Time crystals -- objects whose structure repeats periodically, as with an ordinary crystal, but in time rather than in space -- may exist.
Adam Rifkin stashed this in Time
Holy quantum effects, Batman.
Researchers have defined what it means for time translation symmetry to be spontaneously broken in a quantum system, and show with analytical arguments and numerical simulations that this occurs in a large class of many-body-localized driven systems with discrete time-translation symmetry.
In 2012 Nobel laureate Frank Wilczek first proposed the idea of time crystals. He argued that these hypothetical objects can exhibit periodic motion, such as moving in a circular orbit, in their state of lowest energy, or their "ground state." Theoretically, objects in their ground states don't have enough energy to move at all.
Physicists from the University of California, Santa Barbara (UCSB) and Microsoft Station Q (a Microsoft research lab located on the UCSB campus) have demonstrated that it may be possible for time crystals to physically exist.
The physicists have focused on the implication of time crystals that seems most surprising, which is that time crystals are predicted to spontaneously break a fundamental symmetry called "time-translation symmetry." To understand what this means, the researchers explain what spontaneous symmetry breaking is.
If time crystals really do spontaneously break time-translation symmetry, then the laws of nature that govern time crystals wouldn't change with time, but the time crystals themselves would change over time due to their ground-state motion, spontaneously breaking the symmetry.
Top Reddit comment explains like I'm five:
This is about what happens to things when you take all their energy away. Think of it like dropping something on floor.
Many things fall down on one side or the other when you drop them. The way that the thing falls is called its resting or ground state. Figuring out what makes these things fall on one side or the other can help you learn about the object as well as the floor.
Sometimes things don't literally fall, but still have ground states. Magnets sort of pick one side to be north and the other side to be south. That's their ground state. Learning why they do this is hard and has taken a long time. Because magnets always have a north and a south pole, they are called asymmetrical, which just means they don't look the same on both sides.
Crystals also have asymmetrical ground states. As a crystal reaches its ground state it always has some bits that are pointy and some bits that are smooth. It's not the same on all sides, so it's asymmetrical, just like the magnets.
Lots of things in nature have asymmetrical ground states, but they all have one thing in common: they don't move. You have to give them some energy to make them move or to change their ground state.
Now some people think that there might be some weird objects that have asymmetrical ground states across time rather than space. That's what they mean by time crystals. An object like that would be interesting because, to us, they would look like they are moving in their ground state without any extra energy! Imagine if you dropped a die on the ground but instead of landing on a side, it landed on one corner and just spun forever. That's how weird these things are!
Because this is so hard to explain, these scientists spent most of their time just trying to define what such a weird object would look like and how you would know it when you found one. Once they did that, they used supercomputers to predict where you might find them, if they exist.
So far, no one has actually seen one and a lot of people think they can't exist. But now we might know where to look to see who is right!
Haha, the next Reddit comment asks for someone to explain like I'm two.