Many a poet has bemoaned the steady march of time, its heedless advance, its unremitting crawl into the future. Though we often wish it would move backwards, time never does.
Poets, though, are not alone in their bemusement. Physicists, too, often find themselves perplexed by time's arrow. Time only seems to move forward, but even our best theories of the cosmos struggle to make sense of why this must necessarily be so. Theoretically, it shouldn't make a difference which direction time moves.
So why can't we ever go back and correct past mistakes? Why can we only remember the past, and never the future? Why haven't time machines been invented yet?
Well, fill up the Mr. Fusion, take a seat in your DeLorean, and charge up the flux capacitor. Scientists, for the first time, have managed to turn back time. Or at least, they've created a quantum experiment in the lab where the flow of energy within a controlled system can be reversed. This, according to a paper recently published on the pre-review website arXiv.org.
For the experiment, an international team of physicists used a strong magnetic field to line up the nuclei of the carbon and hydrogen atoms of the molecule chloroform while it was suspended in the organic compound acetone. They then slowly heated the nuclei using a process called nuclear magnetic resonance.
Under normal conditions (when the nuclei of the atoms are not so carefully correlated and "lined up"), nothing unusual happens. As one nucleus warms up, it transfers its random movements to colder particles until they're both the same temperature. Essentially, this is how the forward movement of time is demonstrated through thermodynamics.
But this isn't what physicists observed under the conditions of their experiment. Instead of the particles equalizing in temperature, the heated hydrogen particles got even hotter, while their colder carbon partners got colder.
"We observe a spontaneous heat flow from the cold to the hot system," claimed the study.
This isn't how things are supposed to happen. For all intents and purposes, researchers reversed the flow of energy (and thus, the direction of time), at least for this one tiny, controlled pocket of the universe.
At this time (wink wink, nudge nudge), it's not entirely clear what's happening here. The study has yet to be extensively peer reviewed. But if the results are confirmed, it could open up a whole new way of studying the relationship between quantum mechanics and thermodynamics.
That doesn't mean we'll be able to go back in time to visit the dinosaurs, meet Jesus, or prevent Hitler from ever being born. Time machines are still reserved to the annals of science fiction. But we might finally start to get some idea as to why the dimension of time only seems to move forward, and that's progress.
It's not quite "Back To The Future," but it might represent one small step "Forward To The Past".