Popular Mechanics talks about the science of Episode 10…by Andrew Moseman
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Fringe Pushes Probability to the Limit as Characters Walk Through Walls
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Fringe’s 10th episode, “Safe,” opens with a team of burglars who rob banks without the tedious trouble of picking locks. Instead, the intrepid thieves change the molecular structure of the wall allowing them to pass through the wall. Unfortunately, one member doesn’t make it out in time and the wall resolidifies around him. The next day the Fringe team shows up to find a dead man stuck inside a wall. We talked to experts about the real quantum mechanical phenomenon of tunneling to find out just how unlikely the scenario is.
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Raul stuck in the wall
Can people walk through walls?
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Fringe loves to toe the line between science fact and fiction, but this time its tilted far over onto the fiction side. In the episode, mad scientist Walter Bishop concludes that the thieves would’ve needed cutting-edge knowledge of quantum physics, plus more money than many banks’ assets combined, to make it through the wall. However, the closest thing to a scientific explanation Bishop offers is a lab demonstration with rice—when he puts an action figure on top of a bowl of uncooked rice, it can stand on top, but when he shakes the back it sinks to the bottom. Bishop correctly states that matter is mostly empty space, says MIT physics professor Ray Ashoori—beyond the nucleus made of protons and neutrons, an atom is tremendously spacious, filled only by electrons that essentially have no mass. However, what’s important, and the reason a solid doesn’t just go through another solid, is electrons’ electrical charge—the closer you try to push two electrons together, the more electromagnetic repulsion is created. That’s why the space in a bowl of rice isn’t the same as the space in an atom, Ashoori says. In Fringe, Bishop implies that vibrations like those he uses on the rice bowl would be similar to what the thieves used to change the structure of the wall, but vibrations aren’t going to stop those repulsive charges for a couple minutes and change the wall’s matter into some kind of new state. “It’s absolutely absurd,” says Reed College physics professor David Griffiths. “Nobody’s ever going to walk through a wall.”
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But while people can’t walk through solid barriers—we either carry enough energy to break through them or we bounce back and hurt ourselves—that doesn’t mean it’s impossible to travel through a barrier without having the energy you’d normally need to break through. Electrons break this rule of classical physics all the time, and sometimes even atoms can. It’s called quantum tunneling, and Griffiths explains it with the example of a roller coaster. Say the roller coaster car is traveling down a slope, about to start up the next hill on the course. Unfortunately, it doesn’t have enough speed and therefore doesn’t have the energy to reach the top and start down the other side. If that car were an electron, Griffiths says, there’s a possibility that rather than going over or around the barrier, it could tunnel right through. In the 1920s, he says, scientists used quantum tunneling to explain the problems of radioactive alpha decay, in which alpha particles—equivalent to a helium nucleus—fly out of a larger atom’s nucleus. Alpha particles don’t normally have the energy to overcome the forces holding the nucleus together, but quantum tunneling allows them to escape. Some electrical devices—like cellphones, MP3 players and some microscopes—take advantage of tunneling.
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Tunneling is a particularly mysterious concept because, like most things in quantum mechanics, it’s a statistical phenomenon based on probability rather than causality. You can know the likelihood that a particle will tunnel, but you can’t know if or when a particular particle will do it. The reason tunneling is possible, he says, is the peculiar ability particles have to also act like waves in certain circumstances. “[Waves] can do things particles cannot,” he says. However, you, as an entire human being, do not exhibit wavelike behavior, and that’s one of the reasons that we can’t walk through walls like the Fringe thieves or like Kitty Pryde in X-Men.
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The main reason that running into a wall results in a bruises rather than reaching the other side is the sheer complexity of the human body. A human body contains a huge number of atoms, about 1025. “Each one of those atoms has to tunnel,” he says, “and they need to tunnel in just the right way to reassemble into a human on the other side.” Every single thing would have to go right, he says, and when you multiply all those probabilities together, the result becomes so vanishingly small that it would take not just the age of the universe, but the age of the universe multiplied upon itself for you to even approach the probability of a human walking through a wall and emerging unharmed on the other side. Even then, he says, it would still be “silly” to consider.
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However, though you could try for a 100 billion years and never walk through a barrier the way that electrons can, quantum tunneling is quite common in the universe. In fact, it’s the reason that human life exists in the first place, according to MIT physicist John Negele. Radioactive decay relies on the quantum tunneling phenomenon in order to work, and the energy of the Earth’s interior is powered by radioactive decay. Without radioactive decay, there wouldn’t be enough energy for plate tectonics and continents would never have formed and come out of the water. In addition, he says, the sun couldn’t sustain its ongoing fusion reaction with just its heat alone. “There has to be some tunneling,” he told PM.
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As for other stretches of scientific truth, “Safe” revisits the borrowed memory theme. In our look at last week’s episode, we brought you the science (and mostly nonsense) behind Agent Dunham’s memory mix-up: In the season premiere, she got into a sensory depravation water tank and somehow managed to get inside the head of a fellow agent, John Scott. Last night we learned that when Scott died, his memories lived on inside her head. This twist on the Star Trek Vulcan mind-meld comes in handy for the team this week when Dunham recognizes the unfortunate bank robber stuck in the wall, but can’t figure out where the memory’s from. It turns out that Scott knew him, and she recognized him because she had access to the dead FBI agent’s memories.
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Finally, were the laws-of-physics-defying thieves’ targets pieces of a time machine that Bishop himself developed years ago, then separated and hid? Bishop remembers that he built the machine in the first place because his son, Peter, had a rare form of bird flu called “hepea,” and he wanted to go back in time to retrieve the only doctor to ever cure the disease and bring him into the future to cure his son. First things first: there’s no such bird flu as “hepea.” The most deadly form of bird flu is called H5N1.
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As for time and space travel … we’ll leave that for another week. While scientists say that time travel is theoretically possible, Bishop’s device, with its mysterious glowing tubes, can bring anybody from anywhere, anytime. We bet it will show up in future episodes.
April 7th, 2010 at 7:56 pm
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