Behind the Book
Quantum physics may seem so arcane that even humans don’t need to understand it, let alone dogs. A surprising number of everyday things have their origins in quantum physics, though, making quantum physics crucial for the happy life of a modern dog. Here are five things that wouldn’t be possible without quantum physics:
1) Computers: Modern computers are based on silicon chips containing billions of tiny transistors. The transistors are made by adding tiny amounts of gallium or arsenic to the silicon in different parts of the chip. The amount added is extremely small—less than one atom in 10,000—but it’s enough to change the quantum behavior of the electrons in the different regions, making a transistor. Without quantum physics, it would be impossible to make the computers we use for writing books, playing games, or looking at silly pictures of cats on the Internet.
2) Lasers: Lasers use a quantum phenomenon called “stimulated emission,” first predicted by Einstein in 1917, to amplify light at very specific frequencies. This produces a source of light with a single frequency which behaves as a single wave—all the light waves produced by different atoms are perfectly in synch. Without quantum physics, it would be impossible to build the lasers that are found in the DVD players that we use to watch movies, the fiber-optic telecommunications systems that carry email and phone calls, and the price scanners that supermarkets use to determine the price of dog biscuits.
3) GPS Navigation: The Global Positioning System consists of a collection of satellites orbiting the Earth, each broadcasting a radio signal giving its position and the time. A GPS receiver determines its distance from three different satellites by measuring the time required for the signals to reach the receiver. This determines the position of the receiver on the Earth to within a few meters, provided you know the time within a few nanoseconds (light travels about one foot in one nanosecond). To get this accuracy, the satellites contain atomic clocks, which measure time from the energy difference between two quantum states. Without quantum physics, it would be impossible to build the GPS system that humans need to keep from getting lost because their noses aren’t good enough to sniff out the way home.
4) Magnetic Resonance Imaging: The MRI scanners used by doctors and hospitals work by driving the nuclei of hydrogen atoms back and forth between two quantum states and measuring the radio waves produced. By measuring the amount of radio waves from different parts of the body, they can distinguish between different types of tissues, and make detailed images showing the arrangement of muscles and tendons and ligaments. Without quantum physics, it would be impossible to make the MRI scanners that doctors use to diagnose health problems and help humans heal up so they can take good dogs for walks.
5) Sunlight: The Sun generates vast amounts of energy by fusing two hydrogen atoms together to make helium, and some of that energy travels to the Earth in the form of visible light. But the hydrogen atoms repel each other because their nuclei are both positively charged, and even in the Sun the atoms don’t have enough energy to overcome that repulsion. We have sunlight anyway because a quantum phenomenon known as “tunneling” allows the nuclei to get close enough to fuse even though they don’t have enough energy. Without quantum physics, it would not be possible for a dog to spend a lovely afternoon basking in the sun and keeping an eye out for squirrels trying to infiltrate the yard.