Physics at the Movies

While I don’t go to my local movie theater with a pad of paper and a calculator, waiting for my “physics-sense” to start tingling, I have found that superhero and science fiction films can provide wonderful opportunities to engage with the public. Interest in a recent blockbuster can be leveraged, and the impossible on the big screen can be used as a “teachable moment” about real world physics.

For example, the Black Panther made his solo big screen debut in the Marvel Cinematic Universe this past February, and the broader, non-comic book reading public learned about the technologically advanced country of Wakanda. The wealth of certain nations is correlated with the natural resources found within its borders. Think of the oil-rich countries in the Middle East, or the abundant timber forests of Canada. In the Marvel universe, one of the most fortunate countries on the face of the planet is Wakanda, for in these lands an extra-terrestrial meteorite landed, depositing a rich load of an extremely rare and valuable mineral – vibranium.

As suggested by its name, vibranium’s unique properties relate to how the atoms in this material process external sources of vibrations. In particular, vibranium is a perfect shock absorber, converting the kinetic energy and atomic vibrations from any projectile into non-lethal forms of energy. The king of Wakanda, T’Challa, defends his country as the superhero the Black Panther, wearing a suit composed of vibranium that provides head-to-toe bullet-proof shielding. The kinetic energy of a bullet will ordinarily cause such extreme atomic vibrations that the chemical bonds holding together the outer uniform will be broken, and the bullet will penetrate through to your body, causing comparable damage. When a bullet strikes a vibranium suit its kinetic energy is presumably rapidly shunted away from the point of impact, and transformed into a less destructive form. While vibranium does not exist in our more mundane, non-superhero world, there are real-world materials that can approximate these amazing properties.

A simpler term for vibrating atoms is ‘sound,’ and all matter, whether vapor, liquid or solid, is able to transmit sound waves. How easily sound can propagate through an object depends on factors such as its density and the strength of the connections between neighboring atoms. Sound moves much faster (in general) through a solid than through air – which is why you’ll hear the approach of the distant train much sooner if you feel (or hear) the locomotive’s vibrations through the steel rails, rather than waiting for the sound to reach you through the air.

Sound can be damped if the energy of the atomic vibrations can be deflected into other directions or other channels. The sound in the steel rail does not continue forever – some of the atomic vibrations transfer their energy to the surrounding air, which then carries some of the sound’s energy away from the metal. When enough energy is transferred, the amplitude of the sound’s vibrations becomes comparable to the atomic vibrations that all matter at a given temperature has, and the sound will have dissipated.

So, one way to make a ‘bullet-proof’ analog of vibranium is to make a material that transmits the localized kinetic energy of an incoming projectile away from the point of impact before the atomic vibrations are able to break the chemical bonds holding the material together. A good rule of thumb will be – the faster the speed of sound in a material, the harder it will be to penetrate the material with an external projectile. Recent studies of graphene, a unique ultra-thin form of carbon that is only one atom thick, where the carbon atoms are arranged in a honeycomb, hexagonal pattern, find that its speed of sound is extremely high. Consequently, as experimentally verified by Jae-Hwang Lee, Phillip E. Loya, Jun Lou and Edwin L. Thomas (Science 346, 1092 (2014)) much more energy is needed to penetrate multiple layers of graphene, compared to a comparable mass of steel, or even Kevlar.

Sweeping the atomic vibrations away from the point of impact will protect the region where the external kinetic energy first strikes the graphene, but the energy is still present in the material. One way to handle these vibrations is to convert them into another form of energy that is less harmful to the material (and any person wearing such a super-suit). There is a phenomenon termed ‘sonoluminescence’ where sound waves are converted into light. The energy of a sound wave is typically many times smaller than the energy in a beam of light, so this is one way that a large amount of kinetic energy due to an impacting projectile could be transformed into a non-lethal form.

In the Black Panther film, we learn that the Panther’s sister Shuri, a scientific genius who’s skills rival Tony Stark’s, has refined the Black Panther suit so that it can store incident kinetic energy, and release it in a single focused blast. Perhaps the suit has a series of fiber optic cables woven into its fabric, so that the light generated by the sonoluminescent process can be carried off and stored in some sort of ‘optical battery,’ to be dramatically discharged at some later time. I certainly could not design and fabricate such a suit and mechanism but someone Shuri can!

