David Cronenberg's Scanners is a classic of the sci-fi- and horror genres for a lot of reasons, but it's hard to get past the big, disgusting elephant in the room. Granted, when it comes to Cronenberg, "big and disgusting" are relatively vague descriptors, so I'll be more specific. We're talking about exploding heads here.
For the uninitiated, the 1981 movie involves "scanners" — people with telekinetic or telepathic ability — and the war undertaken between two disparate scanner groups. Darryl Revok (Michael Ironside) is one such scanner, hellbent on killing any other scanner he deems a threat. And he does so with grotesque flare.
The scene that earned Scanners its place in the cult movie hall of fame involves a silent face-off between Revok and another scanner, resulting in bits of bone and brain cascading over the unsuspecting crowd. If you haven't seen it (and you want to) it's included below. Clear any children from the room.
Cronenberg pulled off this disgusting special effect by having a hidden member of the crew fire a shotgun at a fake head made of plaster, gelatin, and even some leftover hamburgers. The exact fictional mechanic that allowed Revok's powers to make the head explode isn't totally clear. Of course, scanners don't exist in the real world (so far as we know) but a look at our own weapons technology offers a potential explanation.
Blowing stuff up is a practice humanity has pretty well figured out. We've been doing it for centuries. Blowing up people, or at least parts of them, is something that sadly followed soon thereafter. Traditional explosives are a little too on the nose, though. We're looking for something a bit subtler.
If we assume Revok's scanning abilities involved inducing some sort of vibration inside the skull of his foe, then we have a close allegory in real-life sonic weapons.
Sonic weapons, of a kind, have been used in warfare for decades. During World War II, German forces annoyed the inhabitants of Stalingrad with Argentine tangos. Similar tactics have been used during the invasion of Panama, the siege at Waco, and the Iraq War. Having to hear any song, loud enough, for long enough, might drive a person to surrender. We're pretty sure playing "Cotton Eye Joe," even once, is against the Geneva Conventions.
These instances have relied heavily on annoying opponents into giving up, but more recent developments have transformed sound from a buzzing fly to a stinging wasp, so to speak.
Enter the development of the Long-Range Acoustic Device (LRAD). It is capable of directing sound along a narrow field, at high power. The result: a sound that is debilitating to those in the firing line. but can barely be heard at far distances or outside of the 30-degree arc of influence.
The device was originally developed as a weapon for the military, which asked the LRAD Corporation to create a machine that could accomplish two tasks. First, it would be a loudspeaker, capable of delivering messages across a distance. Second, it would deliver a deterrent sound.
The LRAD Corporation, now Genasys, delivered on that request. The device was successfully deployed against pirates before making its way to the ground in the United States. LRAD was on-hand for protests at the Republican National Convention in 2004, but ultimately wasn't used. Pittsburgh police first deployed LRAD against G-20 protestors in 2009, and it has since been used against demonstrators in a number of protests, including recent demonstrations against police brutality.
Officially, LRAD is intended as a system for clear, long-distance communication. Essentially, it's intended as the next generation of bullhorns. In practice, it has other results. When speaking to Popular Mechanics, audio engineer Robert Auld characterized the device as a terror weapon on par with tear gas and flash-bang grenades. Those within the LRAD's zone of influence are blasted with sound waves up to 160 dB. For context, that's about 20 decibels above that of a jet engine.
Modern sonic weapons play on overwhelming our senses in the audible range. They cause discomfort and potential hearing loss. They are not, however, subtle. Such an overwhelming sound isn't something you could unleash in a conference room to explode your rival's skull without anyone else being the wiser.
But what about...
Much has been made about infrasound, probably because it does weird things to our bodies without our being totally aware. Infrasound, by definition, is sound beyond what humans are capable of hearing. But, that doesn't mean we can't be aware of it.
Even if we can't hear a sound, the vibrations can impact our bodies, especially if they fall within a frequency that has a physical impact. A sound played at 19 Hz can impact your vision because that's the resonant frequency of your eyes. Turn it up to a sufficient volume, and you might see colors floating along your field of vision, similar to what you might see when you press on your closed eyes in a dark room. This happens because the frequency activates the rods and cones in your eyes, stimulating false visual input.
Other parts of your body have resonant frequencies, too — levels at which vibrations can physically manipulate them. You might be familiar with this phenomenon as it relates to wine glasses. If you've ever wet your finger and run it over the top of a wine glass, you've heard its frequency.
If you want to make a wine glass explode, the trick is to expose it to that frequency long enough and loud enough that it is overwhelmed and breaks. The same relationship exists with all sorts of materials, including your own body.
With that in mind, it's technically possible to explode a human head, if you're able to expose it to the right frequency, at the right volume, for a sufficient duration. But, there are complications.
The resonant frequency of bone is one measure, the frequency of muscle, skin, and brain matter, are different. And in a living human head, all of those tissues and elements are interrelated, playing off one another all the time. There's no one frequency capable of playing off the materials of your head, which could cause them to explode.
When it comes right down to it, if you want to explode a human head (please don't do this. In the name of all that's right in the world, why?) there are more, ahem, conventional methods. The reality is, if you want to silently and secretly explode the heads of your enemies, you'll have to ask Cronenberg because science just isn't there yet.