Of the many complex phenomena in the universe, perhaps none is more relevant to our daily lives than time. And although reminders of its existence are everywhere, in the forms of phone screens and cups of coffee gone cold, we have yet to fully understand the nature of its existence.
At the macroscopic level, the universe follows the "arrow of time." It travels in a preferred direction, one that is dictated by the Second Law of Thermodynamics—towards disorder, or entropy. That’s why a cup of tea left to cool will not spontaneously heat itself back up and why scrambled eggs never unscramble themselves.
But all of this relies on a crucial factor—the initial state of the universe.
The early universe was hot, with its energy distributed evenly in a low entropy state. Over time, however, the chaos has steadily increased, thus determining the arrow of time.
But what if the initial conditions that determined the arrow of time were malleable?
Can we create a closed system that changes the arrow of time in the opposite direction?
That is precisely what Kaonan Micadei and colleagues at the Federal University of ABC in Brazil sought to do.
In their experiment, the quantum physicists created a system in which cold carbon and hydrogen nuclei heated hotter ones. The key was to entangle the nuclei prior to their thermal contact. Entanglement is the phenomenon in which two quantum particles share the same existence.
As a result, heat energy is driven in the opposite direction. “We observe a spontaneous heat flow from the cold to the hot system,” say the team.
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