The popularity of the Black Panther movie led to additional outreach opportunities. A question on the on-line forum Quora.com regarding T’Challa’s vibranium suit and the DC comics superhero the Flash led to a discussion of the physics of vibranium and quantum mechanics.

Devoted fans of any field love to debate, and among the things they love to debate are hypothetical questions. Would the 1927 New York Yankees beat the 1998 Yankees? Which year was better for film: 1939 or 1973 or 1982? Who would win a heavyweight title bout: Muhammad Ali or Rocky (Marciano, not Balboa)? And a perennial favorite of comic book fans: Who is faster, Superman or the Flash?

This last one is easy: the Flash. After all, they have run at least seven races, and they tied twice, with the Scarlet Speedster winning five. (And, as the Flash has noted, those two races that ended in a draw were for charity events). A less obvious hypothetical question was raised on Quora.com: could the Flash vibrate his hand through the Black Panther’s vibranium suit? Of course, both the Flash and the Black Panther are heroes in their respective comic book universes, and there would be no reason for the Flash to try to harm the Black Panther. But given that vibranium has the ability to absorb all external vibrations – could even the Crimson Comet vibrate through such a suit?

Some background, or Flash Facts, if you will. In Showcase no. 4 in 1956, police scientist Barry Allen was struck by lightning while simultaneously being doused with the contents of a bookshelf full of various chemicals. Rather than suffering permanent neurological damage he gained the ability to run at super-speed. Donning a sleek red and yellow costume and calling himself the Flash, Allen fought for justice using his many new super-powers. In addition to secondary powers necessary for an effective use of super-speed (such as super-acceleration, super resistance to air-drag, super-metabolism), the Flash also had the ability to independently control his body’s vibrations, with which he could ‘phase’ through solid walls.

Now while the Sultan of Speed can indeed run through solid objects (I’ve seen him do it on TV and in the comics, and they couldn’t show it if it weren’t true!), he does so not by matching his vibrations to those of the object. Anything that is not at a temperature of absolute zero has some internal kinetic energy, and for the atoms held in fixed positions, as in a solid wall, this energy manifests as the atoms vibrating back and forth about their average position. After all, your own atoms vibrate with a frequency that corresponds to your body temperature of 98.6° Fahrenheit, but don’t try walking through a wall that’s also at 98.6°F.

Rather, I would argue that the Scarlet Speedster makes use of quantum mechanical tunneling. One aspect of the wave-like nature of matter described by quantum mechanics is that there is a probability for the wave to be transmitted through a solid barrier, with the object showing up on the other side. The greater the kinetic energy of an object, the larger is the probability that it can wind up on the other side of a barrier. Thus if the Flash were to run, or just move his hand, fast enough, he could increase the probability of tunneling to near 100%, and would appear to ‘phase’ through the solid barrier. While there is much wrong with this proposed mechanism for ‘phasing,’ it did provide an excuse for me to describe quantum physics and tunneling on the Quora.com board!

So, while the Black Panther’s suit would indeed absorb the excess vibrations of the Flash’s hand moving rapidly back and forth, the Viceroy of Velocity (and yes, these are all nicknames the Flash has had in the comics) could move his hand forward so fast that it behaved like a macroscopic quantum object. When an object tunnels through a barrier, it is not technically inside the barrier (just on one side of the barrier and then on the other side), and thus there is no energy for the vibranium suit to absorb. Fortunately in either comic book universe it would be hard to find two more honorable and decent heroes than the Flash and Black Panther, and this question will remain, thankfully, hypothetical.

James Kakalios is the Vice-Chair of the Forum on Outreach and Engaging the Public, and the Taylor Distinguished Professor in the School of Physics and Astronomy at the University of Minnesota. He is the author of several popular science books, including THE PHYSICS OF SUPERHEROES (Avery, 2009) and THE PHYSICS OF EVERYDAY THINGS (Crown, 2017).