The Marvel Cinematic Universe started in 2008 with Iron Man and has become a staple of the film industry, with a united group of superheroes that all exist in the same world of intrigue, mysticism, spies, superheroes, and betrayal. With each hero in this universe comes a primary tool with a varying degrees of power.
Two of the most famous tools in these films are Captain America's Vibranium shield and Thor's hammer, known as Mjolnir. Both these weapons are not only very powerful, but also unusual in their properties. With the help of some real-world science, we can figure out how these powerful items would work within the real world.
Captain America's Shield
We'll start with the item that is arguably the most famous: Captain America's Shield. This vibranium disc has the ability to absorb all incoming vibrations, turning the wielder into an unmoving sentinel - appropriate for Cap's status as a defender of truth and justice. The shield has also been shown to ricochet extremely well, losing very little velocity and enabling Cap to throw the shield in combat and have it return to his hand via rebounds.
These two attributes appear to be polar opposites. If the shield really did absorb all vibrations, it would lose all velocity and fall to the ground at the point of impact. However, the Law of Conservation of Energy states that energy is neither created nor destroyed, simply transformed. With the exception of a strike from Thor's hammer (which created a powerful shockwave), strikes to Cap's shield have not been shown to create waves of concussive force, incredible heat, or intense sounds (which would show the transformation of energy).
According to Suveen Mathaudhu, a professor of adjunct materials at NC State University, any incoming energy must go somewhere, which indicates that vibranium is capable of storing energy within the bonds of its atoms. This makes the shield capable of functioning as a capacitor, which can absorb and release large amounts of energy very quickly. This same ability also makes the shield capable of functioning as a battery, which releases and stores energy at a more or less constant rate.
This explains why the shield ricochets when thrown, rather than absorbing all the energy from the throw. When the shield's edge strikes a surface, the shield releases stored energy from within its atomic bonds to counteract the energy of the hit, causing the shield to rebound at (or nearly at) the same velocity with which it struck the surface.
So, why did the shield create a shockwave after being hit by Thor's hammer if it's supposed to absorb energy? I believe this may be due to the nature of the shield's energy-storing capabilities, combined with the mystical and cosmic nature of Uru, the metal which Thor's hammer is crafted from. Because vibranium is essentially an immovable object, and (in theory) Thor's hammer is an unstoppable force, the energy was too great for the shield to handle all at once, and so it was released outwardly, creating a powerful wave of concussive force and leaving Cap beneath it, unharmed. You can rewatch the scene in question here:
Which leads us nicely on to the real science behind...
Thor's Hammer (Mjolnir)
Mjolnir is a little harder to explain, mostly due to the magic (advanced science?) of the Asgardians. The best explanation we have as to the physics of the hammer is a single line from the very first Thor movie. During Thor's attempted crowning ceremony, Odin starts listing Thor's accomplishments, citing these as his reason for making him king of Asgard. During this speech is a seemingly innocent line about the origins of Mjolnir, which goes as follows:
"Entrusted with the mighty hammer, Mjolnir, forged in the heart of a dying star, its power has no equal!"
This actually has its basis in real scientific theory. When a massive star "dies", it causes a supernova, releasing a massive wave of energy. After this explosion, an event known as a gravitational collapse takes place, in which the remains of the dead star fall back on themselves, creating what is known as a neutron star. Neutron stars are small, but incredibly dense, having a radius of around 7 miles, but a mass twice that of our sun.
This is where Uru comes into play. Theoretically, the core of a neutron star would also be incredibly dense, as the gravitational pull of a collapsing star would smash the protons and electrons of the remaining matter together, creating a material that is formed completely from neutrons (degenerate neutronium). This matter, if it exists, would have a mass of one hundred million million grams per cubic centimeter, thus explaining why no one can lift Mjolnir.
However, how can Thor (or anyone deemed "worthy") lift Mjolnir with relative ease?
Well, this answer comes to us from the famous Dr. Neil deGrasse Tyson. Given the theoretical weight of neutronium, Mjolnir would have a weight of around twelve thousand trillion pounds. Because the nature of Asgard is given as science that we haven't discovered yet, it is possible that Mjolnir contains a complex nanotechnological biosensor that "reads" whoever is trying to lift it, forms a psychological profile based on an unknown set of factors, and uses this to determine if the person lifting is "worthy". Also, considering that we have voice recognition in our technological society, being able to reprogram the hammer's "operating system" by speech would be very simple for the Asgardians, which is how Odin was capable of making Thor unworthy in the first film.
Finally, the ability to lift something that weighs the better part of a small planet comes to us from another theoretical particle, the graviton. If an object were capable of emitting gravitons, it could increase its weight without increasing mass or density. This means that graviton emission is an innate property of Uru metal, that it can exhibit when acted upon by an outside force, such as the rest of the Avengers trying to lift it, or when at rest, preventing the coffee table, floor, and possibly building from collapsing under the immense weight of Mjolnir.
Although they may never exist in the real life, Captain America's Shield and Thor's hammer are two of the coolest tools ever used in fiction, and now we have some real world science that might explain it! Big thanks to Wired.com and themarysue.com for providing the information that led to this article!
Got any other scientific explanations or another cool theory? Put it in the comments below!