At the tiniest scale, quantum physics reigns. ![]() This is where Autti's team came in, trying to find a way to interact with a quantum time crystal through classical observations. And that concept extends beyond observation: Any strong enough interaction with the external environment that breaks down the quantum state of the time crystal will make it stop being a time crystal. The moment they try to watch one, the quantum rules that allow them to exist break down, and the time crystal grinds to a halt. This implies that physicists can't directly observe time crystals. "In quantum physics, a perpetual motion machine is fine as long as we keep our eyes closed, and it must only start slowing down if we observe the motion," Autti said, referring to the fact that the exotic quantum mechanical states required for time crystals cannot keep operating once they interact with their environment (for example, if we observe them). Instead, time crystals are subject to quantum mechanics, the rules that govern the zoo of subatomic particles. But a time crystal defies that, or simply ignores it, because the rules of thermodynamics don't seem to apply to it. The laws of thermodynamics suggest that systems in equilibrium tend toward more entropy, or disorder - a coffee cup sitting out will always cool, a pendulum will eventually stop swinging, and ball rolling on the ground eventually comes to rest. "This means they are perpetual motion machines, and therefore impossible," remarked Autti. The basic rules of quantum mechanics prevent the motion from becoming completely still, and so the time crystal remains "stuck" in its never-ending cycle. This is possible because the time crystal is in its lowest energy state. "A time crystal keeps moving and repeats itself periodically in time in the absence of external encouragement," said Autti. Related: 'X particle' from the dawn of time detected inside the Large Hadron Collider Quantum secrets A few years later, physicists were able to finally build one. Wilczek made an analogy to normal crystals, but in the dimension of time, dubbing this spontaneous symmetry breaking through time a time crystal. That means any experiment repeated at a later time should produce the same result. In 2012, physicist Frank Wilczek, at the Massachusetts Institute of Technology, noticed that the laws of physics also have a time symmetry.
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