields and magnetic fields. And since all matter is made of electric charges — either with protons or electrons — those protons or electrons experience a force from both the magnetic and electric part of the light that pushes it away, and that’s why, when you look at a comet in space, all the dust coming off the comet is pushed away from the sun — the light from the sun actually pushes it. There are spacecraft with solar sails, which are basically reflective sheets, and light interacts with the sheet to push those spacecraft, the same way wind pushes on a sail. But really, these things function more like fans pushing things away — it wouldn’t be a force field-like wall.
Thomas Hartman
Associate Professor, Physics, Cornell University
Let’s look at our options. According to the known laws of physics, there are four fundamental forces. The first is gravity. The second is electromagnetism, which includes both electric and magnetic forces, but we only count it once because both are created by charged particles like electrons and protons. Electromagnetism is carried by photons, and gravity is believed to be carried by gravitons, theoretical particles that move at the speed of light but are nearly impossible to detect individually.
The last two fundamental forces are called the “strong force” and the “weak force.” The strong force, or quantum chromodynamics, binds together protons and neutrons inside the atomic nucleus. Protons are positively charged, so electromagnetism causes them to repel each other, but the strong force is, well, stronger. The weak force is not really a force in the usual sense, because it doesn’t pull things apart or push them together. Instead it causes some particles to convert into others, leading to effects like radioactive decay. There are particles that carry the strong and weak forces, analogous to the photon and graviton, but they can only travel very short distances, so we don’t notice them in everyday life.
Among the known fundamental forces, your best bet for a sci-fi force field is electromagnetism. Gravity can only attract, so it might be a handy way to design a futuristic tractor beam but is never going to make a decent force shield, and the strong and weak forces can’t reach much further than the atomic nucleus.
Could there be other fundamental forces? Possibly! In fact, one of the main reasons we build particle accelerators is to discover new forces. And dark matter, the mysterious substance that pervades the universe but can only be detected by its gravitational pull, might have forces of its own that mix with electromagnetism. We can also invent new forces in a laboratory by designing materials and substances with exotic properties — for example, superconductivity occurs when an artificial force binds electrons together into pairs.