[Music] can you see this you already know what will happen in five minutes the ice cubes will melt lowering the temperature of the water [Music] but what if after another five minutes the ice cubes reform and after five minutes more they melt and what if they keep cycling back and forth freezing and melting forever this is what scientists would call a time crystal [Music] a new phase of matter that seems to evade the laws of physics and if their discovery stands up to further scrutiny it's also what researchers at google have just created [Music] so
what on earth are time crystals [Music] it's a way of kind of having your cake and eating it too this is frank wilcheck a nobel laureate who first introduced the idea of time crystals in 2012. it came out of teaching actually mostly i was teaching a course about symmetry in physics and more precisely about crystals special solids like diamond or quartz where atoms are ordered in a pattern that repeats itself but i wanted to do something fresh so i thought about well why not think about higher dimensional crystals crystals and more dimensions than three and
to make it physical the extra dimension should be time just like ordinary crystals repeat themselves in space time crystals repeat themselves in time [Music] explaining what a time crystal is and why it's interesting requires a little bit of background so like a good theorist i'll start with the thought experiment this is kurt von kaiserling he played a key role in the theoretical work that led to the recent developments i want you to take a box and fill it with many coins [Music] so as you look down at this box with many coins in it you'll
see that the coins are pointing either heads up or heads down now start to shake the box so if you shake the box let's say a million times and you look down into the box if you count to the number of coins that are pointing up and pointing down you should find that roughly half of them are pointing up and roughly half of them are pointing down that's because a coin has 50 50 chances to let heads or tails random shakes will give you a random configuration and of course you know the same is true
if i shake the box instead of shaking a million times i shake it a million and one times again it's going to be the case that roughly the coins are pointing up and roughly half points are pointing down but time crystals work differently here is what would happen if the coins in our box behave the same way a time crystal does [Music] the surprise is that now you'll find that the spins are still mostly pointing up so unlike in the previous thoughts experiment where everything just looked random the system remembers something about its initial state
you shook the box a million times and it looks pretty much the same no matter how hard you shake the box the coins are all going to point in the same direction but there's an even more dramatic thing which is that if you now shake the box a million and one times you'll find that the spins are now mostly pointing down so depending on whether you shake the box an even or an odd number of times the spins tend to flip-flop shake it once and the point down shake it twice and the point up that's
because time crystals are a new phase of matter [Music] matter normally exists as a solid a liquid or a gas we call these properties the phases of matter in each one of these phases matter behaves a little differently but what they all have in common is that they respect time symmetry a fancy word scientists use to say that the laws of physics don't care what time it is they were the same five minutes ago as they are now [Music] as long as the temperature in the room is the same the ice cubes will melt today
just like they would tomorrow [Music] but our coins are different one of the special things about time crystals is that they don't do this they only do the same thing every two periods their behavior changes with time even if all other conditions are the same they flip flop depending on what time it is and in principle they would keep flip-flopping forever if this sounds impossible it's because it is almost the second law of thermodynamics is a very crude formulation that says that there are no perpetual motion machines but this hasn't stopped people from trying to
build one from bhaskar's will almost 1 000 years ago to counter spendulums to today's ticktocks experiments they all invariably failed that's because things in nature tend towards a low energy state the one where the least amount of energy is required there's no free lunch in the sense that there's no material from which you can extract energy without cost crystals cycle forever between states without losing energy they are in equilibrium when they are in an evolving state they are both stable and ever-changing i didn't know it at the time but it turns out uh in the
tv series doctor who they have time crystals they have something called time crystals the whole thing revolves around his ability to travel in time using time crystals and you can even buy you can buy time crystals on the web based on spinning off on that show no one is proposing to use anything like this for time travel or anything like that but they might have applications because the effect is quite robust you don't necessarily have to finely tune the experiment to see this sort of range of parameters where you see time crystal like behavior and
when you have something that's robust it's often useful time crystals could become tools to detect magnetic fields or be used to diagnose what's going on inside quantum computers but a more profound reason is that they're simply beautiful you will find that there's a real beautiful structure that uh flow from the basic idea beyond what i anticipated in the early days and since it's a new subject probably the most important work hasn't been done yet and so there's room for creativity [Music]
