This 'deceptively simple' question demands a dip into the murky waters of quantum physics.
Our bodies are always moving, even when we don't realize it. We churn through a solar system on a wobbly planet, stand upon shifting tectonic plates, and rise and fall and toss and turn all day and night in a symphony of autonomic and somatic functions. Dizzying though this may seem, life is always in motion, right down to its fundamental building blocks — molecules. Molecules can be thought of as atoms that share electrons. They form electronic bonds that can be visualized like springs, and they jiggle around at a rate that corresponds with the heat energy to which they're exposed. Although molecules are neither alive nor dead, they never cease moving, even when scientists try their damndest to sap them of energy. To unpack why molecules never stop moving, and before we get lost in the fundamental weirdness of quantum mechanics, we must first clarify something a bit more straightforward: What is temperature? In daily life, blustery weather might chill you to the bone, and a cup of tea could warm your lips. When we talk about temperature, we often do so in reference to our own comfort level, body thermoregulation, or climate change. But on a submicroscopic level, temperature measures the average kinetic energy of the molecules or particles in an object or substance. The hotter they get, the more they move; therefore, to "stop" them, we'd just need to take away all their heat energy to achieve absolute zero, or 0 Kelvin — right? Only, "you can never really completely isolate a molecule from its environment," said Justin Caram, an associate professor of chemistry at the University of California, Los Angeles, said in a call with Popular Science. "Whether it's knocking into other molecules in the air — or atoms or whatever — or it's absorbing light and reemitting light, it's always interacting with its environment." Caram added, "You can temporarily cool things down so that they move very, very, very little — and that's how we define a very low temperature, right?…