In an early scene of the film, Army General Hopgood, played by Stephen Lang, attempts to walk through a wall. His effort fails. Big time. What is to blame: Bad teaching or real world physical forces? We asked physicist Jeffrey Hazboun, who studies nature’s fundamental forces at Utah State University, about the physical forces governing walls. Here are three things we learned.

1. We can, of course, walk through some things. The world is filled with gasses and liquids that part to make room for us as we move down the street or swim across a pool. Their behavior has everything to do with how electrons are arranged around a particle’s nucleus. Electrons carry a negative electronic charge, and like bar magnets they can repel one another. In gases, like the oxygen and nitrogen that make up the bulk of our atmosphere, electrons tend to be evenly spread out around the nucleus, so that the repelling force is about equal at all positions. If two particles get near one another, the forces kick into action causing them to bounce away from each other. Our solid bodies, easily displace gas molecules, pushing them out of the way, and allowing us to walk down the street.

In fluids, electrons tend to congregate on one side of a molecule. So one side has a weak positive charge and one has a weak negative charge. “Eventually the group orients itself so most particles are attracted to each other, but they are easily pulled apart,” says Hazboun.

2. Walls are another matter, for humans at least. Walls are made up of atoms and molecules that have formed solid connections through electron sharing. Breaking these bonds is extremely difficult, usually requiring massive amounts of energy.

3. There are exceptions, however. Neutrinos can penetrate even a foot-thick cinder block wall. The tiny particles are similar to electrons, but with one very big difference. They do not carry an electrical charge and rarely interact with other atomic forces. This unique characteristic allows them to travel large distances and through surfaces long thought to be impenetrable. First theorized about in the 1930s, neutrinos are produced during nuclear reactions like those occurring in the sun. It wasn’t until 1956 that they were actually detected through an experiment conducted in the Savannah River nuclear reactor. The wait was worth it; the work went on to garner the Nobel Prize in 1995. “Billions of them produced by the sun are raining through walls, and you, right now,” says Hazboun.

4. One final point. When it comes down to it, we’re all a just a little too big and a little to dense to walk through a wall. “There is a chance that electrons and even atoms can make it through places that should be too difficult for them to pass through,” says Hazboun. “But the chance is pretty small. When you think about all the atoms in your body, and calculate the chance of all of them making it through something as solid as a wall–it’s not likely.”

-Aimee Brown

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