If you overheard someone talking about time crystals in a bar, you'd think they were mad, or drunk. Or both. These things, theoretically, oscillate for eternity without any energy input whatsoever -- and if that sounds like a perpetual motion machine, it's because it is. Impossible, right? But what if it was a Nobel prize-winning physicists making the suggestion?
Because that's exactly the situation we find ourselves in. As Wired reports, Frank Wilczek from MIT has taken the rather bold step of announcing to the world that he thinks time crystals could exist. It wasn't a decision he made lightly -- it could well see him ostracised by the wider scientific community -- but, after months of work, he decided there was nothing else for it. Wired explains his idea:
When matter crystallizes, its atoms spontaneously organise themselves into the rows, columns and stacks of a three-dimensional lattice. An atom occupies each “lattice point,” but the balance of forces between the atoms prevents them from inhabiting the space between. Because the atoms suddenly have a discrete, rather than continuous, set of choices for where to exist, crystals are said to break the spatial symmetry of nature -- the usual rule that all places in space are equivalent... Eventually, his equations indicated that atoms could indeed form a regularly repeating lattice in time, returning to their initial arrangement only after discrete (rather than continuous) intervals, thereby breaking time symmetry. Without consuming or producing energy, time crystals would be stable, in what physicists call their “ground state,” despite cyclical variations in structure that scientists say can be interpreted as perpetual motion.
In other words, he's saying it must be possible to create a crystal that has regular, time-varying motion going on inside -- without any energy being dumped into the system. That's quite a claim. He was right to be unsure though, because he's now picking up criticism from fellow physicists across the world.
Fortunately, he has at least one team of researchers on his side. After publishing his idea late last year, a team of experimentalists based at Berkeley offered to try and make a crystal that exhibits those very properties. If they can do it -- and neither they or Wilczek see why they shouldn't be able to -- the most basic theories of time could be forever rewritten, as time crystals would break the fundamental concept of time symmetry.
The only problem is that progress is slow: the Berkeley researchers have admitted that the project could take “anywhere between three and infinity years” to complete. Until then, a theoretical debate rages on -- and if you want to read more about the subtleties of the arguments, you should go read the feature over on Wired. [WIRED]