Real-life science and comicbook characters aren't really natural bed-fellows, especially considering the whole point of comicbooks is to introduce superheroes with impossible powers and abilities.
Unfortunately, although being bitten by a radioactive spider in the comicbook world might imbue one with the powers of an actual spider, in the real world it's much more likely to give you acute radiation syndrome and a rather nasty itch.
This hasn't prevented Jim Kakalios, the Taylor Distinguished Professor in the School of Physics and Astronomy at the University of Minnesota and author of The Physics of Superheroes, from trying to apply real science to Thor's hammer in an article for Wired.
Science and Thor
Now, as a trans-dimensional demi-God based on Norse mythology, Thor doesn't immediately spring to mind as the most scientifically-accurate superhero. However, as Kakalios explains, in reality the Norse "gods" are a race of highly advanced alien beings. This means their technology is so advanced by 21st century human standards that often it can appear as if it is magic, for as Arthur C. Clarke famously stated: "Any sufficiently advanced technology is indistinguishable from magic."
As you all know, Thor's hammer can only be moved by those which it deems 'worthy.' At the moment, this means it's limited to Thor alone. In a new clip for The Avengers: Age of Ultron, we see the rest of The Avengers attempt to lift Thor's hammer to no avail - although Captain America does seem to make it slightly move. Using this video, Kakalios discusses several scientific theories to explain Mjolnir's apparent magical properties.
Theory 1: Mjolnir Is Forged From Neutron Star Matter
Astrophysicist and Director of the Hayden Planetarium, Dr. Neil deGrasse Tyson has suggested that Mjolnir could be forged from neutron star matter - the densest material in the universe after black holes. This means, Mjolnir would weigh as much as three hundred billion elephants while still retaining its relatively small stature. This could then explain why even Tony Stark and his rocket powered Iron Man glove cannot shift it. However, it also doesn't explain how Thor can lift it, or how any object - such as the coffee table in the video - can support its weight.
Although this argument might explain how Mjolnir can be difficult to move, it doesn't explain the rest of its abilities.
Theory 2: Uru Metal Can Emit Gravitons
To explain these more complex issues, Kakalios developed his own theory. We already know that Thor's hammer is forged from Uru metal - a unique material found only in the heart of a dying star. The properties of this unknown metal are therefore key to solving the dilemma.
Now, Newton's First Law of Motion states that a object at rest will remain at rest if no net force is applied to it. Essentially this means, if two forces acting upon an object are equal - the object will not move. So, in the clip above, the hammer is resting on a table. Gravity is pushing the hammer down, but this force is equal to the counterforce of the table top pushing up against it. As Kakalios explains:
This counter-force, referred to in physics as a Normal force (as it acts perpendicular or normal to any surface) is fundamentally electrostatic in nature, and is easy to take for granted except when it fails (as when one puts a thousand ton object on a table that can only provide a counter force of several hundred pounds).
So, Kakalios hypothesizes that Mjolnir remains at rest when others try to move it because it can increase its gravity to equal the force being applied on it by the individual attempting to move it. Now, as far as we know, there is no officially confirmed way for an object to increase and decrease its gravitational weight or mass. However, there are theoretical elementary particles known as gravitons which could perform this function. As Asgardians are ahead of humans technologically, Kakalios suggests they have have found a way to harness and manipulate gravitons.
So, if someone other than Thor tries to move the hammer, it emits large amounts of gravitons which essentially temporarily increases its mass or weight. Kakalios explains:
When Tony and Rhodey simultaneously exert a larger upward force, the emission rate of gravitons increases, to again neutralize their efforts. The greater weight will not damage the tabletop, as only enough gravitons are emitted to balance out all upward forces, to keep the hammer stationary. Once the lifting force is stopped, the excess graviton emission also ceases.
Kakalios goes even further to suggest this manipulation of gravity and the gravitation field around Mjolnir also explains how it can impossibly find its way back to Thor.
But Why Can Thor Lift It?
So, this all makes sense, but why does the hammer allow itself to be lifted by Thor? Well, the answer once again relies on the advanced nature of Asgardian tech. Kakalios suggests the uru metal could be imbued with nanotechnology and/or a complex biosensor which recognizes when it's being held by Thor.
The nanotech then performs a biological and psychological profile of the person holding it to see if they reach the level of "worthiness" required. This could explain why Captain America - one of the more wholesome superheroes - is able to slightly move it.
He also suggests this power could have been placed on Mjolnir by a kind of voice recognition software. When Odin first banishes Thor to Earth, he whispers to Mjolnor "whoever holds this hammer, if he be worthy, shall possess the power of Thor" - starting a kind of program within the hammer to begin vetting its potential users.
Kakalios' theory has received some rather esteemed approval from one of the comicbook world's most accomplished physicists, Bruce Banner!
In The Indestructible Hulk Number 8, Banner is asked if the Hulk could potentially move Mjolnir. In his explanation, Banner name drops Kakalios and gives a brief run-down of the "graviton emission proposal." Check out the panels below:
Sure, it's still just a theory - but I'm not sure I've heard a better one than that. What do you think?
Which theory do you believe?